With rapidly mounting evidence that direct manipulation of brain rhythms in the cortex could prove useful in treating psychiatric disorders, the question has remained how that can be done. Current technologies that apply stimulation to alter neural oscillations don’t account for the phase of the brainwaves and often end up changing the power of other rhythms.

In a 2018 study in PLOS ONE, Picower Professor Earl Miller and former postdoc Alik Widge, now at the University of Minnesota, demonstrated the initial success of a new “closed loop” system that directly read directly reads out the rhythm to be altered, locks onto its phase and then delivers stimulation directly tuned to that target phase. They key is using analog feedback circuits, which can act much more quickly in closing a feedback loop.

In the paper Miller and Widge’s team showed that with 10 seconds of stimulation delivered via scalp electrodes to the prefrontal cortex of an animal they could produce a small but significant increase in the power of the animal’s own endogenous alpha rhythms (between 8-15 Hz) for another second afterward. The stimulation increased power when open-loop stimulation did not, and it also did not affect other rhythms.

The study was a “proof of concept” in that the effect, while significant, was small. That may be because the duration of stimulation was much briefer than clinical sessions with other technologies where stimulation can last 20 minutes. Widge and Miller continue to develop it and have filed a patent application.

Above: The bandpass filter used for feedback-driven neurostimulation.