Dynamic receptive field substructure in extrastriate cortex of the awake macaque

Abstract

Characterizing receptive fields of visual cortical neurons in the alert primate presents a significant challenge due to the limited duration of fixation bouts. Short fixation bouts also limit the quantitative analysis of behavioral modulation of receptive fields. We adapted the multi-input m-sequence technique to study substructure within receptive field maps by knitting together neural activity obtained across multiple fixation bouts. Reverse-correlation of the spike rate with the stimulus generates a detailed spatiotemporal map of a receptive field. By generating these maps from data selected from specific temporal intervals relative to the start or end of a fixation bout, we determined how the receptive field substructure evolved during an interval controlled, in part, by the monkey. Significant first-order kernels were computed from single-and multi-unit extracellular recordings obtained from cortical areas V2, V3 and TE. Many of the extrastriate single-unit receptive fields had demonstrable substructure. Examination of the receptive fields in 500 ms subintervals of the fixation bouts (lasting at least 1650 ms) revealed significant differences in gain, polarity, spatial extent, and dynamics between the subintervals. These observations suggest that the spatiotemporal structure of extrastriate receptive fields is modulated during the course of prolonged bouts of fixation. The source of this modulation is the subject of further study.

Footnotes

 Supported by NIH grants GM07739 (AH), EY07138 (SK), EY9314 (JV), NS02172 (NS) NS36699 (KP).