A fast conducting, stochastic integrative mode for neocortical neurons in vivo.
Michael Rudolph and Alain Destexhe
Journal of Neuroscience 23: 2466-2476, 2003.
Abstract
During activated states, neocortical neurons receive intense synaptic
background activity, which induces large-amplitude membrane potential
fluctuations and a strong conductance in the membrane. However, little is
known about the integrative properties of neurons during such high-conductance
states. Here we investigated the integrative properties of neocortical
pyramidal neurons under in vivo conditions simulated by computational
models. We show that the presence of high-conductance fluctuations induces a
stochastic state in which active dendrites are fast-conducting and have a
different dynamics of initiation and forward-propagation of Na+-dependent
spikes. Synaptic efficacy, quantified as the probability that a synaptic
input specifically evokes a somatic spike, was roughly independent of the dendritic
location of the synapse. Synaptic inputs evoked precisely timed responses
(milliseconds), which also showed a reduced location dependence. This scheme
was found to apply for a broad range of kinetics and density distributions of
voltage-dependent conductances, as well as for different dendritic
morphologies. Synaptic efficacies were, however, modulable by the balance of
excitation and inhibition in background activity, for all synapses at once.
Thus, models predict that the intense synaptic activity in vivo can
confer advantageous computational properties to neocortical neurons: they can
be set to an integrative mode which is stochastic, fast-conducting, and
optimized to process synaptic inputs at high temporal resolution independently
of their position in the dendrites. Some of these predictions can be tested
experimentally.
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