NEUROMAGNETIC FIELDS REVEAL CORTICAL PLASTICITY WHEN LEARNING AN AUDITORY-DISCRIMINATION TASK

Auditory evoked neuromagnetic fields of the primary and association au ditory cortices were recorded while subjects learned to discriminate s mall differences in frequency and intensity between two consecutive to nes. When discrimination was no better than chance, evoked field patte rns across the scalp manifested no significant differences between cor rect and incorrect responses. However, when performance was correct on at least 75% of the trials, the spatial pattern of magnetic field dif fered significantly between correct and incorrect responses during the first 70 ms following the onset of the second tone. In this respect, the magnetic field pattern predicted when the subject would make an in correct judgment more than 100 ms prior to indicting the judgment by a button press. One subject improved discrimination for much smaller di fferences between stimuli after 200 h of training. Evidence of cortica l plasticity with improved discrimination is provided by an accompanyi ng decrease of the relative magnetic field amplitude of the 100 ms res ponse components in the primary and association auditory cortices. (C) 1997 Elsevier Science B.V.