Inhibitory conductance dynamics in cortical neurons during
activated states
Martin Pospischil, Zuzanna Piwkowska, Michelle Rudolph, Thierry
Bal and Alain Destexhe
Neurocomputing 70: 1602-1604, 2007.
Abstract
During activated states in vivo, neocortical neurons are
subject to intense synaptic activity and high-amplitude membrane
potential (Vm) fluctuations. These ''high-conductance'' states may
strongly affect the integrative properties of cortical neurons. We
investigated the responsiveness of cortical neurons during different
states using a combination of computational models and in vitro
experiments (dynamic-clamp) in the visual cortex of adult
guinea-pigs. Spike responses were monitored following stochastic
conductance injection in both experiments and models. We found that
cortical neurons can operate in a continuum between two different
modes: during states with equal excitatory and inhibitory
conductances, the firing is mostly correlated with an increase in
excitatory conductance, which is a rather classic scenario. In
contrast, during states dominated by inhibition, the firing is mostly
related to a decrease in inhibitory conductances (dis-inhibition).
This model prediction was tested experimentally using dynamic-clamp,
and the same modes of firing were identified. We also found that the
signature of spikes evoked by dis-inhibition is a transient drop of
the total membrane conductance prior to the spike, which is typical
of states with dominant inhibitory conductances. Such a drop should
be identifiable from intracellular recordings in vivo, which
would provide an important test for the presence of
inhibition-dominated states. In conclusion, we show that in
artificial activated states, not only inhibition can determine the
conductance state of the membrane, but inhibitory inputs may also
have a determinant influence on spiking. Future analyses and models
should focus on verifying if such a determinant influence of
inhibitory conductance dynamics is also present in vivo.
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