By achieving layer-specific fMRI in the human spinal cord for the first time, this work reveals that phasic and tonic pain responses segregate across distinct dorsal horn laminae, bringing mesoscopic spinal circuit analysis from animal models into human neuroscience.
Ultra-high-field 7T fMRI with integrated technical improvements enables mesoscopic-scale functional imaging of the human spinal cord, revealing that prolonged heat-pain stimulation evokes temporally distinct phasic and sustained BOLD responses that map differentially onto superficial and deep layers of the dorsal horn, respectively, thereby providing access to fundamental spinal processing units previously inaccessible in humans.
Developments in functional magnetic resonance imaging (fMRI) at ultra-high field (UHF) now allow for insights into human brain function at mesoscopic scale. However, similar progress has not been achieved for the human spinal cord, despite its importance for reciprocal brain-body communication. Here, we therefore integrate substantial methodological improvements that enable previously unattainable high-resolution UHF spinal fMRI. Using a heat-pain paradigm in healthy volunteers, we investigate fMRI responses in the dorsal horn: we characterize their spatial pattern, establish their robustness and demonstrate that they can be reliably observed even for individual participants. Most importantly, we uncover two physiologically relevant spinal response components – phasic and tonic heat responses – that map differentially onto superficial and deep layers of the dorsal horn. Taken together, our novel UHF fMRI approach allows for differentiating responses across fundamental spinal processing units and will enable insights into human spinal cord function at mesoscopic scale in health and disease.