Speech neuroprosthesis for anarthria (Moses, 2021)

One-line verdict: A surface-array speech decoder. Slow and limited to 50 words, but with signals that stayed stable over 81 weeks.

Quick tags: Recording · Cortical surface · Human · NEJM 2021 (385:217-227)

Overview

What it is: A neuroprosthesis for decoding speech in a paralyzed person with anarthria (loss of the ability to articulate speech) and spastic quadriparesis from a brainstem stroke. It uses electrocorticography with custom decoding techniques. An FDA investigational device exemption covered the device.

Hardware: A customized combination of a high-density ECoG electrode array (manufactured by PMT) and a percutaneous connector (manufactured by Blackrock Microsystems). The rectangular array is 6.7 cm long, 3.5 cm wide and 0.51 mm thick, with 128 flat disk-shaped electrodes. It lies on the pial surface in the subdural space, covering several speech-related cortical regions. The connector passes signals through the skin to a detachable digital link and cable, so this is a wired system.

Study: Over 48 sessions, 22 hours of cortical activity were recorded as the participant attempted to say individual words from a 50-word vocabulary. The isolated-word task had 9,800 trials.

Results (as reported): Sentences were decoded in real time at a median 15.2 words per minute, with a median word error rate of 25.6% using a language model (60.5% without one). The lowest word error rate for a single sentence block was 7.0%. In post hoc analyses, 98% of attempts to produce individual words were detected, and words were classified with 47.1% accuracy using cortical signals that were stable throughout the 81-week study period.

Limits: One participant, a 50-word vocabulary, and a percutaneous connector.

Spec Card Grid

Identity

• Paper: “Neuroprosthesis for decoding speech in a paralyzed person with anarthria,” N Engl J Med 2021;385:217-227
• Participant: one person with brainstem stroke

Architecture

• Array: 128 electrodes, 6.7 cm by 3.5 cm by 0.51 mm, subdural, made by PMT
• Connector: percutaneous, Blackrock Microsystems
• Vocabulary: 50 words

Results

• Real-time sentences: median 15.2 words per minute, 25.6% word error rate with language model
• Stability: signals stable across the 81-week study period

Evidence and limits

• Not covered here: electrode diameter and pitch; no 3D model yet
• Related: the 2023 surface-array speech neuroprosthesis entry

References

• Moses DA, Metzger SL, Liu JR, et al. Neuroprosthesis for decoding speech in a paralyzed person with anarthria. N Engl J Med. 2021;385:217-227. https://www.nejm.org/doi/full/10.1056/NEJMoa2027540