researchers explore electrical stimulation of the brain

8/8/2019 Researchers Explore Electrical Stimulation of the Brain

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Researchers Explore Electrical Stimulation of the BrainIn some research that evokes comparisons to Edgar Cayce?s recommendation for

the use of a wet cell appliance, scientists are exploring the curative value of electricalstimulation of the brain. In this research, reported in New Scientist, researchers

place two electrodes on the head and attach them to a nine volt battery.Called transcranial direct current stimulation (tDCS),

The methodology has shown promise in improving mental skills, including learningand memory, as well as in treating migraine headaches and improving recovery fromstrokes. Researchers are also exploring its use for reversing brain deterioration, as in

Alzheimber?s disease.

Speculation exists that a commercial model may be one day available. An electricalthinking cap could improve people?s mental functioning in many ways. The military

has already requested research on its use to keep pilots awake in the cockpit.Source:

Electrify your mind - literally

15 April 2006Exclusive from New Scientist Print Edition

Bijal Trivedi

Testing tDCS against dementia (Image: Marc Asnin/New Scientist)

Enlarge imageMind jolt

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 herright 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 currentwill 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 throughyour 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 motorskills and to improve learning and memory in healthy people -

making fully-functioning brains work even better. It is alsoshowing promise as a therapy to cure migraine and speed recovery

after a stroke, and may extract more from the withering brainsof people with dementia. Some researchers think the technique

will eventually yield a commercial device that healthy peoplecould use to boost their brain function at the flick of a

switch.

?You could use this to boost your brainpower at the flick of aswitch?

Busteed isn't here to test commercial devices, however. The64-year-old suffers from the degenerative brain disease

frontotemporal dementia, which leads to language loss,


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personality changes and mood swings. There is no treatment.

Busteed is one of 20 patients in a phase II clinical trial ledby 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 canimprove her ability to generate lists of words, a hallmarkdeficit 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 elicitsbarely a tingle. If she is getting the real thing, Wassermann

hopes that the current will "squeeze more out of the sickneurons", 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 usewhenever 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 youstarted." It sounds too simple to be feasible, but studies fromaround the world suggest that Wassermann has a good chance of

success. "All the scientific literature points in the samedirection," says neurologist Leonardo Cohen, chief of the stroke

and neurorehabilitation clinic at NINDS. "There must besomething 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 bypenetrating the skull not with electricity but with a magnetic

field, causing all the neurons in a particular region to fire inconcert. After TMS stimulation stops, depending on the frequency

of magnetic pulses, this can have the effect of either switchingthat region on, or turning it off.

TMS has proved exceptionally useful for mapping brain functionsand has also been tested as a therapy, but it can be

unpredictable and dangerous. Neurons in the brain normally fireasynchronously as they communicate, but TMS can produce a

massive synchrony of activity that can propagate through thecortex 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 anytreatments 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, whenneurologists Walter Paulus and Michael Nitsche of the University

of G?ngen in Germany attended a conference at which they


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heard about an experimental technique combining TMS with directcurrent stimulation. They went back to their lab intending to

try it for themselves, starting with electricity alone. Thosefirst results were "so amazing and encouraging", says Paulus,

that they wanted to know more.

In that first experiment, Paulus and Nitsche took a group ofhealthy volunteers and stimulated their motor cortices withdirect 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, theeffect lingered after the current was switched off, sometimes

lasting for several hours. The experiment suggested that tDCSwas safe, painless and non-invasive and that the effects on

neuronal excitability could potentially have a profound, iftemporary, effect on brain function.

Wassermann was intrigued by the impact of tDCS on healthy brainsand began laying the groundwork for his own trials. In the pastfive years, he, the G?ngen team and others have been testing

the potential of tDCS, primarily for the brains of healthyvolunteers but increasingly as a therapy too.

Administering tDCS is relatively easy. It is essentially a

matter of strapping two electrodes to your head, positioningthem, 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 humanhead is a poor conductor, he adds, estimating that at least 50

per cent of the current is lost, shunted across the skin as itfollows the path of least resistance to the other electrode. But

measurements of neural activity prove that some current doespass through the brain.

What exactly is happening is unknown, but experiments withhumans and animals, as well as recordings from individual

neurons, suggest that it can either increase the activity ofneurons 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 theirinformation-gathering dendrites pointing outwards, towards the

scalp, and their information-transmitting axons projectinginwards. When the positively charged tDCS electrode is close to

the dendrites, the current causes active neurons to fire morefrequently. The negative electrode does the opposite. So if you

know the region of the cortex you want to target, you can zap itwith one of the electrodes to either stimulate it or inhibit it.

Of course, the area under the second electrode is experiencing


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the opposite effect. "This bothers me to no end," admitsWassermann. But he says that if you place the second electrode

just above an eye, it is distanced from the brain by bone andsinus.

The overall effect of tDCS, says Cohen, is to make the excited

area work more effectively. "It's like giving a small cup ofcoffee to a relatively focal part of your brain - the one thatyou 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 producedevidence that it does (Journal of Cognitive Neuroscience, vol

15, p 619).

The researchers asked volunteers to press keys in response toinstructions 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 theirprimary motor cortices, the volunteers learned the sequencesignificantly 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 morepositive results. Plying the left prefrontal cortex with

stimulatory tDCS, for example, boosts performance on a differenttest of learning and memory. They showed volunteers combinations

of squares, circles, triangles and diamonds and asked them toguess 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 thanchance. 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 perceivemovement. The result was improved performance on a visual

tracking task in which the subject had to follow a dot on thecomputer 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, shesays, the task is very complicated and produces a lot of neural

activation and noise. Perhaps tDCS improves the signal to noiseratio.

The G?ngen team isn't the only one with success stories. Last

year researchers at Beth Israel Deaconess Medical Center inBoston, Massachusetts, showed that working memory, the sort used

to memorise facts or lists of words, can be improved with


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stimulatory tDCS. "It's a bit like increasing the amount of RAMavailable," 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 theirability to generate lists of words beginning with a given

letter. A handful of people even noticed the difference. "Theydidn't say 'I feel like superman', but they did notice that theywere 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 testinginhibitory tDCS for migraine and the associated sensations of

flashing lights, strange colours and blurred vision, known asauras. 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 wouldhelp them do things such as eat, turn pages and grasp small

objects. "The most important point is that the magnitude ofimprovements correlates with increases in the excitability of

neurons," he says. "This suggests cause and effect."

Overall, it seems that tDCS has real promise, though manyquestions 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, localisedregion of the cerebral cortex is potentially amenable to tDCS.

Anything buried deeper in the brain, however, is probably notaccessible 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 ofpsychiatry at Yale University. "The physiology is plausible. It

doesn't sound nutty." Dominique Durand, director of the neuralengineering centre at Case Western Reserve University in

Cleveland, Ohio, is less impressed. "I think it is pushing itbecause 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 thana 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," saysWassermann. Just as you can become habituated to a strong smell

if you are exposed to it for a long time, it is possible that abrain region exposed to a direct current more than once or twice

in a short space of time will get used to it. If habituation


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does occur, says Wassermann, the technique is useless. "If thiscan't do something for somebody then forget it. It just becomes

a funny phenomenon."

Wassermann and other researchers, however, are satisfied that atthe very least tDCS is safe. What is more, the device itself is

tantalisingly simple and would be cheap and easy to make. "It'scomfortable, easy and inexpensive, and it seems to work," saysCohen. 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 commercialdevice. He points out that you can already buy headgear that

claims to cure insomnia, anxiety and depression by stimulatingyour brain with alternating current, even though there is scant

evidence that it works. Imagine the potential for a brainstimulator 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 learningand visual tracking, for example, might translate into a bettertennis game or improved piano playing. "And if you can enhance

motor learning with tDCS then it might help you learn somethingelse," agrees Wassermann. It's conceivable that enhanced

learning and verbal skills could make it easier to learn asecond language or expand your vocabulary, says Cohen. Students

might even be able to raise their game by giving themselves ablast 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 thetechnology for pilots (New Scientist, 18 February, p 34).

"Fighter pilots land on aircraft carriers at the worst times ofnight after working long hours," says Wassermann. "Suppose you

have this device in your helmet, you could flick it on beforelanding and get much more alertness."

It sounds too good to be true, and it may turn out to be. But iftDCS lives up to its promise perhaps all you'll need to boost

your brainpower is a 9-volt battery, a couple of wires and somepieces of wet sponge. Now there's an electrifying thought.

Weblink:

http://www.newscientist.com/channel/being-human/brain/mg19025471.100-

electrify-your-mind--literally.html

researchers explore electrical stimulation of the brain

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