Subcortical projections to the occipital and parietal lobes of the chimpanzee brain.

The subcortical sources of afferents to occipital and parietal cortex were studied in two chimpanzees with the aid of retrogradely transported horseradish peroxidase (HRP). In chimpanzee 1, HRP was injected into right cortical areas 17 and 18; chimpanzee 2 received HRP into right areas 17, 18, 19, and 39. The following subcortical structures were found to project to area 17 and/or area 18: locus coeruleus, dorsal raphe nucleus, nucleus annularis, nucleus centralis superior, pontine reticular formation, mesencephalic reticular formation, dorsal hypothalamus, lateral hypothalamus, nucleus basalis of Meynert, nucleus of the diagonal band of Broca, claustrum, nucleus basalis lateralis amygdalae, lateral geniculate nucleus, inferior pulvinar, lateral pulvinar, nucleus limitans, medial magnocellular part of the nucleus ventralis anterior, nucleus paracentralis, and nucleus centralis medialis thalami. Some of these structures may also project to area 19 and/or area 39. The following thalamic nuclei were found to project to area 19 and/or area 39 but not to areas 17 and 18: nucleus lateralis posterior, nucleus centralis lateralis, nucleus medialis dorsalis, nucleus ventralis lateralis, nucleus ventralis anterior nucleus lateralis dorsalis, and nucleus anterior ventralis. In several Instances, the HRP-labeled cells traversed specific nuclear borders, extending uninterruptedly from one classically defined nucleus into another. These results in the chimpanzee largely confirm data from a number of other mammalian taxa on the subcortical sources of afferents to the posterior cortex. Because of the close biological relationship between chimpanzee and man, we feel confident that such projections are also features of the human brain.