Characterization of DTI Indices in the Cervical, Thoracic, and Lumbar Spinal Cord in Healthy Humans

The aim of this study was to characterize in vivo measurements of diffusion along the length of the entire healthy spinal cord and to compare DTI indices, including fractional anisotropy (FA) and mean diffusivity (MD), between cord regions. The objective is to determine whether or not there are significant differences in DTI indices along the cord that must be considered for future applications of characterizing the effects of injury or disease. A cardiac gated, single-shot EPI sequence was used to acquire diffusion-weighted images of the cervical, thoracic, and lumbar regions of the spinal cord in nine neurologically intact subjects (19 to 22 years). For each cord section, FA versus MD values were plotted, and a k-means clustering method was applied to partition the data according to tissue properties. FA and MD values from both white matter (average FA = 0.69, average MD = 0.93 × 10−3 mm2/s) and grey matter (average FA = 0.44, average MD = 1.8 × 10−3 mm2/s) were relatively consistent along the length of the cord

Characterization of DTI Indices in the Cervical, Thoracic, and Lumbar Spinal Cord in Healthy Humans

The aim of this study was to characterize in vivo measurements of diffusion along the length of the entire healthy spinal cord and to compare DTI indices, including fractional anisotropy (FA) and mean diffusivity (MD), between cord regions. The objective is to determine whether or not there are significant differences in DTI indices along the cord that must be considered for future applications of characterizing the effects of injury or disease. A cardiac gated, single-shot EPI sequence was used to acquire diffusion-weighted images of the cervical, thoracic, and lumbar regions of the spinal cord in nine neurologically intact subjects (19 to 22 years). For each cord section, FA versus MD values were plotted, and a k-means clustering method was applied to partition the data according to tissue properties. FA and MD values from both white matter (average FA = 0.69, average MD = 0.93 × 10 −3 mm 2 /s) and grey matter (average FA = 0.44, average MD = 1.8 × 10 −3 mm 2 /s) were relatively consistent along the length of the cord

Peer Victimization Is Associated With Neural Response to Social Exclusion

Peer victimization is associated with increased risk for mental health problems. These adverse psychological outcomes are linked with altered cognitive and emotional processes and their related neural functioning. In the present study, by using functional magnetic resonance imaging (fMRI), we examined whether peer victimization was associated with heightened neural response to social exclusion. Participants (N = 45; Mage = 17.7 years, SD = 0.60; 36 women) included three mutually exclusive groups: peer-victimized individuals (targets of bullying), cyberdefenders (defended peers who were being cyberbullied), and controls (not involved as targets or cyberdefenders). All participants underwent an fMRI scan while playing Cyberball, an experimental paradigm that simulates social exclusion. Peer victimization was associated with increased neural response in the left amygdala, left parahippocampal gyrus, left inferior frontal operculum, and right fusiform gyrus. Understanding the acute neural response to social exclusion in peer-victimized individuals may provide insight into their increased risk for poor mental health

Continuous Descending Modulation of the Spinal Cord Revealed by Functional MRI.

Spontaneous variations in spinal cord activity may arise from regulation of any of a number of functions including sensory, motor, and autonomic control. Here, we use functional MRI (fMRI) of healthy participants to identify properties of blood oxygenation-level dependent (BOLD) variations in the spinal cord in response to knowledge that either a noxious stimulus is impending, or that no stimulus is to be expected. Expectation of a noxious stimulus, or no stimulus, is shown to have a significant effect on wide-spread BOLD signal variations in the spinal cord over the entire time period of the fMRI acquisition. Coordination of BOLD responses between/within spinal cord and brainstem regions are also influenced by this knowledge. We provide evidence that such signal variations are the result of continuous descending modulation of spinal cord function. BOLD signal variations in response to noxious stimulation of the hand are also shown, as in previous studies. The observation of both continuous and reactive BOLD responses to emotional/cognitive factors and noxious peripheral stimulation may have important implications, not only for our understanding of endogenous pain modulation, but also in showing that spinal cord activity is under continuous regulatory control

Average time-courses of spinal cord voxels which are significantly correlated with seed regions in (A) (left) the right-dorsal region of C6, and (B) (right) the left-dorsal region of C6.

<p>The voxels are as depicted in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0167317#pone.0167317.g002" target="_blank">Fig 2</a>. Signal intensity patterns obtained during stimulation conditions are shown in blue, and the no-stimulation condition is shown in red. Time-course data were converted to z-scores with mean values of zero. Error bars indicate the standard-error-of-the-mean across fMRI runs. Red and blue asterisks (*) indicate values which are significantly different than the mean value of zero, at p < 10⁻⁴, for no-stimulation and stimulation runs, respectively. Black asterisks indicate intensity values which are significantly different between the two study conditions, at p < 10⁻⁴. Times are indicated corresponding to when participants were informed of the study type, the start of the stimulation period (for studies with heat stimulation), and the time at which the rating scale was displayed in all studies.</p

Connectivity between voxels and selected seed regions.

<p>Anatomical locations of regions with time-courses that are significantly correlated with seed regions in the right/left and dorsal/ventral regions of C6, are shown in colour overlaid on gray-scale anatomical images. Each frame represents a 1 mm thick transverse slice, and slices are shown every 4 mm along the cord (horizontally in the figure) to depict the rostral-caudal range along the spinal cord, and a section of the medulla. The seed regions are identified by the highly correlated (dark red) voxels within the regions. Positions along the cord/brainstem are indicated relative to the seed region center, in millimeters.</p

A structural equation modeling (SEM) analysis was used to investigate input signaling to the spinal cord dorsal horn (DH) in the 6^th cervical segment, from the nucleus raphe magnus (NRM), nucleus gigantocellularis (NGc), and the dorsal reticular nucleus (DRt).

<p>Results are shown for the sub-regions (right panel) which provided the best fit to the BOLD signal intensity variations in the spinal cord DH, when a stimulus was expected and applied, and when a stimulus was not expected and not applied (i.e. no-stimulation). The time-series responses in the identified regions are shown (left panels) for each study condition, as well as the SEM fit to the spinal cord time-series responses (red lines). Plotted values are the average over the region across runs/participants and error bars indicate the standard error of the mean (SE) across participants. The SEM weighting factors that were determined, and used for the fit, are indicated below each time-series plot (± SE). Periods are highlighted when the participants were informed of the study type, and when the stimulus was applied, or was not applied.</p

Dynamic variations in the correlation between time-series responses are shown for the regions identified by the SEM analysis as having the strongest relationships (i.e. the best fit).

<p>Time intervals spanning 41 seconds were selected throughout the fMRI paradigm, and the correlation was computed to investigate how the relationships evolved. Correlations between the cord DH time series and the NRM (red), NGc (green), and DRt (blue), are shown for the no-stimulation condition (brighter tones), and with a stimulus applied (darker tones). Positive correlations are most notable prior to the stimulation period, and are primarily in the NRM, whereas negative correlations predominate during and after the stimulation period, and are primarily in the DRt. Significant correlations are inferred at |R| ≥ 0.74 (indicated by horizontal lines).</p