Fig. 1. Multi-neuron maps of granule cell activity.

a SLM-2PM images of sagittal and coronal cerebellar slices (×20 objective, Fura-2 AM bulk loading). Some cells (red circles) were selected for calcium imaging. b Activity maps, taken from the cells selected in a, show the peak intensity (∆F/F₀) of the granule cell responses to mossy fiber stimulation (10 pulses at 50 Hz, white bars) on a color scale. Each dot corresponds to a neuron. In both sagittal and coronal slices, the maps show variable intensity of responses from cell to cell and a remarkable increase of activity after applying gabazine (10 µM, continuous bath perfusion). The E–I balance maps (see “Methods” section) show that excitation or inhibition tend to prevail in distinct areas. c Examples of stimulus-induced Ca²⁺ signals simultaneously detected from the somas of different granule cells. Fura-2 AM fluorescence signals appear as ∆F/F₀ reductions induced by an intracellular calcium increase (6 points adjacent-averaging smoothing). d Cumulative E–I balance maps show the spatial profile of granule cell activity (n = 5 independent sagittal slices and n = 4 independent coronal slices oriented with respect to the mossy fiber bundle, white bars). It should be noted that the most excited areas reside in the core and are flanked by inhibition. The box and whisker plots show that the cumulative activations of the E and I areas are similar in sagittal and coronal slices (p = 0.8 and p = 0.3, respectively; unpaired t-test).