Optogenetic stimulation of pyramidal neurons in the rat primary visual cortex modulates ON- and OFF- receptive field areas independently.

Retinal ganglion cells detect changes in illuminance. An increase and a decrease in illuminance levels induce ON and OFF responses, respectively. This segregation into two major types of visual responses is carried out through the lateral geniculate nucleus (LGN) to the primary visual cortex area V1. In area V1, these responses are partially merged on single neurons, although domains of ON and OFF responses are still found in layer IV, which receives LGN afferents, and in layers II-III, which have no direct inputs from the LGN. However, it is unclear whether feedback circuits in area V1 can process ON and OFF responses independently. Here, we demonstrate that optogenetic local activation of layer IV-VI pyramidal neurons modulates the receptive field (RF) area of ON and OFF responses independently. Although the RF area was reduced for both ON and OFF responses (77.9% of control, Q1 = 56.0%, Q3 = 93.1%, and 60.7% of control, Q1 = 45.1%, Q3 = 92.2%, respectively; n = 60), there was no correlation between these changes in single neurons (Spearman's rank correlation coefficient ρ = 0.144, p > 0.27, n = 60). In contrast, the ON and OFF response amplitude changes correlated in single neurons (ρ = 0.486, p < 0.0003, n = 60), and the median amplitude change was similar for both types of responses (79.6% and 84.6%, respectively, for OFF and ON responses). These results can be explained by assuming that modulation of the response amplitude is largely dependent on changes in the membrane properties of a neuron, while the RF area is modulated mainly in feedback loops presynaptically.