BCM (Bienenstock et al., 1982) refers to the theory of synaptic modification first proposed by Elie Bienenstock, Leon Cooper, and Paul Munro in 1982 to account for experiments measuring the selectivity of neurons in primary sensory cortex and its dependency on neuronal input. It is characterized by a rule expressing synaptic change as a Hebb-like product of the presynaptic activity and a nonlinear function, \phi(y;\theta_M) , of postsynatic activity, y. For low values of the postsynaptic activity ( y\theta_M , \phi is positive. The rule is stabilized by allowing the modification threshold, \theta_M , to vary as a super-linear function of the previous activity of the cell. Unlike traditional methods of stabilizing Hebbian learning, this "sliding threshold" provides a mechanism for incoming patterns, as opposed to converging afferents, to compete. A detailed exploration can be found in the book Theory of Cortical Plasticity (Cooper et al., 2004). For an open-source implementation of the BCM, amongst other synaptic modification rules, see the Plasticity package at http://plasticity.googlecode.com.