Parkinson's disease is a progressive and degenerative neurological movement disorder that affects thousands of people. The disease is characterized by presenting motor and non-motor symptoms, as the disease progresses, it becomes more disabling, making it impossible for the individual to perform simple tasks. A non-motor symptom increasingly reported by patients and undertreated in clinical practice is pain. During the past few decades, possible neural substrates of pain have been studied extensively, resulting in a potential network of connected brain areas that are believed to underlie pain processing and experience. There is no definitive consensus on all areas involved in such a pain network; however, pain-related regions consistently found across all studies include the thalamus, anterior cingulate cortex (ACC), posterior and anterior insula, amygdala, prefrontal cortex (PFC), secondary somatosensory cortex (IBS), and periaqueductal gray (PAG). With the aim of helping to improve the painful condition, non-pharmacological therapies have been studied, and one of them is phototherapy, a non-invasive method used by several areas of health, which has been shown to be increasingly effective in the treatment of decreased pain sensitivity. The present study aims to evaluate the effects of transcranial photobiomodulation in patients with Parkinson's disease. This is a randomized study, in which investigators will analyze the effect of FBM on pain control and on magnetic resonance images to better elucidate the connectivities of pain areas. Afterwards, the researchers will carry out a better elaboration on the treatments of individuals diagnosed with Parkinson's disease, the researchers will evaluate the pain through questionnaires, and the researchers will also evaluate the motor cognitive capacity of these patients before and after the therapy.

1. Objectives

General:

Evaluate the effects of applying transcranial photobiomodulation in patients with Parkinson's disease who show increased pain intensity when off levodopa.

Specific:

• Evaluate pain intensity using the Visual Analog Scale (VAS) before and after transcranial photobiomodulation sessions;
• Evaluate the sensitive, discriminative, affective-motivational and cognitive dimensions of pain by applying the McGill questionnaire before and after the end of treatment;
• Identify and grade pain by applying the King's Parkinson's Disease Pain Scale (KPPS) before and after treatment;
• Evaluate cognitive motor behavior using the Timed Up Go (TUG) and TUG Dual Task test at the beginning and end of treatment;
• Analysis of brain connectivities related to pain (connectivities of the thalamus, right cingulate cortex, striatum (caudate nucleus and putamen), and substantia nigra) using Functional Magnetic Resonance Imaging at rest before and after the end of treatment

Inclusion Criteria:

• Patients with Hoehn & Yahr 3
• Pain from Parkinson's disease
• Walk independently
• Ability to understand simple command

Exclusion Criteria:

• Wheelchair users
• Severe postural instability
• Severe cognitive impairment
• Contraindications for MRI, such as dyskinesia or deep brain stimulation

The study will be conducted by the main researcher, responsible for the evaluation and application of the questionnaires, who will not be aware of which group will be the experimental and/or placebo. The study will have a collaborator trained in the application of phototherapy, also without prior knowledge of both groups