The large-scale neural network for spatial attention displays multifunctional overlap but differential asymmetry

Functional magnetic resonance imaging (fMRI) was used to determine the brai n regions activated by two types of covert visuospatial attentional shifts: one based on exogenous spatial priming and the other on foveally presented cues which endogenously regulated the direction of spatial expectancy. Act ivations were seen in the cortical and subcortical components of a previous ly characterized attentional network, namely, the frontal eye fields, poste rior parietal cortex, the cingulate gyrus, the putamen, and the thalamus, A dditional activations occurred in the anterior insula, dorsolateral prefron tal cortex, temporo-occipital cortex in the middle and inferior temporal gy ri, the supplementary motor area, and the cerebellum. Direct comparisons sh owed a nearly complete overlap in the location of activations resulting fro m the two tasks. However, the spatial priming task displayed a more pronoun ced rightward asymmetry of parietal activation, and a conjunction analysis showed that the area of posterior parietal cortex jointly activated by both tasks was more extensive in the right hemisphere. Furthermore, the posteri or parietal and temporo-occipital activations were more pronounced in the t ask of endogenous attentional shifts. The results show that both exogenous (based on spatial priming) and endogenous (based on expectancy cueing) shif ts of attention are subserved by a common network of cortical and subcortic al regions. However, the differences between the two tasks, especially in t he degree of rightward asymmetry, suggests that the pattern of activation w ithin this network may show variations that reflect the specific attributes of the attentional task. (C) 1999 Academic Press.