Background: The auditory mismatch negativity (aMMN) is an event-related potential (ERP) elicited by an infrequent change in a stream of continuous, repetitive stimuli. It is thought to result from a comparison between the physical features of the deviant stimulus and a neural sensory memory trace of the standard stimulus. A limited number of investigations have suggested an analogous somatosensory discriminatory response.
Objective: To examine the effects of frequency and duration change on somatosensory discrimination responses using scalp and intracranial recordings.
Methods: Intermittent vibration to the fingertips of either hand was presented in a 2-stimulus oddball paradigm (deviant p = 0.10). Stimulus pairs of 20/70 ms, 50/150 ms and 170/250 ms were presented at 70 Hz to one group (N = 12, 18–38 years), and frequency pairs of 200/70 Hz to a second group (N = 10, 19–34 years). Recordings were made from subdural electrodes to similar stimuli in a third group (N = 9, 6–16 years) undergoing presurgical evaluation for epilepsy.
Results: A negative/positive shift was recorded in the response to the deviant stimuli to both frequency and duration increments/decrements. The initial negativity had a mean onset of 90–170 ms and the peak latencies of both components were dependent on stimulus duration. The negative component appeared maximal over the hemisphere contralateral to the side of stimulation and anterior to the maximum P50/N70 components. The positive component appears more posterior over the mid parietal region, suggesting a separate generator, possibly in the secondary somatosensory cortex. It was most prominent with frequency deviations. Three intracranial cases showed a negative shift over the frontal areas in response to the deviant stimuli, suggesting a third generator.
Conclusion: We propose that these changes in the deviant responses reflect a somatosensory mismatch response with features similar to the aMMN.