Retinotopic patterns of connections of area 17 with visual areas V-II and MT in macaque monkeys.

Patterns of connections of Area 17 with extrastriate visual areas V-II and MT were studied in macaque monkeys by using 3H-proline and HRP as anatomical tracers. The results support previous conclusions that V-II is a split representation of the visual hemifield with most of the outer border formed by the zero horizontal meridian, and that MT is a topological representation of the visual hemifield. V-II was estimated to be about 10-12 mm wide, 110 mm long along its shared border with V-I, and 920 mm2 in surface area, thereby almost equaling Area 17 in size. MT was judged to be 7 mm wide and 12 mm long, with a surface area of 68 mm2, or roughly 7% of the area of Area 17. In some cases, there was evidence for projections from Area 17 to a third area (or areas) of cortex of about 2 mm wide and of uncertain length on the outer boundary of V-II. Terminations in V-II and MT were concentrated in layer IV and extended into inner layer III. Cells projecting back to Area 17 were largely in layers III and V in V-II and in layers III and VI in MT.