At different P values (range 0.1 and 0.9), the overall response pattern in PC output bursts did not change remarkably. In all cases, the output spikes followed the input spikes quite closely during the burst, then one or two extra spikes were generated and the pause occurred. However, at a closer inspection of raster plots, the precision of action potential emission changed. By increasing P (from P = 0.13 to P = 0.91) the PC model responses were characterized by a greater precision, with decreased variability in burst spike pattern and pause length (see also Figure 2C). Increased precision derived from the decreased paired pulse ratio (A2/A1, where A1 and A2 are the amplitudes of the first and second response in a pair). In this way, the first EPSP in the train became more precisely aligned with the input burst leading to a repeatable spike generation independent from the relative phase of background firing activity (see also Figure 8 below). Therefore, the highest precision was obtained when the pf-PC synapse expressed presynaptic pf-PC LTP. This suggests that release probability controls fine regulation of spike timing on millisecond scale.