Abstract
Purpose: :
The basal ganglia are widely regarded as structures involved in sensorimotor co-ordination, but little is known about the sensory background of their function. Our aim was to analyze the responsiveness of the caudate nucleus (CN) and the substantia nigra pars reticulata (SNr) neurons to visual stimuli, and to describe their visual receptive field properties.
Methods: :
Extracellular single-cell recordings were performed via tungsten microelectrodes in anesthetized, immobilized, artificially ventilated, adult cats. In order to investigate the visual properties of the basal ganglia we stimulated the neurons with simple geometric forms (light spots and bars) and drifting sine-wave modulated gratings with several spatio-temporal frequency combinations.
Results: :
The CN and SNr units had extremely large receptive fields that covered almost the whole visual field of the investigated eye. We observed no retinotopical organization within the basal ganglia. The neurons responded optimally to small stimuli moving at intermediate or high velocities and were weakly sensitive to stationary visual stimulation. Concerning the spatio-temporal receptive field properties, the basal ganglia units responded optimally to gratings of low spatial frequencies and exhibited low spatial resolution and fine spatial frequency tuning. On the other hand, the basal ganglia neurons preferred high temporal frequencies, and exhibited high temporal resolution and fine temporal frequency tuning. Moreover, the temporal frequency of the drifting grating modulated the responses of the neurons in the basal ganglia.
Conclusions: :
The physiological properties described above suggest that the basal ganglia are in strong functional connection with the structures of the tectal extrageniculate visual system, i.e. the intermediate and deep layers of the superior colliculus, the suprageniculate nucleus of the posterior thalamus and the visual associative cortical areas along the anterior ectosylvian sulcus. This system of the mammalian forebrain may have a role in dynamic visual information processing and in the evaluation of the changes in the visual environment during self-motion of the animal.
Keywords: receptive fields • electrophysiology: non-clinical • perception