BCM synaptic modification function. Shown is the function φ(c,θM) as a function of c. This function determines the change in the weights, m (Eq. 2). It is characterized by a negative region (LTD) for small postsynaptic depolarization, a positive region (LTP) for large postsynaptic depolarization, and a moving crossover point between LTD and LTP, θM.