Category Archives: Brain stimulation

A slump and a new tDCS montage

Over the last few months I haven’t updated this blog – I have had a slump, which left me somewhat unmotivated about self-improvement and other activities that aren’t central to staying afloat. In the end what shook me out of it was an overseas trip. Jet lags force one to look at things in a new light, waking up at unfamiliar hours, or staying up late without a hint of tiredness.

Still, about the time when I got back, I heard of an interesting new montage mentioned on the /r/tdcs subreddit. It is called a fronto-occipital, or F-O depression montage, and involves placing the anode over Fp1, and the cathode over Oz.

Here is an abstract of a paper detailing this montage. It showed a lot of promise, and the activation of the DLPFC was observed to be even higher than with the most popular bifrontal montage.

Some other data also popped up that made this montage extremely interesting. It would seem, based on animal testing, that the habenula (pineal gland) plays an important role in motivation for both bodily exercise, and the pursuit of pleasurable activities. Of course, being deep inside the brain, targeted stimulation of the habenula is all but impossible without invasive (surgical) techniques, but a front-to-back montage, which directly affects much of the brain, might likely impart some effect to such deep-seated areas as well.

I tried the montage, with a 3×3 inch electrode over Fp1, and a large, 3.5×7 inch one draped horizontally over the occipital lobe – I wanted to avoid creating a cathodal hotspot over the occipital lobe. So far, it seems extremely rewarding. I did notice a significant alleviation of passive behavioral patterns, and an improvement in my mood. Applying tDCS in the morning, as opposed to the afternoon was also a welcome change – it is definitely the superior option, and the jetlag made it a lot easier than it would normally be.

My plan is to keep at it for 7 days, and write about my observations afterwards.

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Casual use of tDCS

As I’ve mentioned in previous posts, I have some pretty good experience with tDCS. I’ll try to quickly go through the protocols I’ve been using, and my experiences.

First experiment

When I first applied tDCS, it was in the middle of a depressive episode with strange behavioral blocks. Such as, I’ve had this inexplicable dread of checking my mail, been unwilling to start or do anything productive, and similar. I have no idea about the exact neuropsychology of it (it would have been interesting to check myself with a QEEG unit if I had one), but I suppose it was some kind of over-inhibition. It’s something that’s characteristic of my basic “personality”, and something that’s caused me much grief in the past.

I applied tDCS in a bifrontal configuration with the anode over F3 (left dlPfC) and the cathode over Fp2 (right supraorbital). This is an extremely widely researched and proven configuration for treating depression, and is associated with increased conscious control over emotions and an improvement of executive functions including short term memory.

A great overview of tDCS montages and their observed effects in experiments is the TDCS State of the Art paper. Another awesome resource everyone should read are the manuals from Trans Cranial Technologies. They have a comprehensive, easy-to-understand manual on the 10-20 QEEG positioning system, proven tDCS montages, and on cortical functions for those who want to experiment with new setups.

The device was extremely simple, consisting of nothing but an array of CRDs (totaling 2.0mA) and a 1k resistor to suppress current spikes. As a bonus I managed to be the idiot I mentioned earlier, and connected my head last to a powered-up loop, so it can be said without doubt that the total current clearly has gone above 2.0mA upon turn-on (which manifested in a weird popping sensation and a feeling of electric shock – though no phosphenes).

The behavioral-cognitive effect was quite noticeable, but I still don’t know if it had more to do with the tDCS or the shock from the transients. Anyway, the behavioral blocks I mentioned were gone in about 5 minutes, and I soon caught up with all the stuff I have been putting off for days or weeks. In total I did 20 minutes of treatment, and disconnected. Upon disconnection, I experienced phosphenes. While from a subjective standpoint I’ve been successful, I decided to put off further experimentation until I’ve built a more secure device.

Following up

Later, when I completed the device described in previous posts, I decided to do a 5-day treatment regimen, using the same bifrontal configuration. This time, I always used the manual start/stop pot, and thus avoided any form of transient.

At this point I was not in any particularly bad condition psychologically (apart from a slight slump in motivation), and thus the effects of this treatment were barely noticeable from a subjective standpoint. I did observe a slight “emotional desensitization”, or increased control over my emotional responses. In a kind of Vulcan-ish way.

The treatment markedly did not help with my lack of motivation, which culminated in spending an entire weekend doing literally nothing but watching Game of Thrones. (In a rather positive mood, but that hardly counts in favor.) So it must be said that tDCS is not a magic bullet. It’s a “hardware level” tuning, and will not necessarily alleviate cognitive, “software level” problems.

A walk in the woods

I did a search over the net looking for ways to increase motivation via tDCS. What I did find was a montage based on anodal stimulation of the right dlPfC (F4), supported by some anecdotal evidence, and unsupported by experimental data. The one relevant experiment I found that used this setup failed to provide statistical data to support its effect on goal-oriented behavior. (That said, the failure might be attributed to a bad choice of measurement task, so I didn’t dismiss it out of hand.)

The protocol was 25 minutes daily for 3 days, using 2mA of total current between the anode over F4 and cathode over Fp1. Though there were no studies showing the effectiveness of this montage for motivation or goal-oriented behavior, it was proven to be without negative effects, and was being researched for alleviating alcohol and drug cravings, so I wasn’t particularly worried.

I did notice some reduction in the compulsive-repetitive behavior that is inherent to my genetic condition (there might be a link with the addictological effects of the montage), and slightly better goal-oriented planning, but nothing particularly striking, so I cannot rule out placebo effect. This slight improvement seems to have dissipated after discontinuing the regimen, though.

Refining the depression montage

I have had some worries about the bifrontal setup, as it has both the anode and cathode over areas of the frontal lobe. Later, I found some data supporting the use of an extracranial cathode. In this setup, the anode is placed over the left dlPfC (F3), and the cathode over the contralateral (right) arm.

I’ve done one 5-day regimen using this since, and I have recently started another. It does seem to help a lot – though I haven’t noticed such marked effects as the first experiment, that may also be because I haven’t experienced such marked behavioral blocks since. It’s hard to pinpoint the effect of treatment, but it’s definitely a thing. It’s not really what “is” there, but what “isn’t”. I definitely feel better and more productive when I’m using tDCS.

What is the resistance of your head

It’s the first question I asked when I set out to design a tDCS device. I didn’t find any sources that were too accurate or particular.

There is some information out there on the galvanic resistance of the human body including on Wikipedia. Also it’s an interesting fact that galvanic skin resistance is highly dependent on sympathetic nervous system activation, can change rapidly, and is used as an important measurement in psychology and psychiatry experiments, in polygraph machines, and in Scientology auditing.

Bottom line is, the resistance of dry skin can be anywhere between 10 kOhm and 1 MOhm, while the resistance of the wet stuff inside us is more in the few hundred Ohms range. In AC stimulation like TENS, the impedance of dry skin is greatly reduced due to the AC nature of the applied electricity, because the electrode and the wet matter below the skin form a capacitor, which allows AC through while blocking DC. With tDCS, naturally we cannot rely on this.

To reduce the resistance of the dry outer skin layer, in medicine people usually use wet electrodes, like gel electrodes in EKG and EEG, and saline-soaked sponges for stimulation and iontophoresis. In fact, there is a good reason why most tDCS systems use wet sponges. It’s really simple, doesn’t cause a mess (not having to wash your hair is a plus), hair doesn’t really mess with the results, and it can handle Wattages that would heat up or break down gels.

While there’s a lot of talk about resistance of the electrodes, the fact is that if they aren’t dry, it’s safe to consider them a dead short. I’ve used sponge electrodes with an approximate area of 25 cm2 and with half as much at about 10 cm2, without any noticeable difference in the voltage dropped.

As for HD tDCS and gel electrodes, there was a research paper by HD tDCS pioneers Soterix Medical some time back, where they tested various electrode configurations. Most of them heated up, broke down under DC, their resistance skyrocketing, but their “winner” stayed below 10 Volts of drop throughout. In fact, I’m convinced a simple wet sponge fares just as well, or probably better, for a fraction of the price. In their case, there were other considerations in favor of gel electrodes &ndash like integration with existing QEEG positioning meshes and electrode bodies.

My experience is that for extracranial electrode configurations (ie. with one electrode placed on a shoulder, arm or otherwise not on the head), the total resistance of electrodes plus body tends to be 3500—4000 Ohms, while with both electrodes on the head, it’s more around 1000—2000 Ohms. These values are for quality sponge electrodes (Amrex) with a metal mesh backplate, and soaked (but not dripping) with standard .9% saline solution.

This means that for a tDCS device to provide enough juice for most scenarios, it has to be able to provide up to 8 Volts on its terminals. Most devices go somewhat above this, to deal with suboptimal connections, but my opinion is that for a DIY, or otherwise non-medical device, it’s better to stay around this value for sake of safety.

Building a good tDCS device – part 2

So basically, to have my super simple and easy to build, yet safe (as can be under the circumstances) brain zapper, I determined the following block components as necessary:

  • Current source
  • Protection against reversed polarity
  • Manual current shunt for start and stop
  • Transient suppression
  • Test points for measuring current and voltage
  • Voltage indicator LED

Current source

I wanted to be able to experiment with various current levels, so I opted for using miltiple CRDs in parallel. Using jumpers to turn them on or off allows me to set the current to 1.0, 1.5 or 2.0 milliAmps.

CRDs are kind of expensive as loose components go, so I wouldn’t necessary do the same for a device that goes into mass production, but that wasn’t the goal here.

Protection against reversed polarity

This one is needed because a CRD acts as a short circuit (well, actually it acts like a forward biased diode) when biased in reverse. Since I was going to build this on a veroboard with an el cheapo pinheader to connect the battery holder, I needed to make sure there won’t be any surprises if I ever connect the thing backwards.

Solution: I just added a diode between the battery and the positive rail. Since I’m using two 9V batteries, the .6 Volts I’m losing there is insignificant.

Manual current shunt for start and stop

If we add a potentiometer the the simple circuit I linked to in my last post, there are two ways we can do it. Either in series with, or parallel to the load (ie. our head).

Manual start/stop configurations

Manual start/stop configurations
a) Potentiometer in series
b) Potentiometer in parallel (shunt)

Now the series configuration is absolute rubbish, the only reason I included it here is to explain what’s wrong with it. We can treat the CRD, for all intents and purposes, as a “smart” resistor that sets its value to whatever is necessary to maintain a specific level of current flow through its terminals.

It is meant to nullify whatever changes might come along in series resistance, and keep the current static, as long as there’s enough voltage to keep things up. So it would end up fighting any series element meant for start or stop. Regardless of the value of the potentiometer I use, the result will always be quite inadequate.

Current curve for potentiometer in series

Potentiometer in series:
This is how the current would change in response to turning the knob. Not so pretty, huh?

The better, and safer way to cut current flow to one’s head is to reroute it, to create an adjustable shunt to ground in parallel with the load. Now this has its own fleas. Due to the nonlinear nature of the current divider equation, I still get most of the current turned on (or off) on the first 10% of the pot’s rotation, and the rest changes naught.

However, “audio taper” potentiometers came to my rescue. They are pots with a nonlinear curve optimized for volume adjustments, to compensate for the logarithmic nature of human perception. In this case, they compensate adequately for the nonlinearity of the current divider law. While not perfectly linear, and subject to change as the resistance of the load changes, it’s good enough.

Current curve for potentiometer in parallel

Potentiometer in parallel:
This is how the current would change in response to turning the knob.

As you can see though on the diagram, we will always lose about 10% of the current with a 50k potentiometer, and an average 3.5k resistance across the electodes (in my experience, using standard 2″ saline sponge electrodes, resistance varies between 1.5 and 4k, so this is a good approximation). Since my CRDs were off by about +10% compared to their nominal value, I decided this might be a good thing even.

Transient suppression

What happens when I connect the trodes to the device after it has been turned on? What happens if the potentiometer malfunctions? If a wire breaks? Well, even though none of these should be dangerous in the strictest sense, they would potentially lead to voltage and current spikes on my brain, which are, in the very least, extremely unpleasant.

The worst case scenario is suddenly connecting up an open circuit. If the loop is broken, the current is zero, and so is the resistance of the CRD. It allows almost the full input voltage onto the terminals. When you first connect up a loop like this, and your head happens to be the last element to be added, you’ll be treated to almost the full 18 Volts for a few moments, and before the CRDs catch up and stop the current, you’ll get transient currents potentially higher than 2mA.

You don’t even have to be an idiot for this to happen. A wire could break, and then by a minute movement, become reconnected, resulting in the above scenario. So what can be done about it? I explained my disdain for “soft start capacitors”. A CRD works by varying voltage in order to keep current stable. A capacitor resists changes in voltage. They are “enemies”, fire and water.

However, an inductor does the exact opposite. It resists changes in current. Just what we need, huh? It’s kind of the electric equivalent of a flywheel. The only problem is that a DC choke large enough to make a noticeable difference is big and heavy – this time I decided to accept the big and heavy, and got a 10H choke, but unfortunately, for a portable device this would be far too much bulk in my opinion.

Note: a choke needs a flyback diode (a diode biased in reverse across its terminals), to make sure it doesn’t create crazy voltages when you take the current away, allowing it to wind down.

I’ll post some oscilloscope screenshots, for now you’ll just have to take my word that without the choke, there was significant ringing, and transient currents up to 4mA upon connecting up a broken loop. With the choke added, the overshoot and ringing were gone, and the current never passed the 2mA threshold.

Test points for measuring current and voltage

Well, I have two multimeters, so I didn’t want to burden the design with any dials or digital meters. Added a 1k precision resistor as a current shunt (making 1V of measured voltage equivalent to 1mA of current), and test points for measuring voltage across the current shunt, across the load, and across the battery terminals.

Voltage indicator LED

My last idea to make this as safe as possible was to include a LED that would light up if there is a voltage on the terminals. Just to make sure I’d never plug my head into a live connector.

To isolate the LED from the load (I sure as hell don’t want a LED’s 30 milliAmps on my head, no matter what happens), I used a 1M resistor, and a darlington pair…

Putting it all together

Based on the above, this is the final design, and the device. It’s pretty small, fit on the tiniest veroboard I could find, is safe, and works good enough. All in all it cost me less than $50, and a few hours of work.

Schematic for my diy device

Schematic for my diy device

The device built

Building a good tDCS device – part 1

After reading all up about tDCS, and deciding it might be a good idea to take a crack at it, I was faced with a dilemma. You see, professional tDCS devices cost a lot, and are medical devices, ie. you can’t just buy them off Amazon.

Of course, there were a few options beside that. One of the awesome things about tDCS is that the technology is so easy it’s almost ridiculous. To have a fully functional tDCS device that does exactly what the professional ones do, all you need is a current regulator set for 2mA, some wire, and two saline sponge electrodes.

Since it caught the fancy of many geeks and makers, there was an awful lot of resources out there. I first came across an initiative to create a kit, called GoFlow. Their webpage is still up and dandy, though the project itself went under years ago. It was intended to be a simple device with a standard bifrontal electrode layout (more on that stuff later, do some googling if you’re interested).

Now even if it was available, it has its shortcomings. For example, they have this big ass, 470uF electrolytic capacitor across the ‘trodes. I fail to see how that would EVER be a good idea in a current regulated loop. I do love the concept pic tho’, all those Apple-esque colors…

The next candidate was the foc.us. If you haven’t seen it already, it’s the big game in town. I’m not entirely convinced what they are doing is legal, but they are popular and the device looks cool. That said, it’s expensive for what it is, requires an iPhone 4S to access all functionality (a regular iPhone 4 just won’t cut it), and seems to have been designed by a herd of insane marketing managers high on MDMA.

So, I decided against it. Since then, it turns out I was even more right than I thought I was. The foc.us is a dog with fleas. I’m particularly struck by the fact that it goes to the length of having 64 Volts as its maximum driving voltage. How irresponsible is that?

That’s when I read this article on the Speakwisdom blog. It’s a beautifully simple design, and as far as I know at least two commercially sold kits (the kind of pricey Biocurrent kit, and the humbly named – and priced – tdcs kit) are based on it.

Simple tDCS design

The design is based on a so-called current regulating diode, or CRD, which is a simple and robust device. It’s a FET wired in a current limiting configuration, and factory-tuned for a specific current level. They are quite stable, very low maintenance.

So I got some, plugged them up in a breadboard, wired up a pair of Amrex electrodes, and well… It worked. However, I felt quite shocked when I turned the thing on, and had lights flash in front of my eyes when I disconnected it. Of course these side effects are well known and harmless (the flashing lights are called phosphenes and are due to some neurons firing in the retina or the optical nerve), but I just couldn’t shake the thought that it could be made safer and nicer.

Of course I wouldn’t think of connecting a big ass “soft start” capacitor across the terminals, like the crazy GoFlow guys, especially not that my design is not a nice, single package like theirs, ensuring constant electrode contact. Things can get disconnected, a wire can break, and then the “soft start capacitor” gets a new job as a “very hard start capacitor”, or more aptly the “help a donkey kicked me in the head capacitor”.

Adding a potentiometer for manual starts and stops seemed like a good idea, but it wasn’t trivial either, due to the nonlinear nature of the entire system. The trick is to get a setup where the intensity is at least somewhat linearly distributed across the movement range of the pot. I didn’t want the current to come up in a jolt at either end – I wanted a smooth, nice ramp.

While I was thinking about solving that, I also gathered a few further requirements pertaining to the device:

  • Should be cheap,
  • Should be simple enough to build on a veroboard,
  • Should be as safe as I can make it,
  • I should be able to build it in a day or two once I have the components delivered…

I think I came pretty close.

The tDCS craze

One of the reasons I started this blog was that I’ve recently learned about, and started experimenting with tDCS (transcranial direct current stimulation). I first read about it in the Wired magazine, which was of course full of journalistic exaggeration, but the idea really made my head spin.

In tDCS, the brain is stimulated with an extremely weak (1-2 mA total) stream of direct current. This is not enough to fire neurons, but seems to have an effect on action potentials, and the neuroplasticity of the brain areas the current passes through. In clinical research, tDCS has been successfully used to alleviate depression, and to improve chances of recovery after brain damage.

The journalistic hysteria was, however, centered on another claim that researchers were making. That tDCS has the potential of improving cognition and learning ability in healthy humans – while being completely safe, as far as researchers can tell. The phrase of “putting one’s thinking cap on” has suddenly become quite literal.

That’s interesting in a way, but what really made this a breakthrough was the simplicity of the hardware required. There is no need for high voltage like in magnetic stimulation (TMS), or complex software. A simple low power current source and a pair of medical electrodes is all that is needed to replicate 95% of the clinical experiments. And thanks to this, a serious community of DIYers has sprung up.

While there are reckless idiots as anywhere else (some have taken a 9V battery, and connected it to their heads), most of the community is made up of responsible, yet adventurous people – some are transhumanists out for the cognitive boost, some are looking to alleviate their depressive symptoms – and it seems to boast a pretty good rate of anecdotal success. This has resulted in the start of a cautious conversation between professional researchers and the community.

tDCS device

Drawn to the idea, I’ve also built a device. For one, I’ve been having trouble with a low-key manic depressive tendency, and also I was wondering if this could be used to address the frontal lobe inactivity problems inherent to my genetic condition.
While I don’t have a too long history to share, so far it seems I’ve both successfully reduced the amount of compulsive repetitive behaviors, and cut a depressive episode short.

In future posts I’ll be writing in detail about the device design, where it came from, and why I decided on building it like this. I’ll also be addressing the electrode montages I’ve been using, and maybe add some subjective updates of my experiment.

In the meantime, I think the best resources to read for general curiosity are the /r/tDCS FAQ and this SpeakWisdom article about depression treatment.