CEREBRAL GENERATORS OF MISMATCH NEGATIVITY (MMN) AND ITS MAGNETIC COUNTERPART (MMNM) ELICITED BY SOUND CHANGES

Infrequent (''deviant'') sounds occurring in a sequence of repetitive (''standard'') sounds elicit an event-related brain potential (ERP) re sponse called the mismatch negativity (MMN) even in the absence of att ention to these sounds. MMN appears to be caused by a neuronal mismatc h between the deviant auditory input and a sensory-memory trace repres enting the standard stimuli. This automatic mismatch process has presu mably a central role in discrimination of changes in the acoustic envi ronment outside the focus of attention. Thus, localizing cerebral gene rators of MMN might help identify brain mechanisms of auditory sensory memory and involuntary attention. This review summarizes results from studies aimed at localizing MMN generators on the basis of (1) scalp- distribution, (2) magnetoencephalographic (MEG), (3) intracranial, and (4) brain-lesion data. These studies indicate that a major MMN source is located in the auditory cortex. However, the exact location of thi s MMN generator appears to depend on which feature of a sound is chang ed (e.g., frequency, intensity, or duration), as well as on the comple xity of the sound (e.g., a simple tone versus complex sound). Conseque ntly, memory traces for different acoustic features, as well as for so unds of different complexity, might be located in different regions of auditory cortex. However, MMN appears to have generators in other bra in structures, too. There is some evidence for contribution of frontal -lobe activity to the MMN, which might be related to the involuntary s witching of attention to a stimulus change occurring outside the focus of attention. In addition, intracranial MMN recordings in animals sug gest that at least in some species, MMN subcomponents also may be gene rated in the thalamus and hippocampus.