Do theta oscillations explain the somatosensory change detection mechanism?

Recent research has indicated that the mismatch negativity (MMN) is elicited in response to a discernible small change of a somatosensory stimulus applied on the hand. However, the neural mechanism for detecting small change of somatosensory stimulus remains unknown. In the present study, we developed a novel pressure stimulation device using air jet applied on the index finger pad, and determined the just noticeable differences (JNDs) of pressure discrimination for each subject. Using the deviant-standard-reversed oddball paradigm, we analyzed the average dynamic changes in MMN amplitude and changes of evoked spectral power. We found a clear MMN component at the frontal and central regions at 100–300 msec after deviant stimulus presentation. Statistical tests showed that theta band activity played pivotal roles in the generation of the MMN elicited by a change in somatosensory pressure stimulation. Our results indicate that the somatosensory discriminatory process reflected on MMN is accompanied by phase-locked oscillation at the theta frequency.