The Development of the Receptive-field Internal Structure of V2 Neurons in Primates

Objective. To study the maturation of the receptive-field (RF) internal structure of the of V2 neurons in primates. Background. Visual capacities of primates are limited near birth. Physiologically, multiple inputs from the primary visual cortex (V1) neurons tuned to various local stimulus features converge on V2 neurons and many of these early extrastriate neurons may acquire new sensitivities to more complex features of visual scenes. The responses of V1 neurons are qualitatively adult-like as early as 6-14 days after birth and well tuned to stimulus orientation, spatial and temporal frequency, size, contrast, and disparity by 4 weeks of age. However, we know very little about the functional maturation of extrastriate visual neurons. Methods. Each V2 neuron was stimulated with a dense dynamic noise array. A local spectrum reverse correlation analysis was performed to reveal the internal structure of the RF. Results. As early as 4 weeks of age, V2 neurons showed facilitatory subfields with similar homogeneity for the preferred orientation and spatial frequency as adults, although the maximum activation strength was significantly lower than those in adults. V2 neurons also showed suppressive subfields with similar degree dishomogeneity for the preferred orientation and spatial frequency as adults. The maximum suppressive strength in infants was not significantly different from those in adults. Conclusion. Our results suggest that, for V2 neurons, an adult-like spatialorganization of receptive-field center is largely attained by 4 weeks of age. Grants. This study was funded by a grant from the NEI R01-EY-08128.