Recent s tudies of transcranial electrical stimulation in human cadaver heads showed a 90% loss of current when delivered through the skin (Buzsáki, tudies of transcranial electrical stimulation in human cadaver heads showed a 90% loss of current when delivered through the skin (Buzsáki, 2016 CNS meeting ).

This is the one song everyone

would like to learn: the song

that is irresistible:



the song that forces men

to leap overboard in squadrons

even though they see the beached skulls



the song nobody knows

because anyone who has heard it

is dead, and the others can't remember.

1

2

Modified from Fig. 1b (Dayan et al., 2013). Bipolar tDCS electrode configuration, with one electrode over left dorsolateral prefrontal cortex and a reference electrode over the contralateral supraorbital region. Bipolar tDCS electrode configuration, with one electrode over left dorsolateral prefrontal cortex and a reference electrode over the contralateral supraorbital region.

My understanding of his remarks

90% loss of electrical current between skin and scalp -György Buzsáki #CNS2016 April 5, 2016

90% charge loss skin-skull using TES. Need 5 mA to affect spiking, FDA approved 2mA, Buzsáki first hand 4mA hard to tolerate. #CNS2016 April 5, 2016

We recorded TES-generated field potentials in human cadavers and anesthetized rats. Stimulation was applied by placing Ag/AgCl EEG electrodes over the external surface of the skull. ... We also measured the shunting effect of the skin during transcutaneous stimulation. In addition to our earlier results, we found that the skin dramatically reduced the generated intracranial electric fields, and alters its geometry.

image via Sue Peters, @nomorewires

Shall I tell you the secret

and if I do, will you get me

out of this bird suit?



–Atwood, Siren Song

“Using a transgenic mouse expressing G-CaMP7 in astrocytes and a subpopulation of excitatory neurons, we find that tDCS induces large-amplitude astrocytic Ca2 + surges across the entire cortex with no obvious changes in the local field potential. Moreover, sensory evoked cortical responses are enhanced after tDCS. These enhancements are dependent on the alpha-1 adrenergic receptor and are not observed in IP 3 R2 (inositol trisphosphate receptor type 2) knockout mice, in which astrocytic Ca2 + surges are absent. Together, we propose that tDCS changes the metaplasticity of the cortex through astrocytic Ca2 + /IP 3 signalling.” (Monai et al., 2016)

—

—

3

This gentleman discusses his burn injuries at the tDCS reddit

1

These techniques [TMS and tCS] have collectively become known as “non-invasive brain stimulation.” We argue that this term is inappropriate and perhaps oxymoronic, as it obscures both the possibility of side-effects from the stimulation, and the longer-term effects (both adverse and desirable) that may result from brain stimulation.

2

Our systematic review does not support the idea that tDCS has a reliable neurophysiological effect beyond MEP amplitude modulation... This work raises questions concerning the mechanistic foundations and general efficacy of this device – the implications of which extend to the steadily increasing tDCS psychological literature.

3

...We are concerned about the validity of the conclusions for various reasons. Since this paper reviews a whole field of research and comes to debatable assumptions, it is especially important that basic quality requirements are fulfilled, which is unfortunately not the case.



First, this review suffers from numerous conceptual flaws and misunderstandings. Second, the work contains relevant design problems, several errors and many incompletely or incorrectly cited data.

. . .



In summary, as shown by the examples given above, this review suffers from important flaws with regard to citing and interpreting available literature, non-transparent, and in many cases erroneous data aggregation, citation of study specifics, and discussion of the results.

Buzsáki's

CNS t alk , along with quotes from t DCS experts who weren't surprised by his

results.

The Neuroscientist . PMID: Fertonani A, & Miniussi C (2016). Transcranial Electrical Stimulation: What We Know and Do Not Know About Mechanisms.. PMID: 26873962

Nature communications, 7 . PMID: Monai H, Ohkura M, Tanaka M, Oe Y, Konno A, Hirai H, Mikoshiba K, Itohara S, Nakai J, Iwai Y, & Hirase H (2016). Calcium imaging reveals glial involvement in transcranial direct current stimulation-induced plasticity in mouse brain.. PMID: 27000523

Society for Neuroscience. Poster# 257.17/Y3. M. VOROSLAKOS, A. OLIVA, K. BRINYICZKI, T. ZOMBORI, B. IVÁNYI, G. BUZSÁKI, A. BERÉNYI. (2015). Targeted transcranial electrical stimulation protocols: Spatially restricted intracerebral effects via improved stimulation and recording techniques.

MORE! (added April 15 2016): Two recent meta-analyses on tDCS and working memory reported “a mix of significant and nonsignificant small effects” and “some evidence of a beneficial effect ... [but] the small effect sizes obtained, coupled with non-significant effects on several analyses require cautious interpretation” (respectively):





Hill AT, Fitzgerald PB, Hoy KE. Effects of Anodal Transcranial Direct Current Stimulation on Working Memory: A Systematic Review and Meta-Analysis of Findings From Healthy and Neuropsychiatric Populations. Mancuso LE, Ilieva IP, Hamilton RH, Farah MJ. Does Transcranial Direct Current Stimulation Improve Healthy Working Memory?: A Meta-analytic Review. J Cogn Neurosci. 2016 Apr 7:1-27 . [Epub ahead of print]Hill AT, Fitzgerald PB, Hoy KE. Effects of Anodal Transcranial Direct Current Stimulation on Working Memory: A Systematic Review and Meta-Analysis of Findings From Healthy and Neuropsychiatric Populations. Brain Stimul. 2016; 9(2):197-208

I don't enjoy it here

squatting on this island

looking picturesque and mythical



with these two feathery maniacs,

I don't enjoy singing

this trio, fatal and valuable.



I will tell the secret to you,

to you, only to you.

Come closer. This song



is a cry for help: Help me!

Only you, only you can,

you are unique



at last. Alas

it is a boring song

but it works every time.



–Atwood, Siren Song

Better living through electricity. The lure of superior performance, improved memory, and higher IQall the hard work. Or at least, in a much shorter amount of time.Transcranial direct current stimulation ( tDCS ), hailed as a “non-invasive”way to alter brain activity,has been hot for years. In fact, peak tDCS is already behind us, with a glut of DIY brain stimulation articles in places like Fortune IEEE Spectrum , and The Daily Dot Simply apply a weak electrical current to your head via a pair of saline soaked sponges connected to a 9 volt battery. Current flows between the positive anode, or stimulating electrode (in blue below), and the negative cathode (in red below). Low levels of electrical stimulation travel through the scalp and skull to a region of cortex underneath the anode. Modeling studies suggest that the electric field generated by tDCS in humans is about 1 mV/mm ( Neuling et al., 2012 ). The method doesn't directly induce spiking (the firing of action potentials), but it's thought to alter neuronal excitability. By facilitating neuroplastic changes during cognitive training, tDCS may improve learning mental arithmetic , and target detection And there you have it. High tech performance enhancement for less than $40 . Or a siren song for wannabe brain hackers?In Symposium Session 7 of the Cognitive Neuroscience Society meeting last week, Dr. György Buzsáki threw a bit of cold water on non-invasive transcranial electrical stimulation (TES) methods, which include tDCS and transcranial alternating current ( tACS ).: Studies of transcranial electrical stimulation (TES) in human cadaver heads showed there's a 90% loss of current when delivered through the skin (which is obviously the case in living humans) vs. through the skull. This implies that a current of at least 5 mA on the scalp would be necessary to generate a 1 mV/mm electric field in the human brain. Based on his personal experience, Dr. Buzsáki reported that 4 mA was hard to tolerate even with anesthetized skin. For comparison, 2 mA is the maximum current recommended by an international panel of experts Others in the audience had similar interpretations:This revelation was in the context of work on focused beam stimulation, which is designed to improve the spatial selectivity of TES ( Voroslakos et al., 2015 ):In turn, the cadaver studies were an extension of very cool research on Closed-Loop Control of Epilepsy by Transcranial Electrical Stimulation . This paper used a rodent model of generalized epilepsy to test a system that (1) records neural activity and (2) triggers TES to quell abnormal activity once it is detected.Having such a system that works in humans would be a huge advance for those who suffer from intractable seizures. Human heads are very different from rat heads, hence the need for human cadavers. And hence the bombshell that 1-2 mA current may have less of an effect on neurons than previously expected.“But wait!” you say. “Aren't there literally thousands of peer-reviewed articles on tDCS? Surely it must be doing something.”If the effects of tDCS are not directly via neurons, what's the mechanism of action? It's glia ! And calcium! Gliotransmission! Maybe.The pre-astrocyte version of purported mechanismbased on direct modulation of the affected neurons' resting membrane potentialis described in the schematic below (click on image for a larger view).But maybe tDCS doesn't really do much in humans after all, as claimed in two recent review articles (Horvath et al., 2015a,b).And remember, transcranial devices are not playthings ! (warn Bikson et al., 2013).But see “Non-invasive” brain stimulation is not non-invasive (Davis & van Koningsbruggen, 2013):But see Evidence that transcranial direct current stimulation generates little-to-no reliable neurophysiologic effect beyond MEP amplitude modulation in healthy human subjects: A systematic review (Horvath et al., 2015a):Not too surprisingly, these papers have not gone unopposed...Berényi A, Belluscio M, Mao D, Buzsáki G. (2012). Closed-loop control of epilepsy by transcranial electrical stimulation 337(6095):735-7. Invading the brain to understand and repair cognition – CNS Press Release When the Hype Doesn’t Pan Out: On Sharing the Highs-and-Lows of Research with the Public – by Jared Cooney Horvath Non-invasive direct current brain stimulation for depression: the evidence behind the hype – by Camilla Nord and Jonathan Roiser Neurostimulation: Bright sparks – by Katherine Bourzac DIY tDCS – Keeping Tabs On Transcranial Direct Current Stimulation Why 2.0 mA as the limit for TDCS? – reddit threadBrunoni AR, Nitsche MA, Bolognini N, Bikson M, Wagner T, Merabet L, Edwards DJ, Valero-Cabre A, Rotenberg A, Pascual-Leone A, Ferrucci R, Priori A, Boggio PS, Fregni F. (2012). Clinical research with transcranial direct current stimulation (tDCS): challenges and future directions . 5(3):175-95.Davis NJ. (2016). The regulation of consumer tDCS: engaging a community of creative self-experimenters . Apr 5:lsw013.Davis NJ, van Koningsbruggen MG. (2013). "Non-invasive" brain stimulation is not non-invasive 7:76.Dayan E, Censor N, Buch ER, Sandrini M, Cohen LG. (2013). Noninvasive brain stimulation: from physiology to network dynamics and back . 16(7):838-44.Edwards D, Cortes M, Datta A, Minhas P, Wassermann EM, Bikson M. (2013). Physiological and modeling evidence for focal transcranial electrical brain stimulation in humans: a basis for high-definition tDCS 74:266-75.Horvath JC, Forte JD, Carter O. (2015a). Evidence that transcranial direct current stimulation (tDCS) generates little-to-no reliable neurophysiologic effect beyond MEP amplitude modulation in healthy human subjects: A systematic review 66:213-36.Horvath JC, Forte JD, Carter O. (2015b). Quantitative Review Finds No Evidence of Cognitive Effects in Healthy Populations From Single-session Transcranial Direct Current Stimulation (tDCS) . 8(3):535-50.Kuo MF, Nitsche MA. (2012). Effects of transcranial electrical stimulation on cognition 43(3):192-9.Parkin BL, Ekhtiari H, Walsh VF. (2015). Non-invasive human brain stimulation in cognitive neuroscience: a primer 87(5):932-45.Santarnecchi E, Brem AK, Levenbaum E, Thompson T, Kadosh RC, Pascual-Leone A. (2015). Enhancing cognition using transcranial electrical stimulation . 4:171-8.Woods AJ, Antal A, Bikson M, Boggio PS, Brunoni AR, Celnik P, Cohen LG, Fregni F, Herrmann CS, Kappenman ES, Knotkova H, Liebetanz D, Miniussi C, Miranda PC, Paulus W, Priori A, Reato D, Stagg C, Wenderoth N, Nitsche MA. (2016). A technical guide to tDCS, and related non-invasive brain stimulation tools . 127(2):1031-48.fromCopyright © 1974, 1976 by Margaret Atwood. Reprinted with the permission of the author and Houghton Mifflin Company in Poetry (February 1974)