Impedance Drift

Impedance drift refers to the progressive change in electrode impedance over the course of a recording session (acute drift) or across sessions (chronic drift). It is one of the most informative indicators of recording quality changes and electrode health.

Acute drift: Within a single session, impedance changes can indicate reference electrode problems, connector instability, fluid ingress, or tissue settling around the probe. Detectable within minutes to hours.

Chronic drift: Across sessions, impedance changes reflect the biological tissue response to the implant — glial encapsulation, protein adsorption, and electrode material degradation. Prasad & Bhatt (2014) documented that drops in single-unit and multi-unit recording quality coincide with large impedance jumps. However, impedance at 1 kHz alone is not a reliable predictor of failure; spectroscopic measurement across frequencies provides more diagnostic information.

Monitoring: Allego computes impedance trends in real time during recording, enabling early detection. Multi-session tracking via the expected signal model reveals chronic drift trajectories before they reach the point of obvious signal degradation.

Key reference: Prasad A, Bhatt DP. Biomaterials. 2014;36:105-113.