Coordination Between Sub-populations of Interneuron in the Spinal Cord Revealed by Information Theory*

Understanding the operation of the nervous system is impossible without knowing how different types of neurons coordinate their responses. Just like the brain, the spinal cord consists of many different neuronal types, whose function, input/out connectivity and electrophysiological properties remain poorly characterized. We use information theory to predict how subpopulations of spinal inhibitory and excitatory interneurons may coordinate their responses to their synaptic inputs to achieve maximal information transmission. The theory makes two predictions: 1) there is a positive correlation between threshold (IC50) and noise (inverse slope) of a neuron’s input-output function; 2) below some critical noise value, neuronal populations are expected to further split into sub-types. We verify the first prediction across inhibitory V1, and excitatory V2a and V3 interneuron populations. The second prediction was used to identify subtypes within both V2a and V3 interneurons, which coordinate their input-output behavior in a manner consistent with encoding maximal information given the synaptic inputs.