S29-2 The concept of temporal integration window and its clinical applications

Abstract

The mismatch negativity (MMN) is an electric brain response which is automatically (task-independently) elicited by any discriminable change in a repetitive sound or sound pattern as long as the memory trace of the previous stimuli lasts. When this change is made smaller in magnitude the MMN is attenuated in amplitude, eventually vanishing at around the discrimination threshold. Therefore the MMN provides a unique objective measure for a subject or patient fs discrimination accuracy. Furthermore, with the MMN, these discrimination thresholds can be separately determined for the different auditory attributes. Moreover, the individual’s ability to discriminate even complex sound stimuli and patterns such as different phonemes can be measured by using the MMN. Several studies have shown that training-induced improvements in different kinds of auditory discrimination abilities are accompanied by increased MMN amplitudes, reflecting learning-related plastic changes in the auditory cortex. In fact, some recent data suggest that the improved discrimination in the course of training might even be preceded by an MMN enhancement. In stroke patients with aphasia, the MMN may index the gradual recovery of auditory discrimination abilities as time from stroke onset elapses. In addition, in cochlear-prosthesis patients, the MMN can similarly index the gradual recovery of different auditory discrimination functions. Furthermore, the MMN can also reflect the plastic changes occurring when an individual is exposed to a certain language environment, most typically when a newborn is exposed to his/her mother tongue, but such MMN changes reflecting the emergence of new phonetic categories also occur when an adult learns a foreign language. Finally, the MMN can also be used as an index of the duration of sensory memory in audition. These studies have shown that this duration (of the order of 10 sec in young individuals) gets shorter with normal aging, being very short in patients with degenerative brain diseases such as Alzheimer’s disease. These results suggest that the MMN could be used as an index of general brain plasticity.