Direct current stimulation boosts hebbian plasticity in  vitro

There is evidence that transcranial direct current stimulation (tDCS) can improve learning performance. Arguably, this effect is related to long term potentiation (LTP), but the precise biophysical mechanisms remain unknown.
Source: BRAIN STIMULATION: Basic, Translational, and Clinical Research in Neuromodulation - Category: Neurology Authors: Source Type: research