Inter- and Intra-Subject Variability in EEG: A Systematic Survey
This addresses the problem of reliability and reproducibility in EEG applications for neuroscience, clinical neurophysiology, and brain-computer interfaces, but it is incremental as it synthesizes existing research without introducing new methods.
The paper systematically reviews studies quantifying EEG variability across different paradigms and populations, finding that inter-subject differences are larger than intra-subject fluctuations, with stability varying by feature such as alpha-band measures being more reliable than higher-frequency metrics.
Electroencephalography (EEG) underpins neuroscience, clinical neurophysiology, and brain-computer interfaces (BCIs), yet pronounced inter- and intra-subject variability limits reliability, reproducibility, and translation. This systematic review studies that quantified or modeled EEG variability across resting-state, event-related potentials (ERPs), and task-related/BCI paradigms (including motor imagery and SSVEP) in healthy and clinical cohorts. Across paradigms, inter-subject differences are typically larger than within-subject fluctuations, but both affect inference and model generalization. Stability is feature-dependent: alpha-band measures and individual alpha peak frequency are often relatively reliable, whereas higher-frequency and many connectivity-derived metrics show more heterogeneous reliability; ERP reliability varies by component, with P300 measures frequently showing moderate-to-good stability. We summarize major sources of variability (biological, state-related, technical, and analytical), review common quantification and modeling approaches (e.g., ICC, CV, SNR, generalizability theory, and multivariate/learning-based methods), and provide recommendations for study design, reporting, and harmonization. Overall, EEG variability should be treated as both a practical constraint to manage and a meaningful signal to leverage for precision neuroscience and robust neurotechnology.