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. Author manuscript; available in PMC: 2014 Mar 17.

Published in final edited form as: Dev Rev. 2011 Dec 1;31(4):207–239. doi: 10.1016/j.dr.2011.07.008

From the perspective of neural circuits, neuroplasticity is what changes the output of neural circuits. There are many different ways in which the output of a neural circuit can change as a result of changes in the pattern of incoming activity.

A. In the simplest form, neural circuits are driven by inputs that come onto them, and their gain is modified by intrinsic inputs (GABA, ACh and other modulatory inputs). Neural circuits in close proximity (in different columns, or processing different features of sensory input) also modulate each other (such as by lateral inhibition, not depicted here) to produce a unified output.

B. If a cell is induced to make new synapses onto existing targets (in the case of axon sprouting, new spines, or new dendrites), the individual output of the affected neuron changes, altering the output of the neural circuit. The output changes in strength.

C. As in B, but instead of new synapses, the existing synapse becomes more efficient in activating the postsynaptic neuron, by for example upregulating the number of receptors at the synapse.

D. If the axon is able to sprout more to extend farther distances, and to form synapses onto a neuron to which it was previously unconnected, then the affected new neuron receives a novel stimulus, changing the character of the output.

E. The output of the neural circuit can also change without any structural change: If one of the inputs coming to the neural circuit is weakened or cut, thus depriving the circuit of its drive, then the interactions between local neural circuits will be influenced, particularly by reducing the lateral inhibition it exerts onto neighboring circuits. Without the local inhibition, the neighboring neuronal circuit will now be more sensitive to its own input, thereby leading to a ‘novel’ output. This “unmasking” change is immediate, since it does not require structural changes that need time.

From the perspective of neural circuits, neuroplasticity is what changes the output of neural circuits. There are many different ways in which the output of a neural circuit can change as a result of changes in the pattern of incoming activity.

A. In the simplest form, neural circuits are driven by inputs that come onto them, and their gain is modified by intrinsic inputs (GABA, ACh and other modulatory inputs). Neural circuits in close proximity (in different columns, or processing different features of sensory input) also modulate each other (such as by lateral inhibition, not depicted here) to produce a unified output.

B. If a cell is induced to make new synapses onto existing targets (in the case of axon sprouting, new spines, or new dendrites), the individual output of the affected neuron changes, altering the output of the neural circuit. The output changes in strength.

C. As in B, but instead of new synapses, the existing synapse becomes more efficient in activating the postsynaptic neuron, by for example upregulating the number of receptors at the synapse.

D. If the axon is able to sprout more to extend farther distances, and to form synapses onto a neuron to which it was previously unconnected, then the affected new neuron receives a novel stimulus, changing the character of the output.

E. The output of the neural circuit can also change without any structural change: If one of the inputs coming to the neural circuit is weakened or cut, thus depriving the circuit of its drive, then the interactions between local neural circuits will be influenced, particularly by reducing the lateral inhibition it exerts onto neighboring circuits. Without the local inhibition, the neighboring neuronal circuit will now be more sensitive to its own input, thereby leading to a ‘novel’ output. This “unmasking” change is immediate, since it does not require structural changes that need time.