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Representation of internal speech by single neurons in human supramarginal gyrus

Author

Listed:
  • Sarah K. Wandelt

    (California Institute of Technology
    California Institute of Technology)

  • David A. Bjånes

    (California Institute of Technology
    California Institute of Technology
    Rancho Los Amigos National Rehabilitation Center)

  • Kelsie Pejsa

    (California Institute of Technology
    California Institute of Technology)

  • Brian Lee

    (California Institute of Technology
    Keck School of Medicine of USC
    Keck School of Medicine of USC)

  • Charles Liu

    (California Institute of Technology
    Rancho Los Amigos National Rehabilitation Center
    Keck School of Medicine of USC
    Keck School of Medicine of USC)

  • Richard A. Andersen

    (California Institute of Technology
    California Institute of Technology)

Abstract

Speech brain–machine interfaces (BMIs) translate brain signals into words or audio outputs, enabling communication for people having lost their speech abilities due to diseases or injury. While important advances in vocalized, attempted and mimed speech decoding have been achieved, results for internal speech decoding are sparse and have yet to achieve high functionality. Notably, it is still unclear from which brain areas internal speech can be decoded. Here two participants with tetraplegia with implanted microelectrode arrays located in the supramarginal gyrus (SMG) and primary somatosensory cortex (S1) performed internal and vocalized speech of six words and two pseudowords. In both participants, we found significant neural representation of internal and vocalized speech, at the single neuron and population level in the SMG. From recorded population activity in the SMG, the internally spoken and vocalized words were significantly decodable. In an offline analysis, we achieved average decoding accuracies of 55% and 24% for each participant, respectively (chance level 12.5%), and during an online internal speech BMI task, we averaged 79% and 23% accuracy, respectively. Evidence of shared neural representations between internal speech, word reading and vocalized speech processes was found in participant 1. SMG represented words as well as pseudowords, providing evidence for phonetic encoding. Furthermore, our decoder achieved high classification with multiple internal speech strategies (auditory imagination/visual imagination). Activity in S1 was modulated by vocalized but not internal speech in both participants, suggesting no articulator movements of the vocal tract occurred during internal speech production. This work represents a proof-of-concept for a high-performance internal speech BMI.

Suggested Citation

  • Sarah K. Wandelt & David A. Bjånes & Kelsie Pejsa & Brian Lee & Charles Liu & Richard A. Andersen, 2024. "Representation of internal speech by single neurons in human supramarginal gyrus," Nature Human Behaviour, Nature, vol. 8(6), pages 1136-1149, June.
  • Handle: RePEc:nat:nathum:v:8:y:2024:i:6:d:10.1038_s41562-024-01867-y
    DOI: 10.1038/s41562-024-01867-y
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    References listed on IDEAS

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    1. Francis R. Willett & Erin M. Kunz & Chaofei Fan & Donald T. Avansino & Guy H. Wilson & Eun Young Choi & Foram Kamdar & Matthew F. Glasser & Leigh R. Hochberg & Shaul Druckmann & Krishna V. Shenoy & Ja, 2023. "A high-performance speech neuroprosthesis," Nature, Nature, vol. 620(7976), pages 1031-1036, August.
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