Development of somatosensory responsiveness in the basal ganglia in awake cats

Single-unit activity was recorded from the caudate nucleus (CD), globus pallidus, and entopeduncular nucleus (GP-ENTO) in awake, partially restrained kittens. The purpose of this experiment was to assess the ability of developing basal ganglia structures to process natural facial somatosensory information and compare this function to that observed in the adult. Somatosensory responsiveness in the CD and GP-ENTO developed slowly during the first three postnatal months. Somatosensory responsiveness had three major developmental trends in these nuclei: 1) The proportion of neurons responding to facial sensory stimulation increased with age; 2) proportionally, the area of face encompassing a receptive field of a neuron was smaller in adults than in young kittens; 3) qualitatively, adultlike responses to sensory stimulation did not appear until approximately three months of age. Units responsive to facial somatosensory stimulation in kittens under three months of age were very limited in the types of information they received. No specific stimuli parameters were encoded by these neurons. At approximately three months of age, units began to respond to varied stimuli (i.e., indentation of the skin as well as to brushing stimuli) and began to encode specific stimulus parameters such as direction of movement and relative location on the face. Kitten units responsive to skin indentation showed no evidence of encoding stimulus magnitude information. This was also true for the majority of adult basal ganglia neurons tested. The present findings suggest that the functions of the basal ganglia may be altered significantly during development. With increasing age, the basal ganglia may change from primarily a relay area for relatively nonspecific sensory information to an active processor of complex afferent information.