Cortical connections of the pulvinar nucleus in Galago

Abstract

In the first series of experiments, small amounts of HRP were injected into areas 17, 18, and 19 and each of the cytoarchitectonic areas of the temporal lobe. The resulting distributions of labeled cells fell into a number of distinctive classes. For example, after injecting the temporal anterior area (Ta), the labeled cells occupied a band on the ventral border of the inferior division of the pulvinar complex; after injecting the temporal ventral area (Tv), the labeled cells were concentrated in the medial extremity of the superior division. In spite of the distinctiveness of these different distributions, there was evidence that in areas that we know to contain a representation of the visual field, the injection of the same part of the field led to labeled cells in the same part of the pulvinar nucleus. Thus, when the representation of the center of the field was injected in areas 17 or 18 or Tm (the temporal middle area), labeled cells were found in the dorsal part of the rostral half of the inferior division. The distinctiveness of the different distributions did not obscure certain features common to all experiments: labeled cells were always found in both subdivisions of the pulvinar complex, and there was always continuity between the population of labeled cells in the inferior division and the population of cells in the superior division. Wherever the site of the injection in the extrastriate region, some labeled cells were found in the caudal half of the inferior division. Since the caudal half of the inferior division corresponds approximately to the tecto-recipient zone as defined earlier, the entire temporal lobe, except for the auditory areas, is visual cortex. Evidence was also found for an overlap in the striate cortex between the projections of the lateral geniculate body and the pulvinar nucleus. In conclusion, the pulvinar complex projects to a vast area of cortex, including all of the occipital lobe and most of the lateral surface of the temporal lobe. This entire region, which comprises a good part of the whole of the neocortex, can be regarded as visual cortex. A second series of experiments involved cortical injections of tritiated amino acids. The results showed that the projections from the thalamus to cortex were precisely reciprocated by descending projections from cortex to thalamus. The results also served as a way of confirming the results of the first set of experiments.