Controlling Brain Function With Wearables
A big part of the research in my lab focuses on how rhythmic sensory stimulation can influence brain function, a process known as sensory entrainment. For example, presenting light flashes and pulses of white noise about 5 times a second (a frequency known as theta, which is linked to memory processes) can improve learning in lab studies. Other labs have shown that entrainment at different frequencies can deepen sleep and may even reduce the buildup of toxic proteins in the brain. An exciting thing about this technology is that because it’s so noninvasive, it has the potential for easy use in daily life. Could we perhaps make a wearable that lets you entrain theta oscillations while sitting in class, to help you remember the material better? Or entrains slow oscillations at night to boost your sleep?
The current systems we use in the lab entrain brainwaves through pulses of light and rhythmic white noise. But there’s another potential way to do it: using vibrations applied to the skin, which is already possible with many wearable devices. Because entrainment happens as a result of the brain processing stimuli, there’s every reason to think that a wearable vibration device should provide an easy, non-intrusive way of influencing brain activity. To test this, I recorded some of my brainwaves while using an OpenHaptic stimulator attached to my ankle. I tested entrainment at two frequencies: theta at 5 Hz (associated with memory) and alpha at 10 Hz (associated with relaxation and mind-wandering). To measure the effects, I recorded EEG using a Muse headset while I listened to audiobooks with my eyes closed. Results To look at how stimulation affected brain activity, I computed the power spectrum of the EEG--a graph which shows how much brain activity is present at each frequency. I compared the EEG from all of the “vibration on” periods to the EEG during the baseline periods, where stimulation was turned off. These graphs are shown below.When alpha stimulation was on (green line), I saw more alpha oscillations than it was off (gray line). The alpha stimulation also appeared to reduce the amount of theta oscillations between 4 and 8 Hz
The Muse has four independent sensors, and breaking down the data by electrode location it’s clear that there’s two things going on: alpha entrainment mostly increased alpha oscillations over the frontal areas, and mostly suppressed theta oscillations over the posterior areas (directly behind the ear)
The data for theta stimulation is similar--stimulation increased power in the broad theta band (4-8 Hz), peaking at around 7 Hz. Unlike alpha, the increases were most pronounced on the rear sensors.
Update 2/26 I also recorded some data in a similar protocol using a Fitbit Sense with 7 H stimulation. Much like with the OpenHaptic, we see a clear peak at the entrainment frequency--which suggests that commercial wearables can also be used for this kind of entrainment!
Conclusions
I think this is a pretty interesting proof of concept for sensory entrainment with a wearable device--suggesting that an unobtrusive, wrist-or ankle worn device can increase brain oscillations at targeted frequencies.
This also suggests that wearable devices might be help to produce some of the behavioral and health benefits associated with brainwave entrainment--such as increasing learning ability with theta stimulation. However, this is something that will still have to be tested, as stimulation with a wearable device is not exactly the same as the stimulation protocols used in labs.
Finally, it seems like these effects can be produced by a wide range of devices, including both the open-source OpenHaptic device and commercial werables like the Fitbit Sense. Some software is available to do this includes OpenWave, which is available for Wear OS and Fitbit smartwatches. A similar app called NeuroStrobe is also available for Android phones.