Different activation patterns for working memory load and visual attention load.

Attention is a basic component of cognition, and is modulated by cognitive load. We aimed to map the common network that supports attentional load across different tasks using functional magnetic resonance imaging (fMRI). Twenty-two healthy volunteers performed two sets of tasks with graded levels of cognitive load: verbal working memory (WM) and visual attention (VA) tasks. For both tasks, increased cognitive load (WM-load and VA-load) activated a common network comprising parietal and occipital cortices, thalamus, and the cerebellum, indicating that these brain regions are involved in higher level of attention. The fMRI signals in the prefrontal cortices increased with WM-load but not with VA-load, suggesting that executive function is involved for the more demanding WM tasks but not for the more difficult VA tasks. Conversely, VA tasks activated more strongly an occipito-parietal network comprising the postcentral (PostCG) and the superior occipital (SOG) gyri, suggesting complex visual processing in this network.