MEMS in the Nervous System 75
In addition to effects on movement disorders, DBS appears able to elicit
strong emotional responses as well. In one patient being treated for Parkinson’s
related movement disorders, stimulation of a certain electrode elicited a case
of severe depression, which stopped upon cessation of stimulation.
In other
patients, stimulation of Broadmann’s area 25 (subgenual cingulated region) al-
leviated depression in patients unresponsive to traditional pharmaceutical and
behavioral therapies.
DBS used in the nucleus acumbens has been suggested as a
treatment for patients with obsessive compulsive disorder that does not respond to
conventional treatments.
There is evidence that DBS can also help patients who
have had a traumatic brain injury recover some functionality.
4.2.5 Peripheral Prosthetic Devices
One of the most common reasons for interfacing MEMs with the human body
are prosthetic devices. Prosthetics range from artificial limbs to retinal and
cochlear implants. They span a wide range of applications, from supplying
sensory feedback to recording and interpreting motor commands. Artificial limbs
with integrated microelectrodes may one day be capable of supplying a patient
with bio-mimetic closed-loop control, effectively mimicking natural function of an
artificial limb. Sensors in the prosthetic device could monitor information, perhaps
about pressure and temperature, and relay that back to the person so they could
module their actions accordingly. This next generation of prosthetic devices could
function essentially just like the lost limb.
Peripheral nerve electrodes are used to monitor and stimulate nerves in the
PNS. There are several varieties of peripheral nerve electrodes. Cuff electrodes
wrap around a peripheral nerve and stimulate it to generate a muscular response.
Polyamide substrates with platinum electrodes have been used to elicit activity
from rat muscle fibers.
Such electrodes could be used to evoke muscular activity
in a patient where communication from the spinal cord to the muscle is discon-
nected. A flexible substrate material is highly desirable in this situation, as it allows
the electrode to be curved around the nerve of interest quite easily. Sieve electrodes
contain holes and are placed between regenerating neurons to allow fibers to grow
through the holes. Electrodes around or near the holes allow for electrical stim-
ulation and recording.
Severed nerves are capable of physically regenerating
through silicon sieve electrodes
and have shown electrophysiological signals for
over one year.
Flat interface nerve electrodes (FINE) consist of a silicone tube
with electrical contacts in it; the FINE electrode flattens peripheral nerve to make
the central portion of it more accessible for stimulation and recording.
This is
not an exhaustive list of peripheral electrodes but rather just a sampling of what is
currently used.
4.2.6 Visual Prosthetics
Visual prosthetics are devices have the potential to help the visually impaired
regain sight or some aspects of it. Blindness can occur at several levels in the
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