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Scaling and context steer LLMs along the same computational path as the human brain
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Compares the temporal order of LLM layer representations with the order of MEG brain responses during 10 hours of audiobook listening, across 22 LLMs, finding that early-to-deep layers align with early-to-late brain responses, increasingly with model size and context length.
Problem
Whether LLM-brain representational alignment reflects a similar sequence of computations over time, and which factors (architecture, size, context length) drive this temporal alignment, remained unknown.
Approach
Introduces a "temporal score" measuring whether the time at which each LLM layer best aligns with MEG responses correlates with layer depth, and uses it to show a shared computational order between LLMs and the brain that emerges with model size and context length.
Key results
- Temporal score averaged across nine LLMs is r = 0.99 (p < 1e-06) between layer depth and MEG peak latency.
- In the Pythia family, temporal score rises from non-significant (r = 0.44) at 14M parameters to r = 0.96 (p < 1e-4) at 12B.
- For Llama-3.2 3B, temporal score rises from non-significant r = 0.19 without context to r = 0.93 at 1000-word context.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Increase model size within the Pythia family from 14M to 12 billion parameters | Pythia · Audiobook MEG | temporal score: 0.44 -> 0.96 | Helped |
| Increase context length from no context to 1000 words | Llama-3.2-3B · Audiobook MEG | temporal score: 0.19 -> 0.93 | Helped |
| Pretrain the model | LLMs · Audiobook MEG | temporal alignment | Helped |
| Use bidirectional rather than causal processing | BERT, RoBERTa, and Wav2vec2.0 · Audiobook MEG | temporal score | Hurt |
| Change architecture from transformer to recurrent or state-space | RecurrentGemma-9B and Mamba-1.4B · Audiobook MEG | temporal alignment | No clear effect |
| Compare most expected versus most surprising words | Llama-3-8B · Audiobook MEG | temporal score: p = 0.61 | No clear effect |
Surprising findings
- Bidirectional models (BERT, RoBERTa, Wav2vec2.0) achieve comparable alignment scores but substantially lower, non-significant temporal scores than causal LLMs.
- Word predictability does not explain temporal alignment: temporal alignment holds for both most expected and most surprising word quartiles.
Limitations
- MEG has limited spatial resolution and cannot capture deep sources or single neurons.
- Only three subjects in the dataset, so inter-individual variability is unknown.
- Only text models are studied; no sensory (speech) modality input.
Experimental setup
Datasets: public MEG dataset of 3 participants listening to 10 h of audiobooks
Benchmarks: MEG responses to 10 h audiobook listening
Metrics: Pearson correlation alignment score temporal score (correlation between peak time and layer dept
Baselines: BERT RoBERTa Wav2vec2.0
Builds on: Pythia ridge regression encoding models
Closest papers by meaning
- Divergences between Language Models and Human Brains (NeurIPS 2024 · similarity 0.90)
- Brain-tuning Improves Generalizability and Efficiency of Brain Alignment in Speech Models (NeurIPS 2025 · similarity 0.89)
- Correlating instruction-tuning (in multimodal models) with vision-language processing (in the brain) (ICLR 2025 · similarity 0.88)
- PaceLLM: Brain-Inspired Large Language Models for Long-Context Understanding (NeurIPS 2025 · similarity 0.88)
- Improving Semantic Understanding in Speech Language Models via Brain-tuning (ICLR 2025 · similarity 0.88)
- fMRI predictors based on language models of increasing complexity recover brain left lateralization (NeurIPS 2024 · similarity 0.88)
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