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.

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1/f noise#: Noise that grows at low frequencies, present in amplifiers and electrodes, and the reason sub-hertz EEG is hard.See also: Noise floor
510(k)#: The FDA pathway that clears a device by showing it is substantially equivalent to one already on the market, its predicate.See also: Predicate device, FDA device classes
A
Action potential#: The brief, all-or-nothing voltage spike a neuron fires, about a millisecond long and about 100 millivolts tall across its membrane.Sodium 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.See also: Membrane potential, Ion channel, Spike, Extracellular recording
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.See also: Dry electrode, Input impedance
ADS1299#: Texas Instruments' 8-channel, 24-bit biopotential front-end chip used in OpenBCI and many research amplifiers.See also: Delta-sigma ADC, OpenBCI
Aliasing#: A frequency above Nyquist masquerading as a lower one after sampling; nothing downstream can undo it.See also: Nyquist frequency, Anti-alias filter
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.Alpha 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.See also: Beta rhythm, Theta rhythm, Thalamocortical loop, Sensorimotor rhythm (mu)
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.See also: Locked-in syndrome, Augmentative and alternative communication (AAC)
Analog-to-digital converter (ADC)#: The chip that measures a voltage at regular instants and turns each into a number.See also: Sampling rate, Quantization, Delta-sigma ADC
Anti-alias filter#: A low-pass filter placed before the ADC to remove everything above Nyquist, so nothing can alias.See also: Aliasing, Low-pass filter
Artifact#: Anything in the recording that did not come from the brain: blinks, muscle, heartbeat, movement, sweat, mains hum, electrode pops.See also: Blink artifact, Independent component analysis (ICA), Artifact subspace reconstruction (ASR)
Artifact subspace reconstruction (ASR)#: An automatic method that detects short high-variance bursts and reconstructs them from clean data; common in real-time pipelines.See also: Artifact
Augmentative and alternative communication (AAC)#: Any tool that helps someone who cannot speak communicate, from picture boards to eye-gaze spellers to BCIs.See also: Amyotrophic lateral sclerosis (ALS)
B
Band-pass filter#: A high-pass and a low-pass together, keeping only a band such as 0.5 to 40 Hz.See also: Filter
Baseline correction#: Subtracting the mean of the pre-stimulus interval from each epoch so trials line up.See also: Epoch
Bayesian estimation#: Updating a belief about a hidden quantity by combining what you expected with what you measured, in proportion to their reliabilities.See also: Kalman filter
BCI Competition IV#: A 2008 set of benchmark EEG datasets, especially dataset 2a (four-class motor imagery), still the most-cited test bed.See also: Motor imagery, MOABB
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.See also: Motor imagery
Beta rhythm#: Roughly 13 to 30 Hz activity, prominent over motor areas and associated with active concentration or holding still.See also: Alpha rhythm, Sensorimotor rhythm (mu)
Biodesign#: Stanford's process for medical technology innovation that starts from an observed clinical need rather than a technology looking for a use.See also: Needs finding, Need statement
Biomedical equipment technician (BMET)#: The hospital staff who maintain and repair medical devices and know every way they fail in real use.
Blink artifact#: The large, slow deflection an eye blink produces in frontal channels, often ten times the size of the brain signal.See also: Electrooculography (EOG), Artifact
Brain-computer interface (BCI)#: A system that turns measured brain activity into control of something outside the body, from a cursor to a wheelchair to a speech synthesizer.See also: Decoder, Closed loop
Braindecode#: A PyTorch library of deep-learning models for EEG, including EEGNet and ShallowConvNet, with dataset loaders.See also: EEGNet, MOABB
BrainFlow#: A library that talks to OpenBCI and most consumer EEG headsets with one API, in Python and other languages.See also: OpenBCI, Lab Streaming Layer (LSL)
Breakthrough Device designation#: An FDA program that speeds review for devices treating serious conditions with no good alternative; most invasive BCI companies have it.
Brian2#: A Python simulator for spiking neural networks in which you write the equations directly.See also: Leaky integrate-and-fire neuron
Butterworth filter#: The IIR filter with the flattest possible passband, the default choice when you do not have a reason to choose something else.See also: IIR filter
C
Calibration#: The session at the start of BCI use in which the decoder is trained on this person, today, because brains and electrodes drift.See also: Transfer learning
Canonical correlation analysis (CCA)#: Finding the combination of channels that correlates best with reference sinusoids at each candidate frequency; the standard SSVEP decoder.See also: Steady-state visual evoked potential (SSVEP)
Characterization#: Measuring what your instrument actually does, such as its noise floor, bandwidth, and rejection, instead of assuming the datasheet.See also: Noise floor, Phantom, Common-mode rejection ratio (CMRR)
Charge balance#: Every stimulation pulse followed by an equal and opposite one, so no net charge accumulates and no electrochemistry runs away.See also: Charge density
Charge density#: The charge injected per pulse divided by electrode area; keeping it below safe limits prevents electrode damage and tissue injury.See also: Shannon safety limit, Charge balance
CITI training#: The online human-subjects research course most universities require before you can touch participant data.See also: Institutional review board (IRB)
Classifier#: An algorithm that assigns each trial a label, such as left hand or right hand, after being trained on labelled examples.See also: Linear discriminant analysis (LDA), Support vector machine (SVM), Cross-validation
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.See also: Brain-computer interface (BCI), Neurofeedback
Cochlear implant#: The most successful neural prosthesis: an electrode array in the inner ear that stimulates the auditory nerve in up to 22 bands.See also: Vocoder (noise vocoder)
Common average reference#: Re-referencing every channel to the mean of all channels, which approximates a neutral reference when electrodes cover the head well.See also: Montage
Common spatial patterns (CSP)#: Spatial filters that maximize the variance of one class while minimizing the other, the classic feature extractor for motor imagery.See also: Motor imagery, Classifier
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.A 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.See also: Common-mode signal, Electrode impedance
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.See also: Common-mode rejection ratio (CMRR), Differential measurement, Driven-right-leg circuit
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.See also: Electrode impedance, Dry electrode
Cross-validation#: Testing a model on data it never saw during training, repeatedly, so the reported accuracy means something.See also: Data leakage, Overfitting
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.See also: Volume conduction, Forward problem
D
DANDI archive#: A public repository of neurophysiology data in NWB format, including human intracortical BCI recordings from published papers.See also: Neurodata Without Borders (NWB)
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.See also: Cross-validation
Datasheet#: The manufacturer's document for a chip: pinout, limits, typical performance, and the reference circuit you should start from.
De Novo#: The FDA pathway for a low-to-moderate-risk device that has no predicate.See also: 510(k)
Decoder#: The algorithm that maps neural signals to intended actions, such as a classifier or a Kalman filter.See also: Classifier, Kalman filter, Brain-computer interface (BCI)
Deep brain stimulation (DBS)#: Electrodes implanted deep in the brain and pulsed continuously, the standard treatment for advanced Parkinson's disease and essential tremor.See also: Charge density
Delta waves#: Slow, large waves below about 4 Hz that dominate deep sleep.See also: Slow wave
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.See also: Analog-to-digital converter (ADC), ADS1299
Design controls#: FDA's required process for developing a medical device: user needs, requirements, design, verification, validation, and the records of all of it.See also: Design history file (DHF), Requirements, Verification, Validation
Design for manufacturability (DFM)#: Designing so the thing can actually be made reliably and cheaply, not just once on your bench.
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.See also: Design controls
Differential measurement#: Measuring the difference between two electrodes rather than one electrode against ground, so anything common to both cancels.See also: Common-mode signal, Common-mode rejection ratio (CMRR), Instrumentation amplifier
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.The 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.See also: Common-mode signal, Ground electrode
Dry electrode#: An electrode used without gel, faster to apply but with higher, less stable impedance and more motion noise; the consumer-headset compromise.See also: Electrode impedance, Active electrode
E
ECoG grid#: A flexible sheet of electrodes laid on the brain's surface, used clinically for epilepsy and in research for speech decoding.See also: Electrocorticography (ECoG)
EEG technologist#: The person who applies electrodes and runs clinical EEGs, with a certification path of its own.
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.See also: Braindecode
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.See also: Leakage current
Electrocardiography (ECG)#: Recording the heart's electrical activity, about a millivolt on the chest; it leaks into EEG as a small regular spike.See also: Artifact
Electrochemical impedance spectroscopy (EIS)#: Measuring an electrode's impedance across many frequencies to characterize its interface, standard in electrode development.See also: Electrode impedance, PEDOT:PSS
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.See also: Electroencephalography (EEG), Intracortical recording, ECoG grid
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.See also: Silver/silver-chloride (Ag/AgCl), Electrode impedance, Half-cell potential
Electrode impedance#: How hard it is to push current through the skin-electrode contact, typically 5 to 50 kilohms with gel and megohms dry, higher at low frequencies.See also: Dry electrode, Conductive gel or paste, Electrochemical impedance spectroscopy (EIS)
Electroencephalography (EEG)#: Recording the brain's electrical activity from electrodes on the scalp, a few tens of microvolts of blurred, summed cortical activity.See also: Electrocorticography (ECoG), Magnetoencephalography (MEG), Volume conduction, Microvolt (µV)
Electromyography (EMG)#: Recording the electrical activity of muscles, hundreds of microvolts to millivolts, much larger than EEG.See also: Myoelectric prosthesis, Electroencephalography (EEG)
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.See also: Blink artifact, Electroencephalography (EEG)
Epilepsy#: A tendency to recurrent seizures; its monitoring units are where seizure-detection algorithms get validated and where ECoG data comes from.See also: Epilepsy monitoring unit (EMU), Seizure detection
Epilepsy monitoring unit (EMU)#: The hospital ward where patients are recorded on video-EEG for days to capture seizures before surgery.See also: Epilepsy
Epoch#: A fixed-length slice of the recording locked to an event, such as one second starting 200 milliseconds before each stimulus.See also: Trial averaging, Baseline correction
Error-related negativity (ERN)#: A sharp negative wave about 50 to 100 milliseconds after you make a mistake, before you consciously notice.See also: Event-related potential (ERP)
ESP32#: A cheap microcontroller with Wi-Fi and Bluetooth, good for streaming data from a sensor board to a laptop.See also: RP2040, Firmware
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.See also: Sensorimotor rhythm (mu), Motor imagery
Event-related potential (ERP)#: The small, stereotyped voltage waveform the brain produces in response to an event, invisible in a single trial and revealed by averaging many.See also: P300, N170, Error-related negativity (ERN), Trial averaging
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.See also: Spike, Local field potential (LFP), Intracortical recording
F
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.See also: Spectrum, Power spectral density (PSD), Window function
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.See also: 510(k), Premarket approval (PMA), De Novo
Filter#: An operation that passes some frequencies and attenuates others; every filter also delays or distorts the timing of what it passes.See also: High-pass filter, Low-pass filter, Notch filter, Phase distortion
FIR filter#: A filter that outputs a weighted sum of recent inputs only; symmetric ones delay every frequency equally, which preserves waveform shape.See also: IIR filter, Phase distortion
Firmware#: The program running on the microcontroller, which configures the chip, reads samples on time, and ships them to the computer.See also: SPI
FMEA#: Failure mode and effects analysis: a table of every way the device could fail, how bad and how likely each is, and what you did about it.See also: ISO 14971
Focused ultrasound#: Concentrating sound energy deep in the brain to modulate or destroy tissue without opening the skull.
Foreign body response#: The scarring the body builds around an implant, which insulates electrodes and degrades recordings over months to years.See also: Intracortical recording
Forward problem#: Given a source in the head, compute the voltages on the scalp; it has a unique answer.See also: Inverse problem, Current dipole
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.See also: Electroencephalography (EEG)
G
Gain#: How many times an amplifier multiplies its input; 1000× turns 50 microvolts into 50 millivolts, enough for an ADC to see.See also: Instrumentation amplifier
Gamma activity#: Fast activity above about 30 Hz, tied to local processing; weak and easily confused with muscle noise on the scalp.See also: Electromyography (EMG), Artifact
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.See also: Driven-right-leg circuit, Reference electrode
Ground loop#: Two paths to ground that form a loop through which stray currents flow, injecting hum into whatever is between them.See also: Electrical isolation
Group delay#: How long a filter delays the envelope of a signal at each frequency; constant for symmetric FIR filters.See also: Phase distortion
H
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.See also: Silver/silver-chloride (Ag/AgCl), Electrode
Haptic feedback#: Information delivered through touch, such as vibration on the skin that tells a prosthesis user how hard they are gripping.
Hermetic packaging#: Sealing implanted electronics against body fluid for decades, one of the hardest unsolved engineering problems in the field.
High-pass filter#: Removes slow drifts and DC offsets, passing everything above a cutoff; set it too high and you erase slow brain activity.See also: Filter
HIPAA#: The US law governing health information privacy; it shapes how clinical data can be stored and shared.
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.See also: Action potential, Leaky integrate-and-fire neuron
Human factors#: Designing so the device fits how people actually behave, especially under stress and fatigue, so that errors are hard to make.See also: IEC 62366, Use error
Hypnogram#: The staircase plot of sleep stage against time across a night, scored in 30-second epochs from EEG, EOG, and EMG.See also: Polysomnography (PSG), Sleep-EDF
I
IEC 60601#: The safety standard for medical electrical equipment, including how much current may leak into a patient (microamps).See also: Leakage current, Electrical isolation
IEC 62366#: The standard for usability engineering of medical devices, aimed at preventing use errors.See also: Human factors, Use error
IIR filter#: A filter that feeds its output back into itself; cheap and sharp, but it delays different frequencies by different amounts.See also: FIR filter, Butterworth filter, Phase distortion
Independent component analysis (ICA)#: A method that unmixes multichannel data into statistically independent sources, so blinks and heartbeat can be identified and removed.See also: Artifact
Informed consent#: A participant's agreement to take part after understanding the risks, in language they can follow; a process, not a signature.See also: Institutional review board (IRB)
Input bias current#: The tiny current an amplifier input draws; through a high electrode impedance it produces an offset and noise.See also: Input impedance
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.See also: Electrode impedance, Input bias current
Institutional review board (IRB)#: The committee that must approve any research on people before it starts, to protect the participants.See also: Informed consent, CITI training
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.See also: Differential measurement, Common-mode rejection ratio (CMRR), Input impedance
Intracortical recording#: Recording from tiny electrodes inserted into the cortex itself, close enough to hear individual neurons.See also: Utah Array, Extracellular recording
Intraoperative neuromonitoring (IONM)#: Recording evoked potentials and EMG during surgery to warn the surgeon before a nerve or the spinal cord is damaged.See also: Event-related potential (ERP)
Inverse problem#: Given voltages on the scalp, find the sources; it has infinitely many answers, so every solution leans on assumptions.See also: Forward problem, Source localization
Investigational device exemption (IDE)#: FDA permission to use an unapproved device in a clinical study.
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.See also: Action potential, Hodgkin–Huxley model
ISO 13485#: The quality management standard for medical device companies; the reason everything is written down.
ISO 14971#: The international standard for medical device risk management that every company follows.See also: FMEA
Izhikevich model#: A two-equation neuron model that reproduces most known firing patterns at a tiny fraction of Hodgkin–Huxley's cost.See also: Leaky integrate-and-fire neuron
J
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.
JLCPCB#: A Chinese board house that fabricates and assembles small-run PCBs for a few dollars, the standard for student projects.See also: Printed circuit board (PCB)
K
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.See also: Decoder, Bayesian estimation
KiCad#: Free, open-source software for drawing schematics and laying out printed circuit boards.See also: Printed circuit board (PCB), JLCPCB
L
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.See also: PsychoPy, BrainFlow
Leakage current#: Current that flows into the patient through unintended paths; limited to tens of microamps for anything touching the body.See also: IEC 60601, Electrical isolation
Leaky integrate-and-fire neuron#: The simplest useful neuron model: a leaky capacitor that fires and resets when it reaches a threshold.See also: Hodgkin–Huxley model, Izhikevich model
Linear discriminant analysis (LDA)#: A simple, robust classifier that draws a straight boundary between classes; the workhorse of EEG decoding for two decades.See also: Classifier
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.See also: Electroencephalography (EEG), Extracellular recording
Locked-in syndrome#: Full awareness with almost no voluntary movement, sometimes only the eyes; communication depends entirely on assistive technology.See also: Amyotrophic lateral sclerosis (ALS)
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.See also: Filter, Anti-alias filter
M
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.See also: Electroencephalography (EEG)
Membrane potential#: The voltage across a cell's membrane, about −70 millivolts at rest, set by ion concentrations and which channels are open.See also: Resting potential, Action potential, Ion channel
Microvolt (µV)#: One millionth of a volt. Scalp EEG is tens of microvolts; a AA battery is 1.5 million of them.See also: Gain
MNE-Python#: The standard open-source Python library for EEG and MEG analysis: filtering, epoching, ICA, topographies, source localization.See also: Independent component analysis (ICA)
MOABB#: Mother of All BCI Benchmarks: a library that runs classifiers across many public EEG datasets the same way so results are comparable.See also: Braindecode, BCI Competition IV
Montage#: The particular arrangement of which electrodes are subtracted from which, such as referential, bipolar, or average reference.See also: Reference electrode, Common average reference, Surface Laplacian
Motor imagery#: Imagining a movement without making it, which changes rhythms over motor cortex in a way a classifier can sometimes detect.See also: Sensorimotor rhythm (mu), Event-related desynchronization (ERD), BCI inefficiency
Myoelectric prosthesis#: An artificial limb controlled by EMG from the remaining muscles.See also: Electromyography (EMG)
N
N170#: A negative deflection about 170 milliseconds after seeing a face, over the back of the head on the right.See also: Event-related potential (ERP)
Need statement#: One sentence, "a way to [do X] for [whom] that [outcome]," with no solution in it.See also: Needs finding
Needs finding#: Observing clinical work to catch the moments that are slow, awkward, or unsafe, before proposing any solution.See also: Biodesign
Neural data privacy#: The question of who may collect, store, and sell recordings of brain activity, now addressed by laws in several US states.See also: Neuroethics
Neurodata Without Borders (NWB)#: The standard file format for neurophysiology data, so recordings from different labs can be read the same way.See also: DANDI archive
Neuroethics#: The study of the ethical questions raised by measuring and changing brains, from privacy of neural data to who owns an implant.See also: Neurorights, Neural data privacy
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.See also: Closed loop
Neuromatch Academy#: A free, online, three-week summer school in computational neuroscience with a large alumni network.
Neuropixels#: Silicon probes with hundreds to thousands of recording sites along a thin shank, the current standard for large-scale animal recording.See also: Spike sorting
Neurorights#: Proposed rights to mental privacy, identity, and agency, already written into Chile's constitution and debated elsewhere.See also: Neuroethics
Neurotransmitter#: A chemical released at a synapse that changes the next neuron's membrane potential.See also: Synapse
Noise floor#: What your instrument records when the input is shorted or connected to a perfectly quiet source; everything smaller than this is invisible to you.See also: Thermal (Johnson) noise, Characterization
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.See also: Filter, Common-mode signal
Nyquist frequency#: Half the sampling rate; anything in the signal above it cannot be represented and will appear as something false.See also: Aliasing, Anti-alias filter
O
Oddball paradigm#: An experiment in which a rare target is mixed in among frequent standards; the rare one produces a P300.See also: P300
OpenBCI#: The open-source EEG hardware company whose Cyton (ADS1299) and Ganglion boards are the default hobby and research-lite amplifiers.See also: ADS1299, BrainFlow
Overfitting#: A model that has memorized its training data, including its noise, and fails on anything new.See also: Cross-validation
P
P300#: A positive bump about 300 milliseconds after a rare or meaningful stimulus, the basis of the classic BCI speller.See also: Event-related potential (ERP), Oddball paradigm
PEDOT:PSS#: A conductive polymer coating that drops a microelectrode's impedance by an order of magnitude and improves charge injection for stimulation.See also: Electrochemical impedance spectroscopy (EIS), Charge density
Phantom#: A physical stand-in for tissue, such as saline gelatin with embedded wires, used to test an instrument against known signals.See also: Characterization
Phase distortion#: Different frequencies being delayed by different amounts, which smears and shifts waveforms such as an ERP peak.See also: Zero-phase filtering, Group delay
Phosphene#: A spot of light perceived when the visual system is stimulated electrically rather than by light.See also: Retinal prosthesis
PhysioNet#: A free archive of physiological recordings including EEG, ECG, and sleep data, run out of MIT.See also: Sleep-EDF
Polysomnography (PSG)#: The overnight sleep study: EEG, EOG, chin EMG, breathing, oxygen, and heart rate recorded together and scored in 30-second epochs.See also: Hypnogram, Sleep technologist
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.See also: Decoder, Rate code
Power spectral density (PSD)#: The spectrum expressed as power per hertz, the standard way to quantify how strong alpha is.See also: Welch's method, Spectrum
Predicate device#: The already-legal device a 510(k) submission compares itself to.See also: 510(k)
Premarket approval (PMA)#: The strictest FDA pathway, requiring clinical evidence of safety and effectiveness; the route for Class III implants.See also: FDA device classes
Printed circuit board (PCB)#: The board that holds and connects your components; designing one is how a breadboard prototype becomes an instrument.See also: KiCad, JLCPCB
PsychoPy#: Free Python software for presenting stimuli with precise timing and logging responses.See also: Lab Streaming Layer (LSL)
Q
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.See also: Analog-to-digital converter (ADC), Resolution (bits)
R
Rate code#: The idea that a neuron carries information in how many spikes per second it fires.See also: Temporal code, Population vector
Recall#: A correction or removal of a marketed device; FDA's public database of them is a catalogue of how designs fail people.
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.
Reference electrode#: The electrode every other channel is measured against; there is no neutral spot on the head, so the choice shapes every trace.See also: Montage, Common average reference
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.See also: Action potential, Ion channel
Requirements#: Testable statements of what the device must do, such as "input-referred noise below 1 microvolt RMS from 0.5 to 40 Hz."See also: Verification
Resolution (bits)#: How finely an ADC divides its range; each extra bit halves the step size.See also: Quantization, Delta-sigma ADC
Resting potential#: The steady membrane voltage of a neuron that is not firing, typically −60 to −70 millivolts.See also: Membrane potential
Retinal prosthesis#: An electrode array on or under the retina that produces spots of light, phosphenes, in people blinded by retinal disease.See also: Phosphene
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.See also: Classifier, Common spatial patterns (CSP)
RP2040#: The Raspberry Pi microcontroller, cheap and well documented, with fast SPI and USB.See also: ESP32
S
Sampling rate#: How many measurements per second the ADC takes; EEG is usually 250 to 1000 per second.See also: Nyquist frequency, Aliasing
Seizure detection#: Automatically flagging seizures in EEG, a real clinical need and a good first machine-learning project on the TUH corpus.See also: TUH EEG Corpus, Epilepsy
Sensorimotor rhythm (mu)#: An 8 to 13 Hz rhythm over motor cortex that weakens when you move, or imagine moving, the corresponding body part.See also: Motor imagery, Event-related desynchronization (ERD)
Sensory substitution#: Delivering information from one sense through another, such as an image as a soundscape, and letting the brain learn to use it.
Shannon safety limit#: An empirical curve relating charge per phase and charge density below which stimulation did not damage tissue in animal studies.See also: Charge density
Shielding#: Surrounding a signal wire with a grounded conductor so electric fields from the room couple into the shield instead of the signal.See also: Common-mode signal
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.See also: Trial averaging, Noise floor
Silent speech interface#: Decoding intended words from muscle activity of the face and throat while the person mouths or subvocalizes without sound.See also: Electromyography (EMG)
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.See also: Electrode, Half-cell potential
Sleep spindle#: A half-second burst of 11 to 16 Hz activity in light sleep, generated in the thalamus.See also: Hypnogram, Thalamocortical loop
Sleep technologist#: The person who runs overnight sleep studies and scores them; a certification path an undergraduate can complete and work nights.See also: Polysomnography (PSG)
Sleep-EDF#: A public PhysioNet dataset of whole-night sleep recordings with expert stage labels, the standard training set for automatic sleep staging.See also: Hypnogram, PhysioNet
Slow wave#: A large, slow (under 1 Hz) oscillation of deep sleep during which most cortical neurons fall silent and then fire together.See also: Delta waves, Hypnogram
Source localization#: Estimating where in the brain scalp signals came from, using a head model and assumptions such as smoothness or sparsity.See also: Inverse problem
Spectrogram#: A spectrum computed over sliding windows and plotted against time, showing how frequency content changes.See also: Wavelet transform, Spectrum
Spectrum#: A plot of how much of a signal lives at each frequency.See also: Fast Fourier transform (FFT), Power spectral density (PSD)
SPI#: A simple four-wire bus for talking to chips like the ADS1299 from a microcontroller.See also: Firmware
Spike#: Shorthand for an action potential as seen by an electrode, a brief blip about a millisecond wide.See also: Action potential, Spike sorting, Extracellular recording
Spike sorting#: Deciding which spikes on an electrode came from which neuron, by clustering their waveform shapes.See also: Spike, Neuropixels
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.See also: Synaptic plasticity
SpikerBox#: Backyard Brains' small battery amplifier that lets you hear action potentials from a cockroach leg on a speaker; easy to build yourself.See also: Action potential, Instrumentation amplifier
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.
Spinal cord stimulation (SCS)#: Electrodes over the spinal cord, long used for pain and now being used to restore stepping after spinal cord injury.
Steady-state visual evoked potential (SSVEP)#: When you stare at something flickering at a fixed rate, visual cortex oscillates at that rate, and the frequency can be read straight out of the EEG spectrum.See also: Canonical correlation analysis (CCA), Brain-computer interface (BCI)
Stentrode#: Synchron's electrode array mounted on a stent and delivered through a blood vessel to sit against the motor cortex without open surgery.
Stroke#: Loss of blood supply to part of the brain; rehabilitation after it is the largest clinical use of neurotechnology today.
Support vector machine (SVM)#: A classifier that finds the boundary with the widest margin between classes; strong on small datasets.See also: Classifier
Surface Laplacian#: Subtracting the average of neighbouring electrodes from each electrode, which sharpens spatial detail and suppresses distant sources.See also: Montage, Volume conduction
Synapse#: The junction where one neuron signals to another, usually by releasing a chemical that opens channels on the next cell.See also: Synaptic plasticity, Neurotransmitter
Synaptic plasticity#: The strengthening or weakening of synapses with use, the physical basis of learning.See also: Spike-timing-dependent plasticity (STDP), Synapse
T
Temporal code#: The idea that the precise timing of spikes, not just their count, carries information.See also: Rate code
Thalamocortical loop#: The two-way circuit between the thalamus and the cortex whose rhythmic activity produces alpha, sleep spindles, and other EEG rhythms.See also: Alpha rhythm, Sleep spindle
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.See also: Noise floor
Theta rhythm#: Roughly 4 to 8 Hz activity, prominent in drowsiness, some memory tasks, and strongly in the rodent hippocampus.See also: Alpha rhythm
Topographic map#: The head-shaped colour plot of voltage or power at each electrode, interpolated between them.See also: Montage
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.See also: Transcranial magnetic stimulation (TMS)
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.See also: Transcranial direct current stimulation (tDCS)
Transfer learning#: Using data from other people or other days to shorten calibration for a new user.See also: Calibration
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.See also: Event-related potential (ERP), Signal-to-noise ratio (SNR)
TUH EEG Corpus#: Temple University Hospital's archive of tens of thousands of clinical EEGs, with a labelled seizure subset.See also: Seizure detection
U
Use error#: A mistake made while using a device that the design invited, as opposed to random user carelessness.See also: Human factors
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.See also: Intracortical recording, Utah Slanted Electrode Array (USEA)
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.See also: Utah Array
V
Vagus nerve stimulation (VNS)#: A cuff electrode on the vagus nerve in the neck, pulsed for epilepsy, depression, and now stroke rehabilitation.
Validation#: Testing that the device meets the user's need in real use; did you specify the right thing.See also: Verification
Verification#: Testing that the device meets its requirements; did you build what you specified.See also: Validation
Vocoder (noise vocoder)#: A simulation of what a cochlear implant delivers: the loudness envelope of each frequency band, applied to noise in that band.See also: Cochlear implant
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.See also: Current dipole, Forward problem, Surface Laplacian
W
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.See also: Spectrogram
Welch's method#: Estimating a spectrum by averaging the spectra of many overlapping short windows, trading frequency detail for a less noisy estimate.See also: Power spectral density (PSD), Window function
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.See also: Fast Fourier transform (FFT), Welch's method
Z
Zero-phase filtering#: Running a filter forward and then backward through recorded data so the delays cancel; impossible in real time.See also: Phase distortion