Transcranial direct current stimulation & cognitive enhancement

There’s so much research out there… So much that some time ago I learned that in science, as probably in other fields too, one has only to choose a side of an argument and then, provided that s/he has some good academic search engines skills and institutional access to journals, get the articles that support that side. Granted, that works for relatively small questions restricted to narrow domains, like “is that brain structure involved in x” or something like that; I doubt you would be able to find any paper that invalidates theories like gravity or central dogma of molecular biology (DNA to RNA to protein).

If you’re a scientist trying to answer a question, you’ll probably comb through some dozens papers and form an opinion of your own after weeding out the papers with small sample sizes, the ones with shoddy methodology or simply the bad ones (yes, they do exists, even scientists are people and hence prone to mistakes). And if you’re not a scientist or the question you’re trying to find an answer for is not from your field, then you’ll probably go for reviews or meta-analyses.

Meta-analyses are studies that look at several papers (dozens or hundreds), pool their data together and then apply some complicated statistics to see the overall results. One such meta-analysis concerns the benefits, if any, of transcranial direct current stimulation (tDCS) on working memory (WM) in healthy people.

tDCS is a method of applying electrical current through some electrodes to your neurons to change how they work and thus changing some brain functions. It is similar with repetitive transcranial magnetic stimulation (rTMs), only in the latter case the change in neuronal activity is due to the application of a magnetic field.

Some people look at these methods not only as possible treatment for a variety of disorders, but also as cognitive enhancement tools. And not only by researchers, but also by various companies who sell the relatively inexpensive equipment to gamers and others. But does tDCS work in the first place?

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Mancuso et al. (2016) say that there have been 3 recent meta-analyses done on this issue and they found that “the effects [of tDCS on working memory in healthy volunteers] are reliable though small (Hill et al., 2016), partial (Brunoni & Vanderhasselt, 2014), or nonexistent (Horvath et al., 2015)” (p. 2). But they say these studies are somewhat flawed and that’s why they conducted their own meta-analysis, which concludes that “the true enhancement potential of tDCS for WM remains somewhat uncertain” (p.19). Maybe it works a little bit if used during the training phase of a working memory task, like n-back, and even then that’s a maybe…

Boring, you may say. I’ll grant you that. So… all that work and it revealed virtually nothing new! I’ll grant you that too. But what this meta-analysis brings new, besides adding some interesting statistics, like controlling for publication bias, is a nice discussion as to why they didn’t find nothing much, exploring possible causes, like the small sample and effects sizes, which seem to plague many behavioral studies. Another explanation which, to tell you the truth, the authors do not seem to be too enamored with is that, maybe, just maybe, simply, tDCS doesn’t have any effect on working memory, period.

Besides, papers with seemingly boring findings do not catch the media eye, so I had to give it a little attention, didn’t I 😉 ?

Reference: Mancuso LE, Ilieva IP, Hamilton RH, & Farah MJ. (Epub 7 Apr 2016, Aug 2016) Does Transcranial Direct Current Stimulation Improve Healthy Working Memory?: A Meta-analytic Review. Journal of Cognitive Neuroscience, 28(8):1063-89. PMID: 27054400, DOI: 10.1162/jocn_a_00956. ARTICLE

 By Neuronicus, 2 August 2016

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TMS decreases religiosity and ethnocentrism

Medieval knight dressed in an outfit with the Cross of St James of Compostela. From Galicianflag.
Medieval knight dressed in an outfit with the Cross of St. James of Compostela. Image from Galicianflag.

Rituals are anxiolytic; we developed them because they decrease anxiety. So it makes sense that when we feel the most stressed we turn to soothing ritualistic behaviors. Likewise, in times of threat, be it anywhere from war to financial depression, people show a sharp increase in adherence to political or religious ideologies.

Holbrook et al. (2015) used TMS (transcranial magnetic stimulation) to locally downregulate the activity of the posterior medial frontal cortex (which includes the dorsal anterior cingulate cortex and the dorsomedial prefrontal cortex), a portion of the brain the authors have reasons to believe is involved in augmenting the adherence to ideological convictions in times of threat.

They selected 38 U.S. undergraduates who scored similarly on political views (moderate or extremely conservative, the extremely liberals were excluded). Curiously, they did not measure religiosity prior to testing. Then, they submitted the subjects to a group prejudice test designed to increase ethnocentrism (read critique of USA written by an immigrant) and a high-level conflict designated to increase religiosity (reminder of death) while half of them received TMS and the other half received shams.

Under these conditions, the TMS decreased the belief in God and also the negative evaluations of the critical immigrant, compared to the people that received sham TMS.

The paper is, without doubt, interesting, despite the many possible methodological confounds. The authors themselves acknowledged some of the drawbacks in the discussion section, so regard the article as a pilot investigation. It doesn’t even have a picture with the TMS coordinates. Nevertheless, reducing someone’s religiosity and extremism by inactivating a portion of the brain… Sometimes I get afraid of my discipline.

Reference: Holbrook C, Izuma K, Deblieck C, Fessler DM, & Iacoboni M (Epub 4 Sep 2015). Neuromodulation of group prejudice and religious belief. Social Cognitive and Affective Neuroscience. DOI: 10.1093/scan/nsv107. Article | Research Gate full text PDF

By Neuronicus, 3 November 2015

Zap the brain to get more lenient judges

Neuronicus3
Reference: Buckholtz et al. (2015). Credit: Neuronicus

Humans manage to live successfully in large societies mainly because we are able to cooperate. Cooperation rests on commonly agreed rules and, equally important, the punishment bestowed upon their violators. Researchers call this norm enforcement, while the rest of us call it simply justice, whether it is delivered in its formal way (through the courts of law) or in a more personal manner (shout at the litterer, claxon the person who cut in your lane etc.). It is a complicate process to investigate, but scientists managed to break it into simpler operations: moral permissibility (what is the rule), causal responsibility (did John break the rule), moral responsibility (did John intend to break the rule, also called blameworthiness or culpability), harm assessment (how much harm resulted from John breaking the rule) and sanction (give the appropriate punishment to John). Different brain parts deal with different aspects of norm enforcement.

The approximate area where the stimulation took place. Note that the picture depicts the left hemisphere, whereas the low punishment judgement occured when the stimulation was mostly on the right hemisphere.
The approximate area where the stimulation took place. Note that the picture depicts the left hemisphere, whereas the low punishment judgement occurred when the stimulation was mostly on the right hemisphere.

Using functional magnetic resonance imaging (fMRI), Buckholtz et al. found out that the dorsolateral prefrontal cortex (DLPFC) gets activated when 60 young subjects decided what punishment fits a crime. Then, they used repetitive transcranial magnetic stimulation (rTMS), which is a non-invasive way to disrupt the activity of the neurons, to see what happens if you inhibit the DLPFC. The subjects made the same judgments when it came to assigning blame or assessing the harm done, but delivered lower punishments.

Reference: Buckholtz, J. W., Martin, J. W., Treadway, M. T., Jan, K., Zald, D.H., Jones, O., & Marois, R. (23 September 2015). From Blame to Punishment: Disrupting Prefrontal Cortex Activity Reveals Norm Enforcement Mechanisms. Neuron, 87: 1–12, http://dx.doi.org/10.1016/j.neuron.2015.08.023. Article + FREE PDF

by Neuronicus, 22 September 2015