FedGLoRA: Grassmann-Manifold Federated Learning via Dual LoRA for Large EEG Models

Abstract

Large EEG Models (LEMs) are drawing increasing attention in EEG, as large-scale pretraining yields transferable representations that improve generalization. As EEG research moves to real-world deployment, objectives and paradigms diversify, yielding increasingly heterogeneous and unevenly scaled datasets across institutions. This evolution induces distribution drift and scale imbalance, making static pretrained LEMs brittle and requiring adaptation to newly collected data. Under the constraints of the high cost of retraining and the privacy sensitivity of newly collected data, federated learning offers a practical route to update LEMs via decentralized parameter updates. Yet standard federated fine-tuning is unstable for pretrained LEMs, suffering backbone drift, misaligned updates under non-IID heterogeneity, and scale imbalance. We propose FedGLoRA: we freeze the backbone and communicate only LoRA adapters via a dual-branch design, with a shared global branch and a private on-device branch. FedGLoRA aggregates global updates on a Grassmann subspace with a Grassmann-proximal constraint, and uses bidirectional distillation to mitigate imbalance. Experiments on motor imagery and emotion recognition show consistent gains and improved stability over strong baselines.