The six territories of neuroengineering

Put an electrodeElectrode 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)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. , Electrode impedanceElectrode 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. , Half-cell potentialHalf-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. . Glossary entry on someone’s scalp and you record a few tens of microvoltsMicrovolt (µV) One millionth of a volt. Scalp EEG is tens of microvolts; a AA battery is 1.5 million of them. Related: GainGain How many times an amplifier multiplies its input; 1000× turns 50 microvolts into 50 millivolts, enough for an ADC to see.. Glossary entry of blurred, summed activity from millions of neurons. Put a needle a millimetre into their cortex and you hear single cells fire. Put a pulse of current into a nerve and you change what the brain does rather than listening to it. These are three different fields with three different careers, and “I’m interested in brain waves” does not yet say which one you mean.

Neuroengineering has six territories. Each one has its own instruments, its own literature, and its own employers. This site visits all six, in a particular order, and by the end of Phase 2 you should know which one feels like home.

Non-invasive sensing

EEGElectroencephalography (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)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., Magnetoencephalography (MEG)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., Volume conductionVolume 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., Microvolt (µV)Microvolt (µV) One millionth of a volt. Scalp EEG is tens of microvolts; a AA battery is 1.5 million of them.. Glossary entry on the scalp, fNIRSFunctional 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)Electroencephalography (EEG) Recording the brain's electrical activity from electrodes on the scalp, a few tens of microvolts of blurred, summed cortical activity.. Glossary entry with near-infrared light, MEGMagnetoencephalography (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)Electroencephalography (EEG) Recording the brain's electrical activity from electrodes on the scalp, a few tens of microvolts of blurred, summed cortical activity.. Glossary entry in a shielded room. Nothing enters the body. The signals are small and blurry, the equipment ranges from a fifty-dollar board to a multi-million-dollar magnetometer array, and this is where hobbyists can do real work.Almost everything in Phases 1 to 3 lives here, because it is the territory you can enter from a dorm room.

Careers: consumer neurotech (sleep headbands, focus trackers), clinical EEGElectroencephalography (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)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. , Magnetoencephalography (MEG)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. , Volume conductionVolume 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. , Microvolt (µV)Microvolt (µV) One millionth of a volt. Scalp EEG is tens of microvolts; a AA battery is 1.5 million of them. . Glossary entry and sleep medicine, epilepsyEpilepsy A tendency to recurrent seizures; its monitoring units are where seizure-detection algorithms get validated and where ECoG data comes from. Related: Epilepsy monitoring unit (EMU)Epilepsy monitoring unit (EMU) The hospital ward where patients are recorded on video-EEG for days to capture seizures before surgery. , Seizure detectionSeizure detection Automatically flagging seizures in EEG, a real clinical need and a good first machine-learning project on the TUH corpus. . Glossary entry diagnostics, non-invasive brain-computer interfaces, research amplifiers.

Invasive interfaces

ECoGElectrocorticography (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)Electroencephalography (EEG) Recording the brain's electrical activity from electrodes on the scalp, a few tens of microvolts of blurred, summed cortical activity., Intracortical recordingIntracortical recording Recording from tiny electrodes inserted into the cortex itself, close enough to hear individual neurons., ECoG gridECoG grid A flexible sheet of electrodes laid on the brain's surface, used clinically for epilepsy and in research for speech decoding.. Glossary entry grids on the brain’s surface, intracorticalIntracortical recording Recording from tiny electrodes inserted into the cortex itself, close enough to hear individual neurons. Related: Utah ArrayUtah 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., Extracellular recordingExtracellular 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.. Glossary entry arrays like the Utah ArrayUtah 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 recordingIntracortical recording Recording from tiny electrodes inserted into the cortex itself, close enough to hear individual neurons., 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.. Glossary entry pushed into cortex, stentrodesStentrode Synchron's electrode array mounted on a stent and delivered through a blood vessel to sit against the motor cortex without open surgery. Glossary entry delivered through blood vessels. The signals are clean enough to hear individual neurons and to decode speech from a paralyzed person. The cost is surgery, the foreign body responseForeign body response The scarring the body builds around an implant, which insulates electrodes and degrades recordings over months to years. Related: Intracortical recordingIntracortical recording Recording from tiny electrodes inserted into the cortex itself, close enough to hear individual neurons.. Glossary entry, and a regulatory path measured in decades.

Careers: the BCIBrain-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. Related: DecoderDecoder The algorithm that maps neural signals to intended actions, such as a classifier or a Kalman filter. , Closed loopClosed 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. . Glossary entry companies (Blackrock, Neuralink, Synchron, Paradromics, Precision), academic BCIBrain-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. Related: DecoderDecoder The algorithm that maps neural signals to intended actions, such as a classifier or a Kalman filter. , Closed loopClosed 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. . Glossary entry labs, neurosurgical research.

Neuromodulation

Instead of listening, you talk. Deep brain stimulationDeep 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 densityCharge density The charge injected per pulse divided by electrode area; keeping it below safe limits prevents electrode damage and tissue injury.. Glossary entry for Parkinson’s, spinal cord stimulationSpinal cord stimulation (SCS) Electrodes over the spinal cord, long used for pain and now being used to restore stepping after spinal cord injury. Glossary entry for pain and now for walking, vagus nerve stimulationVagus nerve stimulation (VNS) A cuff electrode on the vagus nerve in the neck, pulsed for epilepsy, depression, and now stroke rehabilitation. Glossary entry, cochlear implantsCochlear implant The most successful neural prosthesis: an electrode array in the inner ear that stimulates the auditory nerve in up to 22 bands. Related: Vocoder (noise vocoder)Vocoder (noise vocoder) A simulation of what a cochlear implant delivers: the loudness envelope of each frequency band, applied to noise in that band.. Glossary entry, TMSTranscranial 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)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.. Glossary entry, focused ultrasoundFocused ultrasound Concentrating sound energy deep in the brain to modulate or destroy tissue without opening the skull. Glossary entry. This is by far the largest commercial market in the field and the least glamorous, which means the least crowded.

Careers: Medtronic, Boston Scientific, Abbott, LivaNova, Nevro, Cochlear, NeuroPace, and a long tail of startups; clinical engineering in movement disorder and pain clinics.

Peripheral nerve and muscle

EMGElectromyography (EMG) Recording the electrical activity of muscles, hundreds of microvolts to millivolts, much larger than EEG. Related: Myoelectric prosthesisMyoelectric prosthesis An artificial limb controlled by EMG from the remaining muscles., Electroencephalography (EEG)Electroencephalography (EEG) Recording the brain's electrical activity from electrodes on the scalp, a few tens of microvolts of blurred, summed cortical activity.. Glossary entry from muscles, nerve cuffs, myoelectricMyoelectric prosthesis An artificial limb controlled by EMG from the remaining muscles. Related: Electromyography (EMG)Electromyography (EMG) Recording the electrical activity of muscles, hundreds of microvolts to millivolts, much larger than EEG.. Glossary entry prosthetics, hapticHaptic feedback Information delivered through touch, such as vibration on the skin that tells a prosthesis user how hard they are gripping. Glossary entry feedback. Neuro-adjacent, with signals a thousand times larger than EEGElectroencephalography (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)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. , Magnetoencephalography (MEG)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. , Volume conductionVolume 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. , Microvolt (µV)Microvolt (µV) One millionth of a volt. Scalp EEG is tens of microvolts; a AA battery is 1.5 million of them. . Glossary entry, and the fastest route from an idea to a working prototype. The wristband that reads your hand gestures from forearm EMGElectromyography (EMG) Recording the electrical activity of muscles, hundreds of microvolts to millivolts, much larger than EEG. Related: Myoelectric prosthesisMyoelectric prosthesis An artificial limb controlled by EMG from the remaining muscles. , Electroencephalography (EEG)Electroencephalography (EEG) Recording the brain's electrical activity from electrodes on the scalp, a few tens of microvolts of blurred, summed cortical activity. . Glossary entry is this territory.

Careers: prosthetics companies, Meta’s EMGElectromyography (EMG) Recording the electrical activity of muscles, hundreds of microvolts to millivolts, much larger than EEG. Related: Myoelectric prosthesisMyoelectric prosthesis An artificial limb controlled by EMG from the remaining muscles. , Electroencephalography (EEG)Electroencephalography (EEG) Recording the brain's electrical activity from electrodes on the scalp, a few tens of microvolts of blurred, summed cortical activity. . Glossary entry wristband team, rehabilitation engineering, the University of Utah’s own NeuroRobotics lab.

Computational neuroscience

The models: how a neuron produces a spikeSpike Shorthand for an action potential as seen by an electrode, a brief blip about a millisecond wide. Related: Action potentialAction potential The brief, all-or-nothing voltage spike a neuron fires, about a millisecond long and about 100 millivolts tall across its membrane. , Spike sortingSpike sorting Deciding which spikes on an electrode came from which neuron, by clustering their waveform shapes. , Extracellular recordingExtracellular 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. . Glossary entry, how populations encode movement, how a decoderDecoder The algorithm that maps neural signals to intended actions, such as a classifier or a Kalman filter. Related: ClassifierClassifier An algorithm that assigns each trial a label, such as left hand or right hand, after being trained on labelled examples., Kalman filterKalman 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., Brain-computer interface (BCI)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.. Glossary entry should be built. Traditionally academic, and increasingly hired by BCIBrain-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. Related: DecoderDecoder The algorithm that maps neural signals to intended actions, such as a classifier or a Kalman filter. , Closed loopClosed 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. . Glossary entry companies because the decoderDecoder The algorithm that maps neural signals to intended actions, such as a classifier or a Kalman filter. Related: ClassifierClassifier An algorithm that assigns each trial a label, such as left hand or right hand, after being trained on labelled examples. , Kalman filterKalman 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. , Brain-computer interface (BCI)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. . Glossary entry is where the product lives.

Careers: PhD-track research, decoderDecoder The algorithm that maps neural signals to intended actions, such as a classifier or a Kalman filter. Related: ClassifierClassifier An algorithm that assigns each trial a label, such as left hand or right hand, after being trained on labelled examples. , Kalman filterKalman 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. , Brain-computer interface (BCI)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. . Glossary entry and algorithm teams at every company above, a route into machine learning more broadly.

Cellular and molecular

Patch-clamp recordingExtracellular 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: SpikeSpike Shorthand for an action potential as seen by an electrode, a brief blip about a millisecond wide., Local field potential (LFP)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., Intracortical recordingIntracortical recording Recording from tiny electrodes inserted into the cortex itself, close enough to hear individual neurons.. Glossary entry from single cells, optogenetics, organoids, electrodeElectrode 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)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. , Electrode impedanceElectrode 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. , Half-cell potentialHalf-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. . Glossary entry materials tested against living tissue. Lab-bound and PhD-shaped, but it is where the next generation of interfaces is being designed, and the University of Utah’s nanofab sits at its edge.

Careers: academic neuroscience, electrodeElectrode 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)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. , Electrode impedanceElectrode 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. , Half-cell potentialHalf-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. . Glossary entry and materials development, pharmaceutical neuroscience.

The territories overlap on purpose

A speech-decoding BCIBrain-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. Related: DecoderDecoder The algorithm that maps neural signals to intended actions, such as a classifier or a Kalman filter. , Closed loopClosed 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. . Glossary entry is invasive interfaces (the array), computational neuroscience (the decoderDecoder The algorithm that maps neural signals to intended actions, such as a classifier or a Kalman filter. Related: ClassifierClassifier An algorithm that assigns each trial a label, such as left hand or right hand, after being trained on labelled examples. , Kalman filterKalman 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. , Brain-computer interface (BCI)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. . Glossary entry), and neuromodulation (if it stimulates for feedback). A sleep headband is non-invasive sensing and consumer product design. Almost every real job sits at a boundary, and the people who are valuable are the ones who can hold two territories at once: the hardware person who understands the decoderDecoder The algorithm that maps neural signals to intended actions, such as a classifier or a Kalman filter. Related: ClassifierClassifier An algorithm that assigns each trial a label, such as left hand or right hand, after being trained on labelled examples. , Kalman filterKalman 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. , Brain-computer interface (BCI)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. . Glossary entry’s needs, the modeller who has held an electrodeElectrode 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)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. , Electrode impedanceElectrode 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. , Half-cell potentialHalf-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. . Glossary entry.