36 — Electrical synapses between inhibitory neurons shape the responses of principal neurons to transient inputs in the thalamus

In a mouse, whisker signals run from the whiskers themselves through a section of GABAergic neurons in the thalamus — the thalamic reticular nucleus (TRN). This signal then travels to brain areas including the ventrobasal complex (VB). More on that later.

Even though these cells are GABAergic — and thus already generally considered inhibitory in nature — there is very little GABA-synaptic interconnectivity between these TRN cells. In other words, these cells are not inhibiting each others’ signals by GABAergic means. Instead, it seems that the cross-talk that these cells demonstrate is due to gap-junctions (connexin36 electrical synapses).

The authors use a Hodgkin-Huxley single-compartment neuron in their simulation of TRN (and they use Microsoft Word to write their formulas). Using a four-neuron model, this study demonstrates a relationship between the electrical-synapse inhibitions between TRN neurons and the downstream spike-stream outputs to cortex.

This model is interesting because it’s so simple: Four cells are enough to demonstrate this relationship. At first I was suspicious of the small model size and the use of point-neurons to emulate biological ones, but I realize that because these thalamocortical pathways are so one-to-one (that is, each thalamic neuron feeds to one cortical downstream partner), this size of model is actually the perfect reduction of this problem to a tractable simulation. I am still curious if the results would differ on a larger scale with more neighbors and a more spatially-aware simulation using a cable-model neuron, but… I suppose that’s an exercise left to the reader.