Dry-electrode EEG

A scalp recording electrode that makes contact without the conductive gel or paste used in classical wet montages. Common forms are spring-loaded pins or claws that push through hair, conductive rubber or foam pads, textile electrodes woven into a cap, and non-contact capacitive sensors that couple through a thin insulating layer. The motivation is entirely practical: gel dries out, requires skin abrasion and cleanup, and makes self-application impossible, so a wearable or consumer device is almost always dry or semi-dry.

The price is signal quality. Removing the electrolyte raises the skin-electrode impedance by roughly an order of magnitude and, more damagingly, makes that impedance unstable — it drifts as the electrode shifts, as the wearer sweats, and as pins settle into the hair. Higher and more variable impedance means lower signal-to-noise ratio, stronger susceptibility to motion and triboelectric artefacts, and greater sensitivity to power-line pickup. Dry systems are viable for robust, large-amplitude signals such as alpha rhythm or strong steady-state responses, but recover fine, low-amplitude patterns far less reliably than a well-prepped wet cap.