One challenging issue in cognitive neuroscience has been to dissociate a variety of mental processes from one another in order to elucidate brain functions. Attention, in particular, has been a recurrent issue because of its strong links with perceptual, cognitive, and motor performances. This paper reviews data from neurophysiological experiments designed to dissociate neuronal activity related to visuo-spatial attention from preparatory activity in the monkey brain. Cell activity was recorded from the dorsal premotor area (PMd) and compared to the dorsolateral prefrontal cortex (DLPf), from which it receives inputs. PMd has been implicated in the planing and execution of voluntary movements (PMd), and the majority of its cells are active during tasks with instructed delay time. However, the activity of many PMd cells is not specifically correlated with movement preparation, as is observed when the animal is attending to a visual stimulus, although the proportion of attention-related cells is much lower than in the DLPf. The distribution of attention-related and intention-related neurons within PMd tends to vary along the rostrocaudal axis, with the former more frequent rostrally (PMdr) and the latter more predominant caudally (PMdc). In a functional magnetic resonance imaging (fMRI) study in humans, we compared the premotor activation in two tasks: a spatial attention/memory task and a motor preparation task. The results suggest a rostrocaudal specialization within PMd of the human brain, with attention-related activation rostrally and medially and intention-related activation caudally. These studies indicate strong similarities in the functional organization of dorsal premotor cortex of human and monkey.
Copyright 2001 Academic Press.