Society for Neuroscience Chicago, Illinois
October, 2009
Y. WANG1, T. TOELLNER2, K. GRAMANN1, *S. MAKEIG1
1Swartz Center for Computational Neuroscience, Institute for Neural Computation, University of California San Diego, La Jolla, CA; 2University of Munich, Germany
Theta oscillations in the medial frontal cortex during response preparation
Recent fMRI neuroimaging studies have suggested a role for the medial frontal cortex (MFC) in conflict monitoring and response preparation. However, electroencephalography (EEG) correlates of conflict processing during response preparation have been more rarely reported. We recorded 256-channel EEG data from 14 healthy subjects performing a 'Simon'-like visual search task in which they were asked to reach to touch a screen target object with their left or right hand. The response hand was indicated by the orientation of the grating inside a target stimulus (left or right hand indicated by a vertical or horizontal grating respectively). The 'pop-out' target stimuli had either a different color or shape from several similar distractor objects. For 10 of the 14 subjects, independent component analysis (ICA) extracted a tight cluster of medial frontal components. Equivalent dipole localization indicated an origin in the dorsal anterior cingulate cortex (ACC) (Brodmann area 32, Talairach coordinates: x=0, y=9, z=39). Event-related spectral perturbation (ERSP) analysis revealed that these components produced a (4-7 Hz) theta burst peaking just before the manual response. Two trial types (congruent, right|left hand reaching for right|left target, versus incongruent, right|left hand reaching for left|right target) were considered. The incongruent trails were further separated into i-I (previous trial incongruent) and c-I (previous trial congruent) groups. Two-sample t-tests showed that the theta bursts were stronger in incongruent than in congruent stimulus trials (1.07± 0.05 vs. 0.91± 0.04, p<10-6) and in c-I trials than in i-I trials (1.05± 0.04 vs. 0.95± 0.04, p<10-4). These findings are consistent with proposals that higher-conflict actions require more MFC activation, but that this effect is reduced immediately after a high-conflict trial.