The cortical connections of area V6: an occipito-parietal network processing visual information

The aim of this work was to study the cortical connections of area V6 by in jecting neuronal tracers into different retinotopic representations of this area. To this purpose, we first functionally recognized V6 by recording fr om neurons of the parieto-occipital cortex in awake macaque monkeys. Penetr ations with recording syringes were performed in the behaving animals in or der to inject tracers exactly at the recording sites. The tracers were inje cted into the central or peripheral field representation of V6 in different hemispheres. Irrespective of whether injections were made in the centre or periphery, area V6 showed reciprocal connections with areas V1, V2, V3, V3 A, V4T, the middle temporal L-1/area V5 (MT/V5), the medial superior tempor al area L-2 (MST), the medial intraparietal area (MIP), the ventral intrapa rietal area L-3 (VIP), the ventral part of the lateral intraparietal area L -4 (LIPV) and the ventral part of area V6A L-5 (VGA(V)). No labelled cells or terminals were found in the inferior temporal, mesial and frontal cortic es. The connections of V6 with V1, and with all the retinotopically organiz ed prestriate areas, were organized retinotopically. The connection of V6 w ith MIP suggests a visuotopic organization for this latter. Labelling in V6 A and VIP after either central or peripheral V6 injections was very similar in location and extent, as expected on the basis of the nonretinotopic org anization of these areas. We suggest that V6 plays a pivotal role in the do rsal visual stream, by distributing the visual information coming from the occipital lobe to the sensorimotor areas of the parietal cortex. Given the functional characteristics of the cells of this network, we suggest that it could perform the fast form and motion analyses needed for the visual guid ing of arm movements as well as their coordination with the eyes and the he ad.