Neural correlates of covert orienting of visual spatial attention along vertical and horizontal dimensions

Covert orienting of spatial attention along the horizontal meridian of the visual field is mediated by a fronto-parietal neural network. The neural substrates underlying covert orienting of attention along the vertical meridian, however, are less understood. We recorded hemodynamic responses using functional magnetic resonance imaging (fMRI) from healthy volunteers in covert visual orienting tasks that required to detect targets either at the fixation or at peripheral attended locations on the horizontal or vertical meridian in the left (LVF), right (RVF), upper (UVF), and lower (LoVF) visual fields. We found that, relative to when attention was at the fixation, covert orienting of attention along the horizontal and vertical meridia induced enhanced activities in the superior parietal and frontal lobes bilaterally and the cerebellum. In addition, attention to the LoVF and UVF generated stronger activation in the medial frontal cortex, anterior cingulate, precuneus, and the cerebellum relative to attention along the horizontal meridian. The reversed contrast, however, produced stronger activation in the right lingual gyrus and right premotor cortex. The fMRI results suggest that, while a common neural network is engaged in guiding visual spatial attention along the vertical and horizontal dimensions, unique neural correlates are associated with covert attentional orienting along the vertical and horizontal meridia of the visual field.