Functional magnetic resonance imaging of the cervical spinal cord during thermal stimulation across consecutive runs

Abstract

The spinal cord is the first site of nociceptive processing in the central nervous system and has a role in the development and perpetuation of clinical pain states. Advancements in functional magnetic resonance imaging are providing a means to non-invasively measure spinal cord function, and functional magnetic resonance imaging may provide an objective method to study spinal cord nociceptive processing in humans. In this study, we tested the validity and reliability of functional magnetic resonance imaging using a selective field-of-view gradient-echo echo-planar-imaging sequence to detect activity induced blood oxygenation level-dependent signal changes in the cervical spinal cord of healthy volunteers during warm and painful thermal stimulation across consecutive runs. At the group and subject level, the activity was localized more to the dorsal hemicord, the spatial extent and magnitude of the activity was greater for the painful stimulus than the warm stimulus, and the spatial extent and magnitude of the activity exceeded that of a control analysis. Furthermore, the spatial extent of the activity for the painful stimuli increased across the runs likely reflecting sensitization. Overall, the spatial localization of the activity varied considerably across the runs, but despite this variability, a machine-learning algorithm was able to successfully decode the stimuli in the spinal cord based on the distributed pattern of the activity. In conclusion, we were able to successfully detect and characterize cervical spinal cord activity during thermal stimulation at the group and subject level.

Altered Cervical Spinal Cord Resting‐State Activity in Fibromyalgia

“…The specificity of sensory‐ or motor‐related BOLD signal change in the spinal cord is not consistently restricted to gray matter, as demonstrated in most studies (for example, see refs. and ). For example, motor task activation in the spinal cord encompasses the majority of the ipsilateral hemicord (spanning both gray and white matter) and is more focused in the anterolateral quadrant at higher thresholds .…”

Ten Key Insights into the Use of Spinal Cord fMRI

“…Several studies have also shown that BOLD signal activity measured with spinal fMRI can distinguish between different intensities of a painful stimulus (such as varying temperatures of a thermode applied to the skin) [ 31 , 33 , 34 , 40 ], as well as distinguish between painful and non-painful stimuli to the same area [ 24 , 32 , 34 ]. This body of evidence not only shows that different intensities of painful stimuli can be distinguished with spinal fMRI, but that individual differences in the perception of pain are also linked to BOLD signal changes in the spinal cord.…”

“…Depending on the necessity of salience for a chosen task, researchers may also want to train participants to become familiar with the stimulus or task (i.e., motor task, thermal stimulation, etc.) [ 19 , 26 , 28 , 37 , 38 , 40 , 47 , 48 , 50 , 52 , 53 , 57 , 62 , 80 , 81 , 83 ]. For example, Dobek et al trained their participants in two 1 h sessions on the expectation of a noxious thermal stimulus, with or without synchronous presentation of music, and rating this stimulus on a visual analog scale, to obtain reliable reactions to a predictable stimulus [ 47 ].…”

“…A solution to this is to collect data in multiple short runs, with a smaller number of stimuli presented in each one [ 23 , 28 , 33 , 34 , 36 , 38 , 40 , 42 , 44 , 47 , 48 , 53 , 56 , 58 , 59 , 62 , 63 , 82 , 85 , 87 , 88 ]. Murphy et al showed that the minimum number of volumes that should be acquired is determined by the percent signal change that can be detected (effect size), the signal-to-noise ratio ( SNR ) of the fMRI data, and the desired significance threshold [ 84 ].…”

“…As a result, the challenge presented by physiological noise is greater for data acquired with GE-EPI methods than with HASTE. The temporal signal-to-noise ratio has been reported to be approximately 15 with GE-EPI data (after motion correction was applied), and approximately 50 for data acquired with HASTE [ 40 , 44 , 101 ], and simulations yield SNR estimates of 24 and 56, respectively (as discussed in the section “HASTE vs. EPI”).…”