Mechanisms of deep brain stimulation

The mechanism of action of high frequency deep brain stimulation is still unknown. However, in all circumstances and in all target nuclei so far stimulated, the effects mimic those of lesions previously made during thalamotomies, pallidotomies or even subthalamotomies, suggesting an inhibition of at least the neuronal network containing the target, if not of the target itself. On the contrary, fiber bundles are consistently activated at low or high frequencies. The hypothetical mechanisms envisioned should therefore be compatible and even produce these observed effects, to be acceptable as hypotheses. The mechanism could be either one or a combination of several causes: jamming of a feedback loop, activation of inhibitory structures included in a more complex network, blockade of membrane ion channels, deplorisation blockade, synaptic exhaustion, induction of early genes, changes in local blood flow, neuroplasticity, etc. It is probable that some are more involved in the acute effects and others in the long term changes, close to neuroplasticity. It is clear that the understanding of this strange and powerful phenomenon will profit from both clinical observation and well designed animal experiments. (C) 2002 Movement Disorder Society.