Cortical determination of temporal structure of spike trains in the cat ’s lateral geniculate and perigeniculate nuclei

Feedback projections from the, so called, “higher-order” to the “lower order” structures are common feature of sensory systems. Those projections were proposed to control the flow of sensory information from the periphery to the cortex. The cortico-thalamic feedback of the mammalian visual system was extensively studied, yet we are still far away from understanding neuronal and network mechanisms engaged in this modulatory influence. In our earlier studies with cortical cooling as a method of reversible elimination of cortical input to thalamus, we have shown that cortical feedback modulated response magnitude and influenced receptive field organization of neurons in both lateral geniculate (LGN) and perigeniculate (PGN) nuclei. Elimination of the cortical input modified spontaneous firing rate of thalamic neurons, decreasing, as expected, activity of the relay LGN cells, and, surprisingly, increasing the activity of PGN interneurons. Our recent studies show that despite of different effects of the cortical feedback on spontaneous firing rate, elimination of cortical input similarly affects inter-spike intervals within bursts generated by LGN and PGN cells, increasing their length. These results suggest similar cellular mechanism underlying direct cortical influence exerted on the LGN relay cells and PGN interneurons.