Increasing the level of collateral GPe-GPe inhibition shifts the excitation-inhibition balance in STN and GPe in opposite directions. Behavior of the autonomous STN-GPe network for increasing values of GPe-GPe synaptic conductance. (A) Mean PSD of the somatic membrane voltages of STN (Ai) and GPe (Aii) neurons. (B,C) Representative spike trains and phase vectors for STN (column i, green) and GPe population (column iii, red) for two values of the GPe to GPe conductance [scale 0.33; 2.0 in rows (B,C), respectively]. Column ii shows phase vectors of the STN and GPe populations (in green; red, respectively, mean population vectors plotted as thick solid lines and cell vectors as thin transparent lines) reflecting phase locking to the instantaneous GPe phase. (D): Balance of excitation and inhibition in the STN (Di) and GPe (Dii) based on synaptic currents recorded in three neurons. Mean population firing rate (brown), E/I ratio (purple), and net synaptic current (blue). Shaded areas represent estimated total synaptic current from one pre-synaptic population during a simulation. (E) Population vector length and angle of STN and GPe population (green; red, respectively). (F) Metrics that characterize bursting in STN neurons: median burst rate, intra-burst firing rate, and coefficient of variation of ISIs across all STN cells.