Local and global gating of synaptic plasticity

Mechanisms influencing learning in neural networks are usually investigated on either a local or a global scale. The former relates to synaptic proces ses, the latter to unspecific modulatory systems. Here we study the interac tion of a local learning rule that evaluates coincidences of pre- and posts ynaptic action potentials and a global modulatory mechanism, such as the ac tion of the basal forebrain onto cortical neurons. The simulations demonstr ate that the interaction of these mechanisms leads to a learning rule suppo rting fast learning rates, stability, and flexibility. Furthermore, the sim ulations generate two experimentally testable predictions on the dependence of backpropagating action potential on basal forebrain activity and the re lative timing of the activity of inhibitory and excitatory neurons in the n eocortex.