The autoradiographic tracing method has been used to analyze the distribution of ascending tectofugal pathways in the rhesus monkey. Our findings show that axons which arise from deep collicular neurons terminate within several dorsal thalamic nuclei which in turn project upon the frontal eye fields (area 8) and the inferior parietal lobule (area 7). Both of these cortical areas are functionally quite similar to the deep colliculus, and we suggest that ascending channels from the deep tectum must account, at least in part, for these functional similarities. The present autoradiographs reveal projections to several nuclear zones previously not identified as deep collicular targets in the monkey. Such targets include the visceral cell columns of the oculomotor complex, the rostral interstitial nucleus of the medial longitudinal fasciculus, and the magnocellular division of the ventral anterior nucleus. Deep tectal input also has been shown to terminate quite extensively within the paralamellar region of the mediodorsal nucleus and in the parafascicular nucleus; very little input to the central lateral and centromedian nuclei was observed. Radioisotope injections restricted to the superficial layers reveal dense projections to the parabigeminal nucleus, the pretectum, the inferior and lateral pulvinar nuclei, and to the ventral and dorsal lateral geniculate nuclei. Transported protein within the dorsal lateral geniculate nucleus occupied the "S" layers and the interlaminar zones.

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Median nerves to the hands of 8-15-d-old marmoset monkeys were transected and precluded from regeneration by ligation. Following periods of 0.4-1.5 years, features of organization in the cortical area 3b hand map were assessed neurophysiologically, and compared to features in normally reared monkeys. Cortical features in monkeys with both histories were similar in certain respects. (1) Receptive field organization was similar in terms of tactile thresholds and receptive field size, continuity, and glabrous-hairy specificity. (2) Somatotopic organization was similar in terms of the continuity of the glabrous representation, and progressions of receptive field shifts across some parts of the hand map. (3) Finally, the overall size of the hand map did not change. In contrast, other cortical features clearly differed following these developmental histories. (1) Neurons at virtually all recording sites in normal hand maps responded to light mechanical stimulation, whereas, following injury, neurons at about 8% of the recording sites responded only to high-intensity stimuli. (2) Somatotopic organization differed in terms of the presence or absence of the representation of skin autonomously innervated by the median nerve, the number and continuity of representations of hairy skin, and the spatial interfacing of representations. (3) Finally, there were differences in the areas and widths of representations of parts of the hand. The overall impression is that there is a correspondence between the cortical features that changed most after injury, and the features that varied most in individual normal monkeys: in both circumstances the most variable features involved properties of spatial patterning across large aggregates of neurons as reflected by the size, shape, continuity, and interfacing of representations. A hypothesis is proposed that suggests that the cortical hand map normally consists of a number of representations that are capable of developing and surviving somewhat autonomously of each other. The features of spatial patterning in the mosaiclike map of these representations are influenced by postnatal availability of inputs from intact hand nerves.