The tDCS (transcranial direct current stimulation) is like putting a battery on your tongue except it goes on the outside of your skull and it doesn’t shock you (if it was built properly). Some users have gotten headaches, itching, red marks and, in one case of a bipolar patient, a hypomanic episode [R].
In this article I’ll give you a personal story about Direct Current Stimulation, specific issues I found in single studies and questionable techniques in general as well as questionable theoretical support for the technology.
- Electricity Is Dangerous
- Potential Issues In tDCS Research
Electricity Is Dangerous
We did an experiment in class where we pulsed a direct current across the nerve that controls the gripping / clasping muscles of our hands.
Other students were in control of the current and voltage being pulsed into my body even though I asked for otherwise.
The only person who had been taught about the safety and risks of electrical signals in humans was me. The others didn’t know the danger zones and upon seeing how well they could control another person, they became like overexcited hyperactive children.
They twisted the screen away from me and turned the current right up, maxing out the settings to the most dangerous area.
Not only did my hand grip and regrip 60 times in a second, the power in the electricity passed up my arm to my elbow and my shoulder before I could react and my whole arm tensed up and flung into the air.
I managed to rip the electrode off of my wrist before the energy got to my heart. They yelled out “oh my god, I thought the device was rigged to be safe.”
I told them that it was made to do what you wanted and would be safe if you read the manual and use with caution [R]. Electricity isn’t magic, but then again, Clarke’s Third Law says “any sufficiently advanced technology is indistinguishable from magic”.
About The Field of Research
There are over 3000 articles listed on PubMed under this topic and sometimes there are errors so bad that it suggests that the researchers may not know a whole lot about the maths and physics behind what they are doing, for example, current being labeled as frequency [R].
Generally, one doesn’t have to study the necessary material to build the equipment being used in the research to be a researcher using the equipment.
Potential Issues In tDCS Research
Study: tDCS And The Parietal Lobe
A study tested the parietal lobe and, in their view, only 6 days of training tDCS improves learning certain types of maths and lasts a month [R].
Here’s the data that they only included as an attachment.
The patients needed to remember what each symbol meant and perform a task as quick as possible.
Their claim is based on this data and the difference between each group was statistically insignificant (p=0.33). The “improvement” is not supported by their data.
Study: tDCS And GABA / Glutamate
This paper presented the story that tDCS reduces GABA or reduces glutamate depending on which way the voltage is running [R]. Although, when reading their paper I noticed that they measured GABA and Glutamate in reference to NAA (N-acetyl aspartate).
I hunted through the paper until I found a specific sentence “to allow for any changes in tissue water after stimulation, all neurotransmitter concentrations are given as a ratio to NAA”.
This kind of trick is only done in research when the statistics would have given an insignificant result without it. They seem to be stretching the boundaries to prove their claim.
No Reference For A Theory
That sentence about changes in tissue water was not referenced – it appears to be made up.
NAA was in dramatically lower concentrations than the others, so comparing GABA and Glutamate to NAA involves dividing by a really small number. This gives a much bigger number and is a classic technique for manipulating significance.
They then said, “a potential confound to our interpretation of these results could arise if the stimulation induces local edema.”
The researchers gave no measure of likelihood nor reference nor mention to a way of determining whether this was the case; they base their one claim on a guess or a fantasy.
Do they see the faulty logic? “We did this because there might have been a change in water, and if there was a change in water it means we are likely wrong.”
Anodal and cathodal tDCS determines which electrodes are positive and negative. In one study they had the electrodes on the right temple and above the left eyebrow. Anode or cathode stimulation changes which side is positive or negative.
Neurons, with their axons and dendrites, are facing every direction. If anodal stimulation causes a change then the change should be on the other end when the stimulation is.
Correlation does not imply causation; just because something changes when you do something different doesn’t mean what you do causes the change. There are countless examples of this and some people love to document it.
Cherry Picked References
The researchers in this field know that reviews continually report that different studies have found conflicting evidence, some saying it’s good, some saying it’s bad and others saying it doesn’t do anything. When they write up their study they are picking out the ones that support their view – a classic case of confirmation bias – when there are plenty [R, R, R, R, R, R, R, R, R].
Movement of Current
“Current takes the path of least resistance.” That’s not true. Current takes any and every path it can, but the path of the least resistance takes the most current and then that current can induce a decrease in resistance and even more current flows through that path [R].
Electrical current moves in a very interesting pattern and the above picture shows that. One side was a cathode and the other side an anode, yet you cannot tell which was which. This pattern of movement doesn’t match up with neuron configuration.
Some articles don’t mention procedure having a blind or double-blind. Inevitably, the researchers’ findings matched up with their predictions [R, R, R, R, R] whereas the blinded studies often find no improvements [R, R, R, R, R].
Small Sample Size
Another way of getting significance is having a small enough sample size so the natural variance of the population doesn’t average out [R].
How Much Does It Change?
It’s common for these researchers to say that what the tDCS is doing is changing the resting membrane potential of a neuron, making it more or less likely to fire [R]. Different to tDCS, one electrode needs to be inside the cell to measure membrane voltage [R]. If the voltage passes through an enclosed cell opposite sides increase and decrease. Now the signaling is wonky, brilliant.
Under the safe limit of 2.0mA current, the biggest electric field it creates is 0.22 V/m [R]. The neuron plasma membrane (-70 mV) is 10 nm thick therefore has a maximum voltage drop of 2.2 nanoV. Any bigger current causes more irritation.
Is There Another Way?
The transmembrane potential changes 2.2nV but the extracellular action potential changes 2.2-220 mV along an axon, 1-100 million times more. This could explain the anodal and cathodal improvements and inhibitions.
From one side of the cell body to the other is around 22 microV also making a difference.
It’s common to randomly organize patients into testing and control groups. Researchers prefer it minimizes the systematic error of subconscious bias.
But randomly generated numbers can come up with my birth date or phone number or the digits of pi. Similar to how randomly organizing can produce a significant difference between groups before testing begins [R]. I prefer it when they assort people into groups to equalize baseline measurements. If we picked the A-league players onto one sports team, it could be significant. Maybe one day equalizing the baseline will become the standard technique.
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