Brain Generators Implicated in the Processing of Auditory Stimulus Deviance: A Topographic Event‐Related Potential Study

TLDR

Mismatch negativity (MMN) reflects neurophysiological processes that can be inferred by examining the brain generators of this ERP component. ERPs were recorded during a selective dichotic listening task in which subjects silently counted pitch‑deviant stimuli in one ear while ignoring stimuli in the other, and scalp radial current density analysis attributed the asymmetric right‑hemispheric MMN to combined activity of temporal generators contralateral to stimulation and frontal generators in the right hemisphere. The deviant‑elicited MMN showed maximal right‑hemispheric amplitudes regardless of ear or attention, supporting a dissociation between a sensory‑memory process linked to temporal generators and an automatic attention‑switching process linked to frontal generators.

Abstract

The neurophysiological mechanisms underlying mismatch negativity (MMN) can be inferred from an examination of some of the brain generators involved in the process of this event-related potential (ERP) component. ERPs were recorded in two studies in which the subjects were involved in a selective dichotic listening task. Subjects were required to silently count rare stimuli deviating in pitch from a sequence of standard stimuli in one ear, while ignoring all the stimuli (standards and deviants) delivered randomly to the other ear. The results showed that, in all cases, the negative wave elicited by the deviant stimuli showed the highest amplitudes over the right hemiscalp irrespective of the ear of stimulation or the direction of attention. Scalp radial current density analysis showed that this asymmetric potential distribution could be attributed to the sum of activities of two sets of neural generators: one temporal, located in the vicinity of the primary auditory cortex, predominantly activated in the hemisphere contralateral to the ear of stimulation, and the other frontal, involving mainly the right hemisphere. The results are discussed in light of Näätänen's model: we suggest the dissociation of two functional processes on the basis of activity of distinct brain areas: a sensory memory mechanism related to the temporal generators, and an automatic attention-switching process related to the frontal generators.