Efficacy of Transcranial Direct Current Stimulation In Parkinson's Disease MCI

Parkinson's Disease (PD) is the second most common neurodegenerative disorder. The period that apparent cognitive deficits exist without disrupting daily life activities is named as Mild Cognitive Impairment (PD-MCI). Treatments were considered to be more efficacious in PD-MCI than PD dementia as relatively less permanent changes in cortical structures occured. No approved treatments exist in PD-MCI and non-pharmacological treatments are under investigation as drugs have considerable amount of adverse effects.

Event Related Potentials (ERP) measurements have the advantages of providing direct and objective evidence of central nervous system functions, imaging of the activity of the cortical areas and being unaffected by motor deficits. ERP parameters were found to be related to cognitive functions and disrupted in PD and PD-MCI. Thus, ERP parameters were suggested to be useful in treatment efficacy assessment.

Transcranial Direct Current Stimulation (tDCS) is a promising non-invasive brain stimulation method. Ameliorating effects of tDCS on cognition and ERPs were observed. Enhancing effects of tDCS on some cognitive deficits were also reported in PD.

Few studies reported the efficacy of both tDCS and physical therapy/cognitive training and none assessed the efficacy of tDCS solely, compared to a sham control group. All studies assessed the efficacy without using electrophysiological measurements that reflect central nervous system functions directly. In this project, the efficacy of tDCS will be compared to a sham tDCS group and be assessed with electrophysiological measurements for the first time.

The study is a double-blind randomized controlled trial. The sample will be consisted of twenty six participants diagnosed as having PD-MCI due to Movement Disorders Society Level 2 criteria. The participants will be assigned to active or sham groups. Then, neuropsychological test performances and ERP parameters during Oddball paradigm and Continuous Performance Test will be measured. Then, participants will be applied ten active or sham sessions of left anodal/right cathodal tDCS over the dorsolateral prefrontal cortex (DLPFC). All measurements will be repeated both immediately and 1-month after the applications.

Succinctly, the aim of this project is to assess the effect of ten sessions left anodal/right cathodal tDCS over the DLPFC on cognitive functions and electrophysiological parameters in PD-MCI.

Inclusion criteria

• Clinical diagnosis of PD with at least two of the four diagnostic criteria for PD (tremor, rigidity, bradykinesia, and postural instability) in accordance with the United Kingdom Parkinson's Disease Society Brain Bank Diagnostic Criteria, issued by a neurologist specializing in movement disorders;
• Disease staging between I and III, according to the modified Hoehn and Yahr scale;
• Clinical diagnosis of PD- MCI in accordance with Level 2 Movement Disorders Society- Task Force diagnostic criteria;
• An unchanged stable and optimal regimen of dopaminergic medication for at least one month before study entry and able to continue on a stable regimen for the duration of the study;
• Ability to provide written informed consent;
• 5 or more years of education;
• Right-hand dominancy;
• Not taking any psychoactive medications before the previous month of the study and for the duration of the study;
• Naïve to tDCS.

Exclusion criteria

• Diagnosis or evidence of secondary or atypical parkinsonism;
• Patients with dementia;
• Less than 5 years of education;
• Previous history of surgical intervention for PD such as deep brain stimulation (DBS);
• Diagnosis of active major depressive disorder, psychotic disorders, bipolar disorder, alcohol use disorder and substance use disorders;
• Any history of any clinically significant neurological disorder, including organic brain disease, epilepsy, stroke, brain lesions, multiple sclerosis, previous neurosurgery, or personal history of head trauma that resulted in loss of consciousness for > 5 minutes and retrograde amnesia for > 30 minutes;
• Significant hearing loss or visual impairment;
• Diagnosis of any serious or uncontrolled medical condition such as chronic obstructive pulmonary disease, congestive heart failure or renal failure;
• Skin diseases that could potentially cause irritations under electrodes
• Patients missing two consecutive protocol sessions;
• Illiteracy, deficient language or refusal to participate or being not able to follow instructions or complete study tasks;.