MEG activity in visual areas of the human brain during target selection and sustained attention

摘要

We combined MEG and magnetic resonance imaging (MRI) to examine evoked activity in visual areas during a task that involves both target selection and sustained attention. During task trials, 9 human subjects were presented with two white moving random dot patterns (RDPs, the target and the distractor), left and right of a central fixation spot on a dark background. After a brief delay, each RDP color changed to red, blue, or green. Subjects were required to select the target using a color rank selection rule (red blue green), sustain attention to it, and identify a transient change in either its direction (clockwise/counterclockwise) or color (pink/grey). All possible stimulus configurations were presented randomly. We found that following color cue onset, early visual areas along the cuneus and lingual gyrus (V1 and V2) were activated bilaterally starting as early as 120 ms after cue onset. Activation in other areas such as V3, V3A, and V4 was significantly stronger contralateral to the target stimulus, peaking at a??170 ms from color cue onset. These data demonstrate that target selection becomes evident in early visual cortex with a latency of about 170 ms following cue onset. During the sustained attention period, changes in the direction of the RDPs evoked peak activation in contralateral area MT (Talairach: -40/-64/16; 39/-64/17), while changes in color evoked activity in contralateral areas V2/V3 (-21/-74/11; 27/-67/5). These activations were stronger (a??60%) for targets than for distracters, becoming most pronounced at a??180 ms from change onset. Our results reveal that MEG activity in early visual areas of the human brain reflects target selection, as well as the effects of sustaining attention on that stimulus. This may be the result of interactions of feed-forward and feedback signals originated in different areas of the hierarchy of visual processing.