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Local structural balance and functional interaction of excitatory and
inhibitory synapses in hippocampal dendrites
Guosong Liu
MIT
Theoretical and experimental studies on the computation of neural
networks suggest that neural computation results from a dynamic
interplay of excitatory and inhibitory (E/I) synaptic inputs. While
most studies have focused on E/I interactions at the cell body, a
significant portion of inhibitory synapses are instead distributed
along the dendritic tree, resulting in E/I interactions within
individual dendrite branches. If so, E/I synapses may be organized
structurally and functionally according to principles that facilitate
meaningful interaction. Here we show that E/I synapses are indeed
regulated across dendritic trees to maintain a constant ratio of
inputs, and that this structural property is accompanied by an E/I
functional balance maintained by a "push-pull" feedback regulatory
mechanism capable of adjusting E/I efficacies in a coordinated
fashion. We also find that during activity, inhibitory synapses can
determine the impact of adjacent excitatory synapses only if they are
co-localized on the same dendritic branch and are activated
coincidentally. These fundamental relationships between E/I synapses
provide organizational principles relevant to deciphering the
structural and functional basis for neural computation within
dendritic branches.