Transcranial Direct Current Stimulation as a Non-Medication Modality for Attention Enhancement:A Review of the Literature

Objective: Attention is a higher cognitive function and its controlled manipulation has been always a research interest. Transcranial direct current stimulation (tDCS) is a non-invasive neuromodulation technique with promising therapeutic outcomes in different neuropsychiatric disorders. Initial studies have shown potential efficacy of tDCS for enhancing attention in neuropsychiatric and healthy individuals. The present study aims to review the tDCS studies on modulating attention among healthy individuals. The potentials of this technique for controlled modulation of attention related performance are discussed. Methods: The databases of PubMed (1980-2016), Web of Sciences (1985-2016), PsychInfo (1985-2016), and Google Scholar (1980-2016) were explored using the search terms "transcranial direct current stimulation" or 'tDCS", "attention", " healthy individuals", and "modulation". The obtained results were screened for the title and abstract and the relevant papers were selected for a comprehensive review. Results: Ten studies were included in this review. The protocols applied for improving attention in healthy subjects to modulate attention under different attention specific tasks are discussed. Although studies on attention modulation in healthy individuals are in initial step, the outcomes are relatively promising. The most frequent used regions of brain were dorsolateral prefrontal cortex (DLPFC) and right inferior frontal gyrus. The current density ranging 30-35 μA/cm² and anodal over left DLPFC can enhance attention in healthy individuals. Conclusion: Current evidence shows relative efficiency of tDCS for controlled modulation of attention in healthy individuals. For clinical application of this technique as an alternative or adjunctive modality of attention modulation further controlled studies are needed.