Multisensory responses and receptive field properties of neurons in the substantia nigra and in the caudate nucleus.

The basal ganglia are widely regarded as structures involved in sensorimotor co-ordination, but little is known about the sensory background of their function. We publish here descriptions of the excitatory sensory responses and receptive field properties of the visual, auditory, somatosensory and multisensory caudate nucleus and substantia nigra pars reticulata neurons. Altogether 111 caudate nucleus and 124 substantia nigra sensory neurons were recorded in halothane-anaesthetized, immobilized, artificially ventilated cats. The sensory properties of the caudate and nigral neurons were found to be quite similar. A majority of the units were unimodal while a significant proportion of them were multisensory. The visual and the somatosensory modalities predominated for both nuclei. The sensory receptive fields were extremely large. The visual and auditory receptive fields covered the whole physically approachable sensory field and the somatosensory receptive fields covered the whole body surface of the animal. The receptive field properties of the multisensory caudate and nigral units were similar to those of the unimodal neurons. We observed no signs of retinotopical or somatotopical organization within the basal ganglia. The particular sensory receptive field properties, together with the significant number of multisensory neurons in the basal ganglia, suggest the existence of a multisensory pathway of presumably tectal origin involving the caudate nucleus and the substantia nigra that may serve for the sensory feedback of motor actions co-ordinated by the basal ganglia.