About a month ago I got an offer from John (who runs DIYtDCS and Michael Oxley (who runs foc.us)  to review foc.us’s new device (the V2). Since I was curious about how exactly this thing works, I accepted, and promptly received a new V2 which sat on my table for about a month while I wrote a paper. Which is submitted now! So anyway…
The foc.us V2 “controller” module
The box I received contained the foc.us controller/current source, a dock for connecting it to a computer, the “Gamer” headset, a bunch of sponges, and an incredibly ugly shirt.
Shirt aside, the first thing you notice about the foc.us is that it’s slick. When you work around laboratory and DIY versions of this technology for years, there’s something about picking this thing up that makes it feel like it’s from the future.
The V2 is a modular system, which means that the actual device that generates the current is a small black rectangle, about the size of a particularly chubby flash drive. It has a connector on one end, which is where you plug in electrodes, and an internal Bluetooth chip for communicating with a smartphone or computer.. You control it using and integrated screen and a directional knob, which is surprisingly intuitive. The screen also shows you real-time information during a stimulation session.
Speaking of Bluetooth, it’s also important to point out that if you buy a foc.us now, you’re buying the “developer edition”, which means it’s actually not done. While the hardware and basic stimulation functions are all functional, some features in the software are not quite implemented yet. While these are generally not huge issues; some of the features that are advertised don’t yet exist in the device; for instance the device supposedly has a “double-blind mode” which lets you use sham stimulation on yourself; it applies the sham but there’s no way to look back at which sessions were sham and which were real stimulation.
Overall, the build quality of the device is…variable. While the stimulator unit seemed solidly put together, the Gamer headset broke a couple minutes after I took it out of the box. The issue here is that the Gamer headset electrodes are attached to an aluminum frame by a fairly flimsy plastic connector which breaks if it’s twisted (something that’s likely to happen when adjusting the electrodes).
This was perhaps the biggest question I had about new new foc.us device, given the company’s history of safety issues in the past. Luckily, this seems to be one of the areas where they’ve dramatically improved; none of the previous safety issues persisted and at all times the device’s output never exceeded its specifications or a safe envelope.(see footnote)
The most visible change here is the electrodes. Both the Gamer headset and the new Edge headset now use white sponge electrodes which measure 9 and 12.25 square centimeters in area depending on the type. While the current density delivered by these electrodes operating at the maximum 2 mA output is within the range often used in research, it’s also rather high compared to many other tDCS devices. Therefore, it’s prudent to carefully monitor for skin damage when using this device, particularly at higher current intensities.
The foc.us also includes some new safety features designed to reduce the risk of high-current-density induced injuries. The most interesting is a soft voltage limit; while the device can technically output voltages out to 60V, users can specify a lower limit to not exceed. This provides protection if the connection between electrodes and the head starts to fail (due to electrode drying or drift, for instance); rather than increase voltage to the absolute maximum in an attempt to drive the target current over the failing connection (which can result in very high current density through a small patch of skin), the device can be configured to simply allow the current to drop using this limit. Unfortunately, there’s no actual alert that the connection is failing (although this can be deduced from looking at the current monitor during operation) but this still provides a good way to avoid many of the safety issues that the high maximum operating voltage would otherwise entail.
Another important area of safety is the ability of the current regulator to maintain its specified current and voltage outputs under varying conditions.  Here I tested the device under two conditions: with relatively stable impedance at varying levels (simulating a typical use case in a person sitting still) and in an “impulse” condition, where impedance changes instantly from very high to very low or vice versa. The purpose of this testing method is to measure the device’s response to temporary very sharp changes in impedance caused by disconnection and reconnection of the electrodes as might occur in the Edge device when used during athletic performance.
Here the foc.us performed perfectly; neither current nor voltage ever significantly exceeded their specified maximums under varying conditions. The response to impulses was particularly impressive, with no significant “overshoot” even at the maximum voltage output.
Current trace for from testing. When subjected to a sharp drop in impedance, current returns immediatley to the design level, with no evidence of a “spike” or overshoot.
One of the most interesting things about the new foc.us is the stimulation modes that it provides; in addition to tDCS, it includes options for tRNS (random noise stimulation), Â tACS (alternating current stimulation), and tPCS (pulsed current stimulation)
tDCS is your standard anode/cathode tDCS stimulation. On the Gamer headset, this translates to the anode on the left side of the forehead and the cathode on the right. I’m not sure which side is the anode and cathode on the Edge headset (since I didn’t receive one), but the arm electrode is likely to be set as the cathode.
The remaining modes are pretty faithful replications of how these techniques have been used in research. One neat thing is the degree of control the device gives you; you can specify things like whether the oscillation should be bipolar or unipolar (whether the anode and cathode switch) and set DC offsets. I was pleasantly surprised by the degree of control that was offered for the random noise and pulsed current modes; in addition to the previously mentioned controls (offset, max voltage, etc. the device provided really fine-grained control over details like the frequency limits for random noise stimulation and the pulse width for pulsed current stimulation.)
(“What is pulsed current stimulation anywyay?” you might ask? It turns out it’s basically a square wave applied with a specified frequency and duty cycle. There’s not much research into its effects on the brain (although the research there is suggests it’s similar to tDCS), but I suspect foc.us decided to include it just because they could).
From top to bottom: tACS, tPCS, and tRNS current waveforms.
Another interesting feature that can be applied to all the stimulation modes is a sham condition. Here, the current gets ramped down after a configurable delay. There are, in theory, two blinding modes: a “single-blind” mode, where the sham is manually selected and real operating status is displayed on the screen, and a “double=blind mode”, where the device will automatically select whether the a session will be a sham or real session. In this mode, simulated data is displayed on the screen during sham sessions, making it suitable for blinding yourself, although the limitations of the developer edition mean that this mode still lacks logging to tell you whether the session was real or sham.
Strangely, one thing that’s missing is the ability to control which electrode is set as the anode and which as the cathode. When using one of the headsets, both electrodes are hardwired to a single connector, and there’s no way to change this setting from the software—a strange limitation for a device that otherwise allows a great deal of control over stimulation.
This configurability, incidentally, seems both good and bad. On one hand, the device is insanely capable compared to other commercial devices marketed to DIY users. On the other hand, there’s very little instruction provided in the manual or packing about how these modes should be used, and one thing that seems to get lost in foc.us’s manual is that the effect of, say, 10-Hz tACS on the brain is quite different from that of tDCS, and that some of the stimulation methods (like tPCS) are quite new and don’t have the “track record” of regular tDCS in their safety and efficacy. These methods are nice to have, in other words, but make sure you do your homework before using them.
The science or…not
Of course, there’s one major issue with an otherwise nicely-designed device, which is that no one knows what it does to your brain.
That’s not to say that the company doesn’t claim to though.  The webpage for the Gamer headset says that it will “increase your working memory and focus”, which is presumably based on some of the studies showing that stimulation of the dorsolateral prefrontal cortex improves aspects of working memory. There are two issues here, however: first, more recent studies have challenged the idea that stimulating the left prefrontal cortex has any reliable effect on working memory to begin with (In fact, the majority of studies on stimulation of this area have shown no effect), and second, the Gamer headset does not match any of the protocols used to study working memory (its electrodes are located too low on the head).
Electrodes to stimulate the DLPFC (and increase working memory) are generally placed over F3, while the foc.us electrodes naturally sit much lower on the forehead. They can be pushed up slightly, but don’t remain in reliable contact with the head.
So what does stimulating this region do? Unfortunately, very few studies have been conducted on the effects of the gamer headset’s “double supraorbital” placement (although the evidence there is suggests it might make you better at lying) due to a historical trend of considering the supraorbital area to be a sort of “neutral site” where electrodes have little effect on the brain. While this assumption is probably not true, the effects of stimulating this area remain poorly defined.
What about the Edge headset? While I didn’t receive one to test, there are a few things about it that make me go “hmm”. It’s marketed “for exercise” and appears to use an electrode placed vaguely near the left motor/premotor/temporal areas, which is actually not a bad idea if you want to increase endurance.Â
What is a bad idea is where the second electrode is placed—on the same side as the first one! While there’s no doubt many practical advantages to avoiding the awkward wire-across-the-body design that would be required to place the reference electrode contralateral to the active one, the cost is the loss of any relationship to the studies that showed this type of stimulation was effective in the first place. The effects of brain stimulation are crucially dependent on not only where the active electrode is placed but the path current takes between the active and return electrode. This observation is particularly problematic in the case of the Edge headset, where one potential current path, where current flows through the skull, into the brain, and back to the return electrode, likely has much higher resistance than an alternate current path where electricity flows directly through the subcutaneous tissue between the electrodes, avoiding the brain entirely. The ability of the headset to even deliver a physiologically relevant amount of current to the brain is therefore quite questionable (while the amount of current that gets though could theoretically be quantified by FEM modeling, using this type of modeling with extracephalic placements is beyond the capabilities of any modeling software I know of)
Perhaps the biggest thing that really stood out to me about the new foc.us device is the degree of innovation that it represents for the DIY tDCS community.  It’s hard not to come to the conclusion that the V2 is the best commercially available tDCS regulator right now, and that the capabilities it provides (such as double-blinding) will probably open up all sorts of opportunities in the DIY tDCS space), as well as push other device manufacturers to innovate. It’s also encouraging to see that the safety and quality control issues that plagued the previous version have been fixed.
At the same time, between the hardware issues and sketchy science, I was underwhelmed by both of the headsets foc.us currently offers. It’s clear what the goal here is – to be really successful, consumer brain stimulation devices will need to branch out from their current niche as low-cost versions of the devices used in research and start to offer specific, pre-programmed modes that accomplish specific goals. But there are good ways and bad ways to do this.  The startup Thync, for example, has been conducting extensive in house research on the safety and effectiveness of their device before it’s released. Should foc.us do the same, or alternately pivot to making “research type” devices without specific claims  (something they may be interested in, given that they have recently released an adapter for Amrex electrodes), they will have a really great, end-to-end solution for brain stimulation. At present the device is a cable and potentially game-changing DIY brain stimulator—but only if it’s not used how it’s marketed.
1.While most of the testing talked about here applies to the tDCS mode (i.e. ability to maintain a stable current) the device was also tested for abnormal behavior in other modes (i.e. generating spikes or excursions from the set current while in tACS mode) with none found.
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