March 24th 2021
Advanced brain-controlled neural prosthetics require electrodes to be inserted into the brain—which involves significant-risk open-brain surgery that causes acute and chronic local tissue damage—until now. A proof of concept study published in the journal Neuron, using two rhesus macaques, has demonstrated a minimally invasive approach, using functional ultrasound (fUS), for the control of movement and planning. The technique still requires removing a small piece of skull, does not involve opening the brain’s protective membrane.
According to Sumner Norman, a co-first author of the study:
“Invasive forms of brain–machine interfaces can already give movement back to those who have lost it due to neurological injury or disease. Unfortunately, only a select few with the most severe paralysis are eligible and willing to have electrodes implanted into their brain. Functional ultrasound is an incredibly exciting new method to record detailed brain activity without damaging brain tissue.”
The technology was developed with the aid of non-human primates, who were taught to do simple tasks that involved moving their eyes or arms in certain directions when presented with certain cues. As the primates completed the tasks, the fUS measured brain activity in a region of the brain involved in planning movement. To validate the accuracy of fUS, the researchers compared brain imaging activity from fUS to previously obtained detailed electrophysiology data.
Next, the team aimed to see if the activity-dependent changes in the fUS images could be used to decode the intentions of the non-human primate, even before it initiated a movement. The ultrasound imaging data and the corresponding tasks were then processed by a machine-learning algorithm, which learned what patterns of brain activity correlated with which tasks. Once the algorithm was trained, it was presented with ultrasound data collected in real time from the non-human primates.
Excitingly, the algorithm predicted, within a few seconds, what behavior the non-human primate was going to carry out (eye movement or reach), direction of the movement (left or right), and when they planned to make the movement.
A collaboration is in the works to study the technology with human volunteers who, because of traumatic brain injuries, have had a piece of skull removed. Because ultrasound waves can pass unaffected through these “acoustic windows,” it will be possible to study how well functional ultrasound can measure and decode brain activity in these individuals.
This research demonstrates nicely the integral role that animal research plays in human health and disease—in this case with regards to evaluation of proof-of-principle and efficacy prior to trials in humans.
~Speaking of Research
*Taken from the press release from Caltech and edited for style and content.