Spatially directed movement and neuronal activity in freely moving monkey.

The abilities to plan a series of movements and to navigate within the environment require the functions of the frontal and ventromedial temporal lobes, respectively. Neuropsychological studies posit the existence of egocentric (prefrontal) and allocentric (ventromedial temporal) spatial frames of reference that mediate these functions. To examine neural mechanisms underlying egocentric and allocentric guidance of movement, we have developed behavioral and neurophysiological techniques for freely moving monkey. In this chapter, we provide evidence that the dorsolateral prefrontal cortex is important for egocentric spatial tasks in both the visual and tactile modalities, but it does not contribute to performance of an allocentric spatial task. Moreover, neurophysiological recordings indicate that prefrontal neurons are involved in monitoring the spatial nature of behavioral sequences in an egocentric memory task. In contrast, hippocampal neurons are active during spatially directed locomotion, apparently reflecting the monkey's location in a testing room. This discharge is independent of the task's contingencies.