PS-13-7 Negative brain potentials elicited by mismatch between an odorant stimulus and a word stimulus

Abstract

The mismatch negativity (MMN), well established in auditory modality, reflects the automatic processing. In somatosensory modality, however, no MMN like component has been reported, in contrast to numerous studies concerning auditory MMN. In the present study, we investigated the response corresponding to MMN by using the deviant stimuli in a homogenous somatosensory stimuli sequence, while the subjects were reading a novel. In the first block, electric pulses were given repetitively to one finger as standard stimuli (90%) and occasionally to another finger as deviant stimuli (10%). In the second block, the stimulating site was exchanged. Each block was performed randomly and separately. In both blocks with ISI of 500 ms, the deviant stimuli elicited a positive deflection dominant at Cz, ranging from 100 to 200 ms in latency, suggesting that this positive deflection is related to the physical changes of the evoking stimulus. In addition the latency is comparable to one of the auditory MMN. Furthermore, we employed also the longer ISI (1000 ms) to confirm whether or not the present positivity is equivalent to MMN. As a result, the amplitude of this positivity was drastically decreased in the 1000 ms-lSI condition, suggesting that this somatosensory positivity may be related to the sensory memory like the auditory MMN.