BCI glossary

The terms that come up in every BCI paper, press release and trial listing, defined so they stand on their own.

• Brain-computer interface (BCI)

  A brain-computer interface (BCI) is a system that records activity from the brain, translates it with software into commands, and uses those commands to control an external device such as a computer cursor, robotic arm, or speech synthesizer, without relying on the body's muscles or nerves.

• EEG vs intracortical recording

  EEG versus intracortical recording describes the main tradeoff in brain-computer interfaces: EEG measures brain activity noninvasively through electrodes on the scalp, while intracortical recording uses electrodes surgically inserted into the cortex to detect the firing of individual neurons, giving far more detailed signals at the cost of brain surgery.

• Electrocorticography (ECoG)

  Electrocorticography (ECoG) is a method of recording the brain's electrical activity using a thin sheet of electrodes placed directly on the surface of the cortex, under the skull, without penetrating brain tissue.

• Endovascular BCI

  An endovascular BCI is a brain-computer interface whose electrodes are delivered through the blood vessels, typically on a stent-like mesh placed in a vein next to the brain, so that brain signals can be recorded without opening the skull.

• Neural decoder

  A neural decoder is the software model in a brain-computer interface that translates recorded brain activity into an intended output, such as a cursor velocity, a letter, a phoneme, a word, or sound, usually by learning the mapping from examples collected from the user.

• Neural signal drift

  Neural signal drift is the gradual or sudden change in recorded brain signals over hours, days, or months, caused by factors such as tiny electrode movements, tissue reactions, and changes in the brain itself, which makes a BCI decoder trained on earlier data become less accurate.

• Phoneme decoding

  Phoneme decoding is the approach, used by leading speech neuroprostheses, of translating brain activity into a sequence of phonemes, the small units of sound that distinguish words, and then assembling those phonemes into words and sentences with a language model.

• Speech neuroprosthesis

  A speech neuroprosthesis is a brain-computer interface that decodes neural activity from speech-related areas of the brain while a person attempts to speak, and converts it into text, synthesized voice, or an animated face, to restore communication for people who have lost the ability to speak because of paralysis.

• Spike sorting

  Spike sorting is the computational process of detecting brief electrical pulses (spikes, or action potentials) in a microelectrode recording and assigning each spike to the individual neuron most likely to have produced it, based on the shape of its waveform.

• Utah array

  The Utah array is a small, square grid of silicon microneedle electrodes, about 4 mm across, that is implanted into the surface of the cortex to record the electrical activity of individual neurons or small groups of neurons.