Modulation of associative plasticity by general network excitability in the human motor cortex

Introduction: Associative neuroplasticity encompasses the modification of synaptic strength by co-activation of two synaptic inputs to a common target neuron. It is a candidate to represent the neurophysiological basis of learning. Since unlimited neuroplastic network modifications would have dysfunctional effects on neuronal networks, homeostatic mechanisms are suggested to control for stability. Accordingly in human experiments the history of general/background cortical excitability determines the direction of its subsequent modulation: an identical neuroplasticity-inducing stimulation protocol can accomplish…