Neurophysiological and behavioral effects of oscillatory transcranial direct current stimulation (otDCS)

Oscillatory transcranial direct current stimulation (otDCS) is a form of non-invasive electrical stimulation that has shown promise in modulating human cognition and behavior. This method merges constant polarization with an oscillation, resulting in a combination of features that characterize transcranial direct and alternating current stimulation (tDCS, tACS). While tDCS and tACS have been extensively characterized during the last two decades, otDCS remains comparatively underexplored. However, recent studies emphasize its potential efficacy in modulating, e.g., sleep-related slow oscillations, memory, and awake cognition. This review synthesizes the current understanding of otDCS mechanisms, its unique neurophysiological characteristics, and its behavioral and cognitive effects. We describe how the combination of a constant offset and oscillatory component yields an asymmetric electric field, potentially resulting in distinct subthreshold modulation and entrainment dynamics. Empirical findings suggest that otDCS can modulate cortical excitability, activity, and oscillatory power. Furthermore, we describe evidence on how otDCS may enhance memory consolidation during sleep, as well as modulate attention, executive function, and associative learning during wakefulness. Together, the available evidence indicates that otDCS represents a promising approach for frequency-specific and polarity-dependent modulation of cortical activity, warranting further mechanistic and translational research.