Transcranial Direct Current Stimulation Effect on Pain Threshold and Working Memory in Healthy Adolescents, Young Adults and Elderly: a Randomized , Cross-over, Single Blind Trial

Transcranial direct current stimulation (tDCS) is a neuromodulation method that has great potential as an aid in the therapeutic management of neuropsychiatric disorders and chronic pain syndromes. tDCS modulates the neuronal membrane potential , facilitating neuronal depolarization or hyperpolarization, hence modifying the cortical excitability of the stimulated area. However, despite promising results the response to stimulation presents great variability among subjects. Chronological age is an important factor in the variation of brain plasticity. The dorsolateral prefrontal cortex (DLPFC) is associated with cognitive and emotional aspects of pain, in addition to being related to executive components of working memory. Anodal tDCS on DLPFC modulates pain level in patients with chronic pain and modifies working memory performance in healthy subjects and patients with memory impairment. The prefrontal cortex presents a great structural difference throughout lifespan: it is under maturational process in the adolescence, reaching peak of maturation in the adult life, and initiating process of cerebral senescence in elderly subjects. Therefore, the use of tDCS on DLPFC in these three age groups presents potential for a large variation in response. Faced with the potential of tDCS for adjuvant use in the treatment of several diseases, it is imperative to understand the variability of this intervention between different age groups. This knowledge may allow the optimization of neuromodulation protocols, allowing more careful and refined use in the clinic. The study primary outcomes is the difference between and within age groups on the variation of pre and post tDCS on pain threshold evaluated by Heath pain threshold on a Quantitative sensory testing paradigm and working memory performance evaluated by n-back test in healthy subjects of three age groups: adolescents, young adults, elderly. This is a randomized, single blinded, cross-over, sham-controlled clinical trial. The study will be conducted at the Clinical Research Center of the Hospital de Clínicas of Porto Alegre (HCPA). It will include 30 women, 10 women by age group: adolescents between 15 and 16 years,young adults between 30 and 40 years old and elderly women between 60 and 70 years. Participants will be randomized for a cross-over of three sessions: anodal stimulation in DLPFC, anodal stimulation in primary motor cortex (M1) as active control and sham stimulation.