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Diego Contreras; Cortical network dynamics and response gain. Journal of Vision 2009;9(8):25. doi: 10.1167/9.8.25.
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© ARVO (1962-2015); The Authors (2016-present)
The transformation of synaptic input into spike output by single neurons is a key process underlying the representation of information in sensory cortex. The slope, or gain, of this input-output function determines neuronal sensitivity to stimulus parameters and provides a measure of the contribution of single neurons to the local network. Neuronal gain is not constant and may be modulated by changes in multiple stimulus parameters. Gain modulation is a common neuronal phenomenon that modifies response amplitude without changing selectivity. Computational and in vitro studies have proposed cellular mechanisms of gain modulation based on the postsynaptic effects of background synaptic activation, but these mechanisms have not been studied in vivo. Here we used intracellular recordings from cat primary visual cortex to measure neuronal gain while changing background synaptic activity with visual stimulation. We found that increases in the membrane fluctuations associated with increases in synaptic input do not obligatorily result in gain modulation in vivo. However, visual stimuli that evoked sustained changes in resting membrane potential, input resistance, and membrane fluctuations robustly modulated neuronal gain. The magnitude of gain modulation depended critically on the spatiotemporal properties of the visual stimulus. Gain modulation in vivo may thus be determined on a moment-to-moment basis by sensory context and the consequent dynamics of synaptic activation.
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