Neuromodulation denotes controlled electrical stimulation of the central or peripheral nervous system. The three forms of neuromodulation described in this paper-
deep brain stimulation,
vagus nerve stimulation, and
transcranial magnetic stimulation-were chosen primarily for their demonstrated or potential clinical usefulness.
Deep brain stimulation is a completely implanted technique for improving
movement disorders, such as
Parkinson's disease, by very focal
electrical stimulation of the brain-a technique that employs well-established hardware (
electrode and pulse generator/battery).
Vagus nerve stimulation is similar to
deep brain stimulation in being well-established (for the treatment of
refractory epilepsy), completely implanted, and having hardware that can be considered standard at the present time.
Vagus nerve stimulation differs from
deep brain stimulation, however, in that afferent stimulation of the vagus nerve results in diffuse effects on many regions throughout the brain. Although use of
deep brain stimulation for applications beyond
movement disorders will no doubt involve placing the stimulating
electrode(s) in regions other than the thalamus, subthalamus, or globus pallidus, the use of
vagus nerve stimulation for applications beyond
epilepsy-for example, depression and
eating disorders-is unlikely to require altering the hardware significantly (although stimulation protocols may differ).
Transcranial magnetic stimulation is an example of an external or non-implanted, intermittent (at least given the current state of the hardware) stimulation technique, the clinical value of which for neuromodulation and neuroprotection remains to be determined.