It is not definitely known how direct-current stimulation causes its long-lasting effects. Here, we tested the hypothesis that the long time course of transcranial direct-current stimulation (tDCS) is because of the electrical field increasing the plasticity of the brain tissue. If this is the case, then we should see tDCS effects when humans need to encode information into long-term memory, but not at other times. We tested this hypothesis by delivering tDCS to the ventral visual stream of human participants during different tasks (i.e., recognition memory vs. visual search) and at different times during a memory task. We found that tDCS improved memory encoding, and the neural correlates thereof, but not retrieval. We also found that tDCS did not change the efficiency of information processing during visual search for a certain target object, a task that does not require the formation of new connections in the brain but instead relies on attention and object recognition mechanisms. Thus, our findings support the hypothesis that direct-current stimulation modulates brain activity by changing the underlying plasticity of the tissue.

目前尚不清楚直流电刺激是如何产生长期影响的。在这里，我们测试了以下假设：经颅直流电刺激 (tDCS) 的长时间过程是因为电场增加了脑组织的可塑性。如果是这种情况，那么当人类需要将信息编码到长期记忆中时，我们应该会看到 tDCS 效应，但在其他时候则不然。我们通过在不同任务（即识别记忆与视觉搜索）和记忆任务期间的不同时间将 tDCS 传递到人类参与者的腹侧视觉流来测试这一假设。我们发现 tDCS 改善了记忆编码及其神经相关性，但不改善检索。我们还发现tDCS在视觉搜索某个目标对象时并没有改变信息处理的效率，一项不需要在大脑中形成新连接而是依赖于注意力和物体识别机制的任务。因此，我们的研究结果支持直流电刺激通过改变组织的潜在可塑性来调节大脑活动的假设。