Binaural Response Properties and Sensitivity to Interaural Difference of Neurons in the Auditory Cortex of the Big Brown Bat, Eptesicus fuscus

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NEUROSCIENCE 1

RESEARCH ARTICLE Y. Yang et al. / Neuroscience xxx (2018) xxx–xxx

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Binaural Response Properties and Sensitivity to Interaural Difference of Neurons in the Auditory Cortex of the Big Brown Bat, Eptesicus fuscus

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Yin Yang, a* Qi Cai Chen, b Jun Xian Shen c and Philip H.-S. Jen d*

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a

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b

College of Life Sciences, Central China Normal University, Wuhan, Hubei, China

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c

Institute of Biophysics, Chinese Academy of Science, Beijing, China

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d

Division of Biological Sciences, University of Missouri-Columbia, MO, USA

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College of Special Education, Binzhou Medical University, Yantai, Shandong, China

Abstract—This study examines binaural response properties and sensitivity to interaural level difference of single neurons in the primary auditory cortex (AC) of the big brown bat, Eptesicus fuscus under earphone stimulation conditions. Contralateral sound stimulation always evoked response from all 306 AC neurons recorded but ipsilateral sound stimulation either excited, inhibited or did not affect their responses. High best frequency (BF) neurons typically had high minimum threshold (MT) and low BF neurons had low MT. However, both BF and MT did not correlate with their recording depth. The BF of these AC neurons progressively changed from high to low along the anteromedial-posterolateral axis of the AC. Their number of impulses and response latency varied with sound level and inter-aural level differences (ILD). Their number of impulses typically increased either monotonically or non-monotonically to a maximum and the latency shortened to a minimum at a specific sound level. Among 205 AC neurons studied at varied ILD, 178 (87%) and 127 (62%) neurons discharged maximally and responded with the shortest response latency at a specific ILD, respectively. Neurons sequentially isolated within an orthogonal electrode puncture shared similar BF, MT, binaurality and ILD curves. However, the response latency of these AC neurons progressively shortened with recording depth. Species-specific difference among this bat, the mustached bat and the pallid bat is discussed in terms of frequency and binaurality representation in the AC. Ó 2019 IBRO. Published by Elsevier Ltd. All rights reserved. Key words: bat, binaurality and frequency representation, interaural level difference (ILD), tonotopic organization, primary auditory cortex.

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INTRODUCTION

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As the highest center of the ascending auditory pathway, the primary auditory cortex (AC) receives multiple subcortical projections through an array of hierarchical and parallel pathways with excitatory and inhibitory inputs. For example, the ascending fibers from the central nucleus of the inferior colliculus project to the ventral nucleus of the medial geniculate body which then send axons to layers IIIb and IV of the primary AC. Neurons in these two layers then project their axons to neighboring layers of the AC and other parts of the forebrain as well (Mitani and Shimokouchi, 1985; Mitani et al., 1985; Winer, 1992; de Ribaupierre, 1997). On the

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other hand, the AC is also the origin of the descending corticofugal system that is responsible for modulation of subcortical afferent signal processing including tonotopic organization, selective signal amplification and binaurality (Games and Winer, 1988; Winer, 1992; Saldana et al., 1996; Winer et al., 1998). In the past, many studies have been performed to understand the role of the AC during auditory signal processing by examining the response properties, spatial sensitivity and binaurality of AC neurons in many animal species (see review by King et al., 2018). Eholocating bats emit ultrasonic signals and analyze the returning echoes for prey capture and orientation (Griffin, 1958). Because of this unique acoustic behavior and their sharing of common layout of a mammalian auditory system, many studies have been conducted to exam the role of their AC in the biosonar behavior under free field and earphone stimulation conditions. These studies in different bat species have shown that binaural interaction and neural inhibition shapes many response properties of AC neurons including discharge patterns,

*Corresponding authors. E-mail addresses: [email protected] (Y. Yang), jenp@missouri. edu (P. H.-S. Jen). Abbreviations: AC, auditory cortex; BF, best frequency; EE, excitation– excitation; EI, excitation–inhibition; EO, contralateral excitation; FTCs, frequency tuning curves; ILD, inter-aural level differences; LLF, latency-level function; MT, minimum threshold; PST, peri-stimulustime; RLFs, rate-level functions. https://doi.org/10.1016/j.neuroscience.2019.11.024 0306-4522/Ó 2019 IBRO. Published by Elsevier Ltd. All rights reserved. 1

Please cite this article in press as: Yang Y et al. Binaural Response Properties and Sensitivity to Interaural Difference of Neurons in the Auditory Cortex of the Big Brown Bat, Eptesicus fuscus. Neuroscience (2019), https:// doi.org/10.1016/j.neuroscience.2019.11.024

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response latency, rate–intensity functions, spatial sensitivity, binaural response properties, delay-tuning and selectivity in multiple signal parameters (Suga and Jen, 1976; Sullivan, 1982; Suga and Horikawa, 1986; Taniguchi et al., 1986; Jen et al., 1989, 1997, 2002; Hou et al., 1992; Wong et al., 1992; Wu et al., 1996; Galazyuk and Feng, 1997; Liu and Suga, 1997; Shen et al., 1997; Kanwal et al., 1999; Razak et al., 1999; Chen and Jen, 2000; Lohuis and Fuzessery, 2000; Razak and Fuzessery 2002, 2006, 2009; Suga, 2015; Suzuki and Suga, 2017; Teng and Suga, 2017; Butman and Suga, 2019). Other studies have shown that the corticofugal system adjusts and improves subcortical auditory signal processing as well as reorganizes signal parameter representation based on acoustic experience (Zhang and Suga, 2000; Ma and Suga, 2001, 2007; Jen et al., 2002; Zhou and Jen, 2007). Our previous free field study (Jen et al., 1989) has shown that all AC neurons of Eptesicus fuscus are most sensitive to sounds delivered from the contralateral side of the frontal auditory space. While the anteromedially located high best frequency (BF) neurons discharge maximally to sounds delivered from the middle frontal auditory space, the posterolaterally located low BF neurons discharge maximally to sounds delivered from the lateral frontal auditory space. Thus, the lateral auditory space is represented posterolaterally and the middle space anteromedially The high BF neurons have smaller auditory spatial response areas than the low BF neurons have. Furthermore, AC neurons sequentially isolated within an orthogonally punctured electrode share similar frequency tuning curves (FTCs) and auditory spatial response area. However, our free field stimulation study could not determine the binaural properties of these AC neurons. For this reason, we used an earphone stimulation system to study the binaural and frequency representation in the AC of this bat species (Shen et al., 1997). We have reported that AC neurons with the same binaurality, similar BF and minimum threshold (MT) organize in columns or slabs along the dorsoventral axis of the AC. Respectively, the EE (excitation–excitation) and EI (excitation–inhibition) columns occupy about 15% and 85% of the AC. While the EE neurons mainly cluster in the center of the AC, the EI neurons cluster in the surrounding areas of the AC. Furthermore, the segregated bands of iso-frequency and binaural columns intersect each other. Because interaural level or intensity difference (ILD or IID, ILD will be used here) is one of the two essential cues for sound localization and echolocation, we study the binaural interaction in AC neurons by examining the rate-level functions (RLFs) under both monaural and binaural stimulation conditions. We also study the ILD functions of AC neurons in terms of variation in the number of impulses and response latency with ILD. We further examine the columnar organization of these AC neurons in terms of their binaurality, BF, MT, and ILD functions. Since bats have different hunting behavior in their ecological niches, we hypothesize that frequency and binaurality representation in the AC may be

species-specific different. We, therefore, compare and discuss frequency and binaurality representation in the AC of the big brown bat, the mustached bat and the pallid bat in relation to their different hunting behavior.

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EXPERIMENTAL PROCEDURES

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The protocols for surgery and recording have been described in previous studies (Jen et al., 1987, 1989; Shen et al., 1997). Briefly, the flat head of a 1.8 cm nail was glued onto the exposed skull of 17 Nembutalanesthetized bats (Eptesicus fuscus, nine males and eight females, 12–23 g body weight) with acrylic glue and dental cement one or two days before the recording session. During recording, each bat was administered neuroleptanalgesic Innovar-Vet (0.08 mg/kg b. w. of fentanyl, 4 mg/kg b. w. of droperidol) and was tied to an aluminum plate with a plastic band inside a soundproof room (temperature 24–26 °C). Its head was immobilized by fixing the shank of the nail into a metal rod with a set screw. Small holes were then bored in the skull above the primary AC for the insertion of 3 M KCl glass electrodes to record sound-activated neural activities. An indifferent electrode (silver wire) was placed at the nearby temporal muscles. The experiments were conducted complying with NIH publication No. 85-23, ‘‘Principles of Laboratory Animal Care” and with the approval of the Institutional Animal Care and Use Committee (#1438) of the University of Missouri-Columbia. Construction and calibration of earphones for closed system stimulation have been described in previous studies (Schlegel, 1977; Shen et al., 1997; Lu and Jen, 2003). Briefly, two 4-ms tones generated by two independent stimulation systems were fed into two 1/4 inch B&K (4135) microphones. Each microphone was snugly fitted into a custom-made plastic adapter with its tip inserted into the funnel of the external ear. These ‘‘earphones” were calibrated with a 1/8 inch B&K (4138) microphone placed at about 1 mm in front of the adapter tip. The output of each earphone was expressed in dB SPL referred to as 20-mPa root mean square. All recordings were conducted inside a soundproof room and the room temperature was between 24 and 26 °C. When an AC neuron was isolated with 4 ms sound stimuli delivered to the contralateral ear of the bat, its threshold was determined by changing the sound level such that the sound on average evoked a 50% response probability from the neuron to each responsive frequency. The BF was defined as the frequency that elicited the neuron’s response with the lowest sound level (i.e. the MT, hereafter conveniently called contralateral MT). As described in our previous study (Shen et al., 1997), the neuron’s binaurality was determined by delivering BF sounds at different sound levels to the ipsilateral ear. When the AC neuron also responded to ipsilateral sound stimulation, its MT (hereafter conveniently called ipsilateral MT) was determined and the neuron was referred to as an EE neuron. When an ipsilateral sound did not evoke a neuron’s response, a BF sound at 20 dB above the neuron’s MT was delivered to the contralateral ear

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Please cite this article in press as: Yang Y et al. Binaural Response Properties and Sensitivity to Interaural Difference of Neurons in the Auditory Cortex of the Big Brown Bat, Eptesicus fuscus. Neuroscience (2019), https://doi.org/10.1016/j.neuroscience.2019.11.024

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to elicit an excitatory response. Then, the sound level at the ipsilateral ear was systematically adjusted in 10 dB increments from 20 dB lower to 20 dB higher than the contralateral sound level such that the neuron’s binaural response was examined over a dynamic range of 40 dB. When ipsilateral sound stimulation reduced the neuron’s response to contralateral sound stimulation more than 20% at a specific ILD, the neuron was referred to as an EI neuron. Conversely, when ipsilateral sound stimulation reduced the neuron’s response to contralateral sound stimulation less than 20% at all ILDs, this neuron was referred to as a contralateral excitation (EO) neuron. Furthermore, when ipsilateral sound stimulation respectively increased and decreased a neuron’s response to contralateral sound stimulation more than 20% by ipsilateral sound stimulation at certain ILDs, this neuron was referred to as an EI-mixed neuron. The interaural level difference (ILD) curves of these neurons were then measured with the number of impulses and response latency determined at each ILD. Hereafter, they are called impulse inter-aural level difference curves (Impulse–ILD curves) and latency inter-aural level difference curves (latency–ILD curves), respectively. The contralateral RLF and latency-level function (LLF) of all AC neurons were measured with their number of impulses and response latency obtained with a BF sound delivered to the contralateral ear at MT and at 10 dB increments above the MT. Similarly, the ipsilateral RLF and LLF of EI and EO neurons were measured with a BF sound delivered to the ipsilateral ear using the contralateral MT and at 10 dB increments above the MT. On the other hand, the ipsilateral RLF and LLF of EE neurons were measured with a BF sound delivered to the ipsilateral ear using its ipsilateral MT and at 10 dB increments above the MT. Recorded action potentials were amplified, band-pass filtered (Krohn-Hite 3500), and fed through a window discriminator (WPI 121) before being sent to an oscilloscope (Tektronix 5111) and an audio monitor (Grass AM6). They were then sent to a computer (Gateway 2000, 486) for the acquisition of peri-stimulustime (PST) histograms (bin width: 500 ms, sampling period: 50 ms) to 20 stimuli. The PST histograms quantitatively describe a neuron’s temporal discharge pattern under different stimulation conditions. The total number of impulses in each PST histogram was used to quantify a neuron’s response under each specific stimulation condition.

RESULTS

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Binaural response properties

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In this study, we recorded 306 AC neurons at depths of 101–1100 mm with most at 300–800 mm. Each recorded AC neuron discharged no more than 3–5 impulses to 4 ms sound stimuli and lacked background activity. Their BFs ranged between 14 and 92 kHz with most between 25 and 75 kHz. Their MTs were between 12 and 95 dB SPL with most below 70 dB SPL. All AC neurons sequentially recorded within an orthogonally punctured electrode share similar BFs and same

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binaurality (Fig. 1A1, 3; EI neurons; A2: EE neurons). The BF and MT of these AC neurons correlate significantly such that high BF neurons typically have high MT than the low BF neurons have (Fig. 1B). However, the BF and MT of these neurons do not significantly correlate with the recording depth (Fig. 1C, D). Fig. 2 A–C show the discharge patterns of representative EI, EO and EE neurons, respectively. Clearly, all three neurons discharged impulses to contralateral sound stimulation (Fig. 2A–C, contra). However, ipsilateral sound stimulation only elicited impulses from the EE neuron (Fig. 2C ipsi) but not the EI (Fig. 2A ipsi) or EO (Fig. 2B ipsi) neurons. For the EI neuron, the number of impulses elicited by contralateral sound stimulation drastically decreased during binaural sound stimulation (Fig. 2A contra vs bin, decrease 57% from 69 to 30). On the other hand, the number of impulses of the EO neuron elicited by contralateral sound stimulation changed very little when stimulated binaurally (Fig. 2B contra vs bin, 32 vs 30). As for the EE neuron, contralateral sound stimulation elicited a greater number of impulses from the neuron than ipsilateral sound stimulation did (Fig. 2C contra vs ipsi, 36 vs 11). Furthermore, binaural sound stimulation greatly increased the neuron’s number of impulses (Fig. 2C contra vs bin, increase 89% from 36 to 68). Based on the response of these 306 AC neurons under monaural and binaural stimulation at varied ILD, they are described as EE neurons (n = 96, 31%), EI neurons (n = 164, 54%), EO neurons (n = 19, 6%) and EI-mixed neurons (n = 27, 9%). Table 1 compares the MT at BF and the shortest response latency of these four types of AC neurons. A neuron’s shortest response latency was measured with a BF sound delivered at the 20–30 dB above its MT. Clearly, the ipsilateral MT of EE neurons is significantly higher than the contralateral MT as well as the MT of EI, EO and EI-mixed neurons (One way ANOVA p < 0.0001). It is also clear that on average the response latency of EE neurons is longer when measured with ipsilateral than with contralateral sound. The ipsilateral response latency of EE neurons is also longer than the response latency of the other three types of AC neurons. However, their latency differences did not differ significantly (One way ANOVA, p > 0.1).

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Frequency and binaurality representation

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To highlight frequency and binaurality representation in the AC, we have modified and expanded the Fig. 1 of our previous paper (Shen et al., 1997) and shown in Fig. 3. The rectangle shows the maximally exposed area of the AC and sound-activated AC neurons were primarily recorded from the shaded region. Fig. 3B shows all 135 AC neurons recorded from 78 orthogonal electrode punctures in the AC of one bat while Fig. 3C shows all 198 orthogonal electrode punctures performed on the AC of 17 bats. As described previously (Shen et al., 1997), all but two EE neurons were recorded from the central portion of the AC. This EE area is about 15% of the AC. On the other hand, the EI, EO and EI-mixed AC neurons were

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height of its RLF is lower when measured with ipsilateral than with contralateral sound stimulation (Fig. 4C1, solid circle vs solid square). On the other hand, the response latency of these AC neurons progressively decreased with sound level to a minimum and then leveled off (Fig. 4B2) or gradually increased to varying degrees at still higher sound level (Fig. 4A2, C2). As shown in Table 1, the average response latency of the EE neuron was longer when measured with ipsilateral than with contralateral sound stimulation.

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Impulse–ILD curves

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According to the variation of the number of impulses with ILD, five types of impulse–ILD curves can be described for 205 AC neurons studied. The number of impulses Fig 1. (A) Variation in the best frequency (BF, kHz) of auditory cortical (AC) neurons sequentially of the first type (91 EI and 25 EE isolated within three orthogonal electrode punctures (A1, A2, A3). Note that all neurons isolated within the same electrode puncture have same binaurality and similar BF. All neurons in A1 and A3 (solid neurons) progressively decreased circles) were EE neurons that were excited by sound stimulation delivered from either ear. All neurons from a maximum to a minimum in A2 (unfilled circles) were EI neurons that were excited by contralateral sound stimulation but were with the ipsilateral sound inhibited by ipsilateral sound stimulation. (B) and (C): Scatter plots showing the distribution of the BF progressively increased from of 306 AC neurons against their minimum thresholds (dB SPL) and recording depths (mm). (D): The distribution of MT of these AC neurons against their recording depths. The linear regression line and 20 dB weaker to 20 dB stronger correlation coefficient for each plot are shown with a solid line and r. p: significance level. N: number of than contralateral sound (Fig. 5A). AC neurons in each plot. Conversely, the number of impulses of the second type (6 EO and 38 EE neurons) recorded from the remaining 85% area of the AC. The progressively increased from a dashed lines of Fig. 3B, C show the approximate boundminimum to a maximum with the progressive increase in ary of BF of recorded AC neurons. Clearly, the BF of the ipsilateral sound level over the contralateral sound AC neurons tend to decrease progressively from high to level (Fig. 5B). The third type of impulse–ILD curves (9 low along the anteromedial-posterolateral axis of the AC. EI-mixed neurons) was V-shaped in which the number of impulses was maximal when the ipsilateral sound Monaural RLF and LLF was either 20 dB weaker or stronger than the As described earlier, we measured the monaural RLF and contralateral sound (Fig. 5C1, solid square). However, LLF of each AC neuron with a BF sound delivered at MT the number of impulses was minimum when the sound and at 10 dB increments above the MT. Respectively, level delivered to each ear was equal. The fourth type Fig. 4A–C show the monaural RLF and LLF of (18 EI-mixed neurons) of impulse–ILD curves of AC representative EI, EO and EE neurons. When neurons was an inverted V-shaped curve in which the stimulated by contralateral sound, all three types of AC number of impulses was the smallest when the neurons had non-monotonic RLF in which their number ipsilateral sound was either 20 dB weaker or stronger of impulses increased with sound level to a maximum than the contralateral sound. The number of impulses and then either decreased more than 20% (Fig. 4A1, was maximal at equal binaural sound level (Fig. 5C2, B1, C1, contra, solid circle) or reached a plateau at still solid circle). Finally, the number of impulses of AC higher sound level. While ipsilateral sound stimulation neurons of the fifth type of impulse–ILD curves (13 EO did not elicit a response from EI and EO neurons and 5 EE neurons) always changed fewer than 20% (Fig. 4A1, B1, ipsi, solid square), it did evoke response with variation in ILD (Fig. 5D). from EE neurons in which the number of impulses Although there is no clear correlation between the increased either non-monotonically (Fig. 4C1, ipsi, solid binaurality of AC neurons and the type of impulse–ILD square) or monotonically with sound level. Because curves, 87% (178/205) of AC neurons studied each EE neuron had significantly higher MT for discharged maximally at a specific ILD (Fig. 5A, B, C2, ipsilateral than for contralateral sound stimulation, the solid circle). There were 9 (4%) neurons discharged Please cite this article in press as: Yang Y et al. Binaural Response Properties and Sensitivity to Interaural Difference of Neurons in the Auditory Cortex of the Big Brown Bat, Eptesicus fuscus. Neuroscience (2019), https://doi.org/10.1016/j.neuroscience.2019.11.024

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Fig 2. Peri-stimulus-time (PST) histograms showing the discharge pattern of an EI (A), EO (B) and EE (C) cortical neurons to contralateral sound stimulation (A, B, C contra), ipsilateral sound stimulation (A, B, C ipsi) and binaural sound stimulation (A, B, C bin). N: number of impulses within each PST histogram. The BF (kHz), MT (dB SPL), recording depth (mm) and latency (ms) of these neurons were 31.3, 46, 440, 19.5 (A); 41.1, 43, 750, 17.5 (B); 63.6, 54, 784, 8 (C). Note that these three types of AC neurons responded differently under three different stimulation conditions (see text for details).

Table 1. Comparison of minimum threshold and response latency of excitatory–excitatory (EE), excitatory–inhibitory (EI), contralateral excitatory only (EO) and excitatory–inhibitory mixed (EI-mixed) auditory cortical neurons Binaural properties n

EE contra 96 (31%)

EE ipsi 96 (31%)

EI contra 164 (54%)

EO contra 19 (6%)

EI-Mixed contra 27 (9%)

MT (dB SPL)

Range m ± sd

32–78 47.3 ± 10.4 (a)

38–95 62.5 ± 12.8 (b)

32–92 50.7 ± 15.2 (c)

35–89 51.4 ± 14.4 (d)

37–89 49.6 ± 11.7 (e)

Latency (msec)

range m ± sd

7.5–26.5 14.7 ± 3.7

7.5–35 16.4 ± 6.1

7.5–27.5 15.4 ± 4.4

8–19.5 13.7 ± 3.1

7.5–32 15.2 ± 5.33

ANOVA p

<0.0001

>0.1

Contra vs ipsi: contralateral vs ipsilateral sound stimulation. Repeated measures one-way ANOVA shows that all average MTs are significant different (p < 0.0001). A posttest with the Student–Newman–Keuls Multiple Comparison test shows significant differences between (a) and (b) (p < 0.001); (b) and (c) (p < 0.001); (b) and (d) (p < 0.01); (b) and (e) (p < 0.001); p: significance level. n: number of neurons.

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minimally when the sound level was equal at both ears (Fig. 5C1, solid square).

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Latency–ILD curves

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Based on the variation of response latency with ILD, six types of latency–ILD curves can be described for these 205 AC neurons. The response latency of the first type (55 EI, 10 EE, 6 EO, 5 EI-mixed neurons) increased from the shortest to the longest when ipsilateral sound progressively increased from 20 dB weaker to 20 dB stronger than contralateral sound (Fig. 6A). Conversely, the response latency of the second type (5 EI, 22 EE, 1

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EO neurons) progressively decreased from the longest to the shortest with progressive increase in ipsilateral sound level relative to contralateral sound level (Fig. 6B). The latency–ILD curves of the third type (7 EI, 10 EE, 1 EO, 5 EI-mixed neurons) were V-shaped in which the latency was long when the ipsilateral sound was either 20 dB weaker or stronger than the contralateral sound. The latency was the shortest at equal binaural sound stimulation (Fig. 6C1, solid square). Oppositely, the fourth type (3 EI, 11 EE, 3 EO, 3 EI-mixed neurons) of latency–ILD curves was inverted V-shaped in which the response latency was short when the ipsilateral sound was either at 20 dB weaker or

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stronger than the contralateral stound but response latency was the longest at equal binaural sound level (Fig. 6C2, solid circle). The response latency of the fifth type of latency–ILD curves (3 EI, 2 EE, 2 EI-mixed neurons) varied between the longest and shortest at four respective ILDs (Fig. 6D1, solid square). Finally, the response latency of the sixth type (18 EI, 13 EE, 8 EO, 12 EI-mixed neurons) never varied more than 20% with ILD. Often the response latency hardly changed with ILD such that the latency ILD curve was literally a straight horizontal line (Fig. 6D2, solid circle). Similar to the observation on the impulse–ILD curves, no clear correlation was observed between the binaurality of AC neurons and the type of latency–ILD curves.

Nevertheless, 62% (127/205) of AC neurons responded with the shortest response latency at a specific ILD (Fig. 6A, B, C1, solid square). There were 20 (10%) neurons responded with the longest response latency when the sound level was equal at both ears (Fig. 6C2, solid circle).

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Impulse– and latency ILD curves of AC neurons recorded within orthogonal electrode puncture

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Table 2 shows the BF, MT, latency and recording depth of AC neurons sequentially isolated within two orthogonally punctured electrodes. Clearly, AC neurons isolated within the same electrode had the same binaurality and similar BF and MT regardless of their recording depth. The response latency of these neurons tends to shorten with increasing recording depth. Fig. 7 shows the impulse–ILD and latency–ILD curves of these AC neurons isolated within these two electrode punctures. Although the number of impulses and latency of AC neurons sequentially isolated within the same electrode puncture varied in different degrees with ILD, the overall profile of all impulse–ILD and latency–ILD curves of AC neurons recorded within the same electrode puncture was largely comparable. Thus, all impulse–ILD curves of EE neurons isolated from one electrode puncture ascended from a minimum to a maximum or level off with increasing ipsilateral sound level (Fig. 7A1). On the other hand, all the latency–ILD curves of sequentially isolated EE neurons progressively decreased from the longest to the shortest and then reached a plateau or increased again at still stronger ipsilateral sound (Fig. 7A2). On the other hand, the impulse–ILD curves of all EI neurons sequentially isolated from another electrode

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3 Fig. 3. (A). A sketch showing the dorsolateral view of the exposed primary auditory cortex (AC) of an Eptesicus fuscus. The primary AC is within the rectangle and AC neurons were primarily recorded from the shaded area. The cross along the longitudinal fissure represents the reference point for the abscissa and ordinate. The ordinate represents a distance of 2.5–5.5 mm from the horizontal arrow. The abscissa represents a lateral distance of 2.0 mm and 1.5 mm to the right and left of the zero reference point (the vertical arrow). The solid lines represent the main and branching middle cerebral arteries. (CBR cerebrum, CBL cerebellum, Hem hemisphere, IC inferior colliculus, PF paraflocculus, SC superior colliculus, SP spinal cord, Ver vermis.) (B) An enlarged rectangular area in A showing the positions of 78 orthogonal electrode punctures that recorded 135 neurons in the AC of one bat. (C) An enlarged rectangular area in A showing the composite positions of 198 electrode punctures that recorded 306 neurons in the AC of 17 bats. Unfilled triangles: electrode punctures that did not record AC neurons. Filled circles: electrode punctures that recorded only EE (excitation-excitation) neurons. Unfilled circles: electrode punctures that recorded only EI (excitation-inhibition) neurons. Slashed circles: electrode punctures that encountered all EI plus one EO (contralateral excitation only) neurons. Asterisked slashed circle: the electrode punctures that recorded only EO neurons. Cross circles: electrode punctures that isolated both EI and EI-mixed binaural neurons. Asterisked crossed circle: the electrode puncture that isolated all EI-mixed binaural neurons. The double and single solid lines represent the main and branching middle cerebral arteries. The dashed lines with numbers show the approximate boundary of BF of recorded AC neurons (see text for details).

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Fig. 4. Respectively, the rate-level (A1, B1, C1) and latency–level (A2, B2, C2) functions of an EI, EO and EE cortical neurons obtained under contralateral (contra, filled circle) and ipsilateral (ipsi, unfilled circle) sound stimulation. The BF (kHz), MT (dB SPL), recording depth (mm) and latency (ms) of these neurons were 41.4, 48, 754, 16 (A); 57.4, 51, 265, 17 (B); 42.5, 38, 446, 12.5 (C) (see text for details).

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progressively decreased from a maximum to a minimum or reached a plateau with a further increase in the ipsilateral sound level (Fig. 7B1). Conversely, the latency–ILD curves of these EI neurons typically increased from the shortest to the longest with increasing the ipsilateral sound level (Fig. 7B2).

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DISCUSSION

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Frequency representation and tonotopic organization

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Consistent with previous studies in the AC of the same bat (Jen et al., 1989, 1993; Dear et al. 1993; Shen et al., 1997), we observed that BF of AC neurons progressively decreased from high to low along the anteromedialposterolateral axis of the AC (Fig. 3). This orderly frequency representation along a specific axis of the AC has been shown in all animal species studied (Merzenich and Schreiner, 1991). In agreement with our previous findings (Jen et al., 1989; Hou et al., 1992; Chen and Jen, 2000), we found that high BF AC neurons tend to have high MT than low BF neurons have (Fig. 1B). Previous studies in the inferior colliculus of the same bat also show such correlation between BF and MT of recorded neurons (Jen and Schlegel, 1982; Pinheiro et al., 1991). What may be the possible basis underlying all these findings?

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In auditory physiology, it is the well-known textbook knowledge that when complex sounds arrive in the inner ear, their frequencies are analyzed by hair cells located at different places of the basilar membrane. The thickness and width of the basilar membrane progressively decreases and widens from the basal turn to the apical turn of the cochlea. As a result, the basal basilar membrane is thick and stiff while the apical basilar membrane is thin and flexible. It is therefore conceivable that stronger sounds are necessary to activate hair cells located at the basal turn than the hair cells located at the apical turn. Because the hair cells located at the basal turn are responsible for analysis of high frequency sounds while those located at the apical turn are responsible for analysis of low frequency sounds, afferent fibers innervate the hair cells at the basal turn would have a higher threshold than those at the apical turn. Conceivably, this position-dependent frequency analysis along the basilar membrane might be the basis for high BF neurons to have higher MT than the low BF neurons have. In this study, we also found that the BF of most 306 AC neurons is between 25 and 75 kHz (Fig. 1C, 3); similar to those reported for inferior collicular neurons in the same bat (Jen and Schlegel, 1982; Pinheiro et al., 1991). During different phases of hunting, the frequency

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multiple CF–FM signals for orientation and prey capture, adjusts the frequency of emitted signals to compensate for the Doppler-shifted echo frequency to ensure analysis of preferred echo frequency within its acoustic fovea. Schnitzler (1968) first discovered this Doppler-shifted compensation behavior by the CF–FM bat. In the mustached bat, the CF components of two predominant harmonics (i.e., 61–63 kHz and 91–95 kHz) are overrepresented in the main tonotopic axis of the AC and the frequency axis is radially arranged inside this Dopplershifted CF processing area. Furthermore, the two predominant FM components (i.e., 50–60 kHz and 70–90 kHz) are represented in the antero-dorsal part of the AC (Suga and Jen, 1976; Suga, 1982, 1984, 1990; Asanuma et al., 1983; Taniguchi et al., 1986; Ko¨ssl et al., 2014). On the other hand, the pallid bat relies on passive hearing of prey-generated noise (5–35 kHz) for hunting and uses high frequency (60–30 kHz) downwardsweep FM signals for orientation Fig 5. Representative impulse inter-aural level difference (ILD) curves of different types of binaural and obstacle avoidance (Razak AC neurons showing variation in the number of impulses as a function of ILD. The contralateral sound stimulus was always set at 20 dB above each neuron’s MT. The ipsilateral sound stimulus was et al., 1999; Barber et al., 2003). stronger or weaker than the contralateral stimulus as indicated by the positive and negative numbers The frequency representation in in the abscissa. The BF (kHz), MT (dB SPL), recording depth (mm) and latency (ms) of these neurons the AC of this gleaning bat is also were 55.3, 47, 523, 16 (A); 92.1, 60, 908, 7 (B); 60.8, 46, 654, 8 (C1); 39.8, 37, 525, 16 (C2); 63.6, 54, tonotopically organized such that 784, 8 (D) (see text for details). the BF of AC neurons progressively decreases along the of short multiple-harmonic FM signals used by the big anteromedial-posterolateral axis of brown bat sweeps approximately from 90 to 45 kHz or the AC. In addition, there is an overrepresentation of 75 to 30 kHz or 45 to 20 kHz (Simmons et al., 1979; Jen 10–22 and 34–44 kHz neurons but an underand Kamada, 1982; Surlykke and Moss, 2000; Surlykke representation of 24–32 kHz neurons (Razak and et al., 2009; Hulgard et al., 2016). Although the downward Fuzessery, 2002). This bimodal frequency representation sweeping frequency range of the orientation signals varcorrelates well with dual stream processing of high freies with different hunting phase, the frequency band of quency echolocation signals and low frequency prey25–75 kHz is the predominant part in all these three FM generated noise during orientation and ground gleaning sweeps. The fact that a large number of neurons is hunting (Bell, 1982; Razak and Fuzessery, 2002, 2015; devoted to analyzing this predominant frequency band Barber et al., 2003). Furthermore, anatomical studies clearly suggests the importance of these neurons during have shown that there are two separate auditory pathecholocation. Similar overrepresentation of a certain freways underlying this dual stream processing of high and quency band has been shown in the AC of the little brown low frequency bands (Razak et al., 2007, 2009). bat, Myotis lucifugus (Suga, 1965) and cats (Merzenich All these observations suggest that the auditory et al., 1975). system and vocalization system of an animal have While the general decreasing of BF of AC neurons evolved in parallel such that the former can effectively from high to low along the anteromedial–posterolateral process the most predominantly and behaviorally axis of the AC and overrepresentation of a certain relevant vocalization sounds for survival. These frequency band has been also observed in the AC of observations also support the general principle of the mustached bat, Pteronotus parnellii and the pallid orderly neurotopic representation of the sensory bat, Antrozouz pallidus, species-specific difference does epithelium in each sensory cortex with different exist. For example, the mustached bat, which uses magnification factors that allow preferred analysis of

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Binaurality representation

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Previous studies have shown that the EE and EI columns in the AC arrange alternatively along a cortical isofrequency band in cats and ferrets (Imig and Adrian, 1977; Middlebrooks et al., 1980; Middlebrooks and Zook, 1983; Kelly and Judge, 1994) or cluster in the form of patches along the cortical isofrequency bands in albino rats (Kelly and Sally, 1988). Different from these studies, our study of the big brown bat shows that overrepresented EE columns are clustered within the central AC and EI columns are distributed in the surrounding area of the AC (Fig. 3). In the AC of the mustached bat, the EE neurons are represented in the ventral portion (about one-third) of the Dopplershifted constant-frequency area (DSCF) while the overrepresented EI neurons are clustered in the dorsal portion (about two-thirds) of the DSCF area and the remaining tonotopic area of the AC (Manabe et al., 1978; Liu and Suga, 1997). In the AC of the pallid bat, the low frequency region mainly contains EI neurons and a small number of Fig 6. Representative latency ILD curves of different binaural AC neurons showing variation in response latency as a function of ILD. The BF (kHz), MT (dB SPL), recording depth (mm) and latency mixed neurons while the high fre(ms) of these neurons were 55.3, 47, 523, 16 (A); 92.1, 60, 908, 7 (B); 46.9, 46, 562, 12.5 (C1); 50.6, quency region contains mostly 36, 1010, 14 (C2); 35.5, 41, 301, 17 (Da); 67.7, 56, 252, 12.5 (Db) (see Fig. 5 for legends). mixed neurons and EO neurons (Razak and Fuzessery, 2002). However, EE neurons are hardly information from a certain portion of sensory epithelium recorded in this bat species with high acuity and sensitivity. In somatosensory and Previous studies have suggested that EI neurons are visual cortices, a disproportionate number of neurons best for sound localization while EE neurons are suited for are devoted to processing the information from body sound detection or frequency-pattern analysis (Manabe extremities (e.g. hands, lipsthe and fingers) and foveal et al., 1978; Middlebrooks et al., 1980). Because both and parafoveal areas, respectively (Mountcastle, 1957; the mustached bat and big brown bat rely heavily upon Zeki, 1981; Nicholls et al., 2012).

Table 2. The BF, MT, latency and recording depth of all AC neurons isolated within two orthogonal electrode punctures. Penetration

No

BF (kHz)

MT (dB SPL)

Latency (ms)

Depth (mm)

A (all EE neurons)

1 2 3 4 5 6 7

42.4 43.3 42.8 41.2 41.4 41.1 41.2

42 45 45 43 42 42 42

18 18.5 16.5 15.5 15 15 15

634 721 786 865 925 985 1035

B (all EI neurons)

1 2 3 4 5

81.0 82 81.9 82.0 82.3

86 89 89 89 89

21.5 14.5 13 12 11.5

602 653 704 755 805

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example, while AC neurons in layers VI and V that send projects respectively to medial geniculate complex and inferior colliculus to modulate ascending auditory signal processing, the discharge patterns of these AC neurons may be also affected by these ascending influences (Winer, 1992). Furthermore, binaurality of AC neurons in layers III of both cerebral hemispheres can reciprocally influence one another through the commissural fibers in the corpus callosum (Imig and Brugge, 1978; Code and Winer, 1985; Winer, 1992). For all these reasons, the AC likely contains mostly binaural neurons that respond to sound stimulation from both ears. Indeed, we have shown that 94% of AC neurons studied are binaural and only 6% are monaural (Table 1). Our previous free-field study has shown that all AC neurons are most sensitive to a sound delivered from the contralateral frontal auditory space (Jen et al., 1989). This observation indicates that AC neurons primarily receive excitatory inputs from the contralateral ear. Our earphone studies have shown that contralateral Fig 7. Impulse ILD (A1, B2) and latency ILD (A2, B2) curves of AC neurons sequentially isolated within two orthogonal electrode punctures. All AC neurons isolated within one electrode puncture (A) were sound stimulation can excite all EE neurons and those isolated within another electrode puncture (B) were EI neurons. The BF (kHz), AC neurons (Fig. 2, Shen et al., MT (dB SPL), recording depth (mm) and latency (ms) of all AC neurons isolated within these two 1997). electrode penetrations are shown in Table 2. We found that all ipsilateral sound stimulation excited or inhibited the response of binaural echolocation for prey capture and obstacle avoidance, AC neurons evoked by overrepresentation of EI neurons would undoubtedly contralateral sound stimulation (Fig. 2A vs C). These enhance their ability in target localization. On the other findings are in consistence with previous studies in cats hand, the asymmetrical representation of EO and EI neu(Imig and Adrian, 1977; Middlebrooks et al., 1980; rons in the high and low high frequency areas of the AC of Middlebrooks and Zook, 1983; Reale and Kettner, gleaning pallid bat correlates well with their respective 1986), albino rats (Kelly and Sally, 1988) and ferrets roles in orientation and passive prey localization (Razak (Phillips et al., 1988; Kelly and Judge, 1994). and Fuzessery, 2002, 2015; Barber et al., 2003). What may be the neural inhibition that is responsible for formulation of our observed EI neurons and their impulse–ILD and latency–ILD curves (Fig. 2A)? Past Binaural inputs is contralateral dominant studies have shown that GABAergic inhibition In auditory physiology, it has been traditionally considered contributes importantly in shaping the response that the analysis of complex sounds is based on divergent properties of neurons in many auditory nuclei and in the and convergent neural projections through excitatory and AC (Faingold et al., 1989, 1991; Winer and Laurue, inhibitory integration within the ascending auditory 1989; Winer, 1992; Prieto et al., 1994a,b Yang and pathways (Suga, 1997). As described early, the AC is Pollak, 1994; Ebert and Ostwald, 1995; Fuzessery and both the highest auditory center receiving multiple Hall, 1996; Palombi and Caspary, 1996; Lu et al., 1997, ascending excitatory or inhibitory inputs as well as the ori1998; Wang et al., 2000; Lu and Jen, 2001; Razak and gin of the massive corticofugal system that is responsible Fuzessery, 2010; Butman and Suga, 2019). Anatomical for modulation of subcortical afferent signal processing studies have shown that the distribution of the non(Mitani and Shimokouchi, 1985; Mitani et al., 1985; pyramidal GABAergic neurons in the primary AC has a Games and Winer, 1988; Winer, 1992; Saldana et al., density gradient decreasing from high to low along the 1996; de Ribaupierre, 1997; Winer et al., 1998). For Please cite this article in press as: Yang Y et al. Binaural Response Properties and Sensitivity to Interaural Difference of Neurons in the Auditory Cortex of the Big Brown Bat, Eptesicus fuscus. Neuroscience (2019), https://doi.org/10.1016/j.neuroscience.2019.11.024

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dorso-ventral axis of the AC (Prieto et al., 1994a,b). Many studies in different bat species have shown that response properties of AC neurons including the discharge patterns, response latency, rate-intensity functions, frequency selectivity, binaural response properties and duration selectivity are shaped by GABAergic inhibition (Chen and Jen, 2000; Jen et al., 2002; Razak and Fuzessery, 2009). Furthermore, this GABAergic inhibition also shapes the ILD curves of inferior collicular neurons (Pollak et al., 2002, 2003; Lu and Jen, 2003). Based on these studies, it is tempting to speculate that GABAergic inhibition may also be responsible for the formulation of EI neurons and their impulse–ILD and latency–ILD curves observed in our study. Future study is necessary to confirm this speculation. We observed that EE neurons have higher MT and longer response latency when measured with ipsilateral than with contralateral sound stimulation (Table 1, Fig. 4C). Conceivably, these EE neurons may receive stronger and larger excitatory projection fibers from the contralateral ear but weaker and smaller ones from the ipsilateral ear.

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Impulse–ILD and latency–ILD curves

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To localize a sound source, an animal utilizes difference in sound level and arrival time at the two ears (van Bergeijk, 1962). Therefore, many past studies have examined the variation of response of auditory neurons with sound direction under free field stimulation conditions or with interaural disparity in time (ITD) or sound level (ILD) under earphone stimulation conditions (Erulkar, 1972). The magnitudes of these two cues vary with sound frequency, acoustic properties and the size of the head and pinnae of an animal (i.e. head-related transfer function, Jen and Chen, 1988; Chen et al., 1995). We observed that the number of impulses and response latency of AC neurons varied with ILD in several ways (Figs. 5 and 6). However, there is no clear correlation between the binaurality of AC neurons and type of impulse– or latency–ILD curves. Conceivably, variation of number of impulse and response latency of each AC neuron is a concomitant result of varied degree of contribution of stimulus frequency (i.e. BF), binaural disparity and head-related transfer function when measured at each ILD. For example, when all other parameters being equal, head-related transfer function should play a more predominant role in determining the impulse– and latency curves on monaural than binaural AC neurons. On the other hand, when all other parameters being equal, excitation over inhibition ratio should play a predominant role on the two types of curves on EI than EE neurons. For example, an EI neuron may encode an ipsilateral sound direction with minimal discharge or longest response latency at ILD in favor of a stronger ipsilateral sound level. Conversely, an EI neuron may encode a contralateral sound direction with maximal discharge or shortest response latency at ILD in favor of a stronger contralateral sound level. Furthermore, an EE neuron may simply encode a frontal sound with maximal discharge and shortest response latency at equal ILD.

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Judging from the successful orientation and prey capture behavior, a bat apparently can accurate utilize and integrate the change in the number of impulses and response latency of population of AC neurons with ILD to decipher the echo direction.

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Columnar organization in frequency tuning and binaurality

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The concept that cortical neurons with common response properties cluster in columns or slabs in the sensory cortex has been described in the visual cortex (Hubel and Wiesel, 1963, 1974; Michael, 1981; Bonhoeffer and Grinvald, 1991), somatosensory cortex (Mountcastle, 1957) and AC (Suga 1965, 1977; Merzenich and Brugge, 1973; Merzenich et al., 1975; Suga and Jen, 1976; Imig and Adrian, 1977; Middlebrooks et al., 1980; Suga and Manabe, 1982; Asanuma et al., 1983; Kelly and Sally, 1988; Taniguchi et al., 1988; Jen et al., 1989; Merzenich and Schreiner, 1991; Kelly and Judge, 1994). In the visual and somatosensory cortices, cortical neurons within the same column or slabs share the same, orientation movement sensitivity, eye dominance, receptive field position or sensory modality (Nicholls et al., 2012). Cortical neurons that are columnarly organized along the dorsoventral axis of the AC has been shown in the CF-FM bat (Pteronotus parnellii parneIIii), the FM bat, Myotis lucifugus and Eptesicus fuscus (Suga, 1965, 1977; Suga and Jen, 1976; Suga and Manabe, 1982; Asanuma et al., 1983; Jen et al., 1989; Hou et al., 1992; Shen et al., 1997). These studies show that AC neurons recorded within each orthogonally punctured electrode display similar BF, MT, RLF, best amplitudes, best delay, azimuthal location of maximal spatial sensitivity and binaurality. Furthermore, the FTCs of sequentially recorded AC neurons measured within an orthogonally inserted electrode measured before and during bicucculine application are very similar while the FTCs of sequentially recorded AC neurons within an obliquely inserted electrode differ in shape both before and during bicuculine application (Chen and Jen, 2000). In this study, we have confirmed that all AC neurons recorded within an orthogonal electrode puncture displayed similar BF, MT and ILD functions in terms of impulses and response latency (Fig. 1A, 7, Table 2). It is therefore safe to conclude that AC neurons organize in columns along the dorsoventral axis of the AC according to multiple response parameters to sound stimulation. Because the BF and MT of AC neurons are columnarly organized along the dorsoventral axis of the AC (Table 2, Fig. 1A), these two response parameters are not correlated with their recording depth (Fig. 1C, D). On the other hand, we noticed that the response latency of AC neurons sequentially recorded within each orthogonal electrode puncture tend to shorten with increasing recording depth (Table 2). Conceivably, AC neurons recorded at deeper AC may be located at layers IIIb and IV of the primary AC and thus receive projections directly from the medial geniculate body. These AC neurons may in turn send their axons to AC neurons at upper AC and other parts of the forebrain

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(Mitani and Shimokouchi, 1985; Mitani et al., 1985; Winerm, 1992; de Ribaupierre, 1997).

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ACKNOWLEDGEMENTS

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This work was supported by a grant from the Human Frontier Science Program and a grant from the Humanities and Social Sciences Foundation of the Ministry of Education of China (no. 18YJC740128), the Shandong Provincial Natural Science Foundation, China (no. ZR2018LH009).The writing of this manuscript was supported by a fund from Binzhou Medical University to PHS Jen. We thank the anonymous reviewer for their critical comments on an earlier version of this manuscript.

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REFERENCES

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Asanuma A, Wong D, Suga N (1983) Frequency and amplitude representations in anterior primary auditory cortex of the mustache bat. J Neurophysiol 50:1182–1196. Barber JR, Razak KA, Fuzessery ZM (2003) Can two streams of auditory information be processed simultaneously? Evidence from the gleaning bat Antrozous pallidus. J Comp Physiol A 189:843–855. Bell GP (1982) Behavioral and ecological aspects of gleaning by the desert insectivorous bat, Antrozous pallidus (Chiroptera: Vespertilionidae). Behav Ecol Sociobiol 10:217–223. van Bergeijk WA (1962) Variation on a theme of Bekesy: a model or binaural interaction. J Acoust Soc Am 34:1431–1437. Bonhoeffer T, Grinvald A (1991) Iso-orientation domains in cat visual cortex are arranged in pin-wheel-like patterns. Nature 353:429–431. Butman JA, Suga N (2019) Inhibitory mechanisms shaping delaytuned combination-sensitivity in the auditory cortex and thalamus of the mustached bat. Hear Res 373:71–84. Chen QC, Jen PHS (2000) Bicuculline application affects discharge patterns, rate-intensity functions, and frequency tuning characteristics of bat auditory cortical neurons. Hear Res 150:161–174. Chen QC, Cain D, Jen PHS (1995) Sound pressure transformation at the pinna of Mus domestics. J Exp Biol 198:2007–2023. Code RA, Winer JA (1985) Columnar organization and reciprocity of commissural connections in cat primary auditory cortex (AI). Hear Res 23:205–222. Dear SP, Fritz J, Haresign T, Ferragamo M, Simmons J (1993) Tonotopic and functional organization in the auditory cortex of the big brown bat, Eptesicus fuscus. J Neurophysiol 70:1988–2009. Ebert U, Ostwald J (1995) GABA alters the discharge pattern of chopper neurons in the ventral cochlear nucleus. Hear Res 91:160–166. Erulkar SD (1972) Comparative aspects of spatial localization of sounds. Physiol Rev 52:237–360. Faingold CL, Gehlbach GA, Caspary DM (1989) On the role of GABA as an inhibitory neurotransmitter in inferior colliculus neurons: iontophoretic studies. Brain Res 500:302–312. Faingold CL, Boersma-Anderson CA, Caspary DM (1991) Involvement of GABA in acoustically-evoked inhibition in inferior colliculus neurons. Hear Res 52:201–216. Fuzessery ZM, Hall JC (1996) Role of GABA in shaping frequency tuning and creating FM sweep selectivity in the inferior colliculus. J Neurophysiol 76:1059–1073. Galazyuk A, Feng AS (1997) Encoding of sound duration by neurons in the auditory cortex of the little brown bat, Myotis lucifugus. J Comp Physiol 180:301–311. Games KD, Winer JA (1988) Layer V in rat auditory cortex: projections to the inferior colliculus and contralateral cortex. Hear Res 34:1–25.

823

827 828 829 830 831 832 833

Griffin DR (1958) Listening in the dark. New Haven, CT: Yale Univ Press (Reprinted by Comstock Pub Asso Cornell Univ Press 1986). Hou TT, Wu M, Jen PHS (1992) Pulse repetition rate and duration affect the responses of bat auditory cortical neurons. Chin J Physiol 35:259–278. Hubel DH, Wiesel TN (1963) Shape and arrangement of columns in cat’s striate cortex. J Physiol (Lond) 165:559–568. Hubel DH, Wiesel TN (1974) Uniformity of monkey striate cortex: a parallel relationship between field size, scatter, and magnification factor. J Comp Neurol 158:267–294. Hulgard K, Moss CF, Jakobsen L, Surlykke A (2016) Big brown bats (Eptesicus fuscus) emit intense search calls and fly in stereotyped flight paths as they forage in the wild. J Exp Biol 219:334–340. Imig TJ, Adrian HO (1977) Binaural columns in the primary field (AI) of cat auditory cortex. Brain Res 138:241–257. Imig TJ, Brugge JF (1978) Sources and terminations of callosal axons related to binaural and frequency maps in primary auditory cortex of the cat. J Comp Neurol 182:637–660. Jen PHS, Chen DM (1988) Directionality of sound pressure transformation at the pinna of echolocating bats. Hear Res 34:101–118. Jen PHS, Kamada T (1982) Analysis of orientation signals emitted by the CF-FM bat, Pteronotus parnellii parnellii and the FM bat, Eptesicus fuscus during avoidance of moving and stationary obstacles. J Comp Physiol 148:389–398. Jen PHS, Schlegel PA (1982) Auditory physiological properties of the neurons in the inferior colliculus of the big brown bat, Eptesicus fuscus. J Comp Physiol 147:351–363. Jen PHS, Chen QC, Wu FJ (2002a) Interaction between excitation and inhibition affects frequency tuning curve, response size and latency of neurons in the auditory cortex of the big brown bat, Eptesicus fuscus. Hear Res 174:281–289. Jen PHS, Sun XD, Chen DM, Teng HB (1987) Auditory space representation in the inferior colliculus of the FM bat, Eptesicus fuscus. Brain Res 419:7–18. Jen PHS, Sun XD, Lin PJJ (1989) Frequency and space representation in the primary auditory cortex of the frequency modulating bat Eptesicus fuscus. J Comp Physiol 165:1–14. Jen PHS, Hou TT, Wu M (1993) Neurons in the inferior colliculus, auditory cortex and pontine nuclei of the FM bat, Eptesicus fuscus respond to pulse repetition rate differently. Brain Res 613:152–155. Jen PHS, Sun XD, Shen JX, Chen QC, Qian Y (1997) Cytoarchitecture and sound activated responses in the auditory cortex of the big brown bat, Eptesicus fuscus. Acta Otolaryngol 532:61–67. Jen PH, Zhou X, Zhang J, Chen QC, Sun X (2002) Brief and shortterm corticofugal modulation of acoustic signal processing in the bat midbrain. Hear Res 168:196–207. Kanwal JS, Fitzpatrick DC, Suga N (1999) Facilitatory and inhibitory frequency tuning of combination-sensitive neurons in the primary auditory cortex of mustached bats. J Neurophysiol 82:2327–2345. Kelly JB, Judge PW (1994) Binaural organization of primary auditory cortex in the ferret (Mustela putorius). J Neurophysiol 71:904–913. Kelly JB, Sally SL (1988) Organization of auditory cortex in the albino rat: binaural response properties. J Neurophysiol 59:1756–1769. King AJ, Teki S, Willmore BDB (2018) Recentr advances in understanding the auditory cortex. F1000Research 7(F1000 Faculty Rev):1555. https://doi.org/10.12688/ 1000research.15580.1. Ko¨ssl M, Hechavarria J, Voss C, Macias S, Mora E, Vater M (2014) Neural maps for target range in the auditory cortex of echolocating bats. Curr Opin Neurobiol 24C:68–75. Liu W, Suga N (1997) Binaural and commissural organization of the primary auditory cortex of the mustached bat. J Comp Physiol 181:599–605. Lohuis TD, Fuzessery ZM (2000) Neuronal sensitivity to interaural time differences in the sound envelope in the auditory cortex of the pallid bat. Hear Res 143:43–57.

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Lu Y, Jen PHS (2001) GABAergic and glycinergic neural inhibition in frequency tuning of bat inferior collicular neurons. Exp Brain Res 141:331–339. Lu Y, Jen PHS (2003) Binaural interaction in the inferior colliculus of the big brown bat, Eptesicus fuscus. Hear Res 177:100–110. Lu Y, Jen PHS, Zheng QY (1997) GABAergic disinhibition changes the recovery cycle of bat inferior collicular neurons. J Comp Physiol 181:331–341. Lu Y, Jen PHS, Wu M (1998) GABAergic disinhibition affects responses of bat inferior collicular neurons to temporally patterned sound pulses. J Neurophysiol 79:2303–2315. Ma X, Suga N (2001) Plasticity of bat’s central auditory system evoked by focal electric stimulation of auditory and/or somatosensory cortices. J Neurophysiol 85:1078–1087. Ma X, Suga N (2007) Multiparametric corticofugal modulation of collicular duration-tuned neurons: modulation in the amplitude domain. J Neurophysiol 97:3722–3730. Manabe T, Suga N, Ostwald J (1978) Aural representation in the Doppler-shifted CF-processing area of the auditory cortex of the mustache bat. Science 200:339–342. Merzenich MM, Brugge JF (1973) Representation of the cochlear partition on the superior temporal plane of the macaque monkey. Brain Res 50:275–296. Merzenich MM, Knight PL, Roth GL (1975) Representation of cochlea within primary auditory cortex in the cat. J Neurophysiol 38:231–249. Merzenich MM, Schreiner CE (1991) Mammalian auditory cortex— some comparative observations. In: Webster DB, Fay RR, Popper AN, editors. The evolutionary biology of hearing. Berlin: SpringerVerlag. p. 673–689. Michael CR (1981) Columnar organization of color cells in monkey’s striate cortex. J Nerurophysiol 46:587–604. Middlebrooks JC, Dykes RW, Merzenich MM (1980) Binaural response-specific bands in primary auditory cortex (AI) of the cat: topographical organization orthogonal to isofrequency contours. Brain Res 181:31–48. Middlebrooks JC, Zook JM (1983) Intrinsic organization of the cat’s medial geniculate body identified by projections to binaural response-specific bands in the primary auditory cortex. J Neurosci 3:203–224. Mitani A, Shimokouchi M (1985) Neuronal connections in the primary cortex: an electrophysiological study in the cat. J Comp Neurol 235:417–429. Mitani A, Shimokouchi M, Itoh K, Nomura S, Kudo M, Mizuno N (1985) Morphology and laminar organization of electrophysiological identified neurons in the primary auditory cortex in the cat. J Comp Neurol 235:430–447. Mountcastle VB (1957) Modality and topographic properties of single neurons of cat’s somatic sensory cortex. J Neurophysiol 20:408–434. Nicholls JG, Martin AR, Fuchs PA, Brown DA, Diamond ME, Weisblat DA (2012) From neuron to brain. Fifth edition. Sinauer Associates, Inc.. p. 44.–45. 442-443. Palombi PS, Caspary DM (1996) GABA inputs control discharge rate primarily within frequency receptive fields of inferior colliculus neurons. J Neurophysiol 75:2211–2219. Phillips DP, Judge PW, Kelly JB (1988) Primary auditory cortex in the ferret (Mustela putorius): neural response properties and topographic organization. Brain Res 443:281–294. Pinheiro AD, Wu M, Jen PHS (1991) Encoding repetition rate and duration in the inferior colliculus of the big brown bat, Eptesicus fuscus. J Comp Physiol 169:69–85. Pollak GD, Burger RM, Klug A, Bauer EE (2002) Roles of inhibition for transforming binaural properties in the brainstem auditory system. Hear Res 168:60–78. Pollak GD, Burger RM, Klug A (2003) Dissecting the circuity of the auditory system. Trends Neurosci 26:33–39. Prieto JJ, Peterson BA, Winer JA (1994a) Morphology and spatial distribution of GABAergic neurons in cat primary auditory cortex (AI). J Comp Neurol 344:349–382.

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Prieto JJ, Peterson BA, Winer JA (1994b) Laminar distribution and neuronal targets of GABAergic axon terminals in cat primary auditory cortex (AI). J Comp Neurol 344:383–402. Razak KA, Fuzessery ZM (2002) Functional organization of the pallid bat auditory cortex: emphasis on binaural organization. J Neurophysiol 87:72–86. Razak KA, Fuzessery ZM (2006) Neural mechanisms underlying selectivity for the rate and direction of frequency modulated sweeps in the auditory cortex of the pallid bat. J Neurophysiol 96:1303–1319. Razak KA, Fuzessery ZM (2009) GABA shapes selectivity for the rate and direction of frequency modulated sweeps in the auditory cortex. J Neurophysiol 102:1366–1378. Razak KA, Fuzessery ZM (2010) GABA shapes a systematic map of binaural sensitivity in the auditory cortex. J Neurophysiol 104:517–528. Razak KA, Fuzessery ZM (2015) Development of echolocation calls and neural selectivity for echolocation calls in the pallid bat. Dev Neurobiol 75(10):1125–1139. Razak KA, Fuzessery ZM, Lohuis TD (1999) Single cortical neurons serve both echolocation and passive sound localization. J Neurophysiol. 81:1438–1442. Razak KA, Shen W, Zumsteg T, Fuzessery ZM (2007) Parallel thalamocortical pathways for echolocation and passive sound localization in a gleaning bat, Antrozous pallidus. J Comp Neurol 500:322–338. Razak KA, Zumsteg T, Fuzessery ZM (2009) Development of auditory thalamocortical connections in the pallid bat, Antrozous pallidus. J Comp Neurol 515:231–242. Reale RA, Kettner RE (1986) Topographic of binaural organization in primary auditory cortex of the cat: effects of changing interaural intensity. J Neurophysiol 86:663–682. de Ribaupierre F (1997) Acoustical information processing in the auditory thalamus and cerebral cortex. In: Ehret G, Romand R, editors. The central auditory system. Oxford: Oxford University Press. p. 317–397. Saldana E, Feliciano M, Mugnaini E (1996) Distribution of descending projections from primary auditory neocortex to inferior colliculus mimics the topography of intracollicular projections. J Comp Neurol 371:15–40. Schlegel PA (1977) Calibrated earphones for the echolocating bats, Rhinolophus ferrumequinum. J Comp Physiol 118:353–356. Schnitzler HU (1968) Die Ultraschall-Ortungslaute der HufeisenFledermause (Chiroptera-Rhinolophidae) in verschiedenen Orientierungssituationen. Z Physiol 57:376–408. Shen JX, Chen QC, Jen PHS (1997) Binaural and frequency representation in the primary auditory cortex of the big brown bat, Eptesicus fuscus. J Comp Physiol 181:591–597. Simmons JA, Fenton MB, O’Farrell MJ (1979) Echolocation and pursuit of prey by bats. Science 203:16–21. Suga N (1965) Functional properties of auditory neurons in the cortex of echolocating bats. J Physiol 181:671–700. Suga N (1977) Amplitude-spectrum representation in the Dopplershifted-CF processing area of the auditory cortex of the mustached bat. Science 196:64–67. Suga N (1982) Functional organization of the auditory cortex representation beyond tonotopy in the bat (Chapter 6). In: Woolsey CN, editor. Cortical Sensory Organization. Clifton, New Jersey U.S.A.: Humana Press. p. 157–218. Suga N (1984) The extent to which biosonar information is represented in the bat auditory cortex. In: Edelman GM, Gall WE, Cowan WM, editors. Dynamic aspects of neocortical function. New York: John Wiley & Sons. p. 315–373. Suga N (1990) Biosonar and neural computation in bats. Sci Am 262:60–68. Suga N (1997) Parallel-hierarchical processing of complex sounds for specialized auditory function. In: Crocker MJ, editor. Encyclopedia of acoustics. New York: John Wiley and Sons. p. 1409–1418. Suga N (2015) Neural processing of auditory signals in the time domain: delay-tuned coincidence detectors in the mustached bat. Hear Res 324:19–36.

Please cite this article in press as: Yang Y et al. Binaural Response Properties and Sensitivity to Interaural Difference of Neurons in the Auditory Cortex of the Big Brown Bat, Eptesicus fuscus. Neuroscience (2019), https:// doi.org/10.1016/j.neuroscience.2019.11.024

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Suga N, Horikawa J (1986) Multiple time axes for representation of echo delays in the auditory cortex of the mustached bat. J Neurophysiol 55:776–805. Suga N, Jen PHS (1976) Disproportionate tonotopic representation for processing species-specific CF-FM sonar signals in the mustached bat auditory cortex. Science 194:542–544. Suga N, Manabe T (1982) Neural basis of amplitude-spectrum representation in auditory cortex of the mustached bat. J Neurophysiol 47:225–255. Sullivan WE (1982) Neural representation of target distance in the auditory cortex of the echolocating bat, Myotis lucifugus. J Neurophysiol 48:1011–1032. Surlykke A, Moss CF (2000) Echolocation behavior of big brown bats, Eptesicus fuscus, in the field and the laboratory. J Acoust Soc Am 108:2419–2429. Surlykke A, Ghose K, Moss CF (2009) Acoustic scanning of natural scenes by echolocation in the big brown bat, Eptesicus fuscus. J Exp Biol 212:1011–1020. Suzuki M, Suga N (2017) Acuity in ranging based on delay-tuned combination-sensitive neurons in the auditory cortex of mustached bats. Hear Res 350:189–204. Taniguchi I, Niwa H, Wong D, Suga N (1986) Response properties of FM-FM combination sensitive neurons in the auditory cortex of the mustached bat. J Comp Physiol A 159:331–337. Taniguchi I, Arai O, Saito N (1988) Functional laminar and columnar organization of the auditory centers in echolocating Japanese greater horseshoe bats. Neurosci Lett 88:17–20. Teng H, Suga N (2017) Differences in velocity-information processing between two areas in the auditory cortex of mustached bats. Hear Res 350:68–81.

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Wang J, Caspary D, Salvi R (2000) GABA-A antagonist causes dramatic expansion of tuning in primary auditory cortex. NeuroReport 57:1137–1140. Winer JA (1992) The functional architecture of the medial geniculate body and the primary auditory cortex. In: Webster DB, Popper AN, Fay RR, editors. The mammalian auditory pathway neuroanatomy. New York: Springer. p. 222–409. Winer JA, Laurue DT (1989) Populations of GABAergic neurons and axons in layer I of rat auditory cortex. Neurosci 33:499–515. Winer JA, Larue DT, Diehl JJ, Hefti BJ (1998) Auditory cortical projections to the cat inferior colliculus. J Comp Neurol 400:147–174. Wong D, Maekawa M, Tanaka H (1992) The effect of pulse repetition rate on the delay sensitivity of neurons in the auditory cortex of the FM bat, Myotis lucifugus. J Comp Physiol A 170:393–402. Wu M, Hou ETT, Jen PHS (1996) Responses of bat inferior collicular and auditory cortical neurons to pulsatile amplitude modulated sound pulses. Chin J Physiol 39(3):1–7. Yang L, Pollak GD (1994) GABA and glycine have different effects on monaural response properties in the dorsal nucleus of the lateral lemniscus of the mustache bat. J Neurophysiol 71:2014–2024. Zhang YF, Suga N (2000) Modulation of responses and frequency tuning of thalamic and collicular neurons by cortical activation in mustached bats. J Neurophysiol 84:325–333. Zeki S (1981) The mapping of visual functions in the cerebral cortex. In: Katsuki Y, Norgen R, Sato M, editors. Brain mechanisms of sensation. New York: Wiley. p. 105–128. Zhou XM, Jen PHS (2007) Corticofugal modulation of multiparametric auditory selectivity in the midbrain of the big brown bat. J Neurophysiol 98:2509–2516.

(Received 11 September 2019, Accepted 14 November 2019) (Available online xxxx)

Please cite this article in press as: Yang Y et al. Binaural Response Properties and Sensitivity to Interaural Difference of Neurons in the Auditory Cortex of the Big Brown Bat, Eptesicus fuscus. Neuroscience (2019), https://doi.org/10.1016/j.neuroscience.2019.11.024

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