Nonsynaptic activity in the cell is usually expressed as changes in neuronal excitability. This occurs through modulation of membrane components, such as resting and voltage-gated channels and ion pumps. Nonsynaptic processes are thought to be involved in memory storage. One possible mechanism of this action involves marking a neuron that has been recently active with changes in excitability. This would help to link temporally separated stimuli. Another potential mechanism comes from a computational model that indicates that nonsynaptic plasticity may prime circuits for modification in learning because excitability changes may regulate the threshold for synaptic plasticity.
The storage capacity of synaptic based memory storage systems is very large, making it an attractive mechanism to study. There are approximately 104 synapses per neuron and 1011 neurons in the human brain. Nonsynaptic plasticity is often overlooked simply because its storage capacity is not as high. Regulating the density of ion channels in the axon and soma of a neuron would change the throughput and affect all of the synapses. Therefore, its storage capacity would be significantly less than that of synaptic plasticity.
While its storage capacity is too low to make it the sole mechanism for storage, nonsynaptic plasticity could contribute to synaptic storage methods. It has been shown that the modulation of ion channels can occur in regions as small as specific dendrites. This specificity makes the storage capacity of nonsynaptic plasticity larger than if it were taken to be whole neuron modulation. Procedural memories are a good fit for this type of storage system because they do not require the high specificity that declarative memories do. Generalization of motor tasks and conditioned stimuli could be an efficient way to store this information.
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