Reconstruction of cone-system contributions to responses of colour-opponent neurones in monkey lateral geniculate

Responses of colour-opponent X-cells to intensity-modulation at various wavelengths were obtained in the lateral geniculate nucleus (LGN) of the anaesthetized (N2O/O2) rhesus monkey. The gaussian white noise (GWN) analysis method was used to describe the stimulus-response relationship. Two different methods were used to estimate sign and relative strength of the response contribution of each of the three known cone systems as a function of time. Both methods revealed that, in contrast to the well-known variability in gain and sign, the time course of the cone-type contributions was remarkably stereotyped in all cells. Surround-mediated cone-type contributions appeared to have a consistently longer delay than centre-mediated inputs. Response contributions from different types of cone appeared to add linearly in LGN neurones. Apart from rectification, it was possible to predict the response of the same neurone to step-modulation of intensity at various wavelengths successfully with the first-order Wiener kernel. This demonstrates that the cells behaved linearly under our stimulus conditions, which justifies the use of the first-order kernel as a means to characterize the system we wished to study.