Masked excitatory crosstalk between the ON and OFF visual pathways in the mammalian retina

Non‐technical summary  An organizing principle of the visual system is the segregation of ON and OFF responses into parallel streams to signal light increment and decrement. This segregation begins in the retina where the output ganglion cells can be divided into ON and OFF subtypes based on their responses to light. Here we show that blockade of GABAergic inhibition reveals opposite polarity responses in ganglion cells whereby OFF cells display ON responses and ON cells display OFF responses. This crossover excitation was found in both the rabbit and mouse, indicating that it is a common synaptic mechanism in the mammalian retina. Overall, these results challenge the idea that light increment and decrement is signalled by different visual pathways. Moreover, our findings suggest that release of inhibition under certain light conditions can enable single ganglion cells to carry both ON and OFF signals, thereby allowing additional information to be propagated across the limited bandwidth of the optic nerve.