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New evidence on transcranial electric stimulation of the brain

18 Oct

Last year György Buzsáki performed a public experiment showing that electricity passed through electrodes placed on the scalp of a cadaver could not be detected in the brain. This raised serious concerns about the many claims made on behalf of transcranial electrical stimulation of the brain.

Now, in a forth coming paper, published in the journal Brain Stimulation, evidence is presented from an in vivo study (research on a living subject) that detectable changes in brain electrical activity does occur during transcranial alternating current stimulation (tACS).

Stay tuned!

An fMRI study of transcranial alternating current stimulation (tACS)

9 Aug

I have been following the research on transcranial electrical stimulation of the brain and I have blogged about both positive and negative findings. Here’s an interesting paper, just published in Personality and Individual Differences, that shows correlations between transcranial alternating current stimulation and functional changes in the brain:

The past decades have witnessed a huge interest in uncovering the neural bases of intelligence (e.g., Stelmack, & Houlihan, 1995; Stelmack, Knott, & Beauchamp, 2003). This study investigated the influence of transcranial alternating current stimulation (tACS) on fluid intelligence performance and corresponding brain activation. Previous findings showed that left parietal theta tACS leads to a transient increase in fluid reasoning performance. In an attempt to extend and replicate these findings, we combined theta tACS with fMRI. In a double-blind sham-controlled experiment, N = 20 participants worked on two intelligence tasks (matrices and paper folding) after theta tACS was applied to the left parietal cortex. Stimulation-induced brain activation changes were recorded during task processing using fMRI. Results showed that theta tACS significantly increased fluid intelligence performance when working on difficult items in the matrices test; no effect was observed for the visuo-spatial paper folding test. Whole-brain analyses showed that left parietal brain stimulation was accompanied by lower activation in task-irrelevant brain areas. Complemental ROI analyses revealed a tendency towards lower activation in the left inferior parietal cortex. These findings corroborate the functional role of left parietal theta activity in fluid reasoning and are in line with the neural efficiency hypothesis.

Note that this study looks at alternating current stimulation, while most are focused on direct current stimulation.

Transcranial direct current stimulation for dementia?

1 May

Possibly, according to a paper presented at the recent American Academy of Neurology Annual Meeting:

To assess efficacy of transcranial direct current stimulation (tDCS) for improving picture naming abilities in individuals with mild dementia, researchers conducted a double-blind, cross-over study among 12 individuals. Study participants received 10 sessions of training on picture naming plus 30 minutes of anodal tDCS applied to the parietal lobe or sham simulation. Evaluation occurred before stimulation, at the final stimulation session, 2 weeks after stimulation and 2 months after stimulation.

Study participants who received tDCS significantly improved in picture naming, compared with those who received sham stimulation.

This seems like a strong study design and the results are striking. Normally, you would not expect improvement in a memory test on people suffering from dementia. Indeed, drugs, such as Donepezil,  used for treatment of dementia, only claim to reduce the rate of decline, not to cause improvement.

Note that this is a conference paper and has not yet been published in a peer reviewed journal. It would be important to know the magnitude of the effect and to see the research replicated.

Olympic athletes use transcranial direct current stimulation

19 Aug

According to IEEE Spectrum:

“A handful of athletes competing at the Summer Olympic Games in Rio next week will arrive having tried to boost their performance using an unconventional (and not-yet-banned) technology: brain stimulation. The technique, called transcranial direct current stimulation (tDCS), involves channeling a tiny current through specific regions of the brain, making neurons in that area more likely to fire.”

The athletes are using the Halo tDCS device. Here is the promotional video:

Before you run out and buy one of these devices, I suggest you read “An open letter concerning do-it-yourself users of transcranial direct current stimulation” published in The Annals of Neurology.

 

Noninvasive Brain Stimulation for Food Cravings

8 Aug

A paper in the journal Psychosomatic Medicine reviews the research on Brain Stimulation as a treatment for food cravings. The findings suggest that repetitive transcranial magnetic stimulation might be helpful. On the other hand, transcranial direct current stimulation did not seem to have a significant effect.

Here is a video on TMS:

Here is the abstract:

Objective: The primary aim of this review was to evaluate the effectiveness of noninvasive brain stimulation to the dorsolateral prefrontal cortex (dlPFC) for modulating appetitive food cravings and consumption in laboratory (via meta-analysis) and therapeutic (via systematic review) contexts.

Methods: Keyword searches of electronic databases (PubMed, Scopus, Web of Science, PsychoInfo, and EMBASE) and searches of previous quantitative reviews were used to identify studies (experimental [single-session] or randomized trials [multi-session]) that examined the effects of neuromodulation to the dlPFC on food cravings (n = 9) and/or consumption (n = 7). Random-effects models were employed to estimate the overall and method-specific (repetitive transcranial magnetic stimulation [rTMS] and transcranial direct current stimulation [tDCS]) effect sizes. Age and body mass index were examined as potential moderators. Two studies involving multisession therapeutic stimulation were considered in a separate systematic review.

Results: Findings revealed a moderate-sized effect of modulation on cravings across studies (g, -0.516; p = .037); this effect was subject to significant heterogeneity (Q, 33.086; p < .001). Although no statistically significant moderators were identified, the stimulation effect on cravings was statistically significant for rTMS (g, -0.834; p = .008) but not tDCS (g, -0.252; p = .37). There was not sufficient evidence to support a causal effect of neuromodulation and consumption in experimental studies; therapeutic studies reported mixed findings.

Conclusions: Stimulation of the dlPFC modulates cravings for appetitive foods in single-session laboratory paradigms; when estimated separately, the effect size is only significant for rTMS protocols. Effects on consumption in laboratory contexts were not reliable across studies, but this may reflect methodological variability in delivery of stimulation and assessment of eating behavior. Additional single- and multi-session studies assessing eating behavior outcomes are needed.

A “dead salmon moment” for tDCS?

23 May

Another account of  György Buzsáki’s tDCS experiment:

“Buzsáki set up the system on a cadaver and measured how much of the current penetrated the skull and made it into the brain. Not much, so it would seem. He is still writing up his results for peer review, but presented an outline at the annual meeting of the Cognitive Neuroscience Society in New York early last month. In his talk, he explained that so little electrical charge gets through the skull and into the brain that stimulating neurons to fire would require applying roughly twice the current that most commercial devices supply.”

Here are the counterarguments:

“Buzsáki’s critics have two responses. First, they suggest that living tissue has fundamentally different electrical characteristics, and so experiments on dead tissue tell us nothing. Buzsáki disagrees: if anything, more current will make it into the inactive tissue of a cadaver’s brain than into the brain of a live person, he says.

Second, critics argue that there need not be enough current to make neurons fire, just enough to bring them closer to the threshold for firing.”

You can read about dead salmons here.

A Waterloo for transcranial direct current stimulation?

25 Apr

I have been following the research on transcranial direct current stimulation of the brain, with great interest. Many papers have reported positive results, suggesting that the procedure may have real benefits as a cognitive enhancer.

But now a demonstration by  György Buzsáki raises questions:

“When Buzsáki and his colleague, Antal Berényi, of the University of Szeged in Hungary, mimicked an increasingly popular form of brain stimulation by applying alternating electrical current to the outside of the cadaver’s skull, the electrodes inside registered little. Hardly any current entered the brain. On closer study, the pair discovered that up to 90% of the current had been redirected by the skin covering the skull, which acted as a “shunt,” Buzsáki said.

(…)

The new, unpublished cadaver data make dramatic effects on neurons unlikely, Buzsáki says. Most tDCS and tACS devices deliver about 1 to 2 milliamps of current. Yet based on measurements from electrodes inside multiple cadavers, Buzsaki calculated that at least 4 milliamps—roughly equivalent to the discharge of a stun gun—would be necessary to stimulate the firing of living neurons inside the skull. Buzsáki notes he got dizzy when he tried 5 milliamps on his own scalp. “It was alarming,” he says, warning people not to try such intense stimulation at home.”

It is still possible that lower levels of current may be alter the threshold of neuron firing, but, there is now reason for increased skepticism.

 

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