When a bundle of mossy fibers is activated by a short high-frequency bursts, the response depends on the release probability (p) at the involved synapses. A low p, typical of LTD, generates slow temporal summation, while a high p, typical of LTP, generates fast temporal summation. The rate of depolarisation is critical since inhibition arrives after about 5 ms. Therefore, areas with low p are unlikely to transmit any spikes since their granule cells cannot reach threshold before the intervention of synaptic inhibition (D’Angelo and De Zeeuw, 2009). It has been shown that p tends to be higher in the center than in the surround (Mapelli and D’Angelo, 2007). This, combined with observations reported above, makes the granular layer to behave as a complex spatio-temporal filter.