A question that we are getting a lot is if XCSITE 100 can be used outside the lab. Our answer has two parts:
Use of XCSITE 100 as a clinical device (at home)?
We only sell the device to researchers, for regulatory reasons. So if you are a patient interested in tDCS/tACS, we are afraid we are unable to help since there is no FDA clearance of tDCS/tACS for the treatment of any disorder. You will find private practices that offer tDCS and also some older tCS devices that got grandfathered in by the FDA when they started regulating medical devices in seventies. All this is outside the scope of our company.
Use of XCSITE 100 as a research device (at home)?
If you are a researcher and would like to study tDCS/tACS at the homes of your study participants, our answer is a qualified "yes". The device is easy to operate thanks to our (what we think very smooth) app and the research mode, where any type of stimulation can be manually configured, is password protected. In essence, you need to trust the participant enough to use the provided stimulation codes as prescribed by you. You can go and use the encrypted log files to verify correct use of the device (at least in terms of the stimulation applied). In other words, if you trust your participants, this could work very well!
What are you thinking when a researcher applies electrodes to your scalp and tells you that the device may change your brain activity? How about if this is a trial to investigate the effect of tDCS on depression? Well - the short answer is that the situation will consciously and subconsciously affect your thinking - the placebo response! It thus is an absolute imperative that tDCS and tACS studies include a "sham" or placebo condition. This makes sure that both participant and study personnel can never be sure if stimulation was actually applied or not.
For this to work, though, you need blinding. One simple way would be to have different devices but that is cumbersome and expensive. More ideally, you have different codes that are linked to the stimulation parameters but the table that lists which code stands for what is locked away. Simple enough? Can your device do this? Can you specify new codes for every study? Can you set them up or do you need to send your device to the manufacturer? Think about it. These are the kind of issues that prompted us to design XCSITE 100. At the heart of it is a table that you can create for your study. Every row in this table contains a code and the stimulation parameters linked to this code. Do you want to do a study where every single person gets a different stimulation paradigm? You got it! You can have as many of these files as you want and you can thus use one device for as many studies as you want at the same time (well, it can only apply stimulation to one person at the time, but you know what I mean).
There are also small other things that make a big difference. Do you want to know if you still have juice in your battery? Of course, you demand that feature for your convenience! But then, hold on, have you noticed that the battery is still almost full after a placebo stimulation session but half empty after a "verum" (real) stimulation session. If you have not noticed, I am sure one of your smart students / research associates / study coordinators has understood this. Now I think this can introduce a major bias in the interaction with study participants, especially in treatment studies. So no, we will not tell you if the battery is half empty or not. We simply give you ten rechargeable batteries and ask you to use a new one for each session and then charge them all together with our nifty 10 bay charger. BTW, whatever device you are using, please do not use one-way batteries for the sake of the environment but of couese first check with your supplier.
There are more examples like that but I am sure you get my point. Let's make sure we use devices that have smart engineering to enable flexible double-blind study designs and that have engineering controls to avoid accidental unblinding.
Think about it!
The study results in the field of non-invasive brain stimulation are very heterogeneous and the replication crisis has hit the field (quite/very/unsurprisingly) hard. Over the next few posts, I will elaborate on some of the contributing factors and will provide some insights into the steps we have taken / are taking at Pulvinar to help researchers increase the quality of their work and thereby lift up the field. Today, I am writing about quality control and traceability. Quality control is a basic principle were actions are not only planned and performed but also their outcomes assessed to improve the underlying processes. Simple? Yes! Important? Yes! Does your tDCS/tACS device help with this? You tell me and I will tell you about XCSITE 100 ;-)
Typically, stimulation is performed by pressing some buttons on a device (or in a program). Once the stimulation is over, there is no way to verify if the person has received the correct stimulation (waveform). User mistakes can and will happen, especially in the high-stress environment of stimulation patients in clinical trials and if the personnel administering stimulation are not engineers, who are usually more comfortable with operating sophisticated devices. The lack of accountability and the lack of evidence for correct stimulation is fully and simply inconsistent with any kind of quality control you would hope and should implement in such studies.
To address this gap, we designed XCSITE 100. The device records both the stimulation current and voltage and sends the signal via bluetooth to the app that controls the stimulator. The resulting files are encrypted to ensure integrity of the study blind. But if there are any questions about what stimulation a given participant received, it is straightforward to trace back to the specific stimulation applied (including the quality of the electrode attachment which can be determined from the calculated resistance, remember Ohm's law...). We provide a decryption app which can be used on a desktop computer to unlock the files. We know of customers who assign a person not involved in the study (who is unblinded) to look at the recorded file after every single study visit to ensure that 100% of all stimulation were correct. With the tools provided with XCSITE 100, you will find this process very easy. If you want to go fancy and record the current and voltage trace with your own data acquisition system (perhaps at a high sampling rate or together with your EEG signals), we now have the PLUS module for you!
Just imagine being able to write in your method section "Stimulation current and voltage waveforms were independently verified for each stimulation session using the log files provided by the XCSITE 100 stimulator (Pulvinar Neuro, Chapel Hill, NC)."
Please reach out to us if you have any questions/comments (also please leave comments below!).
We have now released the PLUS module, an additional device that works in connection with our XCSITE 100 stimulator. We have designed this device based on feedback we got from you! In essence, the device provides two signals (accessible via standard BNC connectors on the front panel). One signal is proportional to the stimulation current and the other signal is proportional to the applied voltage. Both are isolated from the stimulator with optocouplers rated at 4000 Volts.
What can you do with the PLUS module:
(1) Get involved in the discussion of impedance fluctuations and non-linearities
Remember that tDCS/tACS is current stimulation, meaning that the current is pre-defined and the voltage changes such that the correct current is delivered as a function of impedance. The impedance can fluctuate during stimulation (as the contact of the electrodes with the skin changes). Also, a recent paper by the group of Dr. Siegel suggested that there are physiological process that modulate the impedance. Note that this paper has caused quite some debate, including a rebuttal by Dr. Herrmann (full disclosure, a collaborator of the Frohlich Lab). With PLUS module you can track both current and voltage, record it with your preferred data acquisition system, and join the exciting debate!
(2) Study cognitive processes as a function of tACS phase
There are numerous papers suggesting that the phase of the oscillation modulates cognitive performance. Now you can test this hypothesis in a causal way by applying tACS and apply stimuli/trials relative to the phase of the simultaneously recorded stimulation waveform.
(3) Monitor the stimulation in real-time if you do not mind being unblinded about the stimulation condition
The PLUS module gives you the opportunity to monitor both current and voltage in real-time. You can connect it to an oscilloscope or any other device since the connection to the stimulator is isolated from the BNC connectors of the PLUS module.
(4) Record the stimulation waveform together with the EEG for enhanced artifact removal quality
If you are interested in the challenge of recovering the true EEG waveform in presence of a huge stimulation artifact, including the time series of the stimulation current and stimulation voltage into your ICA will likely make a big difference.
(5) What are your ideas?
Let us know and we will happily discuss them with you.
You can now order the PLUS module in our webstore, for a limited time we offer it with a discount to our early pioneers / customers.
We are now selling a new stimulator cable (PN C-5-R-ST-EL) that allows you to split the stimulation current between two electrodes. We developed this cable in collaboration with the Carolina Center for Neurostimulation. One common application is splitting the stimulation current between two electrodes targeting left and right prefrontal cortex (F3 and F4). If you are using XCSITE 100, you only need this additional cable to form a Y-shaped connection together with the cables delivered with XCSITE 100. Please note that the current split with such a cable is not necessarily 50/50 but under most circumstances the split is good enough since resistance pathways are similar. Contact us if you have questions about this.
Here is the setup: