In Vivo Dynamic-Clamp Manipulation of Extrinsic and Intrinsic Conductances: Functional Roles of Shunting Inhibition and IBK in Rat and Cat Cortex
We present in vivo dynamic-clamp electrophysiological recordings to characterize the influences of shunting inhibition and the potassium current I BK on the input–output (I/O) transfer function of cortical neurons, in response to both artificial (injected current or conductance) and functional visual stimuli. In comparison to previous experimental and theoretical studies, we find that realistic levels of shunting inhibition have a significant divisive effect on the firing gain. We also quantitatively characterize the effect of shunting inhibition on threshold and saturation. Shunting inhibition applied by dynamic-clamp also has a non-linear effect on visual responses, not only reducing the response but also significantly changing the timing of the response. We confirm predictions that I BK facilitates spike firing, despite this being a hyperpolarizing current. This effect is demonstrated by an increase in both the gain of the I/O transfer function, e.g. the f/I curve, and visual responses.
KeywordsSpike Train Visual Response Hippocampal Pyramidal Cell Shunting Inhibition Atropine Methyl Nitrate
This work was supported by an HFSP grant (RGP0049/2002) and an Agence Nationale de Recherche grant (FUNVISYNIN) to Dr. Lyle J. Graham. We also gratefully acknowledge Thomas Gener for his help in developing the protocols and participating in early experiments. We also acknowledge the important contribution of the authors of the VisionEgg and the G-Clamp software packages.
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