Neuroplasticity refers to changes in synapses and/or other parts of neurons that affect how information is processed and transmitted in the nervous system. The amount of neuroplasticity is highest during development and lower afterwards, but transiently increased following nervous system injury. Parts of neurons and chains of neurons that are used often grow stronger, meaning that each action potential will have a larger effect on the target cell. This is called potentiation, and is often referred to as “neurons that fire together, wire together”. Parts of neurons and chains of neurons that used rarely grow weaker, meaning that each action potential will have a smaller effect on the target cell. This is called depression.
Plasticity may occur at individual synapses, or through structural changes to neurons that change the number of synapses connecting a neuron to a target cell. Synaptic potentiation may occur by having more neurotransmitter released per action potential, and/or having more or different neurotransmitter receptors that produce a larger response in the target cell for a given amount of neurotransmitter; the opposite may occur for synaptic depression.
More synapses may develop between frequently used axons and dendrites by sprouting of more axon terminals and/or more dendritic branches.
The structural changes of involved in depression of rarely used neurons or chains of neurons are called pruning, where the number of synapses may decrease by removal of axon terminals, dendritic branches, and/or entire neurons.
Potentiation and depression can be short-term, such as seconds or minutes, or it can be long-term, such as months or years. Neuroplasticity is important for neurodevelopment, memory, learning, and recovery from injury to the nervous system.