You'll have to ask your doctor to get the protocol for this.
http://medicalxpress.com/news/2016-12-extent-human-brain-specific-dose.html#
Until now, no quantitative relationship
between the level of electricity applied to the brain and the extent of
neural activity generated has been plotted in humans.
Researchers at
the Stanford University School of Medicine have determined the amount of
human brain tissue that is excited by a given dose of
electrical stimulation.
"We have, for the first time in humans, established a dose-response
curve that applies to electrical stimulation rather than to drugs," said
Josef Parvizi, MD, PhD, associate professor of neurology and
neurological sciences.
The findings, described in a study published online Dec. 8 in
Neuron, may guide the therapeutic application of electrical brain stimulation via surgically implanted, current-emitting devices.
Parvizi is the senior author of the study. The lead author is former
Stanford postdoctoral scholar Jonathan Winawer, PhD, now an assistant
professor of psychology at New York University.
Devices delivering defined therapeutic doses of electricity to
structures within the brain are now in widespread commercial use for
countering the tremors of Parkinson's disease and controlling seizures
in epilepsy patients, and are approved for some patients with
obsessive-compulsive disorder. Similar devices are undergoing clinical
testing for other conditions, including depression and Tourette's
syndrome.
"We often try to correct a problem occurring in some tiny part of the
brain's complicated circuitry by administering a drug," said Parvizi.
"However, instead of reaching the cells you want to target, much or most
of the drug may wind up in the skin, bone, muscle, liver and elsewhere,
not to mention brain cells you don't want to target." That can cause
all kinds of side effects.
'Immense potential'
"Electrical brain stimulation, targeting only a specific
malfunctioning brain circuit, has immense potential to change medical
practice," Parvizi said. "But figuring out just how much current will be
effective without recruiting unwanted brain circuitry and inducing side
effects has been largely guesswork."
To get a more accurate picture, the new study focused on part of the brain's surface called the
primary visual cortex,
one of the most well-studied regions of the human brain. Located in the
back of the brain on the facing inner surfaces of that organ's two
hemispheres, the primary
visual cortex is the first docking station for visual information from the retina.
Each nerve cell in the primary visual cortex receives its information
from a fixed location in the retina and responds to an object observed
at a given position in a person's visual field. The precision with which
this correspondence has already been mapped out makes the primary
visual cortex an ideal place to examine just how far the effects of a
given electrical input propagate along the brain's surface.
Parvizi, who directs Stanford's Human Intracranial Cognitive
Electrophysiology Program, was taking care of four adult patients under
his evaluation at Stanford Health Care to determine the point of origin
of their recurring, drug-refractory epileptic seizures. In this
procedure, a portion of the skull is temporarily removed and a grid of
electrodes is placed on the brain's surface in order to record seizure
activity and pinpoint the spot in the brain where it begins.
Each of these four patients' primary visual cortex, while perfectly healthy, was partially covered by the electrode grids.
Mapping phosphenes
Investigators showed them geometric forms moving across a computer
screen while they stared at the center of the screen. Using
brain-imaging techniques, the researchers mapped which areas of the
participants' primary visual cortex these displays activated.
Once electrode grids were in place, the team used them to stimulate
and to record activity in the participants' primary visual cortex. After
each stimulation, they asked the participants to chart the location and
size of the hallucinatory phenomena, or phosphenes, they experienced in
their
visual field in response to electrical stimulation.
A phosphene is a visual sensation in the absence of light. Some
phosphenes look like a flickering, fractured formation composed of small
zigzagging lines of color dancing at a specific location in the field
of vision. (For people prone to migraines, such apparitions often herald
the onset of a painful headache.) Others may just be a burst of light
or color. (People often "see" phosphenes when they rub their closed
eyes.) It's long been known that activating the primary visual cortex by
direct electrical stimulation can produce phosphenes, which persist for
the duration of the stimulation and then vanish.
The investigators, always taking care to adhere to strict safety
limits, pulsed electrical current from one or another electrode at
varying frequencies, pulse widths, amplitudes and durations while the
participants stared at the center of the computer screen. After each
instance of stimulation, they were asked to draw on the computer screen,
using its trackpad, the outline of the phosphene they saw in its
perceived location. Then, using the imaging-derived maps of the
individuals' primary visual cortexes they'd constructed earlier, the
researchers were able to connect points on the observed phosphenes to
corresponding points on participants' primary visual cortex, and to
infer from phosphenes' sizes and locations just how much brain-surface
area in that brain region had been excited by each electrode-delivered
stimulation.
"The resulting dose-response relationship can be used now in clinical trials of electrical brain stimulation," Parvizi said.
Scientists have tried to establish this relationship in rodents, said
Winawer. "But you can't easily extrapolate from rodent studies, both
because our brains are quite different from theirs and because the
recording and stimulating instruments used in rodent experiments are
1,000-fold different from those used in humans."
Nor have connections between the physiologically measureable outcome
and perceptual outcome been previously mapped to any extent. (Animals
can't report what they see.)
"Notably, we observed a clear correspondence between the amount of
electricity applied and the size and intensity of the ensuing visual
phenomena subjects reported experiencing," said Parvizi, who has long
been fascinated by the question of how manipulating the brain's strictly
material components alters subjective consciousness.
How well the dose-response relationship as measured at the cortical
surface holds up in deep-brain structures remains to be further tested,
he added.
More information:
Jonathan Winawer et al. Linking
Electrical Stimulation of Human Primary Visual Cortex, Size of Affected
Cortical Area, Neuronal Responses, and Subjective Experience,
Neuron (2016).
DOI: 10.1016/j.neuron.2016.11.008
Henry Shin
Yang Zheng
Xiaogang Hu
