EN
Most of recent studies of the role of cortical feedback in thalamocortical loop focused on its effect on thalamo-cortical relay (TCR) cells of the dorsal lateral geniculate nucleus (LGN). In a previous, physiological study we showed in cat visual system that cessation of cortical input decreased spontaneous activity of TCR cells and increased spontaneous firing of recurrent inhibitory interneurons located in the perigeniculate neucleus (PGN). To identify underlying mechanisms we studied several networks of point neurons with varied membrane properties, synaptic weights and axonal delays in NEURON simulator. We considered six network topologies. All models were robust against changes of axonal delays except for the delay between LGN feed-forward (f-f) interneuron and TCR cell. The best representation of physiological results gave models including reciprocally connected PGN cells driven by the cortex assuming slow decay of intracellular calcium. This indicates that thalamic reticular nucleus plays an essential role in the cortical influence over thalamo-cortical relay cells while the thalamic f-f interneurons are not essential in this process. The models revealed also that dependence of the PGN activity on the rate of calcium removal can be one of the key factors determining TCR response to diminished cortical input.