a) Part of cerebellar circuitry shown in Fig. 1a; Red “X” depicts severed connectivity between MLIs and PCs in the PC-ΔKCC2 mice. ( b) Experimental and modeled eye movements in PC-ΔKCC2 mice as a function of training time of VOR phase-reversal training. Gain values (top panel) are normalized to the initial gain. Experimental data represent averages with SEM (purple shaded area) and SD (grey shaded area) the PC -ΔKCC2 mice. Grey dotted line indicates the values of the littermate controls. Modeled changes are displayed for both gain and phase with SD (red line). ( c) Linear regression plots displaying correlation between modeled and experimental data. ( d) Representative PSTHs from in vivo recording in PC -ΔKCC2 during vestibular stimulation (0.6 Hz). ( e) Polar plots of SS and CS modulation before and after learning (lighter and darker purple, respectively). The plots reveal much lower modulation amplitude than that of the controls. Note that some PCs did not modulate their SS activity (indicated with black arrows). Each dot represents a single cell. Phase of the modeled SS and CS are indicated with the arrows. ( f) Modeled and experimentally measured modulation was initially lower than that of the controls and increased significantly following learning in the PC -ΔKCC2. In contrast to the model, there was no significant increase to the firing frequency after training in PC -ΔKCC2 mice. Error bars denote SD; *denote p < 0.05; **denote p < 0.001. ( g) SS activity as a function of time in the cycle in a control (grey, initial value before learning; black, after training) and in the model with blocked MLI to PC inhibition (light purple, initial value before learning; dark blue, after training).