FUNCTIONAL STREAMS IN OCCIPITO-FRONTAL CONNECTIONS IN THE MONKEY

It is known that the prestriate cortical regions that project to area LIP in parietal cortex and to areas TEO and TE in temporal cortex are mostly separated. Two separate streams of information transfer from oc cipital cortex can thus be distinguished. We wished to determine wheth er the parietal and temporal streams remain segregated in their projec tions to frontal cortex. Paired injections of retrograde fluorescent t racers were placed in parietal and temporal cortex, or in the lateral and medial parts of the frontal eye field (FEF). The cortical regions containing retrogradely labeled cells were reconstructed in two-dimens ional maps. The results show that temporal cortex mainly projects to l ateral FEF (area 45). Parietal cortex sends projections to medial FEF (area 8a) and to lateral FEF, as well as to area 46. Thus, the parieta l and temporal streams converge in lateral FEF. Most of the occipital regions projecting to medial FEF are the same as those projecting to p arietal cortex, whereas lateral FEF receives afferents from the same o ccipital regions as those sending projections to temporal cortex. Thus , one can distinguish two interconnected networks. One is associated w ith the inferotemporal cortex and includes areas of the ventral bank a nd fundus of the superior temporal sulcus (STS), lateral FEF and ventr al prestriate cortex. This network emphasizes central vision, small sa ccades and form recognition. The other network is linked to cortex of the intraparietal sulcus. It consists of areas of the upper bank and f undus of STS, medial FEF and dorsal prestriate cortex. These areas enc ode peripheral visual field and are active during large saccades.