Experimental and Theoretical Analyses of Synchrony in Feedforward Networks

There is a wealth of electrophysiological evidence suggesting that synchronous firing of neurons is present in the normal functioning brain. Synchrony has been postulated to be the substrate for encoding precise timing of action potentials that is necessary for pattern formation or for "binding" activities of neurons that encode distinct features of a stimulus. A hallmark of neural activity during a seizure is the appearance of synchronous events throughout the brain. Synchrony, however, is not exclusively found during a seizure but seems to be ubiquitous under normal conditions and, indeed, may be crucial for information processing. This chapter focuses on recent experimental and theoretical studies of synchrony in feedforward neural networks. This network is the backbone for information transfer in the brain given that signals must be propagated from neuron to neuron, from one nucleus to another, and from one brain region to another. Epileptiform activity may represent an aberrant manifestation of functional synchrony. If so, then understanding the mechanism by which synchrony propagates normally through a neural network might provide clues as to how the synchrony becomes pathological and may suggest preventive measures. As in feedforward networks, epileptiform activity originates from a focal point and then spreads rapidly in a stereotypic manner through a sequence of cortical areas. The simplicity of the feedforward network means that both experimental and rigorous theoretical approaches can be used to derive very general principles, which may then be applied to the study of epilepsy.