Fig. 8.

Illustration of the gamma oscillation mechanism in the model. a Spike raster of 250 ms from a simulation of a model with the same parameters as that shown in Fig. 6. For clarity, spikes from only 5 % of the neurons are shown. A gamma oscillation is apparent in layers 2/3 and 5. b Zoomed spike raster showing only neurons in layer 2/3. Spikes from only 1 % of the neurons are shown. c LFP recording from the virtual electrode with the highest gamma power in the LFP. d Power spectrum of the LFP from this electrode, calculated for 1.5 s simulation time, showing a clear gamma peak. e–h same as a–d, but with synaptic weights from P2/3 cells to B2/3 cells reduced to 1 % of their original value. e–f show B2/3 cell firing is greatly reduced, as they are not receiving excitation from the P2/3 cells. No gamma oscillation emerges. i–l same as a–d, but with synaptic weights from B2/3 cells to P2/3 cells reduced to 1 % of their original value. B2/3 cells fire rapidly and randomly: they are driven by the P2/3 cells but they cannot synchronise them as their synapses are too weak. No gamma oscillation emerges. m–p same as a–d, but with the mean and standard deviation of the stochastic input current to the B2/3 cells increased by 50 %. P2/3 cell firing is suppressed by the increased B2/3 cell firing, so no gamma oscillation occurs