RESPONSES OF NEURONS IN PRIMARY AND INFERIOR TEMPORAL VISUAL CORTICESTO NATURAL SCENES

The primary visual cortex (V1) is the first cortical area to receive v isual 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 vid eos of natural scenes. Responses were analysed to test various hypothe ses concerning the nature of neural coding in these two regions. A var iety of spike-train statistics were measured including spike-count dis tributions, interspike interval distributions, coefficients of variati on, power spectra, Fano factors and different sparseness measures. All statistics showed non-Poisson characteristics and several revealed se lf-similarity of the spike trains. Spike-count distributions were appr oximately exponential in both visual areas for eight different videos and for counting windows ranging from 50 ms to 5 seconds. The results suggest that the neurons maximize their information carrying capacity while maintaining a fixed long-term-average firing rate, or equivalent ly, minimize their average firing rate for a fixed information carryin g capacity.