Unveiling Instruction-Specific Neurons & Experts: An Analytical
  Framework for LLM's Instruction-Following Capabilities
Authors: name: Junyan Zhang; name: Yubo Gao; name: Yibo Yan; name: Jungang Li; name: Zhaorui Hou; name: Sicheng Tao; name: Shuliang Liu; name: Song Dai; name: Yonghua Hei; name: Junzhuo Li; name: Xuming Hu
Published: 2025-05-27 13:40:28

Abstract: The finetuning of Large Language Models (LLMs) has significantly advanced
their instruction-following capabilities, yet the underlying computational
mechanisms driving these improvements remain poorly understood. This study
systematically examines how fine-tuning reconfigures LLM computations by
isolating and analyzing instruction-specific sparse components, i.e., neurons
in dense models and both neurons and experts in Mixture-of-Experts (MoE)
architectures. In particular, we introduce HexaInst, a carefully curated and
balanced instructional dataset spanning six distinct categories, and propose
SPARCOM, a novel analytical framework comprising three key contributions: (1) a
method for identifying these sparse components, (2) an evaluation of their
functional generality and uniqueness, and (3) a systematic comparison of their
alterations. Through experiments, we demonstrate functional generality,
uniqueness, and the critical role of these components in instruction execution.
By elucidating the relationship between fine-tuning-induced adaptations and
sparse computational substrates, this work provides deeper insights into how
LLMs internalize instruction-following behavior for the trustworthy LLM
community.