Origin of correlated activity between parasol retinal ganglion cells

Cells throughout the central nervous system exhibit synchronous activity patterns - i.e. a cell’s probability of generating an action potential depends both on its firing rate and on the occurrence of action potentials in surrounding cells. The mechanisms producing synchronous or correlated activity are poorly understood despite its prevalence and potential impact on neural coding. We find that neighboring parasol retinal ganglion cells receive strongly correlated synaptic input in the absence of modulated light stimuli. This correlated variability appeared to arise through the same circuits that provide uncorrelated synaptic input. In addition, ON but not OFF parasol cells were coupled electrically. Correlated variability in synaptic input, however, dominated correlations in the parasol spike outputs and shared variability in the timing of action potentials generated by neighboring cells. These results provide a mechanistic picture of how correlated activity is produced in a population of neurons of key importance to visual perception.