Peking University and Tsinghua researchers report in Nature Machine Intelligence that task-evoked fMRI activity from reasoning-related brain regions can directly improve LLM deductive reasoning, not just correlate with it. Their framework finds shared directions between model and brain representations, then steers models at inference and during fine-tuning. Across ten models from 1.5B to 72B parameters, gains were orthogonal to language-only supervision, transferred across reasoning types, and reached up to 13 points of absolute accuracy. Why it matters: brain data moves from alignment scoreboards into a practical training lever. Caveat: the method still depends on costly neuroimaging and has not been shown at frontier production scale.