Electrophysiology · reads
Dry-electrode EEG is scalp EEG recorded through electrodes that use no conductive gel or paste. It reads the electrical activity of the cerebral cortex at the scalp. Without gel the electrode-skin impedance is much higher, 150 to 200 kΩ against 5 to 10 kΩ with gel, and a dry cap has lower and more spatially variable channel reliability than a gel cap. Resting-state EEG and the P300 response are captured adequately; activity below 6 Hz and gamma at 40 to 80 Hz are harder to record.
Dry-electrode scalp EEG is a recording of the electrical activity of the cerebral cortex, through scalp electrodes that use no conductive gel or paste. In conventional wet EEG preparation, each site is rubbed with abrasive paste to remove part of the stratum corneum, the outer skin layer that dominates skin impedance, and the popular Ag/AgCl electrodes are impregnated with an electrolyte gel that passes the ionic currents from the tissue into electric currents in the electrode; the electrode-skin impedance is then checked and typically reaches 5 to 10 kΩ. A dry electrode omits the gel and the paste, so its impedance is much larger: typically 150 to 200 kΩ. Needle-type dry electrodes pierce the stratum corneum with microneedles to reach the lower-impedance layers beneath; they are minimally invasive, and an electrode of 8 by 8 pyramidal microneedles in 10 mm² reached 13 kΩ, but such tips can split, cause infection and mismatch the impedance between electrodes. Wet contact also drifts: the impedance of gel electrodes rose from 5 to 15 kΩ within 5 hours of application. A dry cap compared with a gel cap had a mean channel reliability of 84 ± 11% against 97 ± 3%, reduced mainly at central, parietal and neck sites. In dry-electrode recordings, resting-state EEG and the P300 evoked response were adequately captured, whereas low-frequency activity below 6 Hz and induced gamma activity at 40 to 80 Hz presented notable challenges.
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