Inhibitory "noise"
Alain Destexhe
Frontiers in Cellular Neuroscience 4: 9, 2010.
Online Version:
http://frontiersin.org/neuroscience/cellularneuroscience/paper/10.3389/fncel.2010.00009
.
Abstract
Cortical neurons in vivo may operate in high-conductance
states, in which the major part of the neuron's input conductance is
due to synaptic activity, sometimes several-fold larger than the
resting conductance. We examine here the contribution of
inhibition in such high-conductance states. At the level of the
absolute conductance values, several studies have shown that
cortical neurons in vivo are characterized by strong
inhibitory conductances. However, conductances are balanced and
spiking activity is mostly determined by fluctuations, but not much
is known about excitatory and inhibitory contributions to these
fluctuations. Models and dynamic-clamp experiments show that,
during high-conductance states, spikes are mainly determined by
fluctuations of inhibition, or by inhibitory "noise''. This stands in
contrast to low-conductance states, in which excitatory
conductances determine spiking activity. To determine these
contributions from experimental data, maximum likelihood
methods can be designed and applied to intracellular recordings
in vivo. Such methods indicate that action potentials are
indeed mostly correlated with inhibitory fluctuations in awake
animals. These results argue for a determinant role for inhibitory
fluctuations in evoking spikes, and do not support feed-forward
modes of processing, for which opposite patterns are predicted.
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