The caudate nucleus egocentric localization system.

It is hypothesized that the motor and spatial functions ascribed to the caudate nucleus are actually different aspects of a single system for spatial localization. Within this system movement programs are the code for spatial locations, i.e. the position of any point in space is defined by the head/eye movement necessary to bring that point into focus. This is an egocentric system; points in space are defined solely in terms of their distance and direction from the observer. The experimental finding that caudate lesions in rats impair their performance in an egocentric localization task, but not in another, equally difficult spatial task, demonstrates a caudate role in this system. Since, in an egocentric system, positions in space are defined relative to the observer, every movement of the observer must be accompanied by a compensatory updating of the internal representation of any given point. Studies with Huntington's Chorea patients are consistent with a caudate involvement in this feature of the system also. Electrophysiological experiments with cats indicate that vestibular information, which can be used in the compensatory updating process, is available to the caudate. It is suggested that this system is used by normal animals in delayed response performance.