Decoding spoken words using local field potentials recorded from the cortical surface

TLDR

Locked‑in syndrome caused by ALS or brainstem damage leaves patients fully aware but severely paralyzed, restricting communication to slow letter or word selection. The study aims to enable faster, more intuitive communication by directly interfacing with language areas of the cerebral cortex. A grid of closely spaced, nonpenetrating micro‑electrodes recorded local field potentials from the surface of face motor cortex and Wernicke’s area. The recorded LFPs allowed trial‑by‑trial classification of a small set of words above chance, with word‑specific electrode patterns indicating independent processing assemblies, supporting the use of cortical surface potentials for brain‑computer interfaces and potential communication restoration in locked‑in patients.

Abstract

Pathological conditions such as amyotrophic lateral sclerosis or damage to the brainstem can leave patients severely paralyzed but fully aware, in a condition known as 'locked-in syndrome'. Communication in this state is often reduced to selecting individual letters or words by arduous residual movements. More intuitive and rapid communication may be restored by directly interfacing with language areas of the cerebral cortex. We used a grid of closely spaced, nonpenetrating micro-electrodes to record local field potentials (LFPs) from the surface of face motor cortex and Wernicke's area. From these LFPs we were successful in classifying a small set of words on a trial-by-trial basis at levels well above chance. We found that the pattern of electrodes with the highest accuracy changed for each word, which supports the idea that closely spaced micro-electrodes are capable of capturing neural signals from independent neural processing assemblies. These results further support using cortical surface potentials (electrocorticography) in brain–computer interfaces. These results also show that LFPs recorded from the cortical surface (micro-electrocorticography) of language areas can be used to classify speech-related cortical rhythms and potentially restore communication to locked-in patients.