The Effects of Specific tDCS on Cognition in MCI

Study Design This is a multi-center, randomized, controlled study registered and carried out at Medipol University Hospital and Alaaddin Keykubat University Training and Research Hospital. The objective of the study is to evaluate the effectiveness of atDCS stimulation over DLPFC and LPC on cognitive skills of patients with PD-MCI and aMCI.

The patients will be randomized to 2mA tDCS over DLPFC and over LPC, or Sham control. tDCS stimulation will last for 20 minutes a day for 5 consecutive days, a total of 10 sessions in 14 days. The outcome of the simulations will be evaluated by various neurocognitive tests at the baseline, at the end of 14 days and then, 90 days.

Brain connectivity will be analyzed by resting state-functional magnetic resonance imaging (fMRI) and neuronal activity will be analyzed by electroencephalography (EEG) at the baseline, at the end of 14 days and 90 days..

This study aims to give important translational messages in the field of clinical neuroscience by exploring the pro-cognitive effects of tDCS application including its optimal application methods. In this framework, the restorative benefits of tDCS can be critical to understand the cause-effect relationship between certain neural circuits and behavioral outcomes, which might be important in understanding the pathophysiology of MCI and PD. From another point of view, our findings might be valuable in terms of prolonged life-expectancy and the maintenance of preserved cognitive skills in the elderly.

Although tDCS is still in a premature stage, it has certain advantages in terms of portability, cost-effectiveness and user-friendly application compared to other non- invasive stimulation applications. This study will contribute to the growing literature in terms of its optimal application methods, side-effects and long-term (90 days) neurobehavioral results.

Inclusion criteria

• Providing an informed consent;
• Literate and between 45-80 years of age;
• 60 females and 60 males;
• Diagnosed with PD based on criteria suggested by UK Parkinson's Disease Society, Brain Bank and PD-MCI in accordance with the diagnostic criteria suggestions by Litvan;
• Diagnosed with aMCI based on diagnosis criteria (CDR>0.5) suggested by Petersen;
• On a stable pharmacological treatment minimum for one month with no washout period.

Exclusion criteria

• Illiterate or education level less than primary school
• Having an existing and/or prior neurological disease; psychiatric disease or head trauma; and/or irreversible hearing or sight problems or other medical illness (e.g. diabetes mellitus, hypertension);
• Exhibiting signs of dementia for PD group ;
• Having medical issues that prevent undergoing fMRI or for tDCS application.