Figure 7. Phase response curves (PRCs) of the model SNr neuron depend on $E_{GABA}$.

(A and B) Example traces illustrating the effect of a single GABAergic synaptic input on the phase of spiking in a simulated SNr neuron for hyperpolarized and depolarized $E_{GABA}$, respectively. (C) For an ongoing voltage oscillation of a spiking SNr neuron (blue trace), we define a phase variable as progressing from 0 immediately after a spike to one at the peak of a spike. As $E_{GABA}$ is varied from –60 mV to –50 mV, progressively more of the SNr voltage trace lies below $E_{GABA}$, where GABAergic inputs have depolarizing effects. (D) PRCs computed for a model SNr neuron in response to GABAergic input stimuli arriving at different phases of an ongoing SNr oscillation. As $E_{GABA}$ is varied from –60 mV to –50 mV, the PRC transitions from a curve showing a delay of the next spike for most stimulus arrival phases, through some biphasic regimes, to a curve showing an advance of the next spike for almost all possible phases. In panel D, the A and B labels at approximately 0.5 phase on the $E_{GABA}=-60mV$ and $E_{GABA}=-50mV$ PRCs correspond to the examples shown in panels A and B. The conductance of the synaptic input was fixed at 0.1 nS/pF in order to produce deflections in V_m for hyperpolarized $E_{GABA}$ that are consistent with data presented in Higgs and Wilson, 2016.