FIG. 16.

Cortical feedback can control the frequency and synchrony of thalamic oscillations. A: computational model prediction that cortical feedback can force intact thalamic circuits to oscillate at 3 Hz. A scheme of connectivity and receptor types in a circuit of thalamocortical (TC) and thalamic reticular (RE) neurons is shown. Corticothalamic feedback was simulated through AMPA-mediated synaptic inputs (shown on the left of the connectivity diagram) and could be directly triggered by the discharge of TC cells. [Modified from Destexhe (86).] B: a single stimulation of corticothalamic feedback (arrow) entrained the circuit into a 10-Hz mode similar to spindle oscillations. C: after 3-Hz stimulation with high intensity (arrows; 14 spikes/stimulus), RE cells were recruited into large bursts, which evoked IPSPs onto TC cells dominated by GABA_B-mediated inhibition. In this case, the circuit could be entrained into a different oscillatory mode, with all cells firing in synchrony. D: implementation of this paradigm in thalamic slices. Stimulating electrodes were placed in the optic radiation (OR), which contains corticothalamic axons connecting thalamocortical cell in the LGN layers and GABAergic interneurons in the perigeniculate nucleus (PGN). E: weak (single shock) stimulation at a latency of 20 ms after the detection of multiunit bursts activity (top trace). Bottom trace: smooth integration of the multiunit signal. F: a 7-Hz control spindle is robustly slowed to 3-Hz oscillation by the feedback stimulation (5 shocks, 100 Hz, 20-ms delay). [Modified from Bal et al. (18).]