The company Halo Neuroscience is now offering a device, the Halo-Sport, which they claim enhances sports performance through “neuropriming.” Their website claims:

Neuropriming uses pulses of energy to increase the excitability of motor neurons, benefiting athletes in two ways: accelerated strength and skill acquisition.

Regular readers of SBM can probably see where this is going.

A proper threshold of evidence

Before I get into the details of this product, I want to back up and discuss some basic principles. There is a clear pattern that has played itself out countless times on SBM or with regular authors on SBM in their other outlets. A person, company, or industry makes a clinical medical claim. We examine the evidence and find it wanting, and state so. Believers in the claim then attack us for being shills, closed minded, and/or failing to do our research.

What they almost never do is confront the actual basis of our analysis – a basis that we have painstakingly and exhaustively explored in the pages of SBM. Just two days ago David Gorski wrote yet another article discussing the fact that there is a huge false positive bias in the medical literature, that there is an ongoing issue of quality control in medical science, and pointing to some of the reasons to be skeptical of premature clinical claims.

Our analyses tend to focus on three identifiable areas – plausibility, pre-clinical evidence, and the clinical evidence. Plausibility refers to all of existing scientific findings and how compatible the new claim is with current science. Some claims, such as homeopathy, are so implausible they should be treated as magic. Other claims are entirely plausible, but plausibility, while important, is an insufficient basis for a clinical claim.

Pre-clinical data is also important but insufficient. The real purpose of pre-clinical studies (test tube, petri dish, and animal studies) is to see if an intervention is likely to be safe and effective before committing to clinical studies in humans. It should not be used as a basis for clinical claims, however.

There are many reasons for this. Biology is complex and it is difficult to impossible to reliably extrapolate from a basic-science phenomenon to a net clinical effect. Even if we properly identify a clinical effect, it is difficult to know what the magnitude of that effect will be in a living biological system (a person). There may be compensatory mechanisms in play, even to the point of having a net harmful effect. There may be unknown side effects or interactions. Finally, disease states may not respond the same way as healthy states.

Clinical evidence is what we need as a proper basis for clinical claims – this intervention will have this net health effect. Clinical evidence is also complex. There are observational studies, experimental studies, meta-analyses, and systematic reviews. Most clinical studies are preliminary (small studies of weak methodological rigor), and most will turn out to be wrong.

The question then becomes – what is the threshold of clinical evidence that must be crossed before a clinical claim should be accepted as probably true and either approved for the market or used by practitioners? This is a complex question, the very question we often explore here at SBM, but our answer can be summarized as – the threshold should be higher than it often is.

The threshold of sufficient clinical evidence should depend in part on plausibility, or prior probability. It should take more clinical evidence to persuade the community that our basic understanding of biology needs to be adjusted than it takes to establish a slightly different use of a medication from the one that is already proven.

However, as a general rule, we like to see multiple independent studies with large sample sizes, rigorous methodology, with consistent results that are both statistically and clinically significant. These studies should be using the proper outcome measures, proper endpoints, proper comparisons, adequate blinding, reasonable dropout rates, controlling for the proper variables, and addressing the appropriate clinical questions. In other words, there are lots of ways for a clinical study to fail, and we don’t put much faith in them until they have gone through the meat grinder of expert review.

The evidence for tDCS and learning

Halo Neuroscience is claiming that using transcranial direct current stimulation (tDCS, which I have discussed before) to stimulate the motor cortex will enhance the results of training.

The plausibility of this claim is moderate – it is reasonable, but not a home run. A 2016 study, published just last month, summarized the current evidence this way:

The effects of transcranial direct current stimulation (tDCS) on brain functions and the underlying molecular mechanisms are yet largely unknown.

This was the preamble to a mouse study in which they found:

Here we report that mice subjected to 20-min anodal tDCS exhibited one-week lasting increases in hippocampal LTP, learning and memory.

Again – reasonable plausibility, but there is still much that is unknown. The unknowns matter. How much current at what frequency do we give to what part of the brain and for how long? These are not trivial questions, they are vital.

Clearly there is stuff happening in the brain that can be plausibly beneficial, but is it beneficial, how long do the effects last, what are the long term effects? We may be enhancing learning in the short term, but burning out those neurons in the long term.

Published clinical research is a mixed bag, the kind of mixed bag that is compatible with no effect, but does not rule out a real effect either. I wrote recently about a study of tDCS and pilot training that was widely reported as positive, but shockingly was an essentially negative study. They specifically looked at motor cortex stimulation during pilot training and found no effect whatsoever.

A 2016 systematic review (which does not include the above study) looking at motor cortex stimulation and learning found:

Therefore, our findings suggest that application of M1 a-tDCS across the three or five consecutive days can be helpful to improve motor sequence learning.

Evidence is preliminary, but encouraging. There are separate studies looking at stimulating the cerebellum, and others looking at stimulating other areas of the brain involved in memory.

Looking at all the evidence, I am hopeful. I think that overall using electrical or magnetic stimulation to affect brain function is highly plausible, and will likely become a new paradigm of neurological intervention into the future.

However, we are in the early stages of clinical research. There are many questions that need to be answered, and we need to fine tune the details of the intervention to optimize any clinical effect.

We are not yet ready, in my opinion, for devices marketed to consumers. We are in a similar stage as with stem cells – plausible, exciting even, and we are making progress but we are not yet there for many potential applications.

Halo Neuroscience claims to have done in-house studies, but they are not peer-reviewed and therefore cannot be used to support claims.

Conclusion: evidence for tDCS is mixed but encouraging

Using tDCS to enhance learning and training is plausible, and the early clinical studies are mixed but encouraging, but in my opinion we are not yet across the threshold of evidence where marketing claims to the public is justified.

There is no mention on the Halo website that they have FDA approval for the device. The company does make another device that is implantable and used to treat epilepsy, and they proclaim that this device is FDA approved, so it seems likely that if their Halo-Sport device were also FDA approved they would say so.

I have found that the FDA has a very low threshold for electronic devices, probably because they are not drugs, especially if they are not implanted. I would not be surprised if the FDA does approve the device, even with very preliminary evidence. But they have apparently not done so yet.

My advice to consumers is to be skeptical of the marketing claims. We are simply not there yet with the clinical evidence.

Posted by Steven Novella

Founder and currently Executive Editor of Science-Based Medicine Steven Novella, MD is an academic clinical neurologist at the Yale University School of Medicine. He is also the host and producer of the popular weekly science podcast, The Skeptics’ Guide to the Universe, and the author of the NeuroLogicaBlog, a daily blog that covers news and issues in neuroscience, but also general science, scientific skepticism, philosophy of science, critical thinking, and the intersection of science with the media and society. Dr. Novella also has produced two courses with The Great Courses, and published a book on critical thinking - also called The Skeptics Guide to the Universe.