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MontageFL: Privacy-Preserving Federated Learning across Heterogeneous EEG Montages A Leakage-Free Benchmark on Alzheimer’s Disease Classification

Masry B, Shahin A, Karraz G

2026

65 participants

Abstract

Abstract Background. Federated learning (FL) trains shared models across institutions without moving raw data, which is attractivefor clinical electroencephalography (EEG) where data are scarce and privacy-sensitive. A practical obstacle has receivedlittle attention: clinical sites record EEG with different hardware and electrode montages, so the input feature space itselfdiffers across clients and standard aggregation cannot be applied. A second, quieter problem affects the evidence basefor EEG machine learning. Because a single recording yields thousands of short epochs, splitting epochs (rather thansubjects) between training and test sets leaks subject identity and inflates reported accuracy. This study asks a singlequestion: once heterogeneous montages are harmonized and the evaluation is made leakage-free, what do clinical sitesactually gain from federated EEG learning? Methods. We present MontageFL, a montage-agnostic harmonization pipelinethat maps any electrode configuration to a fixed 88-dimensional feature vector through region-based aggregation, combiningspectral biomarkers (Stream A, 32-d) with covariance-derived features (Stream B, 56-d). The harmonized representation letsa 19-channel site and an 11-channel site train together. We benchmark centralized, local, FedAvg, and FedProx training onAlzheimer’s disease (AD) versus healthy control (HC) classification using the Miltiadous et al. (2023) dataset (65 subjects),under a strictly subject-level evaluation…

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