Editing Brain–computer interface (section)

====Dry active electrode arrays====
In the early 1990s Babak Taheri, at [[University of California, Davis]] demonstrated the first single and multichannel dry active electrode arrays.<ref>{{cite journal |vauthors=Taheri BA, Knight RT, Smith RL |date=May 1994 |title=A dry electrode for EEG recording |url=https://zenodo.org/record/1253862 |journal=Electroencephalography and Clinical Neurophysiology |volume=90 |issue=5 |pages=376–383 |doi=10.1016/0013-4694(94)90053-1 |pmid=7514984}}</ref> The arrayed electrode was demonstrated to perform well compared to [[silver]]/[[silver chloride]] electrodes. The device consisted of four sensor sites with integrated electronics to reduce noise by [[impedance matching]]. The advantages of such electrodes are:

* no electrolyte used,
* no skin preparation,
* significantly reduced sensor size,
* compatibility with EEG monitoring systems.

The active electrode array is an integrated system containing an array of capacitive sensors with local integrated circuitry packaged with batteries to power the circuitry. This level of integration was required to achieve the result.

The electrode was tested on a test bench and on human subjects in four modalities, namely:

* spontaneous EEG,
* sensory event-related potentials,
* brain stem potentials,
* cognitive event-related potentials.

Performance compared favorably with that of standard wet electrodes in terms of skin preparation, no gel requirements (dry), and higher signal-to-noise ratio.<ref>{{cite thesis |bibcode=1994PhDT........82A |title=Active Micromachined Scalp Electrode Array for Eeg Signal Recording |vauthors=Alizadeh-Taheri B |degree=PHD Thesis |year=1994 |page=82}}</ref>

In 1999 Hunter Peckham and others at [[Case Western Reserve University]] used a 64-electrode EEG skullcap to return limited hand movements to a [[quadriplegic]]. As he concentrated on simple but opposite concepts like up and down. A basic pattern was identified in his beta-rhythm EEG output and used to control a switch: Above average activity was interpreted as on, below average off. The signals were also used to drive nerve controllers embedded in his hands, restoring some movement.<ref>{{Cite magazine |last=Hockenberry |first=John |date=August 2001 |title=The Next Brainiacs |url=https://www.wired.com/wired/archive/9.08/assist_pr.html |magazine=Wired |volume=9 |issue=8}}</ref>