LW - All The Latest Human tFUS Studies by sarahconstantin

The Nonlinear Library

Welcome to The Nonlinear Library, where we use Text-to-Speech software to convert the best writing from the Rationalist and EA communities into audio. This is: All The Latest Human tFUS Studies, published by sarahconstantin on August 10, 2024 on LessWrong. Transcranial focused ultrasound neuromodulation - altering the brain's activity with low-intensity ultrasound - is really exciting . It allows us to manipulate arbitrary regions of the brain without surgery, potentially replacing the (brain-damaging) electrode implants currently used for serious neurological conditions like epilepsy and Parkinson's, and potentially also expanding applications of brain stimulation to milder conditions not worth the risks of brain surgery, like mental illness, addiction, or chronic pain. The field is rapidly growing, and since I wrote my earlier post series there have been quite a few human studies published. Here's a systematic overview of all the human studies published in 2024, by target brain region. Headline Results This year's papers further confirm, to start with, that ultrasound does things to brain activity, if that was still in doubt, and that it is safe enough to run human experiments with (no adverse effects during experiments with small numbers of participants and brief exposures.) There are notably inconsistent results in whether targeting ultrasound to a given brain area increases or decreases neural activity in that area, even in some cases when the same area is targeted with the same sonication parameters! We clearly need to get a better sense of what ultrasound even does. Most studies don't do the obvious (but admittedly expensive) thing of confirming a change in neural activity via a noninvasive measure like fMRI. Those that do, show different results (more activity in the targeted region, less activity in the targeted region, or neither) depending on which region is targeted; this tells us that "tFUS" as a class doesn't have a globally consistent effect on targeted neural activity. Again, still more to learn. However, despite the primitive state of our understanding of this modality, we do already seem to have some strikingly useful results. Ultrasound stimulation of the thalamus seems to be helpful for essential tremor, stimulation of the posterior insula seems to reduce pain sensitivity, and stimulation of the anterior medial prefrontal cortex seems to have quite strong effects on depression. These are before vs. after results without a control group, not randomized controlled studies, but I think they at least warrant followup. I'm not as excited as I'd want to be about Jay Sanguinetti's default-mode-network-inhibition study. The effects seem subtle and game-able; and anecdotally the stories I hear from people who've tried the protocol from his lab are not "I was in a clearly altered state". But all in all, it continues to be a promising field; tFUS clearly does things, some of those things may be useful, and the more data we get, the closer we'll get to an actual model of what it does. Amygdala Chou, et al1 at Harvard Medical School tested tFUS2 on the left amygdalas of 30 healthy volunteers. Compared to sham stimulation, tFUS resulted in less fMRI-measured activity in the amygdala. The amygdala is involved in fear responses, so reducing amygdala activity could have uses in anxiety disorders and phobias. Hoang-Dang, et al3 at UCLA used tFUS4 on the right amygdala of 21 older adults, and found no effect on state anxiety after tFUS, but did show an increase in negative emotional reaction to viewing negative images. There was also a significant increase in heart rate between trials of this mildly stressful task. Since the amygdala is usually active during fear, this suggests that these stimulation parameters may have activated the amygdala…despite the other study using similar parameters and showing a direct decrease in amygdala activity. The UCLA study doesn't mention the duration of tFUS stimulation, which may be a re...