Electroencephalography (EEG) has been extensively studied for decades in psychiatric research. However, its integration into clinical practice as a diagnostic or prognostic tool remains unachieved. We hypothesize that a key reason for this is the underlying heterogeneity among patients, which is often overlooked in psychiatric EEG research that relies on a case-control approach.

The main objective of this study is to quantify the electrophysiological heterogeneity of psychiatric disorders.

We combine HD-EEG with normative modeling to quantify this heterogeneity using two well-established and extensively investigated EEG characteristics—spectral power and functional connectivity—across a cohort of 1,674 patients with attention-deficit/hyperactivity disorder, autism spectrum disorder, learning disorder, or anxiety, and 560 matched controls, see figure 1.

Normative models revealed that deviations from population norms among patients were highly heterogeneous and frequency-dependent. The spatial overlap of deviations among patients did not exceed 40% for spectral power and 24% for connectivity. Taking individual deviations into account significantly enhanced comparative analysis and the identification of patient-specific markers, which showed a correlation with clinical assessments.

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Our study underscores the necessity of moving EEG research in psychiatry beyond the group-level approach to achieve precision psychiatry.

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