[Study of sensory memory reflected by mismatch negativity and its clinical application]

The event-related brain potential called Mismatch negativity (MMN) reflects the auditory detection system which automatically detects subtle change in the surrounding acoustic environment. This system is based on the pre-attentive mechanism of comparison mechanism between the neural trace of background sounds stored in sensory memory and incoming sound change. This "memory trace theory" has raised the importance of MMN. The features of sound information are extracted from the incoming sound in sensory memory, and is integrated into an auditory unit within the temporal window of 160-170 ms. Since the MMN itself is basically free from the influence of attention and requires no task for measurement, MMN can be applied to various clinical studies. There are two generators, the temporal MMN reflecting the change detection in sensory memory and the frontal MMN reflecting the attentional switch. Therefore, MMN has various clinical applications including memory disturbance and attention disorder. For example, reduced amplitude of MMN is a robust finding in schizophrenia. Some basic MMN studies and their promising clinical applications are described here.