# When Brain Foundation Model Meets Cauchy-Schwarz Divergence: A New Framework for Cross-Subject Motor Imagery Decoding Source: [When Brain Foundation Model Meets Cauchy-Schwarz Divergence: A New Framework for Cross-Subject Motor Imagery Decoding]() Collection index: [llms.txt]() Data updated: 2026-03-27T05:00:04.193Z Authors: Jinzhou Wu, Baoping Tang, Qikang Li, Yi Wang, Cheng Li, Shujian Yu Published: 2025-07-28T17:55:26.000Z ## Abstract Decoding motor imagery (MI) electroencephalogram (EEG) signals, a key non-invasive brain-computer interface (BCI) paradigm for controlling external systems, has been significantly advanced by deep learning. However, cross-subject MI-EEG decoding remains challenging due to substantial inter-subject variability and limited labeled target data, which necessitate costly calibration for new users. Many existing multi-source domain adaptation (MSDA) methods indiscriminately incorporate all available source domains, disregarding the large inter-subject differences in EEG signals, which leads to negative transfer and excessive computational costs. Moreover, while many approaches focus on feature distribution alignment, they often neglect the explicit dependence between features and decision-level outputs, limiting their ability to preserve discriminative structures. To address these gaps, we propose a novel MSDA framework that leverages a pretrained large Brain Foundation Model (BFM) for dynamic and informed source subject selection, ensuring only relevant sources contribute to adaptation. Furthermore, we employ Cauchy-Schwarz (CS) and Conditional CS (CCS) divergences to jointly perform feature-level and decision-level alignment, enhancing domain invariance while maintaining class discriminability. Extensive evaluations on two benchmark MI-EEG datasets demonstrate that our framework achieves average accuracies of 86.17% and 78.41%, outperforming a broad range of state-of-the-art baselines. Additional experiments with a large source pool validate the scalability and efficiency of BFM-guided selection. ## Recorded benchmark results A research result applies to its stated dataset, split, metric and evaluation configuration. Compare like-for-like settings, preserve the metric's unit and direction, and distinguish paper-reported results from independent reproduction. The best result recorded here is not a claim of exhaustive, current global coverage. - [Motor Imagery Decoding on BCI Competition IV 2a I (cross-subject)](): Motor Imagery decoding; BCI Competition IV 2a I (cross-subject); Average Accuracy: 86.17. - [Motor Imagery Decoding on Dataset II (cross-subject)](): Motor Imagery decoding; Dataset II (cross-subject); Subject Accuracy (S1): 80.52. - [Motor Imagery Decoding on GigaDB Dataset II](): Motor Imagery decoding; GigaDB Dataset II; Subject 1 Accuracy: 80.52. ## Original sources and implementation [Original paper]() [PDF]()