Chronic signal degradation
Chronic signal degradation is the progressive, typically months-long decline in recording quality after implantation: falling single-unit yield, shrinking spike amplitudes, a rising noise floor, and outright channel dropout. It is the composite symptom that all of chronic-interface engineering is trying to prevent.
Its causes are dual and it is essential to separate them. Biological causes — glial encapsulation and perielectrode neuronal loss — increase the effective source-to-sensor distance. Abiotic causes — insulation cracking, thin-film water ingress, metal-trace corrosion, coating delamination, and connector or lead-wire fatigue — kill channels through pure materials failure. The two demand opposite remedies: better tissue integration versus better materials reliability.
A common misconception is that decline is mostly the tissue's fault; longitudinal explant analyses attribute a large fraction of channel failures to material and mechanical faults, so 'improve biocompatibility' alone will not fix chronic recording.