A system for calibrating and/or verifying system performance of a remote portable EEG system having at least one EEG sensor. Embodiments of the invention can provide various reference signals to calibrate and quality control the remote performance of the data acquisition EEG system. In addition a calibration cable connects a reference signal source to the EEG sensors to enable remote calibration and quality control assessment. Further, a diagnostic biomarker is included to assess the state or function of a subject's brain and enables the classification, prognosis, diagnosis, monitoring of treatment, or response to therapy applied to the brain by measuring any one of a list of candidate features extracted from a given cognitive or sensory task, and measuring changes in the EEG feature and task combination over time, among multiple states, or compared to a normative database.
