Figure 2. Model of mossy fibre STP.

A, to identify the most reliable model of mossy fibre STP, we tested several different additive and multiplicative interactions of slow and fast facilitatory processes for goodness of fit. The combination ‘s⁴+f’ yielded the lowest χ² values and was therefore chosen for all further analysis (highlighted in grey; n = 12 experiments). B, in our chosen model, a random stimulus train (top) is translated into two dynamical variables, x_slow and x_fast, via first-order kinetics. To account for saturation of facilitatory amplitudes, x_slow is inserted into a nonlinearity x_slow→y_slow=G(x_slow). Powers of y_slow and x_fast are then scaled by amplitudes a_slow and a_fast, respectively. Finally, the two components are added. Incorporating the baseline amplitude A₀, we obtained predictions for the fEPSP amplitudes A.