Figure 2.

The SNN distinguishes between an HFO and an artifact (fast transient) in the ECoG. (a,c) ECoG signal and input spike train to the SNN. Consecutive UP-DN spike bursts in the train define an UP-DN cycle. More cycles occurred during the HFO. (b,d) Activity of the neurons in the SNN. (b) During an HFO, the input spike train excited the dis-inhibitory neuron (membrane potential $I_{\mathit{mem}}$ in purple), which suppressed the global-inhibitory neuron that became silent (input current $I_{\mathit{in}}$ and $I_{\mathit{mem}}$ in orange). A neuron of the core SNN (input current $I_{\mathit{in}}$ and membrane potential $I_{\mathit{mem}}$ in green) integrated the input spike trains and produced an output spike. Several second layer neurons of the core SNN responded to the HFO (green dots). (d) During a short fast transient in the ECoG, the excitation of the dis-inhibitory neuron was so short (purple trace) that it did not silence the global-inhibitory neuron (orange traces), which in turn continued to inhibit the second layer neuron (green traces) and prevented the generation of an output spike. Neither this nor any other neuron of the second layer $I_{\mathit{mem}}$ (green) reached the spiking threshold hence, the raster plot remained empty. (e,f,g) Population characteristics of the UP-DN input spike trains entering the second layer neurons and the dis-inhibitory neuron. (e) The train during an HFO lasted 24 ms (median), with a single cycle lasting 2.6 ms (median). (f) The HFOs comprise more UP-DN cycles (median 6 cycles) than the artifacts (median 2 cycles). (g) The train during an artifact lasted 9 ms (median), with a single cycle lasting 3.2 ms (median). The cycle characteristics were used to select the parameters of the dis-inhibitory neuron and the global-inhibitory neuron (Table 1).