Involvement of prefrontal cortex in visual search.

Visual search for target items embedded within a set of distracting items has consistently been shown to engage regions of occipital and parietal cortex, but the contribution of different regions of prefrontal cortex remains unclear. Here, we used fMRI to compare brain activity in 12 healthy participants performing efficient and inefficient search tasks in which target discriminability and the number of distractor items were manipulated. Matched baseline conditions were incorporated to control for visual and motor components of the tasks, allowing cortical activity associated with each type of search to be isolated. Region of interest analysis was applied to critical regions of prefrontal cortex to determine whether their involvement was common to both efficient and inefficient search, or unique to inefficient search alone. We found regions of the inferior and middle frontal cortex were only active during inefficient search, whereas an area in the superior frontal cortex (in the region of FEF) was active for both efficient and inefficient search. Thus, regions of ventral as well as dorsal prefrontal cortex are recruited during inefficient search, and we propose that this activity is related to processes that guide, control and monitor the allocation of selective attention.