A brain-computer interface (BCI) is a system that establishes a direct communication or control pathway between the brain and an external device, bypassing conventional motor or peripheral pathways. The field splits on two fundamental axes: invasive vs non-invasive recording, and medical vs consumer application.
Invasive BCIs — electrodes implanted into or on cortical tissue. Electrocorticography (ECoG) grids sit on the brain surface (subdural); microelectrode arrays (MEAs, e.g. Utah Array, Neuralink N1) penetrate cortex to record single-unit action potentials, giving the highest spatial resolution (~100 µm). Signal quality degrades over months to years due to glial scarring (the foreign-body response to implanted materials). See Invasive BCI (Neuralink, Synchron, Paradromics).
Non-invasive BCIs — scalp EEG, fNIRS, MEG. Millimetre-to-centimetre spatial resolution; millisecond temporal resolution for EEG. EEG’s ~20 µV signals are two to three orders of magnitude weaker than implanted recordings and are blurred by skull. See Non-Invasive BCI (EEG, in-ear, NIRS).
The signal modalities determine application space: high-bandwidth motor prosthetics and direct speech decoding require implanted electrodes. Attention monitoring, emotion detection, and AR/VR interaction (AR/VR) are accessible with non-invasive approaches. Bioelectronic medicine (Bioelectronic Medicine (vagus nerve, DBS)) closes-the-loop by using implanted electrodes to stimulate peripheral nerves (vagus, sciatic) for therapeutic effect in inflammatory disease, epilepsy, and pain.
Investment relevance: medical BCIs follow a long regulatory path (FDA PMA for implantables). Consumer-grade applications — hearables (Hearables / Silent-Speech Interfaces), AR/VR neural input, silent-speech interfaces — have shorter paths but harder monetisation. The semiconductor opportunity is in ultra-low-power analog front-ends (AFEs) capable of 1,000+ channel recording with on-chip spike sorting.
Frontier
- Can flexible ECoG arrays achieve high channel-count, long-lifetime motor prosthetics without open-skull surgery?
- What is the signal-fidelity ceiling for non-invasive EEG at scalp, and can dry electrodes close the gap?
- How do FDA/CE regulatory pathways shape the viable BCI entry point — medical vs consumer first?