Right fronto-parietal dysfunction underlying spatial attention in bipolar disorder.

Although the neural underpinning of bipolar disorder (BD) is still unknown, recent research suggests that the right fronto-parietal cortex is particularly affected in BD patients. If this were true, we would expect atypical functional cerebral asymmetries in allocation of visuospatial attention. To test this hypothesis, euthymic BD patients and age- and gender-matched healthy controls were compared on the visual line-bisection task, a reliable measure of visuospatial attention, associated with right parietal function. Line bisection performance (i.e. absolute and directional bias) was compared between groups as a function of response hand and line position. The results showed a typical hand-use effect in healthy controls involving a larger leftward bias (i.e. pseudoneglect) with the left hand than with the right hand. Although euthymic BD patients did not differ from healthy controls in the overall accuracy (i.e. absolute bias), they differed significantly in the directional line bisection bias. In contrast to healthy controls, BD patients did not significantly deviate from the veridical center, regardless of which hand was used to bisect horizontal lines. This finding indicates an atypical functional cerebral asymmetry in visuospatial attention in euthymic BD patients, supporting the idea of a dysfunction especially in the right fronto-parietal cortex.