Long-latency suppression of auditory and somatosensory change-related cortical responses

Abstract

Sensory suppression is a mechanism that attenuates selective information. As for long-latency suppression in auditory and somatosensory systems, paired-pulse suppression, observed as 2 identical stimuli spaced by approximately 500 ms, is widely known, though its mechanism remains to be elucidated. In the present study, we investigated the relationship between auditory and somatosensory long-latency suppression of change-related cortical responses using magnetoencephalography. Somatosensory change-related responses were evoked by an abrupt increase in stimulus strength in a train of current-constant square wave pulses at 100 Hz to the left median nerve at the wrist. Furthermore, auditory change-related responses were elicited by an increase in sound pressure by 15 dB in a continuous sound composed of a train of 25-ms pure tones. Binaural stimulation was used in Experiment 1, while monaural stimulation was used in Experiment 2. For both somatosensory and auditory stimuli, the conditioning and test stimuli were identical, and inserted at 2400 and 3000 ms, respectively. The results showed clear suppression of the test response in the bilateral parisylvian region, but not in the postcentral gyrus of the contralateral hemisphere in the somatosensory system. Similarly, the test response in the bilateral supratemporal plane (N100m) was suppressed in the auditory system. Furthermore, there was a significant correlation between suppression of right N100m and right parisylvian activity, suggesting that similar mechanisms are involved in both. Finally, a high test-retest reliability for suppression was seen with both modalities. Suppression revealed in the present study is considered to reflect sensory inhibition ability in individual subjects.

Fig 1. Paired stimulation paradigm using auditory and somatosensory change-related cortical responses.

Data from a representative subject are presented. Shown is the stimulation paradigm, superimposed MEG waveforms from all 204 sensors, and source strength waveforms for each cortical activity in the auditory (A) and somatosensory (B) experiments. T, sensory threshold. Arrowheads show peaks of source activity used for amplitude measurements.

Fig 2. Grand-averaged waveforms for all subjects.

Test responses, except for SI, were suppressed in both Experiment 1 (A) and 2 (B).

Fig 3. Mean %suppression value for each cortical activity.

Values are shown as the mean ± SD. All cortical activities, except for SI, showed a significant reduction in amplitude for the test response.

Fig 4. Correlation of %suppression between experiments.

Plots showing the relationship of %suppression between Experiment 1 (x axis) and Experiment 2 (y axis) for the auditory (A) and somatosensory (B) experiments. The r and p values presented were obtained from all collected data.

Fig 5. Correlation of %suppression between cSII and right N100m.

Plots showing the relationship of %suppression between cSII (x axis) and N100m (y axis).