PRISM Reveals LLM Naming Errors Mirror Brain Lesions.

Xiang Guan, Roger D. Newman-Norlund, Yong Yang, Saeed Ahmadi, Regan Willis, Nadra Salman, Kalil Warren, Srihari Nelakuditi, Chris Rorden, Leonardo Bonilha, Julius Fridriksson· August 14, 2026 View original

Key takeaways

  • PRISM is a new tool for spatially resolved interpretability of LLMs.
  • It adapts human neuroimaging's subtraction analysis to AI models.
  • LLM naming error patterns show parallels with post-stroke aphasia lesion patterns.
  • The method can test functional specialization claims in transformer models.

Who benefits

AI ResearchHealthcare (Neuroscience)Cognitive ScienceSoftware DevelopmentEducation

Summary

This research introduces PRISM (Perturbation-based Regional Interpretability through Subtraction Mapping), a novel tool that applies human neuroimaging's subtraction analysis to perturbed transformer language models, revealing that LLM naming error profiles spatially align with lesion patterns observed in post-stroke aphasia patients.

Understanding how large language models (LLMs) process information and make errors remains a significant challenge. This research introduces PRISM, a new interpretability tool that adapts the "subtraction analysis" method from human neuroimaging to analyze perturbed transformer models. The goal is to determine if internal LLM components specialize in distinct cognitive operations, similar to brain regions. PRISM maps specific naming error categories from the Philadelphia Naming Test onto LLM layers, then performs pairwise subtractions of error classes. This approach is mirrored in a parallel analysis of post-stroke aphasia patients, comparing lesion patterns in the brain to symptom profiles. The study found a robust "phonemic-favoring dissociation" in both LLMs (a deep layer cluster) and human brains (a frontal-perisylvian cortical cluster), indicating that certain components are specialized for phonemic processing. This suggests that PRISM can provide a falsifiable, spatially resolved method to test functional specialization claims within transformer language models, drawing intriguing parallels between AI and biological cognition.

Why it matters

AI researchers and developers can use PRISM to gain deeper mechanistic insights into how LLMs function, identify specialized internal components, and potentially diagnose and mitigate specific types of errors, leading to more robust and explainable AI.

How to implement this in your domain

  1. 1Apply PRISM or similar subtraction mapping techniques to analyze the functional specialization of internal components in custom LLMs.
  2. 2Utilize insights from PRISM to diagnose and debug specific error types in language model outputs.
  3. 3Develop targeted interventions or fine-tuning strategies based on identified functional dissociations within LLMs.
  4. 4Collaborate with cognitive scientists to further explore parallels between AI and human brain function.
  5. 5Integrate interpretability tools like PRISM into the LLM development lifecycle for better understanding and control.

Original post by Xiang Guan, Roger D. Newman-Norlund, Yong Yang, Saeed Ahmadi, Regan Willis, Nadra Salman, Kalil Warren, Srihari Nelakuditi, Chris Rorden, Leonardo Bonilha, Julius Fridriksson

"arXiv:2608.12717v1 Announce Type: new Abstract: Mechanistic interpretability of large language models lacks spatially resolved, falsifiable tools for testing whether internal components are specialized for distinct cognitive operations. We adapt subtraction analysis, the standard…"

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Originally posted by Xiang Guan, Roger D. Newman-Norlund, Yong Yang, Saeed Ahmadi, Regan Willis, Nadra Salman, Kalil Warren, Srihari Nelakuditi, Chris Rorden, Leonardo Bonilha, Julius Fridriksson on X · view source

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