Fig. 1.

Burst stimulation (PF burst) converts Pkj spike output from a simple excitatory response to a biphasic response, and LFS converts Pkj spike output from simple excitatory to monophasic excitatory. (A) A schematic of the feedforward network in the molecular layer of the cerebellar cortex. Granule cell (GC) axons form the PFs. This excitatory input synapses on both Pkjs and INs. The site of stimulation is indicated with a bolt, and the recorded cell is indicated with shading. (B) Spike rasters show 60 sweeps during the 5-min control period, 100 sweeps during the conditioning epoch, and then 240 sweeps after conditioning for three example cells. (C) The peristimulus time histograms (PSTHs, 20-ms bins) compare the pretest period to the last 5 min of the posttest. Bars indicate the average firing rate, normalized to the prestimulus firing rate; lines indicate the SEM. (D) Summary of averaged data over regions indicated: test stimuli s1 (100-150 ms) and s2 (150-200 ms), and the late period (200-280 ms). (E) PF burst stimulation in the presence of a GABA_A antagonist (PTX, 100 μm) induces a potentiation of the excitatory response, but it is not followed by an inhibitory period, as is the case in the control experiments. (F) Bar graphs summarize the data in E.(G-I) Sister experiments were performed by using LFS to condition the circuit. (G) Example data from three cells, in this case 300 sweeps of conditioning, are shown. (H) PSTHs of pretest data and posttest data for seven control cells and six cells in EGLU. Lines in the PSTHs indicate the SEM. (I) Summary of averaged data over regions indicated. A significant increase in firing during the late time window is observed in the posttest. ^*, P < 0.05.