The cause for the increased sensitivity of fibromyalgia (FM) patients to painful stimuli is unclear but sensitization of dorsal horn spinal cord neurons has been suggested. There, critical changes of sensory information occur which depend on the plasticity of second-order neurons and descending pain modulation, including facilitation and inhibition. This study used repetitive stimuli that produce temporal-summation-of-second-pain (TSSP) and central sensitization, relevant mechanisms for patients with chronic pain. We examined spinal cord neural activation during TSSP in FM patients and healthy controls (HC) and used its functional connectivity with several brainstem nuclei to model the observed blood-oxygen-level-dependent (BOLD) time-course with pain ratings. Methods: 16 HC and 14 FM participants received repetitive heat stimuli to the hand at .4 Hz to achieve TSSP during functional imaging with a 3T-Philips Achieva MRI scanner. Stimuli were adjusted to each individual’s pain sensitivity to achieve maximal pain ratings of 50 ± 10 on a numerical pain scale (0-100). Using a 16-channel neuro-vascular coil multiple image series were obtained from the cervical spinal cord to the brainstem using single-shot turbo-spin echo sequences. Results: During repetitive, sensitivity-adjusted heat stimuli, pain ratings of all subjects increased as predicted, consistent with TSSP. HC and FM participants had similar temporal patterns of spinal activation: initial BOLD increase followed by de-activation. Structural equation modeling showed that the observed spinal activity during TSSP was associated with more BOLD activity across/within the brainstem in FM subjects than HC, suggesting differences in pain modulation.