Deep Brain Stimulation
Basic Theory

Currently, scientists are not entirely certain how deep brain stimulation causes similar effects as lesions in the same region of the brain. Somehow the electrode stimulations override pathological activity patterns, but the patterns induced are not necessarily normal. Here are the four dominant theories:

Depolarization blockade

Through stimulation induced alterations in voltage activation of the neural membrane, neural outputs near the stimulating electrode are blocked. Although this theory accounts for the results of DBS being similar to ablation, it doesn't take into account the possible independent activation of the efferent axon of projection neurons. Thus, it does not explain why impulses are still being generated around the area of the electrode.

Synaptic inhibition

Neurons can not generate electrical impulses when electrically stimulated due to activation of axon terminals near the stimulating electrode. However, for the same reason as the depolarization blockade theory, it looses credibility because it does not explain the ability of efferent axons to fire impulses.

Synaptic depression

Synaptic transmission failure of the efferent output of stimulated neurons as a result of transmitter depletion caused by excessive stimulation by the electrode. This theory is discredited because several in vivo experimental studies have shown increases in transmitter release and sustained changes in firing of neurons in efferent nuclei when repeatedly stimulated by an electrode.

Stimulation induced modulation of pathological network activity

This is the only general theory that is consistent with the current available data. It accounts for the continuing of firing of impulses by efferent axons located in the electrode region. The alteration in the neural network could have the same results as ablation therapy induces. Thus, both results are accounted for. However, this theory does not explain much. It simply states that the neural network is altered by the electrodes stimulations. We still are not sure how or why the network is altered.