Makoto Nishihara

Wind-up is a nociceptive-specific phenomenon in which pain sensations are facilitated, in a frequency-dependent manner, by the repeated application of noxious stimuli of constant intensity, with invariant tactile sensations. Thus, cortical activities during wind-up could be an alteration associated with pain potentiation. We aimed to investigate somatosensory-evoked cortical responses and induced brain oscillations during wind-up by recording magnetoencephalograms. Wind-up was produced by the application of 11 consecutive electrical stimuli to the sural nerve, repeated at a frequency of 1 Hz without varying the intensity. The augmentation of flexion reflexes and pain rating scores were measured simultaneously as an index of wind-up. In the time-frequency analyses, the γ-band late event-related synchronization and the β-band event-related desynchronization were observed in the primary somatosensory region and the bilateral operculo-insular region, respectively. Repetitive exposure to the stimuli enhanced these activities, along with an increase in the flexion reflex magnitude. The evoked cortical activity reflected novelty, with no alteration to these repetitive stimuli. Observed oscillations enhanced by repetitive stimulation at a constant intensity could reflect a pain mechanism associated with wind-up.

Previous studies have suggested that change-related cortical responses are phenomena similar to the onset response and could be applied to the loudness dependence of auditory evoked potential (LDAEP) paradigm. In the present study, we examined the relationship between LDAEP and the change-related response using electroencephalography findings in 50 healthy subjects. There were five conditions (55, 65, 75, 85, and 95 dB) for LDAEP and five similar conditions (abrupt sound pressure increase from 70 to 75, 80, 85, 90, and 95 dB) for the change-related response. Both the onset and abrupt sound pressure increase evoked a triphasic response with peaks at approximately 50 (P50), 100 (N100), and 200 (P200) ms. We calculated the peak-to-peak amplitudes for P50/N100 and N100/P200. Medians and slopes for P50/N100 and N100/P200 amplitudes were calculated and compared between the two measures. Results revealed a significant correlation for both the slope and median for P50/N100 (r = 0.36, 0.37, p = 1.0 × 10⁻², 7.9 × 10⁻³), N100/P200 (r = 0.40, 0.34, p = 4.0 × 10⁻³, 1.6 × 10⁻²), and P50/N100/P200 (r = 0.36, 0.35, p = 1.0 × 10⁻², 1.3 × 10⁻²). These results suggested that the change-related response and LDAEP shared generation mechanisms at least partially.

: Rodent behavior assessments have been developed to evaluate pain. However, their fidgety activity and reactivity to human contact make it hard to activate animals in a consistent manner and get uniform and trustworthy responses. The present study was performed on prairie voles (aged 8 weeks). Sham (7 male prairie voles) and chronic constriction injury (CCI) (8 male prairie voles) rodents were investigated before surgery and four and seven days later. Each animal was assessed for nociceptive behavior. Pressure and mechanical threshold tests were conducted by the application of three different pushers to the center of hind paws and arterial clips to the toes while sedated with isoflurane. The CCI affected right lower extremity prominently increased nociceptive behavior scores four and seven days after the experiment, and the CCI affected right hind paw prominently decreased pressure and mechanical threshold tests four and seven days after the experiment . The pressure and mechanical thresholds were relevant to the scorings of nociceptive behavior in CCI model animals.

Recent clinical practice guidelines for chronic pain indicate, with a high evidence level, that the combination of exercise and cognitive behavioral therapy (CBT) is effective. The purpose of this study was to evaluate the effectiveness of an exercise facilitation method in combination with CBT using the “Ikiiki Rehabilitation Notebook” for patients with intractable chronic pain. “Ikiiki” means active in Japanese. A total of 22 cases with chronic low back (n = 13), lower extremity (n = 8), or neck (n = 1) pain were treated using this notebook. Two cases dropped out, leaving 22 cases. Each case was evaluated in terms of the numerical rating scale (NRS) of the pain, activities of daily living (ADL), pain catastrophizing scale (PCS), and quality of life (QOL) at pretreatment and post-treatment. The endpoint of the method was to achieve the long-term goals set by the patients. The mean treatment period was 11.2 months. The outcomes were as follows: improvement of presenteeism: nine cases; enhanced participation in hobbies: seven cases; improved school attendance: two cases; return to work: one case; improvement of self-care and/or self-efficacy: three cases. The NRS, ADL, PCS, and QOL were significantly improved after the treatment. This method is possibly valuable for educating patients about the cause and treatment of chronic pain and actively facilitating exercise and social participation. Further studies are needed to investigate the effectiveness of using this notebook for the patient with intractable chronic pain.

Purpose: The purpose of the present study was to investigate the visual attentional behavior towards a pain-affected area and face/body images using eye tracking in complex regional pain syndrome (CRPS) patients. Moreover, we investigated the relationship between visual attentional behavior and clinical symptoms. Patients and methods: Eight female patients with CRPS type 1 in their upper limbs and 8 healthy adult women participated in this study. First, the participants were asked to watch videoclips in a relaxed manner (Videoclip 1 featured young adults who introduced themselves; Videoclip 2 featured young adults touching the hand of the other person sitting across from them with their hand.) Eye movement data were tracked with eye-tracking glasses. Results: In video clip 1, the fixation duration (FD) and fixation count (FC) on faces tended to be lower in CRPS patients than in healthy controls. This tendency was found in patients with low body cognitive distortions. In video clip 2, CRPS patients displayed significantly lower FD and FC on the unaffected hand while watching a video of the unaffected hand being touched compared with healthy controls. Moreover, patients with low body cognitive distortion displayed significantly longer FD on the affected hand. Conclusion: Some CRPS patients differed in visual attentional behavior toward the face and body compared with healthy controls. In addition, our findings suggest that patients with lower body cognitive distortion may have a high visual attention for the affected hand, while patients with higher distortion may be neglecting the affected hand.

Haptic memory briefly retains somatosensory information for later use; however, how and which cortical areas are affected by haptic memory remain unclear. We used change‐related cortical responses to investigate the relationship between the somatosensory cortex and haptic memory objectively. Electrical pulses, at 50 Hz with a duration of 500 ms, were randomly applied to the second, third, and fourth fingers of the right and left hands at an even probability every 800 ms. Each stimulus was labeled as D (preceded by a different side) or S (preceded by the same side). The D stimuli were further classified into 1D, 2D, and 3D, according to the number of different preceding stimuli. The S stimuli were similarly divided into 1S and 2S. The somatosensory‐evoked magnetic fields obtained were divided into four components via a dipole analysis, and each component's amplitudes were measured using the source strength waveform. The results showed that the preceding event did not affect the amplitude of the earliest 20–30 ms response in the primary somatosensory cortex. However, in the subsequent three components, the cortical activity amplitude was largest in 3D, followed by 2D, 1D, and S. These results indicate that such modulatory effects occurred somewhere in the somatosensory processing pathway higher than Brodmann's area 3b. To the best of our knowledge, this is the first study to demonstrate the existence of haptic memory for somatosensory laterality and its impact on the somatosensory cortex using change‐related cortical responses without contamination from peripheral effects.

Several behavioral tests have been devised to assess pain in rodent models, one of which is the Chronic constriction injury (CCI) model of the sciatic nerve ...