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LORETA analysis of CNV in time perception
International Congress Series 1270 (2004) 291 – 294
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LORETA analysis of CNV in time perception Keiichi Onoda, Jun Suzuki, Hiroshi Nittono, Shogo Sakata, Tadao Hori * Graduate School of Biosphere Science, Hiroshima University, 1-7-1, Kagamiyama, Higashi-Hiroshima, Hiroshima,739-8521, Japan
Abstract. The aim of this study was to specify when and where ‘‘pure’’ temporal processing occurred in the brain. Event-related potentials were recorded from 13 young, healthy volunteers performing interval and pitch discrimination tasks. In the interval task, two 1000-Hz tones (S1 and S2) were presented with an interval of 1000 or 1500 ms. Participants were asked to judge whether the S1 – S2 interval was short or long. In the pitch task, the S1 (1000 Hz) was followed by the S2 (1000 or 1050 Hz) with a fixed interval of 1000 ms. Participants were asked to judge whether the pitch of the S2 was the same as or different from that of the S1. In both tasks, contingent negative variation (CNV) was observed in the period between 500 and 1000 ms after the S1. The amplitude of the CNV was larger in the interval task than in the pitch task. The data were analyzed using lowresolution electromagnetic tomography (LORETA). The right dorsolateral prefrontal cortex (DLPFC) showed more activation in the interval task than in the pitch task. This result suggests that the right DLPFC may play an important role in time perception and processing the temporal dimension of events. D 2004 Elsevier B.V. All rights reserved. Keywords: Time perception; Contingent negative variation (CNV); LORETA; Dorsolateral prefrontal cortex (DLPFC)
1. Introduction Time is an important source of information influencing behavior. However, the neurophysiological basis of time perception remains a matter for debate. Recent studies using functional brain mapping have suggested some brain structures where time-related attributes of an event are processed [1]; nevertheless, these structures are also involved in the perception of other dimensions, such as the intensity, pitch, color, shape, and location of auditory and visual stimuli. In order to conclude that the perception of time is responsible for the observed pattern of activation, it should be demonstrated that this pattern is not elicited by the perception of other attributes of stimuli. In functional brain mapping studies, some patterns of activation described in the timing task are similar to
* Corresponding author. Tel.: +81-824-24-6580; fax: +81-824-24-0759. E-mail address: [email protected] (T. Hori). 0531-5131/ D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.ics.2004.05.002
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those in working memory and attention tasks. As fMRI and PET integrate an activity over a period of many seconds, temporal resolution is often insufficient to specify areas only involved when temporal processing is performed. Therefore, Pouthas et al. [2] examined contingent negative variation (CNV) observed in duration discrimination tasks using dipole analysis. They discovered that the right frontal dipole is active during the CNV, and proposed that the processing of temporal information would specifically involve the right frontal area. The CNV, however, reflects not only temporal processing but also others, such as attention and motivation. In order to argue the contribution of the right frontal lobe in time perception, it is necessary to distinguish the processing of time from other processing tasks. This study used two tasks based on the S1 – S2 paradigm, a task in which the interval of the S1 and S2 was judged, and a task in which the pitch of the S1 and S2 were judged. Sources of the CNV observed in the two tasks were compared using lowresolution brain electromagnetic tomography (LORETA) [3]. 2. Method 2.1. Subjects Participants were 13 (5 females and 8 males) young volunteers between 21 and 25 years old with normal audition. The experiment was conducted with the informed consent of each subject. 2.2. Tasks In the interval task, two 1000-Hz tones (S1 and S2, 70 dB) were presented with an interval of 1000 or 1500 ms. Participants were asked to judge whether the S1 –S2 interval was short or long. The tone duration was 50 ms. The intensity of the stimulus was 70 dB. The ISI lasted between 2600 and 3400 ms (on average, 3000 ms). The probabilities were 0.5/0.5. The button press responses were made with the thumbs of each hand. They were instructed to delay their responses for about 1000 ms in both tasks. Each participant was given 100 trials in this task. In the pitch task, the S1 (1000 Hz) was followed by the S2 (1000 or 1050 Hz) with a fixed interval of 1000 ms. Participants were required to judge whether the pitch of the S2 was the same as or different from that of the S1. Other variables were the same as that of the interval task. The response hands and the task order were counterbalanced across participants. 2.3. ERP recording and analysis Electroencephalograms (EEGs) were recorded digitally from 24 electrode sites and rereferenced to the nose tip. Horizontal and vertical electro-oculograms (EOGs) were simultaneously recorded. The sampling rate was 500 Hz. A bandpass filter of 0.016 – 100 Hz was used. Event-related potentials (ERPs) were obtained for each task. The averaging period was 1200 ms with a 200 ms baseline before the onset of S1. A repeated measure analysis of variance was performed on the mean amplitudes at Cz between 500 and 1000 ms after the S1. LORETA [3,4] was used to find differences in intracerebral
K. Onoda et al. / International Congress Series 1270 (2004) 291–294
293
Fig. 1. Grand mean ERP waveforms recorded at Cz during the S1 – S2 interval period (N = 13). The vertical line shows the onset of S1.
sources of the CNV between the two tasks. The pairwise t-test was performed on a voxelby-voxel basis. 3. Results 3.1. Behavior The correct response rates in the two tasks were 97.8% (S.D. 2.7) for the interval task, and 97.4% (5.0) for the pitch task. No difference in performance was found between the tasks, t(12) = 0.24, n.s. 3.2. ERP Fig. 1 shows ERP waveforms at the vertex (Cz) averaged across subjects in the interval and the pitch discrimination tasks. Following the sensory-evoked potentials, a clear CNV can be observed from 500 to 1000 ms after the S1 in both tasks. The mean amplitude between 500 and 1000 ms was larger in the interval task than in the pitch task, F(1,12) = 13.28, p < 0.01.
Fig. 2. Statistical maps of t value illustrating the differences in current source density between the interval and pitch tasks at the epoch between 500 and 1000 ms. Highlighted voxels (t>3.00) appear in the right dorsolateral prefrontal cortex (DLPFC).
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K. Onoda et al. / International Congress Series 1270 (2004) 291–294
3.3. LORETA To compare the differences in current source density between the CNVs (500 – 1000 ms) in the two tasks, the pairwise t-test was used on a voxel-by-voxel basis. The maximal t value was observed in the right dorsolateral prefrontal cortex (DLPFC) at the Talairach coordinates (25, 31, 36) (Fig. 2). 4. Discussion In the present study, we examined the spatio-temporal organization of cerebral areas involved in temporal processing by LORETA analysis of ERP. The activation of the right DLPFC was found during the CNV in the interval task. Since sustained attention and working memory were also involved in the pitch task, the differential activation in the right DLPFC suggests an important role of this area processing the temporal dimension of the event. Using ERPs combined with PET, Pouthas et al. [2] found the timing of activation in the right inferior prefrontal cortex during time discrimination was strongly aligned with the durations. The contribution of the right dorsolateral and inferior prefrontal cortices in time perception was supported by fMRI studies (e.g. Ref. [4]), although the differences between the roles of these regions are not clear. Some hypotheses about the role of the right DLPFC in time perception proposed that the role of the region may act as a central ‘‘clock’’ mechanism, ‘‘accumulator’’ storing temporal information, ‘‘mediator’’ of time estimation process, and ‘‘maker of decisions’’ [5]. Although the results of this study cannot directly mention the role of the right DLPFC, a more detailed, temporal – spatial analysis using LORETA may help to understand the process of time perception. References [1] P.A. Lewis, R.C. Miall, Distinct systems for automatic and cognitively controlled time measurement: evidence from neuroimaging, Curr. Opin. Neurobiol. 13 (2003) 250 – 255. [2] V. Pouthas, et al., ERPs and PET analysis of time perception: spatial and temporal brain mapping during visual discrimination tasks, Hum. Brain Mapp. 10 (2000) 49 – 60. [3] R.D. Pascual-Marqui, C.M. Michel, D. Lehmann, Low resolution electromagnetic tomography: a new method for localizing electrical activity in the brain, Int. J. Psychophysiol. 18 (1994) 49 – 65. [4] A. Smith, et al., Right hemispheric frontocerebellar network for time discrimination of several hundreds of milliseconds, NeuroImage 20 (2003) 344 – 350. [5] J.A. Mangels, R.B. Ivry, N. Shimizu, Dissociable contributions of the prefrontal and neocerebellar cortex to time perception, Brain Res. Cogn. Brain Res. 7 (1998) 15 – 39.
www.ics-elsevier.com
LORETA analysis of CNV in time perception Keiichi Onoda, Jun Suzuki, Hiroshi Nittono, Shogo Sakata, Tadao Hori * Graduate School of Biosphere Science, Hiroshima University, 1-7-1, Kagamiyama, Higashi-Hiroshima, Hiroshima,739-8521, Japan
Abstract. The aim of this study was to specify when and where ‘‘pure’’ temporal processing occurred in the brain. Event-related potentials were recorded from 13 young, healthy volunteers performing interval and pitch discrimination tasks. In the interval task, two 1000-Hz tones (S1 and S2) were presented with an interval of 1000 or 1500 ms. Participants were asked to judge whether the S1 – S2 interval was short or long. In the pitch task, the S1 (1000 Hz) was followed by the S2 (1000 or 1050 Hz) with a fixed interval of 1000 ms. Participants were asked to judge whether the pitch of the S2 was the same as or different from that of the S1. In both tasks, contingent negative variation (CNV) was observed in the period between 500 and 1000 ms after the S1. The amplitude of the CNV was larger in the interval task than in the pitch task. The data were analyzed using lowresolution electromagnetic tomography (LORETA). The right dorsolateral prefrontal cortex (DLPFC) showed more activation in the interval task than in the pitch task. This result suggests that the right DLPFC may play an important role in time perception and processing the temporal dimension of events. D 2004 Elsevier B.V. All rights reserved. Keywords: Time perception; Contingent negative variation (CNV); LORETA; Dorsolateral prefrontal cortex (DLPFC)
1. Introduction Time is an important source of information influencing behavior. However, the neurophysiological basis of time perception remains a matter for debate. Recent studies using functional brain mapping have suggested some brain structures where time-related attributes of an event are processed [1]; nevertheless, these structures are also involved in the perception of other dimensions, such as the intensity, pitch, color, shape, and location of auditory and visual stimuli. In order to conclude that the perception of time is responsible for the observed pattern of activation, it should be demonstrated that this pattern is not elicited by the perception of other attributes of stimuli. In functional brain mapping studies, some patterns of activation described in the timing task are similar to
* Corresponding author. Tel.: +81-824-24-6580; fax: +81-824-24-0759. E-mail address: [email protected] (T. Hori). 0531-5131/ D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.ics.2004.05.002
292
K. Onoda et al. / International Congress Series 1270 (2004) 291–294
those in working memory and attention tasks. As fMRI and PET integrate an activity over a period of many seconds, temporal resolution is often insufficient to specify areas only involved when temporal processing is performed. Therefore, Pouthas et al. [2] examined contingent negative variation (CNV) observed in duration discrimination tasks using dipole analysis. They discovered that the right frontal dipole is active during the CNV, and proposed that the processing of temporal information would specifically involve the right frontal area. The CNV, however, reflects not only temporal processing but also others, such as attention and motivation. In order to argue the contribution of the right frontal lobe in time perception, it is necessary to distinguish the processing of time from other processing tasks. This study used two tasks based on the S1 – S2 paradigm, a task in which the interval of the S1 and S2 was judged, and a task in which the pitch of the S1 and S2 were judged. Sources of the CNV observed in the two tasks were compared using lowresolution brain electromagnetic tomography (LORETA) [3]. 2. Method 2.1. Subjects Participants were 13 (5 females and 8 males) young volunteers between 21 and 25 years old with normal audition. The experiment was conducted with the informed consent of each subject. 2.2. Tasks In the interval task, two 1000-Hz tones (S1 and S2, 70 dB) were presented with an interval of 1000 or 1500 ms. Participants were asked to judge whether the S1 –S2 interval was short or long. The tone duration was 50 ms. The intensity of the stimulus was 70 dB. The ISI lasted between 2600 and 3400 ms (on average, 3000 ms). The probabilities were 0.5/0.5. The button press responses were made with the thumbs of each hand. They were instructed to delay their responses for about 1000 ms in both tasks. Each participant was given 100 trials in this task. In the pitch task, the S1 (1000 Hz) was followed by the S2 (1000 or 1050 Hz) with a fixed interval of 1000 ms. Participants were required to judge whether the pitch of the S2 was the same as or different from that of the S1. Other variables were the same as that of the interval task. The response hands and the task order were counterbalanced across participants. 2.3. ERP recording and analysis Electroencephalograms (EEGs) were recorded digitally from 24 electrode sites and rereferenced to the nose tip. Horizontal and vertical electro-oculograms (EOGs) were simultaneously recorded. The sampling rate was 500 Hz. A bandpass filter of 0.016 – 100 Hz was used. Event-related potentials (ERPs) were obtained for each task. The averaging period was 1200 ms with a 200 ms baseline before the onset of S1. A repeated measure analysis of variance was performed on the mean amplitudes at Cz between 500 and 1000 ms after the S1. LORETA [3,4] was used to find differences in intracerebral
K. Onoda et al. / International Congress Series 1270 (2004) 291–294
293
Fig. 1. Grand mean ERP waveforms recorded at Cz during the S1 – S2 interval period (N = 13). The vertical line shows the onset of S1.
sources of the CNV between the two tasks. The pairwise t-test was performed on a voxelby-voxel basis. 3. Results 3.1. Behavior The correct response rates in the two tasks were 97.8% (S.D. 2.7) for the interval task, and 97.4% (5.0) for the pitch task. No difference in performance was found between the tasks, t(12) = 0.24, n.s. 3.2. ERP Fig. 1 shows ERP waveforms at the vertex (Cz) averaged across subjects in the interval and the pitch discrimination tasks. Following the sensory-evoked potentials, a clear CNV can be observed from 500 to 1000 ms after the S1 in both tasks. The mean amplitude between 500 and 1000 ms was larger in the interval task than in the pitch task, F(1,12) = 13.28, p < 0.01.
Fig. 2. Statistical maps of t value illustrating the differences in current source density between the interval and pitch tasks at the epoch between 500 and 1000 ms. Highlighted voxels (t>3.00) appear in the right dorsolateral prefrontal cortex (DLPFC).
294
K. Onoda et al. / International Congress Series 1270 (2004) 291–294
3.3. LORETA To compare the differences in current source density between the CNVs (500 – 1000 ms) in the two tasks, the pairwise t-test was used on a voxel-by-voxel basis. The maximal t value was observed in the right dorsolateral prefrontal cortex (DLPFC) at the Talairach coordinates (25, 31, 36) (Fig. 2). 4. Discussion In the present study, we examined the spatio-temporal organization of cerebral areas involved in temporal processing by LORETA analysis of ERP. The activation of the right DLPFC was found during the CNV in the interval task. Since sustained attention and working memory were also involved in the pitch task, the differential activation in the right DLPFC suggests an important role of this area processing the temporal dimension of the event. Using ERPs combined with PET, Pouthas et al. [2] found the timing of activation in the right inferior prefrontal cortex during time discrimination was strongly aligned with the durations. The contribution of the right dorsolateral and inferior prefrontal cortices in time perception was supported by fMRI studies (e.g. Ref. [4]), although the differences between the roles of these regions are not clear. Some hypotheses about the role of the right DLPFC in time perception proposed that the role of the region may act as a central ‘‘clock’’ mechanism, ‘‘accumulator’’ storing temporal information, ‘‘mediator’’ of time estimation process, and ‘‘maker of decisions’’ [5]. Although the results of this study cannot directly mention the role of the right DLPFC, a more detailed, temporal – spatial analysis using LORETA may help to understand the process of time perception. References [1] P.A. Lewis, R.C. Miall, Distinct systems for automatic and cognitively controlled time measurement: evidence from neuroimaging, Curr. Opin. Neurobiol. 13 (2003) 250 – 255. [2] V. Pouthas, et al., ERPs and PET analysis of time perception: spatial and temporal brain mapping during visual discrimination tasks, Hum. Brain Mapp. 10 (2000) 49 – 60. [3] R.D. Pascual-Marqui, C.M. Michel, D. Lehmann, Low resolution electromagnetic tomography: a new method for localizing electrical activity in the brain, Int. J. Psychophysiol. 18 (1994) 49 – 65. [4] A. Smith, et al., Right hemispheric frontocerebellar network for time discrimination of several hundreds of milliseconds, NeuroImage 20 (2003) 344 – 350. [5] J.A. Mangels, R.B. Ivry, N. Shimizu, Dissociable contributions of the prefrontal and neocerebellar cortex to time perception, Brain Res. Cogn. Brain Res. 7 (1998) 15 – 39.