Four series of experiments are proposed. 1) Preliminary data indicate that posterior cingulate neurons encode orbital position, saccade direction and amplitude, and respond to visual stimuli. The first series of experiments is designed to characterize more fully the eye movement related activity and visual responsiveness of posterior cingulate neurons. The monkey will perform a series of tasks to identify relationships to orbital position, direction, and amplitude in the optimal target direction. Dependence on visual feedback will be tested by examining discharge with saccades in the dark. Next (exp 1c) visual response properties will be characterized, in which size, brightness and direction of motion of targets (checkerboards) will be varied. In experiment 1d. the effect of orbital position on visual responsiveness will be tested by presenting stimuli at the same retinal coordinate with the eye in one of nine different positions. 2) The second experiment will examine visuo-spatial encoding of cingulate neurons to test the idea that these neurons have a preferential role in spatial discrimination. Neural activity will be assessed while monkeys make saccades to spatially aligned cues or to color cues, or view visual stimuli in a passive vision paradigm in which no saccade is made. 3) The third experiment will test the hypothesis that posterior cingulate cortex is a substrate for process underlying working memory. Neural activity will be assessed while monkeys perform the same three tasks of experiment two, but with a mnemonic component. The paradigm will involve a delayed-match-to- sample tasks design for spatial, color or """"""""passive"""""""" cues. 4) The fourth experiment will test the hypothesis that posterior cingulate cortex is involved in the control of visual attention. In the first part of this experiment, neuronal activity will be examined during Posner-like tasks in which a reaction measure is used to test for covert shifts of attention. A correlation of neural activity with cue probability conditions will suggest that cingulate neurons may mediate cognitively driven attention. The second part of this experiment will examine the role of cingulate of neurons in spontaneous orienting. A visual stimulus will be given intermittently during a fixation task to determine whether visual responses are stronger on trials in which there is an orienting movement.
