P195 Electrical coupling in thalamocortical networks cumulatively reduces cortical correlation to sensory inputs
Austin J. Mendoza1, Julie S. Haas*1
1Department of Biological Sciences, Lehigh University, Bethlehem PA
*Email: julie.haas@lehigh.edu
Introduction
Thalamocortical (TC) cells relay sensory information to the cortex, as well as driving their own feedback inhibition through their excitation of the thalamic reticular nucleus (TRN). The inhibitory cells of the TRN are extensively coupled through electrical synapses. Although electrical synapses are most often noted for their roles in synchronizing rhythmic forms of neuronal activity, they are also positioned to modulate responses to transient information flow across and throughout the brain, though this effect is seldom explored. Here we sought to understand how electrical synapses embedded within a network of TRN neurons regulate the processing of ongoing sensory inputs during relay from thalamus to cortex. Methods We utilized Hodgkin-Huxley point models to construct a network of a 9 TC and 9 TRN cells, with one cortical output neuron summing the TC activity. Pairs of TC and TRN cells were reciprocally coupled by chemical synapses. The TRN cells were each electrically coupled to two neighboring cells, forming a ring topology. Each TC cell received an exponential current input in sequence, with intervals between inputs varying from 10 to 50 ms across simulations. This architecture and sequence of inputs allowed us to assess the functional radius of an electrical synapse. We compared the cumulative effects of each additional TRN electrical synapse on modulating responses of the TRN and TC cells and the cortical output. Results Increasing coupling strength between TRN cells modulated TRN responses by decreasing spike latency and increasing duration of TRN spike trains. Effects were strongest for smaller intervals between inputs, and cumulative with additional synapses. In TC cells, we also observed changes in latency and duration of responses and decorrelation of the responses from the inputs. These effects were strongest for larger intervals between inputs and also increased with coupling strength. Coupling within TRN modulated cortical integration of TC inputs by increasing spike rate but reducing spike correlation to the input sequence that was presented to the TC layer. These effects were robust to additive noise. Discussion Here we show that TRN electrical synapses exert powerful influence on thalamocortical relay, unexpectedly reducing cortical output correlation to inputs presented to thalamus. We noted that effects of electrical synapses were cumulative. Coupling between pairs alone did not predict the effects seen in a network context, as coupling coefficient measured across multiple neurons drops to unmeasurable levels. These results show that multi-synaptic influences of electrically coupled cells should be included in more complex and realistic network topologies.
