SA-GA: Surrogate-Assisted Genetic Algorithm for Optimizing Activation Function Approximations in Privacy-Preserving EEG Classification Networks
摘要
Electroencephalography (EEG) data is highly sensitive, requiring strong privacy protection in brain–computer interfaces and neurological diagnosis. Homomorphic encryption enables secure EEG classification with deep neural networks, but standard activation functions (e.g., ReLU) are incompatible with encrypted arithmetic, causing severe computational overhead. Polynomial approximations mitigate this issue yet fail to capture EEG’s distinctive spectral patterns, temporal dynamics, and inter-subject variability. We propose a surrogate-assisted genetic algorithm (SA-GA) to optimize activation function approximations for encrypted deep learning models. SA-GA uses fixed-length chromosome encoding and a Gaussian Process surrogate to efficiently search the approximation space while avoiding costly encrypted evaluations. Applied to motor imagery classification (BCI Competition IV Dataset 2a), our method achieves 89.7% accuracy—7.2% higher than conventional polynomial approaches—while remaining feasible for real-time use. This enables practical, privacy-preserving deployment of EEG deep learning systems in clinical and BCI applications.