Heterosynaptic plasticity

Heterosynaptic plasticity is a subtype of synaptic plasticity, in which changes in synaptic strength are induced by activity at other synapses or by modulatory inputs. More broadly, synaptic plasticity refers to molecular changes that are associated with learning and memory, by altering neuronal firing frequency. Modern synaptic plasticity theory, building on the work of Santiago Ramón y Cajal, separates plasticity into two categories, Hebbian plasticity, also known as homosynaptic plasticity, and heterosynaptic plasticity. Synaptic plasticity is typically input-specific, meaning that the activity of a postsynaptic neuron, is altered by the release of neurotransmitters from presynaptic neurons in response to stimuli. In homosynaptic plasticity, only the input from a presynaptic neuron synapsing with a specific postsynaptic neuron can undergo plasticity. However, in the case of heterosynaptic plasticity, plasticity can result from either activity in a presynaptic neuron or from a separate modulatory interneuron, resulting in synaptic depression or potentiation. Thus, Hebbian or homosynaptic plasticity is often referred to as activity dependent, while heterosynaptic plasticity is referred to as modulator-dependent. A number of distinct forms of heterosynaptic plasticity have been identified in a variety of brain regions and organisms. These different forms of heterosynaptic plasticity are associated with a variety of neural processes including associative learning, the development of neural circuits, and the homeostasis of synaptic input.