Whereas plasticity refers to a change in signalling efficacy at a given synapse, metaplasticity is a change in the ease of which that change in signalling efficacy (plasticity) can take place. Thus, it is a change in the changiness of synaptic strength, or the plasticity of plasticity. Hence the term metaplasticity.
This may play a role in some of the underlying mechanisms thought to be important in memory and learning such as LTP, LTD and so forth. These mechanisms depend on current synaptic "state", as set by ongoing extrinsic influences such as the level of synaptic inhibition, the activity of modulatory afferents such as catecholamines, and the pool of hormones affecting the synapses under study. Recently, it has become clear that the prior history of synaptic activity is an additional variable that influences the synaptic state, and thereby the degree, of LTP or LTD produced by a given experimental protocol. In a sense, then, synaptic plasticity is governed by an activity-dependent plasticity of the synaptic state; such plasticity of synaptic plasticity has been termed metaplasticity.
There is little known about metaplasticity, and there is much research currently underway on the subject, despite its difficulty of study, because of its theoretical importance in brain and cognitive science.
- Abraham WC (1999). Metaplasticity: Key Element in Memory and Learning?. News Physiol Sci., 14:85.