The connections of area PG, 7a, with cortex in the parietal, occipital and temporal lobes of the monkey.

The cortico-cortical connections of area PG, 7a, in the parietal, occipital and temporal lobes have been studied after injections of HRP in this area and in certain of the areas connected with it. After such injections in PG there are labelled cells in architectonic areas OA and PE (visual area PO), the cingulate and retrosplenial areas situated medial to PG; posteriorly labelled cells are present in OA, visual areas MST, MT, V2, V3, V4 and in the walls and floor of the lower part of the superior temporal sulcus. Injections in PE and V4 show that these connections are reciprocal. Small injections in PG result in cell labelling in different parts of the areas connected to PG, suggesting that the connections are well organized and that there may be an ordered representation of the visual field in PG. In the lower wall of the lower part of the superior temporal sulcus there is overlap of the two visual pathways in the cortex, that to the temporal lobe with that to the parietal lobe; and in a restricted part of this sulcus there is convergence and overlap of the sequences of cortico-cortical connections related to the visual, somatic and auditory sensory systems. There may be certain common principles in the sequences of cortical connections to the parietal and temporal lobes from the primary visual and somatic sensory areas; in both there are well organized hierarchical and parallel pathways, and both are related to the superior temporal sulcus and to the cingulate cortex.