Neural correlates of switching set as measured in fast, event-related functional magnetic resonance imaging

Abstract

Attentional switching has shown to involve several prefrontal and parietal brain regions. Most cognitive paradigms used to measure cognitive switching such as the Wisconsin Card Sorting Task (WCST) involve additional cognitive processes besides switching, in particular working memory (WM). It is, therefore, questionable whether prefrontal brain regions activated in these conditions, especially dorsolateral prefrontal cortex (DLPFC), are involved in cognitive switching per se, or are related to WM components involved in switching tasks. Functional magnetic resonance imaging (fMRI) was used to examine neural correlates of pure switching using a paradigm purposely designed to minimize WM functions. The switching paradigm required subjects to switch unpredictably between two spatial dimensions, clearly indicated throughout the task before each trial. Fast, event-related fMRI was used to compare neural activation associated with switch trials to that related to repeat trials in 20 healthy, right-handed, adult males. A large cluster of activation was observed in the right hemisphere, extending from inferior prefrontal and pre- and postcentral gyri to superior temporal and inferior parietal cortices. A smaller and more caudal cluster of homologous activation in the left hemisphere was accompanied by activation of left dorsolateral prefrontal cortex (DLPFC). We conclude that left DLPFC activation is involved directly in cognitive switching, in conjunction with parietal and temporal brain regions. Pre- and postcentral gyrus activation may be related to motor components of switching set.

Figure 1

Illustration of switch task and correct response.

Figure 2

Regions of brain activation associated with switch contrasted with repeat trials. a: Whole brain cut away to reveal large activation cluster in the right hemisphere extending from inferior prefrontal lobe, pre‐ and post‐central gyri to middle temporal gyrus. b: Whole brain cut away to reveal activation cluster in the left hemisphere including DLPFC, post‐central gyrus, and superior temporal gyrus. c: Whole brain cut away to reveal activation in anterior cingulate gyrus and right hemispheric precentral and superior temporal activation (also seen in a). d: Whole brain cut away to reveal putamen activation and right hemisphere activation of post‐central gyrus (also seen in a).