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Mechanistic Interpretability of EEG Foundation Models via Sparse Autoencoders

Summary

This study applies TopK Sparse Autoencoders (SAEs) to three architecturally distinct EEG transformers (SleepFM, REVE, and LaBraM) to extract sparse feature dictionaries. Using a clinical taxonomy (abnormality, age, sex, medication), it benchmarks monosemanticity and entanglement across architectures. A concept steering framework with a "target vs. off-target" probe area metric reveals three operational regimes and critical representational failures, including "wrecking-ball" interventions and age-pathology confounding. A spectral decoder maps interventions to physiologically interpretable frequency signatures.

SourcearXiv Machine LearningAuthor: William Lehn-Schi{\o}ler, Magnus Ruud Kj{\ae}r, Rahul Thapa, Magnus Guldberg Pedersen, Anton Storgaard Mosquera, Nick Williams, Radu Gatej, Tue Lehn-Schi{\o}ler, S\'andor Beniczky, Sadasivan Puthusserypady, James Zou, Lars Kai Hansen
Mechanistic Interpretability of EEG Foundation Models via Sparse Autoencoders
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[2605.13930] Mechanistic Interpretability of EEG Foundation Models via Sparse Autoencoders

[Submitted on 13 May 2026]

Title:Mechanistic Interpretability of EEG Foundation Models via Sparse Autoencoders

View a PDF of the paper titled Mechanistic Interpretability of EEG Foundation Models via Sparse Autoencoders, by William Lehn-Schi{\o}ler and 11 other authors

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Abstract:EEG foundation models achieve state-of-the-art clinical performance, yet the internal computations driving their predictions remain opaque: a barrier to clinical trust. We apply TopK Sparse Autoencoders (SAEs) across three architecturally distinct EEG transformers: SleepFM, REVE, and LaBraM to extract sparse feature dictionaries from their embeddings. By grounding these features in a clinical taxonomy (abnormality, age, sex, and medication), we benchmark monosemanticity and entanglement across architectures. A single hyperparameter procedure, driven by an intrinsic dictionary health audit, transfers robustly across all three architectures. Via concept steering, we introduce a "target vs. off-target" probe area metric to quantify steering selectivity and reveal three operational regimes: selectively steerable, encoded but entangled, and non-encoded. This framework exposes critical representational failures: "wrecking-ball" interventions that collapse global model performance, and clinical entanglements, such as age-pathology confounding, where it is impossible to suppress one concept without corrupting the other. Finally, a spectral decoder maps these interventions back to the amplitude spectrum, translating latent manipulations into physiologically interpretable frequency signatures, such as pathological slow-wave suppression and $\alpha$-band restoration.

Comments: Preprint. 14 pages, 7 figures, 4 tables

Subjects:

Machine Learning (cs.LG); Human-Computer Interaction (cs.HC); Neural and Evolutionary Computing (cs.NE)

Cite as: arXiv:2605.13930 [cs.LG]

(or arXiv:2605.13930v1 [cs.LG] for this version)

https://doi.org/10.48550/arXiv.2605.13930

arXiv-issued DOI via DataCite (pending registration)

Submission history

From: William Lehn-Schiøler [view email] [v1] Wed, 13 May 2026 16:02:56 UTC (5,592 KB)

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Key points and analysis

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Key points

  • Applied TopK SAEs to extract sparse feature dictionaries from EEG foundation models
  • Benchmarked monosemanticity using a clinical taxonomy
  • Introduced concept steering and probe area metric revealing three regimes
  • Spectral decoder links latent manipulations to interpretable frequency signatures

Highlights and analysis are generated automatically and may contain errors. Check the original source.