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Temporal and spectral information processing in the auditory cortex: a steady-state auditory-evoked potential study
International Congress Series 1278 (2005) 27 – 30
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Temporal and spectral information processing in the auditory cortex: a steady-state auditory-evoked potential study Tomomi Kurokawa-Kuroda*, Takao Yamasaki, Yoshinobu Goto, Shozo Tobimatsu Department of Clinical Neurophysiology, Neurological Institute, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, 812-8582, Japan
Abstract. We examined the temporal and spectral information processing in the auditory cortex by using steady-state auditory-evoked potentials (S-AEPs). Tone-burst stimuli at carrier frequencies of 500 and 2000 Hz were presented monaurally to elicit S-AEPs in 10 normal subjects. Modulation frequency was varied from 15 to 90 Hz at every 5 Hz. Nine recording electrodes were placed coronally, including Cz, referring to an electrode at the seventh cervical spinous process (SC7). A total of 100 responses of 1-s epoch was averaged and subjected to discrete fast Fourier transforms (FFTs), to yield the amplitude of the first harmonic (1F) component and interhemispheric coherence (Coh) value between homologous electrodes. Three amplitude peaks at around 15–20, 40–45 and 80 Hz were observed against the modulation frequency at both carrier frequencies. The interhemispheric Coh value between T3 and T4 of the right-ear stimulation was greater at around 35–45 Hz than those of the left-ear stimulation, and vice versa, from 50 to 90 Hz at a carrier frequency of 500 Hz. However, this characteristic was not observed at the carrier frequency of 2000 Hz. Three tuning peaks indicate the presence of neuronal subgroups for the temporal processing, as observed in the visual system. In addition, left-hemisphere predominance for rapid temporal processing depends on the carrier frequency, suggesting differential processing of temporal and spectral information in the auditory cortices. D 2004 Elsevier B.V. All rights reserved. Keywords: Steady-state auditory-evoked potentials; Tone-burst stimulation; Temporal and spectral information processing; Interhemispheric coherence
* Corresponding author. Tel.: +81 92 642 5543; fax: +81 92 642 5545. E-mail address: [email protected] (T. Kurokawa-Kuroda). 0531-5131/ D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.ics.2004.11.139
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T. Kurokawa-Kuroda et al. / International Congress Series 1278 (2005) 27–30
1. Introduction Temporal and spectral information of auditory signals is important for the perception of complex auditory stimuli. Based on the previous study, temporal information was predominantly processed in the left auditory cortex, while the right side plays an important role in spectral information processing [1]. Our recent study using steady-state auditoryevoked potentials (S-AEPs) with the coherence (Coh) analysis has also shown that 40-Hz auditory information was predominantly processed in the left auditory cortex [2]. However, the characteristics of the activation and interaction between both auditory cortices with modulation and carrier frequencies are still unclear. Thus, we recorded S-AEPs to elucidate this question. 2. Methods Ten healthy subjects (6 males and 4 females), aged 24–40 years, participated in this study. All subjects were right handed and reported no clinical history of hearing loss or neurological disorders. An auditory stimulator (Neuropack 8, Nihon Kohden, Japan) delivered a controlled tone-burst stimulation, which was given to each ear via the earphone. The carrier frequency was held at 500 or 2000 Hz, and the modulation frequency was varied from 15 to 90 Hz at every 5-Hz steps, with an intensity of 50 dBSL. White noise was given to the contralateral ear at an intensity of 40 dBSL. Nine recording electrodes were placed coronally, including Cz, referring to an electrode at the seventh cervical spinous process (SC7). The analog data were digitized at a sampling rate of 1 kHz, and 100 samples of 1-s epoch were averaged. Then, they were subjected to fast Fourier transforms (FFTs) to yield the amplitude of the first harmonic (1F) component for each modulation frequency. The interhemispheric Coh value of 1F between homologous electrode pairs was measured [2]. A three-way analysis of variance (ANOVA) with repeated measures was performed to determine the effects of the electrode positions (T3 vs. T4), stimulus sides (left vs. right) and carrier frequencies (500 vs. 2000 Hz) on the 1F amplitude. A two-way analysis of covariance (ANCOVA) was also used for the Coh values between modulation frequencies at carrier frequencies of 500 and 2000 Hz. 3. Results Temporal electrodes (T3 and T4) are less affected by volume conduction [2], hence, we mainly analyzed the amplitudes and Coh values at these electrodes. S-AEPs were characterized by quasi-sinusoidal waveforms that corresponded to each modulation frequency, and the 1F component was the major component in the amplitude spectrum of FFTs. Fig. 1A shows the mean 1F amplitudes of T3 and T4 electrodes at the responses of right-ear stimulation against each modulation frequency at the carrier frequency of 500 Hz. Three peaks at around 15–20, 40–45 and 80 Hz were observed in both electrodes. The 1F amplitudes of contralateral to the stimulated ear were significantly larger than those of ipsilateral side [ F(1,9)=19.44, pb0.05]. In addition, the 1F amplitudes of 500 Hz tended to be greater than those of 2000 Hz [ F(1,9)=5.02, p=0.0518].
T. Kurokawa-Kuroda et al. / International Congress Series 1278 (2005) 27–30
29
Fig. 1. 1F amplitudes of S-AEPs at T3 and T4 electrodes (A) and interhemispheric Coh values between T3 and T4 electrodes (B) as the function of modulation frequency at carrier frequency of 500 Hz in the rightear stimulation.
Fig. 1B shows the interhemispheric Coh values of 1F between T3 and T4 against each modulation frequency at the carrier frequency of 500 Hz. The Coh values between 35 and 45 Hz of the right-ear stimulation tended to be greater than those of the left-ear stimulation, and vice versa, between 50 and 90 Hz. This tendency was less clearer at 2000 Hz [ANCOVA, F(1,169)=3.80, p=0.0528]. 4. Discussion Three amplitude peaks were observed against the modulation frequency (Fig. 1A), which suggested that the auditory system has a temporal tuning function, as found in the visual system [3]. This temporal resonance plays an important role in extracting the stimulus features as neural filters in the temporal domain. Interestingly, a reversible hemispheric contribution to the temporal processing was observed (Fig. 1B). Recent animal [4] and MEG studies [5] have shown that the stimulus rate of 40 Hz was critical for temporal and spectral information processing. Our recent study has demonstrated that 40-Hz auditory information was predominantly processed in the left auditory cortex. Therefore, the dominant hemisphere for temporal processing can be reversible, depending on the modulation frequency in the human auditory system. Carrier frequencies of 500 and 2000 Hz showed the differential effects on the amplitudes and Coh values of 1F. A recent neuroimaging study has demonstrated that the activation area of the lower tone was larger than that of the higher tone [6]. It is likely that the carrier frequency differentially modulates the temporal processing. In summary, our results suggest the importance of modulation and carrier frequencies for the temporal and spectral processing in the auditory cortex. Acknowledgements This study was supported, in part, by Grant-in Aid for the 21st Century COE Program.
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T. Kurokawa-Kuroda et al. / International Congress Series 1278 (2005) 27–30
References [1] R.J. Zatorre, P. Belin, Spectral and temporal processing in human auditory cortex, Cereb. Cortex 11 (2001) 946 – 953. [2] T. Yamasaki, et al., Left hemisphere specialization for rapid temporal processing: a study with auditory 40 Hz steady state responses. Clin. Neurophysiol. (in press). [3] D. Regan, Human brain electrophysiology, Evoked Potentials and Evoked Magnetic Fields in Science and Medicine, Elsevier, New York, 1989, pp. 383 – 390. [4] T. Lu, L. Liang, X. Wang, Temporal and rate representations of time-varying signals in the auditory cortex of awake primates, Nat. Neurosci. 4 (2001) 1131 – 1138. [5] A. Gutschalk, et al., Sustained magnetic fields reveal separate sites for sound level and temporal regularity in human auditory cortex, NeuroImage 15 (2002) 207 – 216. [6] D. Bilecen, et al., Tonotopic organization of the human auditory cortex as detected by BOLD-FMRI, Hear. Res. 126 (1998) 19 – 27.
www.ics-elsevier.com
Temporal and spectral information processing in the auditory cortex: a steady-state auditory-evoked potential study Tomomi Kurokawa-Kuroda*, Takao Yamasaki, Yoshinobu Goto, Shozo Tobimatsu Department of Clinical Neurophysiology, Neurological Institute, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, 812-8582, Japan
Abstract. We examined the temporal and spectral information processing in the auditory cortex by using steady-state auditory-evoked potentials (S-AEPs). Tone-burst stimuli at carrier frequencies of 500 and 2000 Hz were presented monaurally to elicit S-AEPs in 10 normal subjects. Modulation frequency was varied from 15 to 90 Hz at every 5 Hz. Nine recording electrodes were placed coronally, including Cz, referring to an electrode at the seventh cervical spinous process (SC7). A total of 100 responses of 1-s epoch was averaged and subjected to discrete fast Fourier transforms (FFTs), to yield the amplitude of the first harmonic (1F) component and interhemispheric coherence (Coh) value between homologous electrodes. Three amplitude peaks at around 15–20, 40–45 and 80 Hz were observed against the modulation frequency at both carrier frequencies. The interhemispheric Coh value between T3 and T4 of the right-ear stimulation was greater at around 35–45 Hz than those of the left-ear stimulation, and vice versa, from 50 to 90 Hz at a carrier frequency of 500 Hz. However, this characteristic was not observed at the carrier frequency of 2000 Hz. Three tuning peaks indicate the presence of neuronal subgroups for the temporal processing, as observed in the visual system. In addition, left-hemisphere predominance for rapid temporal processing depends on the carrier frequency, suggesting differential processing of temporal and spectral information in the auditory cortices. D 2004 Elsevier B.V. All rights reserved. Keywords: Steady-state auditory-evoked potentials; Tone-burst stimulation; Temporal and spectral information processing; Interhemispheric coherence
* Corresponding author. Tel.: +81 92 642 5543; fax: +81 92 642 5545. E-mail address: [email protected] (T. Kurokawa-Kuroda). 0531-5131/ D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.ics.2004.11.139
28
T. Kurokawa-Kuroda et al. / International Congress Series 1278 (2005) 27–30
1. Introduction Temporal and spectral information of auditory signals is important for the perception of complex auditory stimuli. Based on the previous study, temporal information was predominantly processed in the left auditory cortex, while the right side plays an important role in spectral information processing [1]. Our recent study using steady-state auditoryevoked potentials (S-AEPs) with the coherence (Coh) analysis has also shown that 40-Hz auditory information was predominantly processed in the left auditory cortex [2]. However, the characteristics of the activation and interaction between both auditory cortices with modulation and carrier frequencies are still unclear. Thus, we recorded S-AEPs to elucidate this question. 2. Methods Ten healthy subjects (6 males and 4 females), aged 24–40 years, participated in this study. All subjects were right handed and reported no clinical history of hearing loss or neurological disorders. An auditory stimulator (Neuropack 8, Nihon Kohden, Japan) delivered a controlled tone-burst stimulation, which was given to each ear via the earphone. The carrier frequency was held at 500 or 2000 Hz, and the modulation frequency was varied from 15 to 90 Hz at every 5-Hz steps, with an intensity of 50 dBSL. White noise was given to the contralateral ear at an intensity of 40 dBSL. Nine recording electrodes were placed coronally, including Cz, referring to an electrode at the seventh cervical spinous process (SC7). The analog data were digitized at a sampling rate of 1 kHz, and 100 samples of 1-s epoch were averaged. Then, they were subjected to fast Fourier transforms (FFTs) to yield the amplitude of the first harmonic (1F) component for each modulation frequency. The interhemispheric Coh value of 1F between homologous electrode pairs was measured [2]. A three-way analysis of variance (ANOVA) with repeated measures was performed to determine the effects of the electrode positions (T3 vs. T4), stimulus sides (left vs. right) and carrier frequencies (500 vs. 2000 Hz) on the 1F amplitude. A two-way analysis of covariance (ANCOVA) was also used for the Coh values between modulation frequencies at carrier frequencies of 500 and 2000 Hz. 3. Results Temporal electrodes (T3 and T4) are less affected by volume conduction [2], hence, we mainly analyzed the amplitudes and Coh values at these electrodes. S-AEPs were characterized by quasi-sinusoidal waveforms that corresponded to each modulation frequency, and the 1F component was the major component in the amplitude spectrum of FFTs. Fig. 1A shows the mean 1F amplitudes of T3 and T4 electrodes at the responses of right-ear stimulation against each modulation frequency at the carrier frequency of 500 Hz. Three peaks at around 15–20, 40–45 and 80 Hz were observed in both electrodes. The 1F amplitudes of contralateral to the stimulated ear were significantly larger than those of ipsilateral side [ F(1,9)=19.44, pb0.05]. In addition, the 1F amplitudes of 500 Hz tended to be greater than those of 2000 Hz [ F(1,9)=5.02, p=0.0518].
T. Kurokawa-Kuroda et al. / International Congress Series 1278 (2005) 27–30
29
Fig. 1. 1F amplitudes of S-AEPs at T3 and T4 electrodes (A) and interhemispheric Coh values between T3 and T4 electrodes (B) as the function of modulation frequency at carrier frequency of 500 Hz in the rightear stimulation.
Fig. 1B shows the interhemispheric Coh values of 1F between T3 and T4 against each modulation frequency at the carrier frequency of 500 Hz. The Coh values between 35 and 45 Hz of the right-ear stimulation tended to be greater than those of the left-ear stimulation, and vice versa, between 50 and 90 Hz. This tendency was less clearer at 2000 Hz [ANCOVA, F(1,169)=3.80, p=0.0528]. 4. Discussion Three amplitude peaks were observed against the modulation frequency (Fig. 1A), which suggested that the auditory system has a temporal tuning function, as found in the visual system [3]. This temporal resonance plays an important role in extracting the stimulus features as neural filters in the temporal domain. Interestingly, a reversible hemispheric contribution to the temporal processing was observed (Fig. 1B). Recent animal [4] and MEG studies [5] have shown that the stimulus rate of 40 Hz was critical for temporal and spectral information processing. Our recent study has demonstrated that 40-Hz auditory information was predominantly processed in the left auditory cortex. Therefore, the dominant hemisphere for temporal processing can be reversible, depending on the modulation frequency in the human auditory system. Carrier frequencies of 500 and 2000 Hz showed the differential effects on the amplitudes and Coh values of 1F. A recent neuroimaging study has demonstrated that the activation area of the lower tone was larger than that of the higher tone [6]. It is likely that the carrier frequency differentially modulates the temporal processing. In summary, our results suggest the importance of modulation and carrier frequencies for the temporal and spectral processing in the auditory cortex. Acknowledgements This study was supported, in part, by Grant-in Aid for the 21st Century COE Program.
30
T. Kurokawa-Kuroda et al. / International Congress Series 1278 (2005) 27–30
References [1] R.J. Zatorre, P. Belin, Spectral and temporal processing in human auditory cortex, Cereb. Cortex 11 (2001) 946 – 953. [2] T. Yamasaki, et al., Left hemisphere specialization for rapid temporal processing: a study with auditory 40 Hz steady state responses. Clin. Neurophysiol. (in press). [3] D. Regan, Human brain electrophysiology, Evoked Potentials and Evoked Magnetic Fields in Science and Medicine, Elsevier, New York, 1989, pp. 383 – 390. [4] T. Lu, L. Liang, X. Wang, Temporal and rate representations of time-varying signals in the auditory cortex of awake primates, Nat. Neurosci. 4 (2001) 1131 – 1138. [5] A. Gutschalk, et al., Sustained magnetic fields reveal separate sites for sound level and temporal regularity in human auditory cortex, NeuroImage 15 (2002) 207 – 216. [6] D. Bilecen, et al., Tonotopic organization of the human auditory cortex as detected by BOLD-FMRI, Hear. Res. 126 (1998) 19 – 27.