Title : Inhibitory conductance dynamics in cortical neurons during activated states
Authors : Martin Pospischil, Zuzanna Piwkowska, Michelle Rudolph, Thierry Bal and Alain Destexhe
Year : 2007
Journal : Neurocomputing
Volume : 70
Pages : 1602-1604
During activated states in vivo, neocortical neurons are subject to intense synaptic activity and high-amplitude membrane potential ðVmÞ ?uctuations. 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 ?ring is mostly correlated with an increase in excitatory conductance, which is a rather classic scenario. In contrast, during states dominated by inhibition, the ?ring 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 ?ring were identi?ed. 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 identi?able from intracellular recordings in vivo, which would provide an important test for the presence of inhibition-dominated states. In conclusion, we show that in arti?cial activated states, not only inhibition can determine the conductance state of the membrane, but inhibitory inputs may also have a determinant in?uence on spiking. Future analyses and models should focus on verifying if such a determinant in?uence of inhibitory conductance dynamics is also present in vivo.