Early brain wiring: activity-dependent processes.

One of the leading theories of the neuropathology of schizophrenia is that it is a developmental disorder of "neural connectivity." To assess this theory, it is first necessary to understand how precise neural connections normally are established. Sensory-driven neural activity has been widely recognized as crucial for this process. Recent studies have revealed a similar requirement for endogenous neural activity generated by the nervous system itself, long before there is any sensory input. These patterns of sensory-driven and endogenously generated neural activity sculpt the precise circuits that are crucial to the many complex functions of the adult brain. This article summarizes the principles of activity-dependent neural development as determined from basic neuroscience experiments, particularly those done using the mammalian visual system, to illustrate the role of patterned activity, neuronal competition, and critical periods in shaping neural circuitry. The potential molecular mechanisms involved in these features of activity-dependent neurodevelopment are discussed and possible links to the etiology of schizophrenia are briefly explored.