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

In the retina 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 V1, these responses are partially merged on single neurons, although domains of ON and OFF responses are still found in layers II-III with no direct inputs from the LGN. However, it is unclear whether V1 feedback circuits can process ON and OFF responses independently. Here, we demonstrate that local optogenetic 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% and 60.7% of control, respectively; n = 60), these changes did not correlate in single neurons (Spearman’s rank correlation coefficient ρ = 0.144, p > 0.27, n = 60). In contrast, the response amplitudes correlated in single neurons (ρ = 0.486, p < 0.0003, n = 60). These results can be explained by assuming that the response amplitude is largely dependent on intrinsic neuronal properties, while the RF area is modulated in feedback loops of V1 presynaptically.