Abstract
Visual attention and working memory (WM) are two different cognitive functions. However, because of their close relationship, it is often claimed that they share the same neuronal substrates. Here we examined whether the brain areas and neurons that are modulated by selective attention to a visual feature are the same as or different from those encoding WM representations of the same feature. Two macaque monkeys performed a WM-guided feature attention task that required maintaining a visual motion direction representation in WM and then selectively attending to stimuli with that motion direction. We recorded activity of motion direction-selective neurons in areas MT, MST, LIP, and LPFC-p, a posterior prefrontal subregion. We found that the percentage of neurons exclusively showing either attentional modulation or WM coding far exceeded the percentage showing both signals. This dissociation was most striking in LPFC-p, a region proposed as a source for feature attentional signals that modulate activity in visual cortex. To examine whether LPFC-p plays a causal role in feature attention and WM, we developed a method for large-scale bilateral inactivation of LPFC-p during either the WM period or the sustained attention period. LPFC-p inactivation during the sustained attention period reduced the strength of feature attentional effects not only locally but also in MST and LIP. In contrast, inactivation during the WM period reduced the strength of WM coding only in MST neurons and did not affect the strength of feature attentional effects in any area. Interestingly, LPFC-p inactivation during the sustained attention period impaired task performance, whereas inactivation during the WM period did not, suggesting that LPFC-p plays a critical role in feature attention but not in WM. Together, our results indicate that across multiple visual processing stages, the neuronal substrates underlying feature attention and WM are largely dissociable.