Spinal fMRI investigation of human spinal cord function over a range of innocuous thermal sensory stimuli and study-related emotional influences

Functional magnetic resonance imaging (fMRI) of the human spinal cord has revealed important details of activity involved with innocuous sensory stimuli, including the primary input to ipsilateral dorsal gray matter and activity in bilateral ventral gray matter regions. The latter is hypothesized to reflect descending modulation from the brainstem and cortex. Here, the functions corresponding to these areas of activity are investigated by varying the temperature of innocuous thermal stimuli, and the order they are presented, across repeated fMRI experiments in the spinal cord and brainstem. Group results and connectivity analyses reveal that the ipsilateral dorsal gray matter (dGM), the primary site of sensory input, also receives inhibitory input from the rostral ventromedial medulla and the locus coeruleus, two components of the brainstem opiate analgesia system. Ipsilateral ventral gray matter (vGM) receives input from the ipsilateral dGM and inhibitory input from the pontine reticular formation, which is involved with coordination of movements by modulation of ventral horn cells. Contralateral vGM regions appear to receive input from only the ipsilateral dGM in these studies. These results provide an unprecedented view of details of human spinal cord function and descending modulation, and have important implications for assessment of the effects of spinal cord trauma and disease by means of fMRI.