Information bandwidth of a BCI
The rate, in bits per second, at which information actually crosses the interface — as opposed to the raw data rate of the electronics. It is usefully split into an input side (how many bits about the brain's state the recording resolves per second) and an output side (how many bits of intended command a decoder delivers), and the two can differ by orders of magnitude.
A hard, often-missed point is the asymmetry between raw data and information. A thousand-channel probe streams hundreds of megabits per second of voltage, yet the best communication and control BCIs deliver on the order of only a few bits per second of intended command — the handwriting and speech neuroprostheses being among the fastest. The gap reflects redundancy in neural signals, noise, and the limited entropy of the user's intent, and it is why channel count alone is a poor proxy for capability.
Communication BCIs are still measured in a few bits per second: Wolpaw-style information transfer rates for spellers, and tens of words per minute for the fastest handwriting and speech decoders — orders of magnitude below the hundreds of megabits per second the electronics stream.
Raw data rate and information rate are not the same number.