We used an acousto-optic deflector UV uncaging system (Shoham et al., SFN 2004, 737.19) to stimulate multiple sites within the granule cell layer of sagittal slices from rat (P18-20) cerebellum. Responses were recorded using whole-cell patch clamp recordings made from Purkinje neurons. Locations were activated by uncaging 170 μM MNI-glutamate within 0.5 ms at a 3 x 3 array of points spaced at 1.3-2.0 μm intervals. Responding locations were identified by measuring the change in a post-uncaging time window of 70-90 ms over many sweeps, and defining a t-score as the mean divided by the SEM. Locations with t > 2 were scored as responding. Responses were reduced somewhat by APV (200-400 μM) and were completely eliminated by subsequent addition of lidocaine (500 μM), consistent with the hypothesis that photolyzed glutamate triggered synaptic responses via activation of granule cells and not by direct activation of Purkinje cells, which have AMPA but not NMDA receptors. Averaged responses had short onset delays f...