Physics / mechanism
Invasive BCI places electrodes in direct contact with neural tissue to record action potentials or local field potentials with sub-millisecond temporal resolution and single-neuron spatial resolution. Three main insertion paradigms: Utah array (96–1024 electrodes, 400 µm pitch, silicon substrate), Neuralink’s “threads” (~1024 channels, flexible polyimide, robotic insertion to minimize gliosis), and Synchron’s Stentrode (endovascular, ~16 electrodes, no craniotomy). Signal chain: electrode → impedance matching amplifier → ADC (typically 16-bit, 20–30 kSps per channel) → compression/spike-sorting → wireless telemetry. Bandwidth bottleneck is the transcutaneous wireless link; Neuralink’s N1 chip targets ~1 Mbps. Chronic recording stability degrades over 6–24 months due to foreign body response and electrode impedance drift. Paradromics pursues high-channel-count cortical surface arrays targeting 1M+ electrodes long-term.
Competitive landscape
Non-invasive EEG competes on safety and cost but delivers ~64–256 channels, poor spatial resolution (~cm vs. µm), and no single-unit access. ECoG sits between—subdural grid, ~1mm resolution, used clinically. fNIRS and fMRI are research tools, not real-time BCI substrates. MEG offers good temporal resolution but zero implantability.
Companies using
Connected ideas
Sources
Frontier (open questions)
- To be added.