Mental Representation Techniques for the Treatment of Parkinson´s Disease-related Pain

Pain is an under-reported but prevalent symptom in Parkinson´s Disease (PD), impacting patients' quality of life. Both pain and PD conditions cause cortical excitability reduction, but mental representations techniques are thought to be able to counteract it, resulting also effective in chronic pain conditions. The investigators of the present project aim to evaluate the efficacy of a novel mental representation protocol in the management of pain in PD patients during the ON state. The investigators hypothesize that Action Observation (AO) and Motor Imagery (MI) training through a Brain-Computer Interface (BCI) using Virtual Reality (AO+MI-BCI) can improve clinical pain and its central processing features.

Parkinson´s Disease (PD) affects between 4.1 and 4.6 million people in the world. The diagnosis of PD is currently clinical and based on its motor manifestations (bradykinesia, rest tremor, and rigidity). However, non-motor symptoms such as pain, fatigue, and neuropsychiatric manifestations are present in more than 70% of subjects. Pain affects about 85% of patients but is paradoxically under-reported and consequently under-treated in PD patients with a great impact on their quality of life. Levodopa, which is the election treatment in PD, has shown controversial results regarding pain sensitivity and has been shown ineffective for enhancing the endogenous pain modulation system. Furthermore, there is a lack of management protocols and nonpharmacologic treatments for pain in PD. Several syndromes are hypothesized to be involved in PD pain generation. Generally, PD patients suffer from alterations in peripheral transmission, sensitive-discriminative processing, pain perception, and pain interpretation in multiple levels, due to neurodegenerative changes in dopaminergic pathways and non-dopaminergic pain-related structures. Therefore, central mechanisms are proposed to be crucial for the development and establishment of pain in PD patients. Regarding pain processing features, PD patients have reduced pain thresholds, an augmented Temporal Summation (TS) after repetitive nociceptive stimulus, and the impairment of their Conditioned Pain Modulation (CPM) is correlated with greater severity and premature onset of the disease. Cortical excitability reduction is common in patients with pain. Therefore, diverse therapies are being developed to counteract this cortical excitability reduction and obtaining, consequently, effective pain relief. In consonance with these findings, in PD condition, especially in off state, there is also evidence of cortical excitability decrease but, to the best of investigators´ knowledge, there are no studies targeting cortical excitability to treat pain in PD. Thus, the present study proposes mental representation techniques for the treatment of PD-related pain. The mental representation techniques included in the protocol will be Action Observation (AO) and Motor Imagery (MI). The combination of AO and MI has shown to synergically increase cortical excitability, influencing the activation of cortical areas such as M1 and DLPFC. Specifically in PD, AO and MI have also demonstrated to produce corticomotor facilitation. In addition, mental representation training can produce neurophysiological activity similar to actual exercise training, which has shown to decrease the intensity and severity of pain in PD patients. The main aim of this study is to conduct an independent parallel randomized controlled trials based on AO+MI-BCI targeting changes in 1. validated general and specific PD related pain scales and 2. psychophysical measurements of pain modulation mechanisms. The investigators´ main hypothesis is that AO+MI-BCI will be superior to their respective control placebo intervention.

Eligibility Criteria:
Inclusion Criteria:

* Neuroimaging study without previous pathologies.
* Score \> 5 in transfers (bed to chair and back) item in Barthel Index.
* Score = or \> 24 in Mini-Mental State Examination.
* Able to provide informed consent to participate in the study.

Exclusion Criteria:

* History of neurologic disease different from PD.
* Presence of non-related to PD pain.
* Dermatologic problems, wounds, or ulcers in the electrode's application area.
* Significative difficulties in language.
* History of alcohol or drugs abuse.
* Non-controlled medical problems.
* Pregnancy.