Figure 7.

Golgi cells and combinatorial operations. (A) When the granular layer is stimulated through multiple mossy fiber bundles (called Stim1 and Stim2), the variable arrangement of synaptic contacts can generate combined excitation of granule cells or combined excitation of Golgi cells. Combined excitation of granule cells determines responses which are stronger than those caused by each individual bundle, while combined excitation of Golgi cells results in granule cell responses smaller than those generated by each individual bundle. The plots show the intensity of granular layer responses (recorded as VSD traces) to a short mossy fiber burst (indicated by broken lines) in areas in which there is either an increase (left: combined excitation) or decrease (right: combined inhibition) of the response with combined Stim1&2 compared to Stim1 or Stim2 alone (Mapelli et al., 2010a). The effect of combined inhibition becomes evident after stimulation is terminated, probably indicating that during repeated stimulation the inhibitory effect is partially suppressed (see Figure 5). (B) Spatial distribution of areas of combined excitation and combined inhibition in the granular layer of a cerebellar slice (data elaborated from VSD recordings). Combined inhibition disappears when Golgi cell transmission is blocked with the GABA-A receptor antagonist gabazine (Mapelli et al., 2010a).