Synaptic plasticity provides the basis for most models of learning, memory
and development in neural circuits. To generate realistic results, synapse-specific
Hebbian forms of plasticity, such as long-term potentiation and depression,
must be augmented by global processes that regulate overall levels of neuronal
and network activity. Regulatory processes are often as important as the more
intensively studied Hebbian processes in determining the consequences of synaptic
plasticity for network function. Recent experimental results suggest several
novel mechanisms for regulating levels of activity in conjunction with Hebbian
synaptic modification. We review three of them—synaptic scaling, spike-timing
dependent plasticity and synaptic redistribution—and discuss their functional
implications.
