Idan Segev , Department of Neurobiology and Interdisciplinary Center for Neural Computation, The Hebrew University of Jerusalem
EE Department, Mayer building , room 861 at 16:00 (please note the change of room)
3 May, 2011
Design principles for inhibition in dendrites
In both the hippocampus and the neocortex, individual inhibitory axons from distinct input sources targeting specific dendritic subdomains, where they form multiple synaptic contacts. This domain-specific dendritic inhibition is expected to play a key role in controlling local nonlinear and plastic dendritic processes. However, our understanding of dendritic inhibition is currently dominated by the viewpoint that considers the impact of inhibition at the soma/axon’s initial segment; we lack the conceptual framework for understanding the local and global impact of dendritic inhibition (a “dendro-centric” viewpoint). I will present an analytic approach that fills this gap; this provides several new and counterintuitive insights on the operation of dendritic inhibition. I will show that inhibition in regions lacking inhibitory synaptic contacts might exceed the inhibition at individual contact sites and that distal inhibition is more effective than the corresponding proximal inhibition in dampening local dendritic regenerative processes. Both of these results are in marked contrast to the prevailing view that inhibition is always maximal at the synaptic site itself, that it acts highly locally, and that the optimal site of inhibition for reducing soma depolarization is on the path between the soma and the dendritic site of the excitatory current source. These theoretical predictions are verified in a detailed experimentally based model of layer 5 pyramidal cells receiving multiple inhibitory contacts from Martinotti interneurons at known dendritic loci. These results therefore suggest a major re-evaluation in our understanding of synaptic inhibition.