The Utah Array, a history

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 is a four-millimetre square of silicon with a hundred needles, each 1 to 1.5 millimetres long, tipped with platinum or iridium oxide, arranged in a ten-by-ten grid. It was developed in Richard Normann’s laboratory in the University of Utah’s bioengineering department starting in the late 1980s, originally as a possible visual prosthesis, and it became the 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 of record for human brain-computer interfaces. Nearly every person who has moved a cursor, a robotic arm, or a speech 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 with their thoughts has done it through one. It was invented where you are studying.

The idea

Normann wanted to stimulate visual cortex to produce phosphenesPhosphene A spot of light perceived when the visual system is stimulated electrically rather than by light. Related: Retinal prosthesisRetinal prosthesis An electrode array on or under the retina that produces spots of light, phosphenes, in people blinded by retinal disease. . Glossary entry for the blind and needed many electrodesElectrode 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 penetrating a millimetre into the cortex, spaced closely. Existing microwires were placed one at a time. The array’s manufacturing insight was to make all hundred needles from one silicon block: dice a grid of deep cuts, etch the resulting columns into sharp tapered needles in acid, insulate them, and expose and metallize the tips. The process, refined by Patrick Rousche, Kelly Jones, and others through the 1990s, produced arrays whose geometry was reproducible, which made them a research tool rather than a craft object.

From cats to humans

Recording rather than stimulation turned out to be the first application. The array recorded populations of neurons in cat and monkey cortex through the 1990s, and the Utah group and others showed that its hundred channels captured enough of motor cortex to decode arm movement. BrainGate, the academic consortium led from Brown University, implanted the first array in a person with tetraplegia in 2004; he moved a cursor, opened email, and controlled a prosthetic hand. Every human intracortical 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 result for the next two decades (cursor control, robotic arms, handwriting at 90 characters per minute, speech at 60 to 80 words per minute, touch feedback through microstimulation) used Utah ArraysUtah 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.

The company

Cyberkinetics licensed the technology for the first human work, then Blackrock Microsystems, founded in Salt Lake City in 2008 by Marcus Gerhardt and Florian Solzbacher (a Utah faculty member and Nanofab director), took over manufacturing. Blackrock, now Blackrock Neurotech, made the arrays and the recording systems for the entire human field, obtained the first FDA clearance for a 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-based system for research use in humans, and has Breakthrough Device designationBreakthrough Device designation An FDA program that speeds review for devices treating serious conditions with no good alternative; most invasive BCI companies have it. Glossary entry for a 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 system aimed at paralysis. The Utah Slanted 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 Array, with graded needle lengths for peripheral nerves, is the same platform pointed at a different tissue and is the basis of Greg Clark’s and the NeuroRobotics lab’s work on restoring touch to amputees.

The regulatory path

The array reached humans through investigational device exemptions: research-use studies under IRBInstitutional review board (IRB) The committee that must approve any research on people before it starts, to protect the participants. Related: Informed consentInformed consent A participant's agreement to take part after understanding the risks, in language they can follow; a process, not a signature. , CITI trainingCITI training The online human-subjects research course most universities require before you can touch participant data. . Glossary entry and FDA oversight, a handful of participants at a time, for two decades. No 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 system is approved as a treatment; every participant has been in a trial. Blackrock’s clearance covers the array as a research recording device. The approval of any intracortical 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 as a therapy, by anyone, has not yet happened, and its path (a pivotal trial, a PMAPremarket approval (PMA) The strictest FDA pathway, requiring clinical evidence of safety and effectiveness; the route for Class III implants. Related: FDA device classesFDA 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. . Glossary entry, a reimbursement code) is what the industry is now walking.

The limits

Ninety-six channels, when modern probes have a thousand or more. Rigid silicon, with the tissue response described in the materials explainer: recording yield declines over years. A percutaneous pedestal through the skin for the cable, which is an infection risk and the thing patients most want gone. A fixed 1.5 millimetre depth that reaches layer 5 in some cortex and not others. The array was designed in an era of hand-placed microwires and was revolutionary; the next generation (flexible threads, thin-film grids, fully wireless cans) is defined largely by trying to keep what it gave and remove what it costs.

Why it matters that it was here

Because the physical center of invasive 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 hardware is thirty minutes from campus and the people who built it are still on the faculty. Because the Nanofab that makes new electrodesElectrode 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 trains student users. Because the history above means that a student who walks into Blackrock or Ripple with a characterized amplifier and a coated microelectrode is walking into a company that knows exactly what those are worth. The Utah map is the rest of the argument.