Truth Neurons
Authors: name: Haohang Li; name: Yupeng Cao; name: Yangyang Yu; name: Jordan W. Suchow; name: Zining Zhu
Published: 2025-05-18 00:47:21

Abstract: Despite their remarkable success and deployment across diverse workflows,
language models sometimes produce untruthful responses. Our limited
understanding of how truthfulness is mechanistically encoded within these
models jeopardizes their reliability and safety. In this paper, we propose a
method for identifying representations of truthfulness at the neuron level. We
show that language models contain truth neurons, which encode truthfulness in a
subject-agnostic manner. Experiments conducted across models of varying scales
validate the existence of truth neurons, confirming that the encoding of
truthfulness at the neuron level is a property shared by many language models.
The distribution patterns of truth neurons over layers align with prior
findings on the geometry of truthfulness. Selectively suppressing the
activations of truth neurons found through the TruthfulQA dataset degrades
performance both on TruthfulQA and on other benchmarks, showing that the
truthfulness mechanisms are not tied to a specific dataset. Our results offer
novel insights into the mechanisms underlying truthfulness in language models
and highlight potential directions toward improving their trustworthiness and
reliability.