Disclaimer

This blog is a record of personal experiences. All information presented here is solely for study and entertainment, and should never be treated as medical advice, endorsement or promotion of any practice or product. The writer is not a medical professional, and will not be held responsible for any damages that have resulted from any practice or action, or lack of action inspired by reading this blog.

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.

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.

If the mountain fights back

Just a quick mention, last week Mark Sisson of the awesome Mark’s Daily Apple Blog and the Primal Blueprint has also written about using identity in achieving our goals. It’s cool to be in a synchronicity event with someone I consider a role model.

Anyway, what I wanted to write about is that sometimes even though we have the tools to create or increase motivation, it just isn’t enough. The problem is not in not trying hard enough, it’s in the strategy, or rather, the field itself that we are trying to attack. This is when you’re no longer just fighting your own body, the mountain you’re trying to climb has started to fight back.

This is surprisingly widespread in our current culture, some of it intentional, some unconscious, but much of human knowledge and skill has been written up, and is being taught in a way that creates an artificial barrier to understanding and assimilating it.

Most of it is just the fact that the percentage of great teachers among mankind is rather low. Even experts of a given field often turn out to be quite subpar when it comes to giving their knowledge over to the next generation. Textbooks are often arduous reads that spend far too much time on insignificant details, and hamfist the explanation of key concepts, while university lectures are often seen by students as an ideal place to take a power nap, and through no fault of their own.

However, that is not all. We are, as a society, captives of an idea of specialization. The only people we see as valid are those who streamlined their whole lives toward a single carreer, a single area of expertise from early childhood, and much of education seems to concentrate on selecting the best candidates for each pursuit of life, as opposed to building whole human beings.

In many countries, the role of PE is not to give children a health-conscious mindset and improve their physical prowess – it is to selectively pick out the children who are best suited to become professional atheletes, while (intentionally or no) instilling a sense of failure in the rest. The same goes for music education, but in this area the problem is even more widespread, and, particularly, in mathematics and the sciences.

The idea of “teaching kids that life is no walk in the park” is a rather old maxim among teachers, and I’ve seen an otherwise extremely liberal and enlightened professor of philosophy, mathematics and psychology write that the fact that most children get a sense of failure and inadequacy from mathematics or PE classes is in fact a good thing, as it teaches them that they cannot do anything.

And this was a liberal, well-rounded, polymathic professor regarded as a role model by many students, probably the person closest to the reneissance ideal at the psychology faculty of the Eötvös Lóránd University in Budapest that I knew. If people like him hold such satanic ideas, no wonder we’re faced with so many problems.

Of course, most people who did chew themselves through all the hardships and artificial roadblocks will not be very happy to see others master their field with ease and fun, so anyone looking for help from those “in the know” will often be faced with jargon, an in-group vs. out-group mindset, and some open resentment for trying to “cheat”.

So it’s safe to assume that most fields do not want you to master them. It’s not that you cannot, you just need to find the best path of attack. Sometimes “renegade” teachers with novel ideas will create seminars and books that allow outsiders to sidestep the artificial roadblocks, and assimilate the field according to one’s own capabilities and the field’s true complexity. (An example for this would be Duncan Lorien, a pop music producer who, seeing the abysmal state of music education in the west, took it up to become the best music teacher of our generation – some would say he has succeeded.)

In other cases, while there is no sherpa to lead you up, there is an easy trail up the mountain. A segment or pursuit within the field you’re aiming toward that has a lower entry barrier than others, one that will yield positive feedback in a measureable amount of time. Ironically enough, these pursuits very often have a bad name.

Take body building for example. Many athletes and coaches will openly tell you that body building is not a sport. However, while in most sports the aim of the coaches is to pick the best and weed out the rest through unenjoyable and monotonous practice, the very atmosphere in body building is different. Honestly, I haven’t seen as many newbie-friendly and helpful people in any other walk of life as in body building. And while some of the worries about “cosmetic-focused training” are valid, if you follow a good exercise regime, body building can help you become athletic, and allow you to later enter any other field of sports at your own pace.

Similarly, cycling, while boasting a much less helpful community, is an activity that scales very well, and is extremely suited to people with a traditionally “wimpy” phisique, and is thoroughly fun and enjoyable. Also, cycling is very good at providing positive feedback. You’ll notice improvements in your physique and stamina very early on, which helps one keep on track.

Sometimes there will be no clear easy road, but often the choice of textbook or teacher can mean the difference between success and failure. Anthony Lee of GetLimitless has recently blogged about a new way of learning, using short bursts of concentrated information, with resting periods inbetween. While this is extremely promising, and I know it to work (I’ve used a similar pattern to assimilate most university courses I took), getting the information in digestable, concentrated format is what is hard.

Unfortunately, United States textbooks tend to be extremely superfluous, and full of unproductive banter. In Hungary (my birth country), university textbooks are usually extremely terse. A textbook that would be a 1000 pages in the US is likely to be somewhere around 150 pages in Hungary, with the exact same amount of knowledge crammed in. I’ve had textbooks with little or no natural language explanations, the pages filled with equations and a few figures. I’m wondering if this might have anything to do with Hungary’s awesome track record for raising great scientists and inventors.

I’ve raised the idea on Reddit that a movement could be grounded for creating terse, concentrated learning materials for various fields. I think if it took off, it might even grow to be a world-changing endeavor.

A practical guide on how to be someone else

Though as I explained before, I didn’t find any proof as to the qualities usually attributed to hypnosis, I did run into ways to effect change in our personalities and behavior. Some of these are extremely powerful techniques.

The world is full of methods allowing us to mess with our heads, but in this post I’ll concentrate on something most people are looking to achieve – changing who we are, and how we act. I’ve used these techniques several times in the past to effect positive change in my life – of course, it has also happened time to time that later I fell back into negative patterns and behaviors, so it’s not a magic bullet by any means. However, it can help a lot.

When a desire to act differently comes up in someone’s life, they usually think of symptomatic, superficial changes, and fantasize about ways to “program their subconscious” to automatically work out 30 minutes a day, not to eat sweets or pizza, stop smoking, spend more time studying, etc. The greatest lure of hypnosis is the belief that someone can just tell you that “from now on, you will find the taste of cigarette smoke revolting”, and poof, life problem solved. Well it doesn’t work that way.

The simplest approach

To change how we act, we need to change who we are. Our image of self is one of the major driving forces behind our daily acts. If I see myself as an athlete, I’ll be motivated to work out every day – if I see myself as a geek and a gamer, I’ll be motivated to spend a copious amount of time playing video games.

Our current mainstream culture seems to shun the idea of changing oneself. It’s all over television, movies, etc. “Be who you are”. The fat geeky kid tries to be sporty and cool, and ends up as laughing stock. It’s the absolute worst advice you can give a child. Self-representations, and our place in society are not constant, are built and developed as we mature, and well into old age, preferrably up until death. Being discouraged from a course of life because of ones self-representation is one of the most common ways people make themselves miserable.

The absolutely easiest way to change who we are is through changing what we put in our brains. I mean entertainment, media, leisure reading, etc. If someone wants to become stronger and more athletic, the best thing they can do is go and buy a bodybuilding magazine, watch the Muscle Channel on cable, go read Internet forums and watch Youtube videos about strength training.

Note though that Internet forums can be a double-edged sword. If they are full of people who are either trolls and assholes, or hold totally opposing beliefs to one’s core alignments, participating in such can actually discourage one from adopting a certain identity. Say, one decides to eat healthy, and the healthy eating forums are packed with anti-science, anti-medicine, anti-vaccination conspiracy theory tinfoil-hat nutjobs, it can really really work as a motivation to just leave the whole healthy eating shit for the birds, go drop by a McDonalds right now, and kiss the website of Monsanto while thanking God for GMO soybeans. Unfortunately there is nothing one can do about people being stupid, so my suggestion is that if beliefs in a community go against your core ideas, just leave them, and try to find other sources that you find more acceptable.

The maxim that “you are what you eat” is particularly true of information. The Japanese seem to be particularly aware of this, as each year they push a plethora of children’s cartoons out the door, each showcasing a sport or activity of some kind, often in exaggerated ways that Western viewers tend to find hilarious. It’s solid fact that this sort of push from the media does manifest in an increased interest in sports. Years ago it was all over the news that after a cartoon was made about the game of Go, considered to be an “old man’s game”, with little interest from young people, suddenly Go clubs sprang up at schools country-wide, and the game enjoyed a nationwide revival.

Many of these sports cartoons do have a trick to them. The protagonist usually starts out as a non-athletic, weak kid, and through the story, progresses to be a top class athlete. This is very important, because it does not allow the viewers to disassociate themselves from the theme. It breaks down the wall of self-doubt that inevitably stands in the way of change.

Similarly in the US, television shows that cast African Americans in non-stereotypical roles, such as Liutenant Uhura in the original Star Trek as a high-ranking officer, or the upper-middle-class Banks family in The Fresh Prince of Bel Air, actively helped young African Americans change the way they looked at their future, and aim for university and well-paying carreers.

In my experience, if the motivation is there to change, then it doesn’t take too much input to affect a change in self-representation. Humans naturally learn by imitating others, and if you provide yourself with plenty of role models to imitate, change will come naturally.

If the simple approach fails

Well, sometimes it’s a bit harder to adopt a new way of life, maybe the emotional motivation isn’t as strong, or one just can’t muster the strength to make the change.

There are ways to help in cases like this. The best tool, I believe, is NLP, or NeuroLinguistic Programming. It’s a form of therapy developed years ago, which has undergone quite a lot of changes since. I do not agree with most of the tenets of oldschool, orthodox NLP, but there are really good techniques there if you know where to look. In fact it’s NLP that makes most hypnotherapy work. Hypnosis without NLP (or some other form of actualy therapy) is worthless, but NLP does quite fine without hypnosis, thank you.

The primary goal in NLP is to change our mental representations. It can be applied by a therapist, or you can do it to yourself. Contrary to the name, it has little to do with “neuro” – it is not based on any kind of neurological or neuropsychological tenet, I guess it just sounded cool. As for “linguistic”, while there’s a lot in NLP written about words and wording, I’d say the best techniques are the ones that do not use words at all.

My favorite “do it yourself” book on NLP is Anthony Robbins’ Unlimited Power. In case you’ve never heard of him (though I doubt it), Anthony Robbins is a world-famous life coach and “guru”, and this book is a crash course in his technique and approach to NLP. It’s a fun, engaging read, and extremely hands-on.

As I’m no NLP expert by any stretch of imagination, I suggest you read the book, and make your own conclusions, but let me give you two examples of what you can do with NLP to help change your representations of yourself.

One is called modeling. It’s basically a conscious approach to imitating a role model. In simple terms, it entails trying to mimic their posture and facial expressions (one of the tenets of NLP is that the state of our body creates effects in the state of our mind), creating a model of what this person would live and act like, and periodically comparing our own conduct with this ideal. For example, “Would Arnold Schwarzenegger sit here and watch Office, or would he rather go down to the gym?”

The other favorite of mine is called reframing, and is one of the most basic techniques in NLP. This allows you to change your own perceptions about what’s possible or impossible, and what’s significant or unimportant. For example, you want to learn music, but all your life you’ve heard nothing but that you have to be born a musician, or at least start learning as a very small child. Of course, since you have such representations, it will be very hard to muster the will to pour energy into something you think is impossible.

To change this belief, you conjure up an image of you as a musician with people listening and enjoying your music in your mind, and then an image of something that you do know is possible. Say if you’re a great programmer, imagine yourself in the act of winning a coding competition. Then compare the two images based on modalities – how large they are, where they are in space, how colorful they are, do they have movement or sound, do you have kinesthetic feelings from them, do they have a frame or border, etc. Then you take the “impossible” image, and forcefully make it like the possible one.

By doing this regularly, over time you can change even deep-seated fears and beliefs, and set your sights on new horizons.

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.