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

Abstract

The subcortical sources of aff erents to occipital andparietal cortex were studied in two chimpanzees with the aid of retrogradely transported horseradish peroxidase (HRP). In chimpanzee 1, HRP was inj ected 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 coerulcus, dorsalraphe 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, inferiorpulvinar.lateralpul-vinar, nucleus limitans, medial magnocellularpartof the nucleus ventralis anterior, nucleus paraccnlralis, 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 Hftp-labeledcells traversed specific nuclear borders, extending uninterruptedly fromone classically definednucleus into another. Thesere-sults 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.