I don't think they actaully want 1 - 2 millimaps going into the brain.
They are accounting for the loss. Here's the article:
LINDA BUSTEED sits nervously as two electrodes wrapped in large, wet
sponges are strapped to her head. One electrode grazes the hairline
above her left eye while the other sits squarely on her right eyebrow.
Wires snake over her head to a small power pack fuelled by a 9-volt
battery. Busteed drums her fingers on the table as she anticipates the
moment when an electric current will start flowing through her brain.
It sounds like quackery, but it's not. A growing body of evidence
suggests that passing a small electric current through your head can
have a profound effect on the way your brain works. Called transcranial
direct current stimulation (tDCS), the technique has already been shown
to boost verbal and motor skills and to improve learning and memory in
healthy people - making fully-functioning brains work even better. It
is also showing promise as a therapy to cure migraine and speed
recovery after a stroke, and may extract more from the withering brains
of people with dementia. Some researchers think the technique will
eventually yield a commercial device that healthy people could use to
boost their brain function at the flick of a switch.
"You could use this to boost your brainpower at the flick of a switch"
Busteed isn't here to test commercial devices, however. The 64-year-old
suffers from the degenerative brain disease frontotemporal dementia,
which leads to language loss, personality changes and mood swings.
There is no treatment.
Busteed is one of 20 patients in a phase II clinical trial led by Eric
Wassermann, head of the brain stimulation unit at the US National
Institute of Neurological Disorders and Stroke (NINDS) in Bethesda,
Maryland. He wants to know whether a 40-minute burst of direct current
directed at her left frontal lobe can improve her ability to generate
lists of words, a hallmark deficit of her disease. Wassermann's study
is double-blind, so he won't know whether Busteed is receiving current
or not. Busteed probably won't know either - tDCS is silent and elicits
barely a tingle. If she is getting the real thing, Wassermann hopes
that the current will "squeeze more out of the sick neurons", enabling
Busteed to perform better.
If the trial proves successful, Wassermann would like to develop a
brain stimulation device that patients can take home and use whenever
they want. He envisages a gizmo about the size of an MP3 player,
perhaps incorporated into a hat. "Turn it on and you feel better," he
says. "Turn it off and you're back where you started." It sounds too
simple to be feasible, but studies from around the world suggest that
Wassermann has a good chance of success. "All the scientific literature
points in the same direction," says neurologist Leonardo Cohen, chief
of the stroke and neurorehabilitation clinic at NINDS. "There must be
something to it."
Zapping the brain with electricity to cure various maladies has slipped
in and out of vogue over the past two millennia (see "Zaps from the
past"). In recent years, however, it has fallen out of favour,
superseded by a more powerful non-invasive technique called
transcranial magnetic stimulation. TMS works by penetrating the skull
not with electricity but with a magnetic field, causing all the neurons
in a particular region to fire in concert. After TMS stimulation stops,
depending on the frequency of magnetic pulses, this can have the effect
of either switching that region on, or turning it off.
TMS has proved exceptionally useful for mapping brain functions and has
also been tested as a therapy, but it can be unpredictable and
dangerous. Neurons in the brain normally fire asynchronously as they
communicate, but TMS can produce a massive synchrony of activity that
can propagate through the cortex like a Mexican wave through a stadium.
If this happens brain activity shuts down momentarily and causes
seizures. Despite an established safety margin for TMS, there is always
a remote possibility of triggering a seizure, which means that any
treatments have to be monitored by a physician. The bulky nature of the
device also makes it difficult to use outside a hospital.
The rediscovery of electrical stimulation began in 1999, when
neurologists Walter Paulus and Michael Nitsche of the University of
Göttingen in Germany attended a conference at which they heard about
an experimental technique combining TMS with direct current
stimulation. They went back to their lab intending to try it for
themselves, starting with electricity alone. Those first results were
"so amazing and encouraging", says Paulus, that they wanted to know
more.
In that first experiment, Paulus and Nitsche took a group of healthy
volunteers and stimulated their motor cortices with direct current.
They found that tDCS increased the neuronal firing rate by up to 40 per
cent. Where the effect differed from TMS was that it only affected
neurons that were already active - it didn't cause resting neurons to
start firing. They also discovered that if they applied tDCS for 3
minutes or more, the effect lingered after the current was switched
off, sometimes lasting for several hours. The experiment suggested that
tDCS was safe, painless and non-invasive and that the effects on
neuronal excitability could potentially have a profound, if temporary,
effect on brain function.
Wassermann was intrigued by the impact of tDCS on healthy brains and
began laying the groundwork for his own trials. In the past five years,
he, the Göttingen team and others have been testing the potential of
tDCS, primarily for the brains of healthy volunteers but increasingly
as a therapy too.
Administering tDCS is relatively easy. It is essentially a matter of
strapping two electrodes to your head, positioning them, adjusting the
current to between 1 and 2 milliamps and choosing the right duration.
The current is very weak and most people feel nothing, except in some
cases a "slight tingle or itch", says Wassermann. The human head is a
poor conductor, he adds, estimating that at least 50 per cent of the
current is lost, shunted across the skin as it follows the path of
least resistance to the other electrode. But measurements of neural
activity prove that some current does pass through the brain.
What exactly is happening is unknown, but experiments with humans and
animals, as well as recordings from individual neurons, suggest that it
can either increase the activity of neurons that are already firing, or
damp it down, depending on the direction of the current and how the
neurons are aligned.
Neurons in the cerebral cortex tend to be arranged with their
information-gathering dendrites pointing outwards, towards the scalp,
and their information-transmitting axons projecting inwards. When the
positively charged tDCS electrode is close to the dendrites, the
current causes active neurons to fire more frequently. The negative
electrode does the opposite. So if you know the region of the cortex
you want to target, you can zap it with one of the electrodes to either
stimulate it or inhibit it. Of course, the area under the second
electrode is experiencing the opposite effect. "This bothers me to no
end," admits Wassermann. But he says that if you place the second
electrode just above an eye, it is distanced from the brain by bone and
sinus.
The overall effect of tDCS, says Cohen, is to make the excited area
work more effectively. "It's like giving a small cup of coffee to a
relatively focal part of your brain - the one that you know will be
engaged in the performance of certain tasks," he says. "The one you
need to do the task better."
So far so good, but does this trickle of charge have any effect on
cognitive performance? In 2003, Paulus's team produced evidence that it
does (Journal of Cognitive Neuroscience, vol 15, p 619).
The researchers asked volunteers to press keys in response to
instructions on the computer screen. What the volunteers didn't know
was that the sequence of keystrokes followed a subtle but predictable
pattern. With stimulatory tDCS applied to their primary motor cortices,
the volunteers learned the sequence significantly faster than normal.
Stimulating different brain areas or applying inhibitory or "sham" tDCS
had no effect.
Paulus and colleagues have since gone on to produce more positive
results. Plying the left prefrontal cortex with stimulatory tDCS, for
example, boosts performance on a different test of learning and memory.
They showed volunteers combinations of squares, circles, triangles and
diamonds and asked them to guess whether that combination was "sunny"
or "rainy". At first the task is baffling, but eventually, by trial and
error, volunteers discover hidden rules and start scoring higher than
chance. According to the researchers, volunteers who received tDCS
stimulation got the gist significantly faster.
It's not just stimulatory tDCS that can give your brain a boost. Last
year Andrea Antal, a member of Paulus's team, reported that inhibitory
tDCS can work too. She used tDCS to inhibit activity in a region of the
visual cortex called V5, which helps perceive movement. The result was
improved performance on a visual tracking task in which the subject had
to follow a dot on the computer screen that could come from one of four
directions.
"At first we were utterly surprised that inhibitory tDCS makes
something better - it should be worse," says Antal. However, she says,
the task is very complicated and produces a lot of neural activation
and noise. Perhaps tDCS improves the signal to noise ratio.
The Göttingen team isn't the only one with success stories. Last year
researchers at Beth Israel Deaconess Medical Center in Boston,
Massachusetts, showed that working memory, the sort used to memorise
facts or lists of words, can be improved with stimulatory tDCS. "It's a
bit like increasing the amount of RAM available," says team leader
Alvaro Pascual-Leone.
Wassermann himself tested tDCS on the left prefrontal cortex of 103
volunteers and saw a 20 per cent improvement in their ability to
generate lists of words beginning with a given letter. A handful of
people even noticed the difference. "They didn't say 'I feel like
superman', but they did notice that they were performing better," says
Wassermann. Taken together, he says, these results suggest that tDCS
really can be used to boost brainpower beyond its normal limits.
It is also showing promise as a therapy. Antal is testing inhibitory
tDCS for migraine and the associated sensations of flashing lights,
strange colours and blurred vision, known as auras. She says that while
tDCS does not work for all types of migraine, in many people it reduces
pain and stops the auras.
Cohen, meanwhile, has tested the technique on stroke patients. He
stresses that he has tried it on less than 40 people so far, and that
up to now the results are only proof of principle. Still, from what he
has seen he thinks that tDCS in combination with rehab could help some
patients regain movements that would help them do things such as eat,
turn pages and grasp small objects. "The most important point is that
the magnitude of improvements correlates with increases in the
excitability of neurons," he says. "This suggests cause and effect."
Overall, it seems that tDCS has real promise, though many questions
remain. Key among those is the full range of brain functions that could
be enhanced. Wassermann speculates that almost any brain function
associated with a specific, localised region of the cerebral cortex is
potentially amenable to tDCS. Anything buried deeper in the brain,
however, is probably not accessible except via dangerously strong
currents.
Independent experts are somewhat divided. "Whether low DC current can
produce cognitive effects is an open question but I wouldn't rule it
out," says Ralph Hoffman, professor of psychiatry at Yale University.
"The physiology is plausible. It doesn't sound nutty." Dominique
Durand, director of the neural engineering centre at Case Western
Reserve University in Cleveland, Ohio, is less impressed. "I think it
is pushing it because this is not selective," he says. "It basically
stimulates a large part of the brain."
The biggest unknown, however, is whether tDCS will be more than a flash
in the pan. "What we are most concerned about is that it will work a
couple of times and then won't work again," says Wassermann. Just as
you can become habituated to a strong smell if you are exposed to it
for a long time, it is possible that a brain region exposed to a direct
current more than once or twice in a short space of time will get used
to it. If habituation does occur, says Wassermann, the technique is
useless. "If this can't do something for somebody then forget it. It
just becomes a funny phenomenon."
Wassermann and other researchers, however, are satisfied that at the
very least tDCS is safe. What is more, the device itself is
tantalisingly simple and would be cheap and easy to make. "It's
comfortable, easy and inexpensive, and it seems to work," says Cohen.
Adds Wassermann: "Anyone with the know-how could go to an electronics
store, buy the components and build one." If tDCS proves its worth, he
is interested in developing a commercial device. He points out that you
can already buy headgear that claims to cure insomnia, anxiety and
depression by stimulating your brain with alternating current, even
though there is scant evidence that it works. Imagine the potential for
a brain stimulator that really does the business.
So if the day comes when you can buy a battery-powered thinking cap,
what use might it be? One possibility is that it could help you learn
new, improved skills. The results with motor learning and visual
tracking, for example, might translate into a better tennis game or
improved piano playing. "And if you can enhance motor learning with
tDCS then it might help you learn something else," agrees Wassermann.
It's conceivable that enhanced learning and verbal skills could make it
easier to learn a second language or expand your vocabulary, says
Cohen. Students might even be able to raise their game by giving
themselves a blast of tDCS before class.
Another possibility, says Wassermann, is using tDCS to boost your
alertness. Researchers funded by the US military have already expressed
interest in developing that side of the technology for pilots (New
Scientist , 18 February, p 34). "Fighter pilots land on aircraft
carriers at the worst times of night after working long hours," says
Wassermann. "Suppose you have this device in your helmet, you could
flick it on before landing and get much more alertness."
It sounds too good to be true, and it may turn out to be. But if tDCS
lives up to its promise perhaps all you'll need to boost your
brainpower is a 9-volt battery, a couple of wires and some pieces of
wet sponge. Now there's an electrifying thought.
