14.10 Insight 796 Abbott

ever-changing manner. The effect of a signal transmitted synaptically from one neuron to another can vary enormously, depending on the recent history of activity at either or both sides of the synapse, and such variations can last from milliseconds to months. Activity-dependent changes in synaptic transmission arise from a large number of mechanisms known collectively as synaptic plasticity. Synaptic plasticity can be divided into three broad categories: (1) long-term plasticity, involving changes that last for hours or longer, is thought to underpin learning and memory; (2) homeostatic plasticity of both synapses and neurons allows neural circuits to maintain appropriate levels of excitability and connectivity despite changes brought about by protein turnover and experience-dependent plasticity; (3) short-term plasticity, which is the main focus of this review, occurs over milliseconds to minutes and allows synapses to perform critical computational functions in neural circuits. It is clear that we cannot understand neural coding or information processing without taking synaptic dynamics into account. Here, we review some of the forms of synaptic plasticity and discuss their implications for neuronal coding and signalling.