Frances Chance

Synaptic Input Variance Controls the Gain Not the Variability of Cortical Neuronal Responses

New York University

The excitatory and inhibitory synaptic inputs that drive and suppress the responses of cortical neurons appear to ride on a large background of roughly canceling excitation and inhibition. Although this self-canceling or balanced component contributes little net synaptic current, it can be a dominant source of synaptic current variability. To explore the functional significance of the resulting high synaptic input variance, we introduced excitatory and inhibitory synaptic conductances, mimicking conditions encountered in vivo, into pyramidal neurons in slices of rat somatosensory cortex. Surprisingly, changing the level of balanced synaptic input, which changes the variance of the synaptic current, does not significantly modify response variability. Instead, the level of balanced synaptic input controls the gain of the neuronal response, as characterized by the sensitivity of the firing rate to injected current. This provides a cellular mechanism for gain modulation, a general means by which cortical neurons combine and process information. Furthermore, it suggests that, in vivo, cortical neurons operate in a transistor-like mode, quite different from in vitro, in which responses driven by excitatory and inhibitory inputs acting in a push-pull configuration are gated by balanced sets of synaptic inputs.
Friday, February 23, 2024
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