Task-specific sensory and motor preparatory activation revealed by contingent magnetic variation.

The present report studied the magnetic counterpart (CMV) of the auditory contingent negative variation (CNV). The ear where the target auditory stimulus would be presented was cued with a visual central arrow at a validity of 84%. The subject's behavioral response and the magnetoencephalographic (MEG) and electroencephalographic (EEG) signals were recorded. The central cue diminished reaction times (RTs) to the auditory target in the valid conditions with respect to the invalid conditions, indicating that the attentional manipulation was effective. The averaged magnetic field power during the preparatory period was significantly higher than baseline, suggesting the simultaneous presence of a magnetic counterpart of the electric CNV--the CMV. The field maps of the CMV grand averages showed two different and well-established periods: an early one with a magnetic field distribution that suggests a central source, and a late one with a field topography comparable to a low-intensity auditory-evoked field (M1). Single-dipole analysis of the preparatory phase in the subject's magnetic resonance images (MRI) demonstrated the presence of dipolar activity in the posterior cingulate (PCC) and posterior parietal cortices (PPC), superior temporal gyrus (STG) and motor cortices (MC). The lateralization of this activity depended on the orientation of the central cue. These results suggest that the action and perceptual-related areas needed to process the expected subsequent imperative task are recruited during the preparatory periods, influencing the behavioral RTs.