Spatial Representations in Posterior Cingulate Cortex

Posterior cingulate cortex (CGp) is strongly connected with both visual and oculomotor areas, and we previously reported that CGp activation is modulated by visual stimulation, eye movements, and eye position. These observations, as well as recent imaging and lesion data, suggest that CGp might integrate visual and oculomotor data to compute spatial representations used in orienting and navigation The goal of the present study is to determine whether CGp neuronal responses are anchored to the eyes, head, or world. To differentiate between retinotopic and higher order coordinate frames (first row), single CGp neurons are studied while monkeys perform delayed-saccade trials initiated from different starting positions to targets appearing along an axis passing through the neuronal response field. Neuronal activity is measured during 12 sequential epochs on each trial, segregated by fixation position, and plotted as a function of both movement vector and eye position. In order to differentiate between coordinate frames anchored to the head or to the world (second row), subjects are rotated with respect to the visual display and asked to make saccades from a central fixation point to the array of targets used previously. Tuning curves for saccades made from central fixation to each target before and after rotation are compared for alignment. Preliminary results indicate CGp cells may encode spatial information in coordinates anchored to the world rather than the head or eye.