Abstract Introduction and Objectives: High-resolution functional magnetic resonance imaging (fMRI) allows the mapping of functional organization of intraspinal circuits. This study aimed to identify nociceptive heat processing regions within the gray matter of the lumbar spinal cords and delineate their functional organization using task and resting-state fMRI in rats under anesthesia. Methods: High-resolution fMRI BOLD data were acquired from L3-L5 spinal segments during noxious heat (47.5°C) stimulation of the left hind paw and at rest at 9.4T MRI. Results: Noxious heat-elicited BOLD signal increases were detected at deep layers of dorsal horns and intermediate zone within the rostral lumbar enlargement (L3) and deep layers of the ipsilateral dorsal horn in lumbar segment L4. Resting-state functional connectivity (rsFC) analysis revealed the strongest rsFC strengths between dorsal–dorsal and ventral–ventral horns within each lumbar segment. No significant rsFC was found between the horns in different segments. Conclusion: Our results demonstrate that lumbar enlargement (L3 and L4) was involved in processing heat nociceptive information and bilateral dorsal and ventral horns were strongly interconnected at rest. We hypothesize that the intermediate zone in the rostral subsegment of L3 serves as a modulation center for nociceptive processing within the lumbar cord.
Zhang et al. (2026) studied this question.