ABSTRACT
Brain reorganization following spinal cord injury (SCI) has been well-established using animal and human studies. Yet, much is unknown regarding functional recovery and adverse secondary outcomes after SCI. Functional near-infrared spectroscopy (fNIRS) is a neuroimaging technique that offers methodological flexibility in a real-world setting. We used fNIRS to examine the cortical functional differences between 12 males with thoracolumbar SCI (46.41 ± 11.09 years of age) and 12 healthy males (47.61 ± 11.94 years of age) during resting state and task conditions-bilateral finger tapping (FT), mental imagery of bilateral FT with action observation (FTI+AO), and bilateral ankle tapping (AT). We found an overall decrease in hemodynamic response of the SCI group during all three task conditions. Task modulated functional connectivity (FC) computed using beta series correlation technique was compared using independent sample t-tests at α = 0.05. Connectivity between the right mediolateral sensorimotor network (SMN) and the right medial SMN was reduced during the FT task in SCI. A mixed analysis of variance revealed that the FC within the right mediolateral SMN was reduced during FT but preserved during FTI+AO (i.e., comparable to controls) in the SCI group. Lower FC of these regions was associated with longer injury durations. Additionally, we found a general decrease in resting state FC of the SCI group, specifically in the Slow-3 frequency range (0.073 to 0.1 Hz). These results, though preliminary, are consistent with past studies and highlight the potential of fNIRS in SCI and rehabilitative research.
Subject(s)
Magnetic Resonance Imaging , Spinal Cord Injuries , Male , Animals , Humans , Child , Spectroscopy, Near-Infrared , Brain , Spinal Cord Injuries/diagnostic imaging , NeuroimagingABSTRACT
BACKGROUND: Patients undergoing surgical procedures are vulnerable to repetitive evoked or ongoing nociceptive barrage. Using functional near infrared spectroscopy, the authors aimed to evaluate the cortical hemodynamic signal power changes during ongoing nociception in healthy awake volunteers and in surgical patients under general anesthesia. The authors hypothesized that ongoing nociception to heat or surgical trauma would induce reductions in the power of cortical low-frequency hemodynamic oscillations in a similar manner as previously reported using functional magnetic resonance imaging for ongoing pain. METHODS: Cortical hemodynamic signals during noxious stimuli from the fontopolar cortex were evaluated in two groups: group 1, a healthy/conscious group (n = 15, all males) where ongoing noxious and innocuous heat stimulus was induced by a contact thermode to the dorsum of left hand; and group 2, a patient/unconscious group (n = 13, 3 males) receiving general anesthesia undergoing knee surgery. The fractional power of low-frequency hemodynamic signals was compared across stimulation conditions in the healthy awake group, and between patients who received standard anesthesia and those who received standard anesthesia with additional regional nerve block. RESULTS: A reduction of the total fractional power in both groups-specifically, a decrease in the slow-5 frequency band (0.01 to 0.027 Hz) of oxygenated hemoglobin concentration changes over the frontopolar cortex-was observed during ongoing noxious stimuli in the healthy awake group (paired t test, P = 0.017; effect size, 0.70), and during invasive procedures in the surgery group (paired t test, P = 0.003; effect size, 2.16). The reduction was partially reversed in patients who received a regional nerve block that likely diminished afferent nociceptive activity (two-sample t test, P = 0.002; effect size, 2.34). CONCLUSIONS: These results suggest common power changes in slow-wave cortical hemodynamic oscillations during ongoing nociceptive processing in conscious and unconscious states. The observed signal may potentially promote future development of a surrogate signal to assess ongoing nociception under general anesthesia.
