Different mechanosensory stimulations of the lower back elicit specific changes in hemodynamics and oxygenation in cortical sensorimotor areas—AfNIRSstudy

Abstract

Background and ObjectivesThis study aimed at investigating the feasibility of functional near‐infrared spectroscopy (fNIRS) to measure changes in cerebral hemodynamics and oxygenation evoked by painful and nonpainful mechanosensory stimulation on the lower back. The main objectives were to investigate whether cortical activity can be (1) detected using functional fNIRS, and (2) if it is possible to distinguish between painful and nonpainful pressure as well as a tactile brushing stimulus based on relative changes in oxy‐ and deoxyhemoglobin ([O2Hb] and [HHb]).MethodsTwenty right‐handed subjects (33.5 ± 10.7 years; range 20–61 years; 8 women) participated in the study. Painful and nonpainful pressure stimulation was exerted with a thumb grip perpendicularly to the spinous process of the lumbar spine. Tactile stimulation was realized by a one‐finger brushing. The supplementary motor area (SMA) and primary somatosensory cortex (S1) were measured bilaterally using a multichannel continuous‐wave fNIRS imaging system.ResultsCharacteristic relative changes in [O2Hb] in the SMA and S1 after both pressure stimulations (corrected for multiple comparison) were observed. [HHb] showed only much weaker changes (uncorrected). The brushing stimulus did not reveal any significant changes in [O2Hb] or [HHb].ConclusionThe results indicate that fNIRS is sensitive enough to detect varying hemodynamic responses to different types of mechanosensory stimulation. The acquired data will serve as a foundation for further investigations in patients with chronic lower back pain. The future aim is to disentangle possible maladaptive neuroplastic changes in sensorimotor areas during painful and nonpainful lower back stimulations based on fNIRS neuroimaging.

Signal Processing in Functional Near-Infrared Spectroscopy (fNIRS): Methodological Differences Lead to Different Statistical Results

“…Each light source contains two LEDs that emit at 760 nm and 850 nm. Further information about the device can be found elsewhere (Piper et al, 2014 ; Vrana et al, 2016 ). Textile EEG caps of different sizes (i.e., circumferences of 54, 56, 58 and 60 cm) were used to take the participants’ head anatomy into account (for head circumferences between two cap sizes, the smaller cap was used).…”

Cortical Sensorimotor Processing of Painful Pressure in Patients with Chronic Lower Back Pain—An Optical Neuroimaging Study using fNIRS

“…Additionally, grand-averages for the patients with CLBP are also displayed in Figures 2–4 (calculated using the Analysis_All approach), visualizing the dynamics of the hemodynamic responses and their significance against baseline. The dynamics of the hemodynamic responses (against baseline) of the HC group have been already published elsewhere (Vrana et al, 2016). Patients with CLBP exhibited significant changes in [O 2 Hb] only in the painful condition in right S1 and also in one channel in the brushing condition, while HC exhibited significant changes in [O 2 Hb] in both pressure conditions as well as both ROIs (for detailed results see Table 4).…”

“…A possible habituation and/or sensitization effect in the hemodynamic responses in the healthy population in our study was analyzed in our previous article (Vrana et al, 2016). Neither a habituation nor a sensitization effect at group level in this healthy population was found for our pressure stimulation on the lower back.…”

“…In contrast, the second approach included only those channels in the group-level analysis, which were already showing statistical significance at single-subject level ( Analysis_Responders ). Therefore, only channels which showed a neural or systemic task-related change were included, while channels which did not show any response were excluded from the group analyses in order to enhance specificity and decrease the false-positive rate (Tachtsidis and Scholkmann, 2016; Vrana et al, 2016). Both approaches are provided for all statistical within-group analyses.…”

“…The main disadvantage of fNIRS is its limited penetration depth, which limits the reachable regions. Nevertheless, important parts of the sensorimotor system are placed at the cortical surface, being therefore accessible by using fNIRS (Vrana et al, 2016). Based on these facts, the S1 and the SMA were assigned as regions of interest, both known to be active during non-painful pressure on the lower back (Boendermaker et al, 2014) and also involved in cortical sensorimotor pain-related processing in healthy subjects (Bushnell et al, 1999; Coghill et al, 1999; Xie et al, 2009; Yücel et al, 2015).…”