Responses of neurons in primary and inferior temporal visual cortices to natural scenes

The primary visual cortex (V1) is the first cortical area to receive visual input, and inferior temporal (IT) areas are among the last along the ventral visual pathway. We recorded, in area V1 of anaesthetized cats and area IT of awake macaque monkeys, responses of neurons to videos of natural scenes. Responses were analysed to test various hypotheses concerning the nature of neural coding in these two regions. A variety of spike–train statistics were measured including spike–count distributions, interspike interval distributions, coefficients of variation, power spectra, Fano factors and different sparseness measures. All statistics showed non–Poisson characteristics and several revealed self–similarity of the spike trains. Spike–count distributions were approximately exponential in both visual areas for eight different videos and for counting windows ranging from 50 ms to 5 s. The results suggest that the neurons maximize their information carrying capacity while maintaining a fixed long–term–average firing rate, or equivalently, minimize their average firing rate for a fixed information carrying capacity.