A comparison of neuronal properties in macaque areas V2 and V3

Purpose. To quantitatively assess the spatio-temporal and chromatic properties of cells in area V3 and to compare the processing in this area to that in V2, its preceding stage in the visual pathways. Methods, We recorded extracellularly from single cells in visual areas V2 and V3 of anesthetized and paralyzed macaque monkeys using standard acute recording techniques. The range of receptive field eccentricities was matched in both samples. For each cell, we determined tuning to drifting sinewave gratings of different spatial and temporal frequencies, orientations, directions, sizes and color. Results. Neurons in area V3 preferred lower spatial, but higher temporal frequencies than neurons in area V2. In both V2 and V3, most neurons (>90%) were selective to orientation. Selectivity to size (20%) was also equally frequent in both areas. The largest difference in tuning characteristics was a higher selectivity to direction of motion in V3 (50%) than in V2 (20%). Although overall selectivity for color was about equal in both areas (50%), the tuning characteristics of the color selective cells were quite different. In V2 a significant subpopulation of cells (30%) showed specific responses to a narrow range of colors. In V3 the responses of all cells were well described by a linear summation of cone inputs. Whereas preferred colors were evenly distributed around the color circle in area V2, there was a tendency for V3 cells to prefer yellow-blue modulations. Conclusions. The preference of V3 cells for higher temporal frequencies and the similarity in color tuning to V1, indicate that V3 may not be receiving its main input from V2, as a hierarchical model would predict, but from area V1 directly