Retinal waves are governed by collective network properties

Propagating neural activity in the developing mammalian retina is required for the normal patterning of retinothalamic connections. This activity exhi bits a complex spatiotemporal pattern of initiation, propagation, and termi nation. Here, we discuss the behavior of a model of the developing retina u sing a combination of simulation and analytic calculation. Our model produc es spatially and temporally restricted waves without requiring inhibition, consistent with the early depolarizing action of neurotransmitters in the r etina. We find that highly correlated, temporally regular, and spatially re stricted activity occurs over a range of network parameters; this ensures t hat such spatiotemporal patterns can be produced robustly by immature neura l networks in which synaptic transmission by individual neurons may be unre liable. Wider variation of these parameters, however, results in several di fferent regimes of wave behavior. We also present evidence that wave proper ties are locally determined by a single variable, the fraction of recruitab le (i.e., nonrefractory) cells within the dendritic field of a retinal neur on. From this perspective, a given local area's ability to support waves wi th a wide range of propagation velocities-as observed in experiment-reflect s the variability in the local state of excitability of that area. This pre diction is supported by whole-cell voltage-clamp recordings, which measure significant wave-to-wave variability in the amount of synaptic input a cell receives when it participates in a wave. This approach to describing the d eveloping retina provides unique insight into how the organization of a neu ral circuit can lead to the generation of complex correlated activity patte rns.