Visuospatial and motor attention in the monkey.

Visuospatial attention involves the selection of stimuli from the environment for further neural processing. The attention-related enhancement of visual responses in posterior parietal cortex is a possible neural substrate for visuospatial attention. By analogy with the selection process in the spatial domain, motor attention is postulated to involve a selection among simultaneous upper motor signals. Selection of motor programs within the oculomotor system is used as an example of this attentional process. Since attentive fixation modulates the effect on the oculomotor system of electrical stimulation of the frontal eye fields, a given upper motor neuronal signal need not necessarily invoke a movement. That the brain has multiple simultaneous motor signals is apparent from the profusion of sensory-driven upper motor neurons. The frontal cortex is probably important in selecting which upper motor signals actually evoke movements, by elaborating motor programs for purposive behavior, but not for all movements.