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Safety and cognitive effect of frontal DC brain polarization in healthy individuals

From the Brain Stimulation Unit and Cognitive Neuroscience (Drs. Iyer, Grafman, and Wassermann, and U. Mattu), Human Motor Control (Dr. Lomarev), and EEG Sections (Dr. Sato), National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD.

Address correspondence and reprint requests to Dr. Eric M. Wassermann, Building 10, Room 5N254, 10 Center Dr. MSC 1430, Bethesda, MD 20892-1430; e-mail: wassermanne{at}ninds.nih.gov

Background: Data from the human motor cortex suggest that, depending on polarity, direct current (DC) brain polarization can depress or activate cortical neurons. Activating effects on the frontal lobe might be beneficial for patients with frontal lobe disorders. This phase 1 study tested the safety of frontal DC, including its effects on frontal and other brain functions.

Methods: The authors applied 20 minutes of anodal, cathodal, or sham DC to the left prefrontal cortex in three groups of right-handed subjects and looked for effects on global measures of processing and psychomotor speed, emotion, and verbal fluency, a measure of local cortical function. In one experiment (n = 30), the authors tested before and after 1 mA DC and monitored EEG in 9 subjects. In two other experiments using 1 mA (n = 43) and 2 mA (n = 30), the authors tested before and then starting 5 minutes after the onset of DC.

Results: All subjects tolerated DC well. There were no significant effects on performance with 1 mA DC. At 2 mA, verbal fluency improved significantly with anodal and decreased mildly with cathodal DC. There were no clinically significant effects on the other measures.

Conclusions: Limited exposure to direct current polarization of the prefrontal cortex is safe and can enhance verbal fluency selectively in healthy subjects. As such, it deserves consideration as a procedure to improve frontal lobe function in patients.

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