The objective of this research program is to understand the structural and functional significance of the cerebral cortex. Our previous research has focused upon the long cortical connections that link sensory, association and limbic cortical areas. These studies have revealed underlying principles of the organization of cortical connections. Our recent investigations have focused on the intrinsic connectivity and cytoarchitecture of the auditory cortices and have revealed that the intrinsic connections of the auditory areas are organized according to a set of principles that appears linked to the cytoarchitectonic subdivision of these areas. This organizational pattern is also reflected in the thalamocortical connections of each subdivision. Additional studies have suggested that similar organizational principles may govern the local connectivity of the inferotemporal and posterior parahippocampal areas of the ventral temporal lobe, regions that may constitute parallel streams for the outflow of visual information from the occipital lobe. The visual input to the inferotemporal cortex appears to originate primarily in areas where the central part of the visual field is represented while input to the posterior parahippocampal gyrus originates in areas where the peripheral part of the visual field is represented. This suggests that these two areas may constitute two distinct visual pathways through the temporal lobe. Our proposed studies are designed to examine this hypothesis by investigating the connections of the occipital cortices leading to both the inferotemporal and posterior parahippocampal areas. We also propose to investigate the differential thalamocortical and corticothalamic connectivity of each stage along these parallel pathways. Additionally, in the posterior parahippocampal gyrus we will determine the relationship of these visual and thalamic afferents to afferents from the parietal, superior temporal, frontal and limbic cortices. Finally, we will investigate the efferent outflow from these various architectonic subdivisions of the inferotemporal and posterior parahippocampal areas into the limbic system of the medial temporal lobe: the entorhinal areas, the hippocampal formation and the amygdala. These studies will be conducted in the rhesus monkey using complementary anterograde and retrograde tracing techniques.
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