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231 terms · one sentence each, more where it helps

Glossary

Every dotted term on the site points here. Each entry is one plain sentence first. Where the one sentence hides something important, a second paragraph follows. Entries also say where the term is first introduced and which lessons use it.

Phase 0: Orientation

Biodesign#
Stanford's process for medical technology innovation that starts from an observed clinical need rather than a technology looking for a use.Related: Needs finding, Need statementUsed in: The six spines, and why you need one, Needs finding, The reading track, Career forks
CITI training#
The online human-subjects research course most universities require before you can touch participant data.Related: Institutional review board (IRB)Used in: The safety charter, Project D: Your own ERPs
Common-mode rejection ratio (CMRR)#
How much better an amplifier responds to a difference between its inputs than to a signal shared by both, in decibels; 100 dB means 100,000 times.
MoreA high CMRR is necessary but not sufficient. If the two electrodes have different impedances, the common-mode hum is turned into a real difference at the amplifier's inputs, and no amount of amplifier quality can remove it. That is why electrode preparation matters as much as the chip.
Related: Common-mode signal, Electrode impedanceUsed in: The six spines, and why you need one, How to read a datasheet, Why so small?, Project B: Reverse-engineer a bought board, Project D: The phantom head
Deep brain stimulation (DBS)#
Electrodes implanted deep in the brain and pulsed continuously, the standard treatment for advanced Parkinson's disease and essential tremor.Related: Charge densityUsed in: The six territories of neuroengineering, What was that sound?, Where oscillations come from, A reading order for Kandel, Neuromodulation, mechanisms and evidence
Design controls#
FDA's required process for developing a medical device: user needs, requirements, design, verification, validation, and the records of all of it.Related: Design history file (DHF), Requirements, Verification, ValidationUsed in: The six spines, and why you need one, Project A: A speller for someone with ALS, Design controls and the design history file, The reading track, Career forks
Design history file (DHF)#
The complete record of how a device was designed, showing every requirement traced to a test; writing a mock one teaches more than any lecture.Related: Design controlsUsed in: The six spines, and why you need one, Design controls and the design history file, Career forks
Driven-right-leg circuit#
A third electrode fed with an inverted copy of the common-mode signal, so the body's hum is actively cancelled instead of merely rejected.
MoreThe name comes from ECG, where the third electrode went on the right leg. In EEG it usually goes on the earlobe or forehead. It is a feedback loop: measure the average of the two inputs, invert, amplify, drive the body with it. Done right it buys 30 to 40 dB of extra hum rejection.
Related: Common-mode signal, Ground electrodeUsed in: The notebook, and the build log, How to read a datasheet, Project B: One channel of you, Project C: Muscle to motion, Project D: Eyes as a joystick
Electrocorticography (ECoG)#
Recording from electrodes placed on the surface of the brain under the skull, usually during epilepsy surgery evaluation; cleaner and sharper than EEG.Related: Electroencephalography (EEG), Intracortical recording, ECoG gridUsed in: The six territories of neuroengineering, Electrode materials and the foreign body response
Electrode#
The conductor that turns ion currents in tissue into electron currents in a wire; its chemistry and contact quality set the noise you live with.Related: Silver/silver-chloride (Ag/AgCl), Electrode impedance, Half-cell potentialUsed in: The six territories of neuroengineering, The six spines, and why you need one, Why being in Utah changes the plan, Set up a bench, The safety charter
Electroencephalography (EEG)#
Recording the brain's electrical activity from electrodes on the scalp, a few tens of microvolts of blurred, summed cortical activity.Related: Electrocorticography (ECoG), Magnetoencephalography (MEG), Volume conduction, Microvolt (µV)Used in: The six territories of neuroengineering, Set up a bench, The notebook, and the build log, How to read a datasheet, Project B: One channel of you
Extracellular recording#
Recording with an electrode near neurons rather than inside one; you see small, fast blips from nearby cells rather than the full membrane swing.Related: Spike, Local field potential (LFP), Intracortical recordingUsed in: The six territories of neuroengineering, Project A: The SpikerBox, What was that sound?
FDA device classes#
Class I is low risk (a tongue depressor), Class II moderate (most EEG amplifiers), Class III highest (implanted BCIs), each with heavier review.Related: 510(k), Premarket approval (PMA), De NovoUsed in: The six spines, and why you need one, Regulatory pathways
Focused ultrasound#
Concentrating sound energy deep in the brain to modulate or destroy tissue without opening the skull.Used in: The six territories of neuroengineering, Neuromodulation, mechanisms and evidence, The industry landscape
Foreign body response#
The scarring the body builds around an implant, which insulates electrodes and degrades recordings over months to years.Related: Intracortical recordingUsed in: The six territories of neuroengineering, Synapses and plasticity, Project E: Intracortical data, Electrode materials and the foreign body response
Functional near-infrared spectroscopy (fNIRS)#
Shining near-infrared light through the scalp and measuring how much comes back to estimate blood oxygenation in the cortex underneath; a pulse oximeter pointed at the brain.Related: Electroencephalography (EEG)Used in: The six territories of neuroengineering, The safety charter, Project C: Other windows on the brain, The industry landscape
Haptic feedback#
Information delivered through touch, such as vibration on the skin that tells a prosthesis user how hard they are gripping.Used in: The six territories of neuroengineering, Sensory systems as prosthesis targets, Project E: Haptic feedback for a prosthetic hand, Competitions: Bench to Bedside, DEBUT, and RESNA
Hermetic packaging#
Sealing implanted electronics against body fluid for decades, one of the hardest unsolved engineering problems in the field.Used in: The six spines, and why you need one, Packaging, power, and telemetry
Human factors#
Designing so the device fits how people actually behave, especially under stress and fatigue, so that errors are hard to make.Related: IEC 62366, Use errorUsed in: The six spines, and why you need one, Project A: A speller for someone with ALS, Human factors and use error, The industry landscape, Career forks
IEC 60601#
The safety standard for medical electrical equipment, including how much current may leak into a patient (microamps).Related: Leakage current, Electrical isolationUsed in: The safety charter, Project B: One channel of you, Why the hum?, Electrical safety, with the numbers, KiCad to JLCPCB
Input bias current#
The tiny current an amplifier input draws; through a high electrode impedance it produces an offset and noise.Related: Input impedanceUsed in: How to read a datasheet
Input impedance#
How hard the amplifier's inputs are to push current into; it must be far higher than the electrode impedance or the signal is lost in the divider.Related: Electrode impedance, Input bias currentUsed in: How to read a datasheet, Project B: One channel of you, Why so small?, Instrumentation amplifiers, properly
Instrumentation amplifier#
A precision differential amplifier with very high input impedance and high CMRR, built from three op-amps and sold as a single chip such as the INA128 or AD8232.Related: Differential measurement, Common-mode rejection ratio (CMRR), Input impedanceUsed in: Set up a bench, How to read a datasheet, Project A: The SpikerBox, Project B: One channel of you, Project C: Muscle to motion
Intracortical recording#
Recording from tiny electrodes inserted into the cortex itself, close enough to hear individual neurons.Related: Utah Array, Extracellular recordingUsed in: The six territories of neuroengineering, Project E: Large-scale neural data, Privacy, neuroethics, and the abandoned implant, Project E: Intracortical data
ISO 14971#
The international standard for medical device risk management that every company follows.Related: FMEAUsed in: The safety charter, Risk management and the FMEA
JLCPCB#
A Chinese board house that fabricates and assembles small-run PCBs for a few dollars, the standard for student projects.Related: Printed circuit board (PCB)Used in: Set up a bench, Project A: The ADS1299 board, KiCad to JLCPCB
Leakage current#
Current that flows into the patient through unintended paths; limited to tens of microamps for anything touching the body.Related: IEC 60601, Electrical isolationUsed in: The safety charter, Electrical safety, with the numbers
Magnetoencephalography (MEG)#
Recording the tiny magnetic fields produced by cortical currents with superconducting sensors in a shielded room; less blurred by the skull than EEG, and far more expensive.Related: Electroencephalography (EEG)Used in: The six territories of neuroengineering, Event-related potentials and oscillations, Project B: The forward and inverse problems, The math track
Microvolt (µV)#
One millionth of a volt. Scalp EEG is tens of microvolts; a AA battery is 1.5 million of them.Related: GainUsed in: The six territories of neuroengineering, Why so small?
Myoelectric prosthesis#
An artificial limb controlled by EMG from the remaining muscles.Related: Electromyography (EMG)Used in: The six territories of neuroengineering, Project C: Muscle to motion, Project E: Haptic feedback for a prosthetic hand
Needs finding#
Observing clinical work to catch the moments that are slow, awkward, or unsafe, before proposing any solution.Related: BiodesignUsed in: The six spines, and why you need one, Needs finding
Notch filter#
A very narrow filter that removes one frequency, usually 60 Hz mains hum; it also rings and distorts nearby content, so fix the hum at the source first.Related: Filter, Common-mode signalUsed in: How to read a datasheet, Project A: The SpikerBox, Project B: One channel of you, Project C: Muscle to motion, Why the hum?
PhysioNet#
A free archive of physiological recordings including EEG, ECG, and sleep data, run out of MIT.Related: Sleep-EDFUsed in: Set up a bench, Project B: One channel of you, Project E: The zero-dollar version, Alpha and the back of the head, Python for signals
Printed circuit board (PCB)#
The board that holds and connects your components; designing one is how a breadboard prototype becomes an instrument.Related: KiCad, JLCPCBUsed in: Set up a bench, KiCad to JLCPCB
Recall#
A correction or removal of a marketed device; FDA's public database of them is a catalogue of how designs fail people.Used in: The six spines, and why you need one, Project E: The sleep band, Sleep neuroscience, Design controls and the design history file, Risk management and the FMEA
Sampling rate#
How many measurements per second the ADC takes; EEG is usually 250 to 1000 per second.Related: Nyquist frequency, AliasingUsed in: How to read a paper, What the spectrum did, Analog to digital
SpikerBox#
Backyard Brains' small battery amplifier that lets you hear action potentials from a cockroach leg on a speaker; easy to build yourself.Related: Action potential, Instrumentation amplifierUsed in: Set up a bench, The safety charter, Project A: The SpikerBox, Project B: One channel of you, A reading order for Kandel
Spinal cord stimulation (SCS)#
Electrodes over the spinal cord, long used for pain and now being used to restore stepping after spinal cord injury.Used in: The six territories of neuroengineering, Neuromodulation, mechanisms and evidence, Packaging, power, and telemetry
Stentrode#
Synchron's electrode array mounted on a stent and delivered through a blood vessel to sit against the motor cortex without open surgery.Used in: The six territories of neuroengineering, Electrode materials and the foreign body response, The industry landscape
Transcranial direct current stimulation (tDCS)#
Passing a milliamp or two through the head between sponge electrodes; trivially easy to build, weakly supported by evidence, and not for self-experiment.Related: Transcranial magnetic stimulation (TMS)Used in: The safety charter, Neuromodulation, mechanisms and evidence
Transcranial magnetic stimulation (TMS)#
A coil on the head that induces currents in the cortex with a brief magnetic pulse; approved for depression, and only for lab use with a trained operator.Related: Transcranial direct current stimulation (tDCS)Used in: The six territories of neuroengineering, The safety charter, Neuromodulation, mechanisms and evidence, The industry landscape
Utah Array#
The 10-by-10 grid of 1.5 mm silicon needles invented at the University of Utah, the electrode in nearly every human intracortical BCI study to date.Related: Intracortical recording, Utah Slanted Electrode Array (USEA)Used in: The six territories of neuroengineering, Why being in Utah changes the plan, Project E: Intracortical data, Electrode materials and the foreign body response, Packaging, power, and telemetry
Vagus nerve stimulation (VNS)#
A cuff electrode on the vagus nerve in the neck, pulsed for epilepsy, depression, and now stroke rehabilitation.Used in: The six territories of neuroengineering, Neuromodulation, mechanisms and evidence, The industry landscape
Verification#
Testing that the device meets its requirements; did you build what you specified.Related: ValidationUsed in: Why being in Utah changes the plan, The characterization report, Design controls and the design history file

Phase 1: First contact

Action potential#
The brief, all-or-nothing voltage spike a neuron fires, about a millisecond long and about 100 millivolts tall across its membrane.
MoreSodium channels open and the inside of the cell swings positive; potassium channels open and it swings back. From outside the cell, with an electrode nearby, you see a much smaller, faster blip, which is what a SpikerBox amplifies into a click.
Related: Membrane potential, Ion channel, Spike, Extracellular recordingUsed in: Project A: The SpikerBox, What was that sound?, Project A: Neurons from the equations up, Neuron biophysics, A reading order for Kandel
Active electrode#
An electrode with a small amplifier or buffer built into it, so the high-impedance signal travels only millimetres before being made robust.Related: Dry electrode, Input impedanceUsed in: Why so small?, Project C: Make your own electrodes, The electrode-electrolyte interface
Aliasing#
A frequency above Nyquist masquerading as a lower one after sampling; nothing downstream can undo it.Related: Nyquist frequency, Anti-alias filterUsed in: Why the hum?, Analog to digital, Digital filters, and what they do to time
Alpha rhythm#
A roughly 8 to 12 Hz oscillation over the back of the head that appears when the eyes close and fades when they open.
MoreAlpha is the first thing anyone sees in their own EEG. It arises from thalamocortical loops in visual cortex idling; opening the eyes gives that cortex something to do and the rhythm breaks up. The same eyes-closed test is how you check that an electrode setup is actually recording brain.
Related: Beta rhythm, Theta rhythm, Thalamocortical loop, Sensorimotor rhythm (mu)Used in: Project B: One channel of you, Why so small?, Alpha and the back of the head, Project A: The ADS1299 board, Analog to digital
Amyotrophic lateral sclerosis (ALS)#
A progressive disease of motor neurons that removes movement and eventually speech while leaving thought intact; the population many BCIs are built for.Related: Locked-in syndrome, Augmentative and alternative communication (AAC)Used in: Project D: Eyes as a joystick, Motor cortex and the systems BCIs target, Project A: A speller for someone with ALS, Needs finding, Design controls and the design history file
Analog-to-digital converter (ADC)#
The chip that measures a voltage at regular instants and turns each into a number.Related: Sampling rate, Quantization, Delta-sigma ADCUsed in: Project B: One channel of you, Tool: The Web Serial plotter, Why so small?, Why the hum?, Analog to digital
Anti-alias filter#
A low-pass filter placed before the ADC to remove everything above Nyquist, so nothing can alias.Related: Aliasing, Low-pass filterUsed in: Project B: One channel of you, Why the hum?, Analog to digital
Band-pass filter#
A high-pass and a low-pass together, keeping only a band such as 0.5 to 40 Hz.Related: FilterUsed in: Project A: The SpikerBox, Deep learning for EEG
Common-mode signal#
A voltage that appears equally on both inputs of a differential amplifier, such as 60 Hz hum picked up by the whole body.Related: Common-mode rejection ratio (CMRR), Differential measurement, Driven-right-leg circuitUsed in: Project B: One channel of you, Why so small?, Why the hum?, Instrumentation amplifiers, properly, KiCad to JLCPCB
Differential measurement#
Measuring the difference between two electrodes rather than one electrode against ground, so anything common to both cancels.Related: Common-mode signal, Common-mode rejection ratio (CMRR), Instrumentation amplifierUsed in: Why so small?
EEG technologist#
The person who applies electrodes and runs clinical EEGs, with a certification path of its own.Used in: Alpha and the back of the head, The artifact bestiary, The clinic
Electrocardiography (ECG)#
Recording the heart's electrical activity, about a millivolt on the chest; it leaks into EEG as a small regular spike.Related: ArtifactUsed in: Why so small?, The artifact bestiary, Electrical safety, with the numbers
Electrooculography (EOG)#
Recording eye position from the standing voltage across the eyeball, which moves with the eyes; also the main source of blink artifacts in EEG.Related: Blink artifact, Electroencephalography (EEG)Used in: Project D: Eyes as a joystick, Why so small?, The artifact bestiary, Artifact removal, three ways, Project A: A speller for someone with ALS
Event-related desynchronization (ERD)#
The drop in rhythmic power over a cortical area when it becomes active, such as mu weakening when you imagine moving your hand.Related: Sensorimotor rhythm (mu), Motor imageryUsed in: Alpha and the back of the head, Project F: The software pipeline, Event-related potentials and oscillations
Fast Fourier transform (FFT)#
The algorithm that breaks a stretch of signal into the sinusoids that would add up to it, giving amplitude and phase at each frequency.Related: Spectrum, Power spectral density (PSD), Window functionUsed in: What the spectrum did
Ground electrode#
The electrode that ties the body to the amplifier's zero and, in a good design, is driven to cancel common-mode hum.Related: Driven-right-leg circuit, Reference electrodeUsed in: Why so small?
Ground loop#
Two paths to ground that form a loop through which stray currents flow, injecting hum into whatever is between them.Related: Electrical isolationUsed in: Why the hum?
Hodgkin–Huxley model#
The 1952 set of four differential equations for the squid axon that reproduces the action potential from voltage-dependent sodium and potassium channels.Related: Action potential, Leaky integrate-and-fire neuronUsed in: What was that sound?, Project A: Neurons from the equations up, Project D: Neuromatch Academy, Neuron biophysics, The math track
Independent component analysis (ICA)#
A method that unmixes multichannel data into statistically independent sources, so blinks and heartbeat can be identified and removed.Related: ArtifactUsed in: The artifact bestiary, Project F: The software pipeline, Artifact removal, three ways, Spatial filters and montages, Classification done honestly
Ion channel#
A protein pore in the membrane that lets specific ions through, often only when the voltage or a chemical tells it to open.Related: Action potential, Hodgkin–Huxley modelUsed in: What was that sound?, A reading order for Kandel
Membrane potential#
The voltage across a cell's membrane, about −70 millivolts at rest, set by ion concentrations and which channels are open.Related: Resting potential, Action potential, Ion channelUsed in: What was that sound?, Neuron biophysics, Synapses and plasticity, A reading order for Kandel, Neuromodulation, mechanisms and evidence
Nyquist frequency#
Half the sampling rate; anything in the signal above it cannot be represented and will appear as something false.Related: Aliasing, Anti-alias filterUsed in: What the spectrum did, Analog to digital
Power spectral density (PSD)#
The spectrum expressed as power per hertz, the standard way to quantify how strong alpha is.Related: Welch's method, SpectrumUsed in: What the spectrum did
Reference electrode#
The electrode every other channel is measured against; there is no neutral spot on the head, so the choice shapes every trace.Related: Montage, Common average referenceUsed in: Project B: One channel of you, Why so small?, The artifact bestiary, Project A: The ADS1299 board, Project D: The phantom head
Refractory period#
The millisecond or so after a spike during which the neuron cannot fire again because its sodium channels are inactivated; it caps firing rates at a few hundred per second.Related: Action potential, Ion channelUsed in: What was that sound?, Project A: Neurons from the equations up, Project E: Large-scale neural data
Resting potential#
The steady membrane voltage of a neuron that is not firing, typically −60 to −70 millivolts.Related: Membrane potentialUsed in: What was that sound?, Neuron biophysics
Sensorimotor rhythm (mu)#
An 8 to 13 Hz rhythm over motor cortex that weakens when you move, or imagine moving, the corresponding body part.Related: Motor imagery, Event-related desynchronization (ERD)Used in: Alpha and the back of the head, Project C: Motor imagery
Sleep technologist#
The person who runs overnight sleep studies and scores them; a certification path an undergraduate can complete and work nights.Related: Polysomnography (PSG)Used in: Alpha and the back of the head, Sleep neuroscience, The clinic
Source localization#
Estimating where in the brain scalp signals came from, using a head model and assumptions such as smoothness or sparsity.Related: Inverse problemUsed in: Project E: The zero-dollar version, The math track
Spectrogram#
A spectrum computed over sliding windows and plotted against time, showing how frequency content changes.Related: Wavelet transform, SpectrumUsed in: What the spectrum did, Project E: The sleep band, Event-related potentials and oscillations, Project E: Large-scale neural data
Spike sorting#
Deciding which spikes on an electrode came from which neuron, by clustering their waveform shapes.Related: Spike, NeuropixelsUsed in: What was that sound?, Project E: Large-scale neural data
Thalamocortical loop#
The two-way circuit between the thalamus and the cortex whose rhythmic activity produces alpha, sleep spindles, and other EEG rhythms.Related: Alpha rhythm, Sleep spindleUsed in: Alpha and the back of the head
Topographic map#
The head-shaped colour plot of voltage or power at each electrode, interpolated between them.Related: MontageUsed in: Project E: The zero-dollar version, Project F: The software pipeline, Spatial filters and montages, Project B: The forward and inverse problems
Welch's method#
Estimating a spectrum by averaging the spectra of many overlapping short windows, trading frequency detail for a less noisy estimate.Related: Power spectral density (PSD), Window functionUsed in: What the spectrum did, Python for signals
Window function#
A smooth taper, such as a Hann window, applied to a segment before an FFT so its abrupt edges do not smear the spectrum.Related: Fast Fourier transform (FFT), Welch's methodUsed in: What the spectrum did

Phase 2: Build the instrument

1/f noise#
Noise that grows at low frequencies, present in amplifiers and electrodes, and the reason sub-hertz EEG is hard.Related: Noise floorUsed in: Instrumentation amplifiers, properly, Noise, and where the microvolt goes
Artifact subspace reconstruction (ASR)#
An automatic method that detects short high-variance bursts and reconstructs them from clean data; common in real-time pipelines.Related: ArtifactUsed in: Artifact removal, three ways
Biomedical equipment technician (BMET)#
The hospital staff who maintain and repair medical devices and know every way they fail in real use.Used in: Electrical safety, with the numbers, The clinic
BrainFlow#
A library that talks to OpenBCI and most consumer EEG headsets with one API, in Python and other languages.Related: OpenBCI, Lab Streaming Layer (LSL)Used in: Project A: The ADS1299 board, Lab Streaming Layer and PsychoPy
Butterworth filter#
The IIR filter with the flattest possible passband, the default choice when you do not have a reason to choose something else.Related: IIR filterUsed in: Digital filters, and what they do to time
Common spatial patterns (CSP)#
Spatial filters that maximize the variance of one class while minimizing the other, the classic feature extractor for motor imagery.Related: Motor imagery, ClassifierUsed in: Spatial filters and montages, Project C: Motor imagery, Classification done honestly, Deep learning for EEG
Current dipole#
The simplest model of a patch of active cortex: a tiny current source and sink close together, with a strength and a direction.Related: Volume conduction, Forward problemUsed in: Project D: The phantom head, Spatial filters and montages, Where oscillations come from, The math track
Delta-sigma ADC#
A converter that samples very fast with a crude 1-bit decision and averages, achieving 24-bit resolution at modest rates; what the ADS1299 uses.Related: Analog-to-digital converter (ADC), ADS1299Used in: Project A: The ADS1299 board, Analog to digital
Dry electrode#
An electrode used without gel, faster to apply but with higher, less stable impedance and more motion noise; the consumer-headset compromise.Related: Electrode impedance, Active electrodeUsed in: Project C: Make your own electrodes, Project E: The eight-channel EMG armband, The electrode-electrolyte interface, Noise, and where the microvolt goes
Electrical isolation#
A barrier, such as a battery, an optocoupler, or an isolated USB link, with no conductive path from the mains to the patient.Related: Leakage currentUsed in: Electrical safety, with the numbers
ESP32#
A cheap microcontroller with Wi-Fi and Bluetooth, good for streaming data from a sensor board to a laptop.Related: RP2040, FirmwareUsed in: Project A: The ADS1299 board, Electrical safety, with the numbers
FIR filter#
A filter that outputs a weighted sum of recent inputs only; symmetric ones delay every frequency equally, which preserves waveform shape.Related: IIR filter, Phase distortionUsed in: Project F: The software pipeline, Digital filters, and what they do to time
Group delay#
How long a filter delays the envelope of a signal at each frequency; constant for symmetric FIR filters.Related: Phase distortionUsed in: Digital filters, and what they do to time
Half-cell potential#
The DC voltage that appears wherever a metal meets an electrolyte; two electrodes with different half-cell potentials produce an offset that can swamp the signal.Related: Silver/silver-chloride (Ag/AgCl), ElectrodeUsed in: Project C: Make your own electrodes, The electrode-electrolyte interface
High-pass filter#
Removes slow drifts and DC offsets, passing everything above a cutoff; set it too high and you erase slow brain activity.Related: FilterUsed in: Project F: The software pipeline
IIR filter#
A filter that feeds its output back into itself; cheap and sharp, but it delays different frequencies by different amounts.Related: FIR filter, Butterworth filter, Phase distortionUsed in: Digital filters, and what they do to time
KiCad#
Free, open-source software for drawing schematics and laying out printed circuit boards.Related: Printed circuit board (PCB), JLCPCBUsed in: KiCad to JLCPCB
Lab Streaming Layer (LSL)#
A protocol that timestamps and synchronizes streams from many devices and stimulus programs on a network; every BCI lab uses it.Related: PsychoPy, BrainFlowUsed in: Project A: The ADS1299 board, Project B: Reverse-engineer a bought board, Lab Streaming Layer and PsychoPy, Project A: The SSVEP speller, Project B: The P300 speller
Linear discriminant analysis (LDA)#
A simple, robust classifier that draws a straight boundary between classes; the workhorse of EEG decoding for two decades.Related: ClassifierUsed in: Project E: The eight-channel EMG armband, Project B: The P300 speller, Project C: Motor imagery, Classification done honestly, Deep learning for EEG
Low-pass filter#
Removes fast content above a cutoff; the anti-alias filter is one, and so is the smoothing you apply to a noisy trace.Related: Filter, Anti-alias filterUsed in: Analog to digital
Phase distortion#
Different frequencies being delayed by different amounts, which smears and shifts waveforms such as an ERP peak.Related: Zero-phase filtering, Group delayUsed in: Digital filters, and what they do to time
Quantization#
Rounding each sample to one of a finite set of levels; a 10-bit ADC has 1024 of them, a 24-bit one about 16 million.Related: Analog-to-digital converter (ADC), Resolution (bits)Used in: Analog to digital
Signal-to-noise ratio (SNR)#
How big the thing you want is compared to everything else, often in decibels; the number every design decision is trying to raise.Related: Trial averaging, Noise floorUsed in: Noise, and where the microvolt goes, Project E: Large-scale neural data, Project E: Intracortical data
Silent speech interface#
Decoding intended words from muscle activity of the face and throat while the person mouths or subvocalizes without sound.Related: Electromyography (EMG)Used in: Project E: The eight-channel EMG armband, Project C: Silent speech
Silver/silver-chloride (Ag/AgCl)#
The standard electrode material for biopotentials, because its chemistry produces a stable, low-noise, low-drift interface with salty gel.Related: Electrode, Half-cell potentialUsed in: Project C: Make your own electrodes, Project D: The phantom head, The electrode-electrolyte interface, Project C: Other windows on the brain, Project D: Stimulation, studied properly
SPI#
A simple four-wire bus for talking to chips like the ADS1299 from a microcontroller.Related: FirmwareUsed in: Project A: The ADS1299 board, Project B: Reverse-engineer a bought board, Firmware and SPI for a biopotential chip, Project B: Build a lab a rig
Surface Laplacian#
Subtracting the average of neighbouring electrodes from each electrode, which sharpens spatial detail and suppresses distant sources.Related: Montage, Volume conductionUsed in: Spatial filters and montages
Thermal (Johnson) noise#
The random voltage every resistor produces just by being warm; about 13 nanovolts per root hertz for 10 kilohms, which matters at microvolt levels.Related: Noise floorUsed in: Noise, and where the microvolt goes
Volume conduction#
The spreading of currents from a source through the conductive tissues of the head, which is why one source shows up on many electrodes and why scalp EEG is blurry.Related: Current dipole, Forward problem, Surface LaplacianUsed in: Project D: The phantom head, Event-related potentials and oscillations, Project B: The forward and inverse problems
Zero-phase filtering#
Running a filter forward and then backward through recorded data so the delays cancel; impossible in real time.Related: Phase distortionUsed in: Digital filters, and what they do to time

Phase 3: Read intent

Baseline correction#
Subtracting the mean of the pre-stimulus interval from each epoch so trials line up.Related: EpochUsed in: Project D: Your own ERPs
Bayesian estimation#
Updating a belief about a hidden quantity by combining what you expected with what you measured, in proportion to their reliabilities.Related: Kalman filterUsed in: Bayesian decoding and the Kalman filter, The math track
BCI Competition IV#
A 2008 set of benchmark EEG datasets, especially dataset 2a (four-class motor imagery), still the most-cited test bed.Related: Motor imagery, MOABBUsed in: Project F: Reproduce a paper, Deep learning for EEG
Braindecode#
A PyTorch library of deep-learning models for EEG, including EEGNet and ShallowConvNet, with dataset loaders.Related: EEGNet, MOABBUsed in: Project C: Motor imagery, Project E: The sleep band, Project F: Reproduce a paper, Deep learning for EEG
Canonical correlation analysis (CCA)#
Finding the combination of channels that correlates best with reference sinusoids at each candidate frequency; the standard SSVEP decoder.Related: Steady-state visual evoked potential (SSVEP)Used in: Project A: The SSVEP speller
Closed loop#
A system in which the output feeds back to influence the input, such as a user adjusting their brain activity while watching the cursor it controls.Related: Brain-computer interface (BCI), NeurofeedbackUsed in: Bayesian decoding and the Kalman filter, Project E: Haptic feedback for a prosthetic hand, Neuromodulation, mechanisms and evidence
DANDI archive#
A public repository of neurophysiology data in NWB format, including human intracortical BCI recordings from published papers.Related: Neurodata Without Borders (NWB)Used in: Project F: Reproduce a paper, Project E: Intracortical data
Data leakage#
Information from the test set sneaking into training, for example by shuffling trials from one session across both; it inflates accuracy and is the most common flaw in student BCI papers.Related: Cross-validationUsed in: Classification done honestly
EEGNet#
A compact convolutional neural network for EEG, published in 2018, that became the standard deep-learning baseline because it is small enough to train on a laptop.Related: BraindecodeUsed in: Project C: Motor imagery, Project F: Reproduce a paper, Deep learning for EEG
Error-related negativity (ERN)#
A sharp negative wave about 50 to 100 milliseconds after you make a mistake, before you consciously notice.Related: Event-related potential (ERP)Used in: Project D: Your own ERPs, Event-related potentials and oscillations
Hypnogram#
The staircase plot of sleep stage against time across a night, scored in 30-second epochs from EEG, EOG, and EMG.Related: Polysomnography (PSG), Sleep-EDFUsed in: Project E: The sleep band, Sleep neuroscience, Project C: Other windows on the brain
Kalman filter#
An estimator that blends a prediction from a motion model with a noisy measurement, weighting each by how much it trusts it; the decoder behind most intracortical cursor control.Related: Decoder, Bayesian estimationUsed in: Project F: Reproduce a paper, Bayesian decoding and the Kalman filter, Project E: Intracortical data, The math track
MOABB#
Mother of All BCI Benchmarks: a library that runs classifiers across many public EEG datasets the same way so results are comparable.Related: Braindecode, BCI Competition IVUsed in: Project F: Reproduce a paper, Classification done honestly, Deep learning for EEG
N170#
A negative deflection about 170 milliseconds after seeing a face, over the back of the head on the right.Related: Event-related potential (ERP)Used in: Project D: Your own ERPs, Event-related potentials and oscillations, Designing an experiment that can fail
Neurofeedback#
Showing someone a measure of their own brain activity in real time so they can try to change it; its clinical claims range from plausible to unsupported.Related: Closed loopUsed in: Project G: Neurofeedback, and how to test whether it does anything, Statistics for small experiments, Synapses and plasticity
Oddball paradigm#
An experiment in which a rare target is mixed in among frequent standards; the rare one produces a P300.Related: P300Used in: Project D: Your own ERPs
Overfitting#
A model that has memorized its training data, including its noise, and fails on anything new.Related: Cross-validationUsed in: Deep learning for EEG
Population vector#
A way to read out intended movement direction by adding up the preferred directions of many motor cortex neurons, weighted by how fast each is firing.Related: Decoder, Rate codeUsed in: Bayesian decoding and the Kalman filter, Project E: Large-scale neural data, Neural coding, Motor cortex and the systems BCIs target
Riemannian geometry classifiers#
Methods that treat each trial's covariance matrix as a point on a curved space and classify by distance there; the strongest simple baseline for EEG today.Related: Classifier, Common spatial patterns (CSP)Used in: Project C: Motor imagery, Project F: Reproduce a paper, Classification done honestly
Seizure detection#
Automatically flagging seizures in EEG, a real clinical need and a good first machine-learning project on the TUH corpus.Related: TUH EEG Corpus, EpilepsyUsed in: Deep learning for EEG
Sleep spindle#
A half-second burst of 11 to 16 Hz activity in light sleep, generated in the thalamus.Related: Hypnogram, Thalamocortical loopUsed in: Project E: The sleep band, Neuron biophysics, Where oscillations come from, Sleep neuroscience
Sleep-EDF#
A public PhysioNet dataset of whole-night sleep recordings with expert stage labels, the standard training set for automatic sleep staging.Related: Hypnogram, PhysioNetUsed in: Project E: The sleep band, Sleep neuroscience
Slow wave#
A large, slow (under 1 Hz) oscillation of deep sleep during which most cortical neurons fall silent and then fire together.Related: Delta waves, HypnogramUsed in: Project E: The sleep band, Event-related potentials and oscillations, Where oscillations come from, Sleep neuroscience
Transfer learning#
Using data from other people or other days to shorten calibration for a new user.Related: CalibrationUsed in: Classification done honestly
TUH EEG Corpus#
Temple University Hospital's archive of tens of thousands of clinical EEGs, with a labelled seizure subset.Related: Seizure detectionUsed in: Project F: Reproduce a paper, Deep learning for EEG
Validation#
Testing that the device meets the user's need in real use; did you specify the right thing.Related: VerificationUsed in: Deep learning for EEG, Design controls and the design history file, Human factors and use error, Regulatory pathways
Wavelet transform#
A time-frequency analysis that uses short wiggles at high frequencies and long ones at low, matching the trade-off to the frequency.Related: SpectrogramUsed in: Event-related potentials and oscillations

Phase 4: The brain behind the signal

Brian2#
A Python simulator for spiking neural networks in which you write the equations directly.Related: Leaky integrate-and-fire neuronUsed in: Project A: Neurons from the equations up, Where oscillations come from
Forward problem#
Given a source in the head, compute the voltages on the scalp; it has a unique answer.Related: Inverse problem, Current dipoleUsed in: Project B: The forward and inverse problems
Inverse problem#
Given voltages on the scalp, find the sources; it has infinitely many answers, so every solution leans on assumptions.Related: Forward problem, Source localizationUsed in: Project B: The forward and inverse problems
Izhikevich model#
A two-equation neuron model that reproduces most known firing patterns at a tiny fraction of Hodgkin–Huxley's cost.Related: Leaky integrate-and-fire neuronUsed in: Project A: Neurons from the equations up, Neuron biophysics
Leaky integrate-and-fire neuron#
The simplest useful neuron model: a leaky capacitor that fires and resets when it reaches a threshold.Related: Hodgkin–Huxley model, Izhikevich modelUsed in: Project A: Neurons from the equations up
Local field potential (LFP)#
The slow, summed electrical activity of many neurons near an electrode, below a few hundred hertz, as opposed to individual spikes.Related: Electroencephalography (EEG), Extracellular recordingUsed in: Project D: Neuromatch Academy, Project E: Large-scale neural data, Where oscillations come from, Project E: Intracortical data, Electrode materials and the foreign body response
Neuroethics#
The study of the ethical questions raised by measuring and changing brains, from privacy of neural data to who owns an implant.Related: Neurorights, Neural data privacyUsed in: Neural coding, Privacy, neuroethics, and the abandoned implant
Neuromatch Academy#
An online, three-week summer school in computational neuroscience with a large alumni network, on a country-scaled tuition.Used in: Project D: Neuromatch Academy, Community, The calendar
Neuropixels#
Silicon probes with hundreds to thousands of recording sites along a thin shank, the current standard for large-scale animal recording.Related: Spike sortingUsed in: Project E: Large-scale neural data, Electrode materials and the foreign body response, The industry landscape
Neurotransmitter#
A chemical released at a synapse that changes the next neuron's membrane potential.Related: SynapseUsed in: Synapses and plasticity
Phosphene#
A spot of light perceived when the visual system is stimulated electrically rather than by light.Related: Retinal prosthesisUsed in: Project C: Prosthesis simulators, Sensory systems as prosthesis targets, Neuromodulation, mechanisms and evidence, The Utah Array, a history
Rate code#
The idea that a neuron carries information in how many spikes per second it fires.Related: Temporal code, Population vectorUsed in: Neural coding, Sensory systems as prosthesis targets
Retinal prosthesis#
An electrode array on or under the retina that produces spots of light, phosphenes, in people blinded by retinal disease.Related: PhospheneUsed in: Project C: Prosthesis simulators, Sensory systems as prosthesis targets, The industry landscape
Sensory substitution#
Delivering information from one sense through another, such as an image as a soundscape, and letting the brain learn to use it.Used in: Synapses and plasticity, Project D: Sensory substitution
Spike-timing-dependent plasticity (STDP)#
A rule in which a synapse strengthens if the input spike arrives just before the output spike and weakens if it arrives just after.Related: Synaptic plasticityUsed in: Synapses and plasticity
Stroke#
Loss of blood supply to part of the brain; rehabilitation after it is the largest clinical use of neurotechnology today.Used in: Synapses and plasticity, Motor cortex and the systems BCIs target, Neuromodulation, mechanisms and evidence, The industry landscape, The clinic
Synaptic plasticity#
The strengthening or weakening of synapses with use, the physical basis of learning.Related: Spike-timing-dependent plasticity (STDP), SynapseUsed in: Synapses and plasticity
Temporal code#
The idea that the precise timing of spikes, not just their count, carries information.Related: Rate codeUsed in: Neural coding
Theta rhythm#
Roughly 4 to 8 Hz activity, prominent in drowsiness, some memory tasks, and strongly in the rodent hippocampus.Related: Alpha rhythmUsed in: Neural coding

Phase 5: Build for a person

510(k)#
The FDA pathway that clears a device by showing it is substantially equivalent to one already on the market, its predicate.Related: Predicate device, FDA device classesUsed in: Regulatory pathways
Breakthrough Device designation#
An FDA program that speeds review for devices treating serious conditions with no good alternative; most invasive BCI companies have it.Used in: Regulatory pathways, The Utah Array, a history
De Novo#
The FDA pathway for a low-to-moderate-risk device that has no predicate.Related: 510(k)Used in: Regulatory pathways
IEC 62366#
The standard for usability engineering of medical devices, aimed at preventing use errors.Related: Human factors, Use errorUsed in: Risk management and the FMEA, Human factors and use error
Investigational device exemption (IDE)#
FDA permission to use an unapproved device in a clinical study.Used in: Regulatory pathways, The Utah Array, a history, The industry landscape
ISO 13485#
The quality management standard for medical device companies; the reason everything is written down.Used in: Design controls and the design history file
Neural data privacy#
The question of who may collect, store, and sell recordings of brain activity, now addressed by laws in several US states.Related: NeuroethicsUsed in: Privacy, neuroethics, and the abandoned implant
Neurorights#
Proposed rights to mental privacy, identity, and agency, already written into Chile's constitution and debated elsewhere.Related: NeuroethicsUsed in: Privacy, neuroethics, and the abandoned implant
Predicate device#
The already-legal device a 510(k) submission compares itself to.Related: 510(k)Used in: Regulatory pathways
Premarket approval (PMA)#
The strictest FDA pathway, requiring clinical evidence of safety and effectiveness; the route for Class III implants.Related: FDA device classesUsed in: Regulatory pathways, The Utah Array, a history, The industry landscape
RP2040#
The Raspberry Pi microcontroller, cheap and well documented, with fast SPI and USB.Related: ESP32Used in: Project F: An adaptive game controller, Project B: Build a lab a rig
Use error#
A mistake made while using a device that the design invited, as opposed to random user carelessness.Related: Human factorsUsed in: Risk management and the FMEA, Human factors and use error

Phase 6: Beyond the scalp

Augmentative and alternative communication (AAC)#
Any tool that helps someone who cannot speak communicate, from picture boards to eye-gaze spellers to BCIs.Related: Amyotrophic lateral sclerosis (ALS)Used in: The industry landscape
Charge balance#
Every stimulation pulse followed by an equal and opposite one, so no net charge accumulates and no electrochemistry runs away.Related: Charge densityUsed in: Project D: Stimulation, studied properly, Stimulation safety and electrochemistry
Charge density#
The charge injected per pulse divided by electrode area; keeping it below safe limits prevents electrode damage and tissue injury.Related: Shannon safety limit, Charge balanceUsed in: Project A: Electrode fabrication, Project D: Stimulation, studied properly, Stimulation safety and electrochemistry
Electrochemical impedance spectroscopy (EIS)#
Measuring an electrode's impedance across many frequencies to characterize its interface, standard in electrode development.Related: Electrode impedance, PEDOT:PSSUsed in: Project A: Electrode fabrication, Project D: Stimulation, studied properly, Electrode materials and the foreign body response
Neurodata Without Borders (NWB)#
The standard file format for neurophysiology data, so recordings from different labs can be read the same way.Related: DANDI archiveUsed in: Project E: Intracortical data
PEDOT:PSS#
A conductive polymer coating that drops a microelectrode's impedance by an order of magnitude and improves charge injection for stimulation.Related: Electrochemical impedance spectroscopy (EIS), Charge densityUsed in: Project A: Electrode fabrication, Stimulation safety and electrochemistry, Electrode materials and the foreign body response
Shannon safety limit#
An empirical curve relating charge per phase and charge density below which stimulation did not damage tissue in animal studies.Related: Charge densityUsed in: Stimulation safety and electrochemistry

Threads

Epilepsy monitoring unit (EMU)#
The hospital ward where patients are recorded on video-EEG for days to capture seizures before surgery.Related: EpilepsyUsed in: The clinic
HIPAA#
The US law governing health information privacy; it shapes how clinical data can be stored and shared.Used in: The clinic
Polysomnography (PSG)#
The overnight sleep study: EEG, EOG, chin EMG, breathing, oxygen, and heart rate recorded together and scored in 30-second epochs.Related: Hypnogram, Sleep technologistUsed in: The clinic

Other terms

BCI inefficiency#
The finding that around one in five people cannot control a motor-imagery BCI even after training; once called "BCI illiteracy," a label the field is retiring.Related: Motor imagery
Beta rhythm#
Roughly 13 to 30 Hz activity, prominent over motor areas and associated with active concentration or holding still.Related: Alpha rhythm, Sensorimotor rhythm (mu)
Common average reference#
Re-referencing every channel to the mean of all channels, which approximates a neutral reference when electrodes cover the head well.Related: Montage
Conductive gel or paste#
Salty gel between electrode and skin that lowers impedance, stabilizes the chemistry, and is the reason research EEG takes half an hour to set up.Related: Electrode impedance, Dry electrode
Delta waves#
Slow, large waves below about 4 Hz that dominate deep sleep.Related: Slow wave
Design for manufacturability (DFM)#
Designing so the thing can actually be made reliably and cheaply, not just once on your bench.
ECoG grid#
A flexible sheet of electrodes laid on the brain's surface, used clinically for epilepsy and in research for speech decoding.Related: Electrocorticography (ECoG)
Gamma activity#
Fast activity above about 30 Hz, tied to local processing; weak and easily confused with muscle noise on the scalp.Related: Electromyography (EMG), Artifact
Intraoperative neuromonitoring (IONM)#
Recording evoked potentials and EMG during surgery to warn the surgeon before a nerve or the spinal cord is damaged.Related: Event-related potential (ERP)
Jig or fixture#
A purpose-built holder or tool that makes a repeated lab task faster or more repeatable; labs are full of ones nobody has built yet.
Locked-in syndrome#
Full awareness with almost no voluntary movement, sometimes only the eyes; communication depends entirely on assistive technology.Related: Amyotrophic lateral sclerosis (ALS)
Receptive field#
The set of stimuli, such as a patch of the visual field or a spot on the skin, that makes a particular neuron respond.
Resolution (bits)#
How finely an ADC divides its range; each extra bit halves the step size.Related: Quantization, Delta-sigma ADC
Shielding#
Surrounding a signal wire with a grounded conductor so electric fields from the room couple into the shield instead of the signal.Related: Common-mode signal
Spinal cord injury (SCI)#
Damage to the cord that cuts communication between brain and body below the injury; the population for motor BCIs and spinal stimulation.
Support vector machine (SVM)#
A classifier that finds the boundary with the widest margin between classes; strong on small datasets.Related: Classifier
Trial averaging#
Adding many time-locked epochs together so the consistent response grows and the random noise shrinks by the square root of the number of trials.Related: Event-related potential (ERP), Signal-to-noise ratio (SNR)
Utah Slanted Electrode Array (USEA)#
A version of the Utah Array with needles of graded lengths, designed to reach different depths of a peripheral nerve.Related: Utah Array
Vocoder (noise vocoder)#
A simulation of what a cochlear implant delivers: the loudness envelope of each frequency band, applied to noise in that band.Related: Cochlear implant