transcranial direct current stimulation

 Can you zap your brain back to health? Electrifying brain circuits may decrease depressive symptoms and chronic pain

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Rather than taking medication, a growing number of people who suffer from chronic pain, epilepsy and drug cravings are zapping their skulls in the hopes that a weak electric current will jolt them back to health.

This brain hacking—”transcranial direct current stimulation” (tDCS)—is used to treat neurological and psychiatric symptoms. A do-it-yourself community has sprouted on Reddit, providing unconventional tips for how to use a weak electric current to treat everything from depression to schizophrenia. People are even using commercial tDCS equipment to improve their gaming ability. But tDCS is not approved by the U.S. Food and Drug Administration, and scientists are split on its efficacy, with some calling it quackery and bad science.

Here’s the issue: Until now, scientists have been unable to look under the hood of this do-it-yourself therapeutic technique to understand what is happening. Danny JJ Wang, a professor of neurology at the USC Mark and Mary Stevens Neuroimaging and Informatics Institute, said his team is the first to develop an MRI method whereby the magnetic fields induced by tDCS currents can be visualized in living humans. Their results were published Oct. 4 in Scientific Reports, a Nature Publishing Group journal.

“Although this therapy is taking off at the grassroots level and in academia [with an exponential increase in publications], evidence that tDCS does what is being promised is not conclusive,” said Wang, the study’s senior author. “Scientists don’t yet understand the mechanisms at work, which prevents the FDA from regulating the therapy. Our study is the first step to experimentally map the tDCS currents in the brain and to provide solid data so researchers can develop science-based treatment.”

People in antiquity used electric fish to zap away headaches, but tDCS, as it is now known, was introduced in 2000, said Mayank Jog, study lead author and a graduate student conducting research at the David Geffen School of Medicine at UCLA.

“Since then, this noninvasive, easy-to-use, low-cost technology has been shown to improve cognition as well as treat clinical symptoms,” Jog said.

The study is a technological breakthrough, said Maron Bikson, study co-author and a professor of biomedical engineering at The City College of New York.

“You cannot characterize what you cannot see, so this is a pivotal step in the development of tDCS technology,” Bikson said.

How tDCS works

The science on tDCS is inconclusive. The brain-hacking technique has been shown to improve symptoms in a wide swath of neurological and psychiatric disorders, including depression, drug cravings and stroke. Scientists also have pointed to how it enhances learning, affects working memory and imparts other cognitive benefits among healthy people. However, some people say tDCS is ineffective and even harmful. In rare cases, the technique causes burns where the electrodes were applied.

Researchers have mapped the human brain and demonstrated that putting a positive current (anode) in one area and a negative current (cathode) in another will foster an environment that prompts nearby neurons either to fire more rapidly or slowly, respectively.

Theoretically, putting an anode on the right prefrontal (right side of the forehead) and parietal lobe (above the eyes and behind the right ear) influences the executive network and could enhance attention and motor ability, Wang said. Stroke patients could apply an anode in the damaged hemisphere and a cathode in the good hemisphere. This rehabilitative technique may suppress the healthy part of the brain from overcompensating and pushes the damaged area to try to become fit again.

“This technique is very cheap,” Jog said. “You can do it at home. Most studies show people only need two weeks to show improvements, and the effects can last beyond the treatment period. So the technique fosters hope, but researchers need to get a better grasp on what is happening.”

There has been some debate about whether the 1-2 milliamp (mA) zap that creates a tingling sensation in most people actually travels to the brain. A New York University researcher tested tDCS on a cadaver and said no current reached the brain. He insisted that at least 4 mA—roughly equivalent to the discharge of a stun gun—is needed to stimulate neurons to fire.

Wang, however, said tDCS does not cause neurons to fire. It creates an environment that makes it more or less likely for neurons to fire.

A new way to visualize the current delivered to the brain

The researchers validated their MRI algorithm with a phantom, where the current path and induced was known. Then they tested the method using simple biological tissue: a human calf. Finally, they repeated the process on the scalp of 12 healthy volunteers.

After 20 to 30 minutes in a scanner, the new algorithm produced an image of the magnetic field tDCS created. Researchers noted that a current did enter the body and brain. Next, scientists compared the technique with that of a computer simulation.

The phantom test highly matched the computational modeling, thus verifying the algorithm. The calf test was a moderate match. The brain test showed expected magnetic field changes under and between the electrodes. However, computational modeling was not performed on the brain test because there are too many variables, strengthening the argument that using is not ideal for understanding what really happens inside people’s heads when tDCS is applied, Wang said.

Another tDCS measurement technique in use today is fMRI, which looks at the change in blood-oxygen levels to infer which areas the current passes through. This measurement is not directly related to the electric current and could introduce false positives. So rather than playing a game of telephone, it is best to go to the primary source.

“Scientists who have comprehensively studied the tDCS literature are in broad agreement that tDCS can change function, but that application in central health and neuro-enhancement will benefit from a deeper understanding of mechanism and enhanced technology,” Bikson said. “This study is an important step in both directions.”

Make New Memories But Keep the Old, With a Little Help From Electrodes

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Matthew Walker thinks there may be a way to simulate deep sleep—vital for memory—by sending a low current to a person’s brain

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Lack of sleep has been linked to everything from erratic mood swings to weight gain to a weakening of the immune system. In 2007, the World Health Organization even declared shift work a “probable carcinogen,” because it fundamentally interferes with an individual’s circadian rhythms and rest patterns.

Matthew Walker, a neuroscience and psychology professor and director of the Sleep and Neuroimaging Lab at the University of California, Berkeley, spoke about sleep and how it is vital to a person’s physical and mental health at Smithsonian magazine’s “Future is Here” festival this past weekend. During his talk, he described a bold idea to improve older individuals’ ability to create and retain memories by stimulating their brains with a low current while they sleep.

Deep sleep, a period that’s known as vital for memory formation, becomes rarer as people age, waning more and more after individuals hit their mid-30s. By attaching two electrodes to a person’s scalp, Walker can direct a current into the prefrontal area and simulate the slow waves of deep sleep while the wearer slumbers.

The technique is called transcranial direct-current stimulation (tDCS), and while the equipment to do it is commercially available, it is not FDA approved for use on medical conditions. The devices in their current form aren’t intelligent enough to know when a wearer is in deep non-rapid eye movement (NREM) sleep, and so they aren’t able to start stimulating in that sleep stage on their own and sync up with the brain’s waves. “At present, we scientists need to do this in a sleep lab,” says Walker. “We have to measure someone’s sleep, and then switch the stimulator on at the desired stimulating rhythm to have a beneficial effect.” That said, he believes in five to eight years these issues will be resolved, and these devices could help those with Alzheimer’s, dementia, insomnia, depression and anxiety.

Matthew Walker kept the audience at the
Matthew Walker kept the audience at the “Future is Here” festival wide awake with a fascinating talk on sleep. 

Walker’s body of research has examined sleep’s pivotal role in helping the brain create and preserve memories as well as maintain emotionally balanced behavior. When it comes to establishing strong memories, sleep is a necessary factor for both their formation and retention.

“Sleep after learning is essential to hit the ‘save’ button,” says Walker. “It is also vital before learning.”

In a study he conducted, Walker looked at two groups of students: a control group that had a standard full night’s rest and an experimental one that was asked to stay awake all night. After their respective nights, the students were tasked with learning a set of words holding positive, negative and neutral associations. Following two days of recovery sleep, they were asked to take a recognition test. Walker discovered that those who hadn’t slept retained 40 percent less than their well-rested counterparts.

Walker monitored the hippocampus of study participants, the part of the brain where memories are conceived, with an electroencephalogram (EEG) which tracked electrical activity, while they were being taught this new information. He found the sleep-deprived individuals showed minimal signs of any brain activity while their wakeful friends had plenty of learning-related activity taking place.

“It is as though sleep deprivation has shut down the brain’s inbox,” he says. “They could not accept any new, incoming memories.”

When it came to emotional responses, Walker witnessed the sleepless participants becoming increasingly more volatile, oscillating between impromptu giddiness and expletive-laced anger. In measuring their reactions, he found that the tired students exhibited an “amplified, aggravated degree of reactivity by well over 60 percent.”

“Without sleep you are all emotional gas pedal and no brake,” he says, a behavioral pattern that’s also associated with many psychiatric disorders, including depression, anxiety and post-traumatic stress disorder.

So why, Walker wondered, were the students who slept better equipped to create memories? What exactly did they gain by sleeping? Using electrodes, he measured the brain activity of the students as they slept, and witnessed “powerful bursts of brain activity” that occur during a particular stage of deep sleep known as the slow-wave phase.

“These spectacular bursts of electrical activity act as a file transfer mechanism,” says Walker, “refreshing and enhancing learning and memory.”

In another study, Walker, his Berkeley colleague Bryce A. Mander and researchers from the California Pacific Medical Center in San Francisco, the University of California, San Diego and the Lawrence Berkeley National Laboratory discovered a connection between sleep, aging and memory loss. It’s long been observed that as individuals get older, their memories become less sharp. As people age, their quality of sleep also declines. Mander and Walker found that physical changes that happen in the brain as humans age actually disrupt the quality of their sleep, and these changes in their sleep then hinder their long term memory.

 Matthew Walker kept the audience at the
Matt Walker speaks at Smithsonian magazine’s 2015 Future Is Here Festival

Walker wonders if it would be possible to replicate or amplify the “powerful bursts of brain activity” of deep sleep to help people, like those with Alzheimer’s, improve their memory formation and retention. Using electrodes attached to the head, scientists could infuse a low current into patients’ prefrontal areas and simulate the slow waves of deep sleep, while wearers were already resting.

“Our hope for the future is that, by applying this affordable technology to older adults and those with dementia, we can amplify and restore some quality of sleeping brainwave activity, and in doing so, rescue learning and memory,” Walker says. “Sleep is a treatable target.”

POPULAR BRAIN STIMULATION DOESN’T BOOST IQ

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Despite its popularity, using a weak electric current to boost brainpower doesn’t live up to the hype. A new study shows that the most common form of the treatment actually has a statistically significant detrimental effect on IQ scores.

Published in the journal Behavioural Brain Research, the study adds to the increasing amount of literature showing that transcranial direct current stimulation—tDCS—has mixed results when it comes to cognitive enhancement.

“It would be wonderful if we could use tDCS to enhance cognition because then we could potentially use it to treat cognitive impairment in psychiatric illnesses,” says Flavio Frohlich, study senior author and assistant professor of psychiatry, cell biology and physiology, biomedical engineering, and neurology at the UNC School of Medicine.

“So, this study is bad news. Yet, the finding makes sense. It means that some of the most sophisticated things the brain can do, in terms of cognition, can’t necessarily be altered with just a constant electric current.”

TWO TYPES OF BRAIN STIMULATION

Frohlich, though, says that using less common alternating current stimulation—so-called tACS—could be a better approach, one that he has been investigating. Earlier this year, Frohlich’s lab found that tACS significantly boosted creativity, likely because he used it to target the brain’s natural electrical alpha oscillations, which have been implicated in creative thought.

With tDCS, scientists don’t target these brain waves, which represent neuronal patterns of communication throughout regions of the brain. Instead, they use tDCS to target brain structures, such particular regions of the cortex.

“All of our brain structures look more or less the same, but the reason why we’re all so different is that the electrical brain activities in our brains are very different,” Frohlich says. “We have to better understand this and target specific brain activity patterns.”

‘EXPLOSION’ OF STUDIES

Using a weak electrical current to boost the brain’s natural abilities has been around for decades, but the current boom within the science community started in 2000, when German scientists published a paper showing that tDCS could change the excitability of neurons in the motor cortex—the brain region that controls voluntary body movement.

Since then, there’s been an explosion of tDCS studies to try to make neurons more active or less active and therefore change outcomes for a variety of brain functions, such as working memory and cognitive acuity, and for illnesses, such as depression and schizophrenia.

But Frohlich says that scientists still don’t know exactly what the direct current does to neural activity. He also says some of the studies that have made waves were poorly designed. Some studies were not properly double-blinded or properly placebo controlled. Other studies were very small—fewer than 10 people.

A recent meta-analysis of a large number of tDCS papers showed that tDCS is far from a magic pill for cognitive enhancement or brain-related health conditions.

“Aside from stimulating the motor cortex, which has very exciting implications for stroke rehabilitation, I think the jury is still out on tDCS,” says Frohlich, who is a member of the UNC Neuroscience Center.

PUTTING ON THE ELECTRODES

In the new, Frohlich’s team—including graduate student Kristin Sellers, the paper’s first author—recruited 40 healthy adults, each of whom took the standard WAIS-IV intelligence test—the most common and well-validated test of IQ, which includes tests for verbal comprehension, perceptional reasoning, working memory, and processing speed.

A week later, Frohlich’s team divided the participants into two groups. Electrodes were placed on each side of each participant’s scalp, under which sat the frontal cortex. A third electrode, which sent electricity back to the device that that produced the electric current, was placed on top of the scalp.

Duke University collaborator and coauthor Angel Peterchev created imaging simulations to ensure Frohlich’s team targeted the same parts of the cortex that previous tDCS studies had targeted.

Then the placebo group received sham stimulation—a brief electrical current, which led participants to think they had been receiving the full tDCS. The other participants received the standard tDCS for twenty minutes—a weak electrical current of 2 millioamperes.

All participants then retook the IQ tests. Frohlich expected that most, if not all, IQ scores would improve, but that the participants who received tDCS would not improve their scores any more than would the people who did not undergo tDCS

SCORES THAT SANK

Frohlich’s team did find that all scores improved—most likely because of the “practice effect” of previously taking the test. Surprisingly, the participants who did not receive tDCS saw their IQ scores increase by ten points, whereas participants who received tDCS saw their IQ scores increase by just shy of six points, on average.

When Frohlich and colleagues analyzed the test scores, they saw that the scores for three of the four kinds of cognitive tests were very similar between the two groups of participants. But the scores for perceptual reasoning were much lower among people who underwent tDCS.

Perceptual reasoning tests fluid intelligence, which is defined as the ability to think logically and apply innovative problem solving to new problems.

Within the category of perceptual reasoning, the researchers saw the biggest differences in the subcategory of matrix reasoning—when participants viewed two groups of symbols and had to find the one symbol missing from the other group.

“This is one of the classical assays of fluid intelligence,” Frohlich says, “where you have to identify hidden rules and apply logic to find a missing element.”

NO ‘MAGIC PILL’

Frohlich emphasizes, “Our findings do not preclude the possibility that other tDCS paradigms may be less harmful or even beneficial. However it is time to make sure that everybody uses gold standard, placebo-controlled, double-blind study designs. Also, our study demonstrates the importance of more research on how stimulation interacts with brain activity.”

Frohlich stresses that the scientific community should be careful not to create simplistic storylines about tDCS being a “magic pill” for many brain-related conditions.

“There could be dangerous consequences, especially if tDCS is used daily,” he says. “Ours was an acute study. We don’t know what the long-term effects are. There is so much more we need to understand before tDCS is ready for home use without medical supervision”

Frohlich adds, “I think our study demonstrates that we need to think of smarter ways to engage the brain to really target the specific brain dynamics involved in what we want to improve, such as cognition for people with depression or schizophrenia. I think tACS is an option, as well as more sophisticated modalities we’ve yet to develop.”