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Summary
Interaction between the motor and nociceptive systems seems to play an important role in chronic pain. In this pilot study we used a combination of functional near-infrared spectroscopy (FNIRS) and laserevoked potentials (LEPs) during concurrent finger tapping task and noxious laser stimulation in fibromyalgia (FM) patients and controls. The study included 9 healthy subjects and 15 FM patients. During concurrent FNIRS and LEP recording, participants were required either to remain in resting relaxed condition or to execute a finger tapping task with the right hand. In the control group, the left motor cortex showed increased oxyhaemoglobin levtls, while the early N1 LEP component was reduced, during the finger tapping task. In FM patients, motor cortex oxyhaemoglobin concentrations were lower during movement, which did not reduce LEPs. The left motor cortex oxyhaemoglobin concentrations had 79.2% diagnostic accuracy. The interplay between motor and pain-related circuits seems to be dysfunctional in FM patients. These results may support a role for motor cortex modulation in the treatment of this disabling disease.
KEY WORDS: fibromyalgia, functional near-infrared spectroscopy, laser-evoked potentials, motor cortex, somatosensory cortex.
Introduction
According to clinical and experimental studies, the motor cortex seems to interfere with distant neural structures beyond those involved in motor control, for example with cortical pain networks (Leite et al., 2017). The effectiveness of non-invasive neurostimulation of the primary motor cortex in improving chronic pain, including fibromyalgia (FM) (Mhalla et al., 2011; Zhu et al., 2016; Lefaucheur et al., 2006), provides robust confirmation of this hypothesis. The mutual interference between motor activity and pain control is very complex, as pain itself can change motor cortex function in a way that could facilitate the maintenance of chronic symptoms (Chang et al., 2018).
Fibromyalgia is a chronic disorder whose features are diffuse pain, fatigue, impaired sleep and cognitive dysfunction (Wolfe et al., 2010). It seems to be characterized by abnormal pain processing with involvement of the central and probably the peripheral nervous system (de Tommaso et al., 2011,2014). Patients with FM avoid physical activity due to pain and this can reduce their fitness (Cohen, 2017). Motor cortex function and its relationships with pain circuits may be an interesting topic to explore in FM in view of the therapeutic approach based on M1 neurostimulation or...