Local structural balance and functional interaction of excitatory and inhibitory synapses in hippocampal dendrites

Guosong Liu


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.