Cortical dynamics of a self driven choice: A MEG study during a card sorting task

Objective: The aim of this study was to disclose the dynamics of the frontal processes involved in a task shifting between two attentional states. Methods: Magnetoencephalographic activities were recorded during a Wisconsin Card Sorting Test where subjects had to match card stimuli according to one of three possible dimensions ("maintained condition"). The matching dimension was intermittently changed and subjects, after feedback presentation, had to identify the new correct dimension ("shifted condition"). Results: Source activations following the feedback to the subject's response in these two attentional conditions did not differ before 350 ms post feedback. After 350 ms, in the shifted condition, a lateral/posterior frontal activation was maintained later, while a medial/anterior frontal activation appeared up to 450 ms. Conclusions: The dynamics of activities corresponding to the two conditions disclose a spread of activation from posterior lateral frontal in the "maintained condition" to anterior medial frontal in the "shifted condition". Significance: These results are consistent with fMRI results concerning the major involvement of medial frontal cortex in tasks involving reasoning and choice making. (C) 2009 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.