A number of clinical and complimentary therapies use electrical impulses
to affect neural activity in the brain and central nervous system.
They either involve permanent electrode implants (VNS
& DBS), or temporary application of electric
fields (ECT, TMS & TENS).
Electro Convulsive Shock Therapy (ECT)
Probably the oldest form of neural-excitation therapy, ECT is usually
applied to affective disorders, as a second or third line of treatment,
as it causes global disruption of short term memory. ECT involves
placing electrodes on either side of the head, at the temples, and
applying substantial bursts of current while the patient
is sedated and restrained. Electric charge surges through the brain
and nervous system, activating almost every neuron. It has been described
as 'rebooting the brain', due to it's profound effect on memory and
personality.
ECT is considered to be one of the most effective treatments for depression
of all types, backed up by a long history of use. Unlike the other
treatments it is not targeted at specific neural networks, but acts
on the entire system. However it's effectiveness is attributed to
a specific activation of the hippocampus, boosting expression of neurotrophins,
in turn enhancing transmission and plasticity.
[Altar et al, 2003]
Transcutaneous Electrical Nerve Stimulation (TENS)
TENS is basically a scaled down version of ECT, used around the
body as a form of physiotherapy, and for acute and chronic pain. A
control units generates user-controllable pulses that can be adjusted
for the circumstances. Conductive gel pads are used to conduct through
the skin, into underlying nerves and muscle. This is also the basis
for muscle toning machines, which stimulate muscle contraction electronically,
saving the user the effort of actually trying to exercise. Unfortunately
TENS is poor when used through thick cutaneous fat, requiring large
voltages to penetrate to the tissue below, restricting its use to
the relatively slim. See a TENS unit
TENS could have use in neuropathic conditions which cause muscle
wasting, by maintaining nerve and muscle activity. Some studies have
also found TENS, given at the maximal intensity without causing discomfort,
to facilitate healing in amputees. It was also attributed to reliving
phantom limb pain shortly after treatment, but not in long term.
[Finsen et al,1988]
Trans-cranial Magnetic Stimulation (TMS)
Pioneered by Thompson
and D’Arsonval in the late 1800s, TMS was found to create flashes
in the vision of subjects. TMS has few clinical uses as yet, although
it is a great tool for research, allowing on-invasive control and
modulation of brain activity. It comprises a portable electromagnetic
coil that is charged with massive currents (around 6000 amps) to generate
brief burst of magnetic field. The field strength needed to penetrate
the skull and affect deep brain tissue is around 2 or 3 tesla. By
aiming the field generator one can affect specific brain areas. Despite
not directly applying current into the brain, TMS is still a form
of ESB, as the magnetic fields induce current flow within target tissues.
TMS is used in bursts of between 5 and 20 seconds, at frequencies
ranging from 1 to 30hz. The stimulation profiles used are quite arbitrary,
each researcher having their own preferred technique. Research into
the long term effects of TMS is scant, though due to a long history
of use, if there are any bizarre or adverse effects they are very
subtle.
Studies have found TMS to be of little help for depressives when
applied grossly across the whole brain. This is generally the case
for TMS therapy, although there are also odd cases which show great
success. Perhaps the area of application and stimulation profile are
important in determining TMS's effects. Indeed one review found stimulation
to the left prefrontal cortex to be most effective in treating depression.
[Martin et al,2003; Hasey et al,2000; Gershon
et al,2003]
Vagus Nerve Stimulation (VNS)
VNS is used primarily to treat epilepsy, though it has been suggested
for depression and other disorders. A device like a heart pacemaker
is implanted, connected to an electrical coil wrapped around the vagus
nerve. The effect of VNS is usually to reduce seizure activity, although
the mechanism behind this is unknown. There are some mild effects
on autonomic function, especially intestinal motility, although prolonged
treatment usually allows adaptation to these effects.
[Handforth et al,1998]
Deep Brain Stimulation (DBS)
DBS is primarily used for movement disorders, although other uses
are becoming apparent. It is discussed indetail in it's own page -
DBS
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