Brain-Machine Interface Device Predicts Internal Speech

New Caltech research is showing how devices implanted into people’s brains, called brain-machine interfaces (BMIs), could one day help patients who have lost their ability to speak. In a new study presented at the 2022 Society for Neuroscience conference in San Diego, researchers demonstrated that they could use a BMI to accurately predict which words a tetraplegic participant was simply thinking (not speaking or miming).


“You may already have seen videos of people with tetraplegia using BMIs to control robotic arms and hands, for example to grab a bottle and to drink from it or to eat a piece of chocolate,” says Sarah Wandelt, a Caltech graduate student in the lab of Richard Andersen, James G. Boswell Professor of Neuroscience and director of the Tianqiao and Chrissy Chen Brain-Machine Interface Center at Caltech. “These new results are promising in the areas of language and communication.”


The new research is the most accurate yet at predicting internal words. In this case, brain signals were recorded from single neurons in a brain area called the supramarginal gyrus, located in the posterior parietal cortex. The researchers had found in a previous study that this brain area represents spoken words.


Now, the team has extended its findings to internal speech. In the study, the researchers first trained the BMI device to recognize the brain patterns produced when certain words were spoken internally, or thought, by the tetraplegic participant. This training period took about 15 minutes. They then flashed a word on a screen and asked the participant to say the word internally. The results showed that the BMI algorithms were able to predict eight words with an accuracy up to 91 percent.


The study, which is in the process of journal submission but is not yet peer reviewed, is titled “Online internal speech decoding from single neurons in a human participant.” It was funded by the National Institutes of Health, the Tianqiao and Chrissy Chen Brain-Machine Interface Center, and the Boswell Foundation. Other Caltech authors besides Wandelt and Andersen include David Bjanes, Kelsie Pejsa, Brian Lee, and Charles Liu. Lee and Liu are Caltech visiting associates who are on the faculty of the Keck School of Medicine at USC.


Read more on the TCCI for Neuroscience website