Synchronization of Isolated Downstates (K-Complexes) May Be Caused by Cortically-Induced Disruption of Thalamic Spindling
Figure 8
Parametric analysis of evoking KCs by directly versus indirectly depolarizing RE.
The effect of increasing levels of RE depolarization or PY stimulation was inspected at individual time points. The schematic to the left outlines the connectivity and the order of effects on: 1) RE neurons, 2) TC neurons, and 3) PY neurons, based on RE depolarization (A) or PY stimulation (B). Five simulations with different random seeds were run for each value plotted, as well as a no stimulation baseline run. Baseline correction was performed for membrane potential (Vm) and high gamma power. Percent change was calculated for spindling power and firing. The average of five runs at a particular stimulation value and time point is plotted ± SEM. A, As the level of applied RE depolarization increases, so does the RE membrane potential (purple asterisk); however, RE firing does not increase until high levels of depolarization are reached (red box and orange asterisk). The green box highlights a level of RE depolarization that is subthreshold for evoking KCs. At 114.4pA (purple box), PY firing and high gamma power drop (blue and black asterisks, respectively), indicating a KC. Spindling also decreases in all three cell populations (red asterisk). The red box outlines a level of stimulation where RE firing increases, leading to the production of a KC. B, When stimulating 6 PY neurons projecting to all RE neurons, the spindling in all three populations drops 100 ms after stimulation is applied at a level of 20pA or higher (red asterisk). At 20pA (purple box), the firing in all cell populations (blue asterisk) and high gamma power in PY neurons (black asterisk) drop 300 ms after stimulation, indicating a KC. The green box highlights a subthreshold level of PY stimulation. At 80pA of PY stimulation (grey box), there is a drop in spindling but no KC, presumably because the direct cortical excitation is sufficient to counteract the removal of thalamic input (green asterisks).