Functional Properties of Neurons in Macaque Area V3

Karl R. Gegenfurtner 1 , Daniel C. Kiper 2 , and Jonathan B. Levitt 3 1 Max-Planck-Institut für Biologische Kybernetik, 72076 Tubingen, Germany; 2 Institut d'Anatomie, Faculté de Médecine, Université de Lausanne, 1005 Lausanne, Switzerland; and 3 Department of Visual Science, Institute of Ophthalmology, University College London, London EC1V 9EL, United Kingdom Gegenfurtner, Karl R., Daniel C. Kiper, and Jonathan B. Levitt. Functional properties of neurons in macaque area V3. J. Neurophysiol. 77: 1906-1923, 1997. We investigated the functional properties of neurons in extrastriate area V3. V3 receives inputs from both magno- and parvocellular pathways and has prominent projections to both the middle temporal area (area MT) and V4. It may therefore represent an important site for integration and transformation of visual signals. We recorded the activity of single units representing the central 10° in anesthetized, paralyzed macaque monkeys. We measured each cell's spatial, temporal, chromatic, and motion properties with the use of a variety of stimuli. Results were compared with measurements made in V2 neurons at similar eccentricities. Similar to area V2, most of the neurons in our sample (80%) were orientation selective, and the distribution of orientation bandwidths was similar to that found in V2. Neurons in V3 preferred lower spatial and higher temporal frequencies than V2 neurons. Contrast thresholds of V3 neurons were extremely low. Achromatic contrast sensitivity was much higher than in V2, and similar to that found in MT. About 40% of all neurons showed strong directional selectivity. We did not find strongly directional cells in layer 4 of V3, the layer in which the bulk of V1 and V2 inputs terminate. This property seems to be developed within area V3. An analysis of the responses of directionally selective cells to plaid patterns showed that in area V3, as in MT and unlike in V1 and V2, there exist cells sensitive to the motion of the plaid pattern rather than to that of the components. The exact proportion of cells classified as being selective to color depended to a large degree on the experiment and on the criteria used for classification. With the use of the same conditions as in a previous study of V2 cells, we found as many (54%) color-selective cells as in V2 (50%). Furthermore, the responses of V3 cells to colored sinusoidal gratings were well described by a linear combination of cone inputs. The two subpopulations of cells responsive