Characterization of synaptic conductances and integrative properties during
electrically-induced EEG-activated states in neocortical neurons in vivo.
Michael Rudolph, Joe-Guillaume Pelletier, Denis Paré and Alain
Journal of Neurophysiology 94: 2805-2821, 2005.
The activation of the electroencephalogram (EEG) is paralleled with an increase
in the firing rate of cortical neurons, but little is known concerning the
conductance state of their membrane, and its impact on their integrative
properties. Here, we combined in vivo intracellular recordings with
computational models to investigate EEG-activated states induced by stimulation
of the brainstem ascending arousal system. Electrical stimulation of the
pedonculopontine tegmental (PPT) nucleus produced long-lasting (approx. 20 sec)
periods of desynchronized EEG activity similar to the EEG of awake animals.
Intracellularly, PPT stimulation locked the membrane into a depolarized state,
similar to the up-states seen during deep anesthesia. During these EEG-activated
states, however, the input resistance was higher than during up-states.
Conductance measurements were performed using different methods, which all
indicate that EEG-activated states were associated with a synaptic activity
dominated by inhibitory conductances. These results were confirmed by
computational models of reconstructed pyramidal neurons constrained by the
corresponding intracellular recordings. These models indicate that, during
EEG-activated states, neocortical neurons are in a high-conductance state
consistent with a stochastic integrative mode. The amplitude and timing of
somatic EPSPs was nearly independent of the position of the synapses in
dendrites, suggesting that EEG-activated states are compatible with coding
paradigms involving the precise timing of synaptic events.
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