Additional information to published papers
Rudolph M and Destexhe A. A fast conducting, stochastic integrative mode
for neocortical neurons in vivo. Journal of
Neuroscience 14: 239-251, 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 approximately 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.
Additional information to this paper:
This package contains all the mechanisms necessary to implement the models
investigated in this paper, using the NEURON simulation environment (NEURON is
freely available at
http://www.neuron.yale.edu). The mechanisms included here are the
voltage-dependent Na+, K+ and Ca2+ currents, as
well as synaptic (AMPA, GABAA) receptor types. Further instructions
are provided in a README file, as well as comments in each file.
Color movies:
These computer animations illustrate the dynamics of spiking in soma and
dendrites in a simulated neocortical layer VI pyramidal neuron. They are an
excellent complement to the figures of the paper (see also cover of the issue).
The somatodendritic distribution of membrane potential is shown by colors in
three cases:
Spontaneous activity in the active state (Vm fluctuations and spontaneous
dendritic spikes). 70 ms activity are shown; Vm scale as in the cover picture;
correlated background activity (Pearson correlation of 0.1).
Initiation and propagation of dendritic spike in active state evoked by synaptic
stimulation in the distal part of upper dendrite (stimulation amplitude of 4.8
nS, 2 stimulations are shown). A local dendritic spike is initiated, propagates
reliable to the soma and initiates there a response. The Vm traces below are:
green - dendrite an site of stimulation; red - soma; blue - axon initial segment
(70 ms duration).
Same as preceding case, but without background activity. The stimulation
amplitude was in this case of 9.6 nS (2 stimulations shown), which inititates a
local dendritic spike, which propagates only over limited distance and does not
elicit a somatic response.