Transcranial alternating current stimulation of the posterior parietal cortex enhances episodic memory consolidation

Transcranial alternating current stimulation (tACS) has been reported to improve episodic memory (EM) by entraining neural oscillations. However, the effects of tACS delivered over the posterior parietal cortex (PPC) immediately after learning remain unclear. We aimed to determine whether tACS over the PPC, administered immediately after learning, enhances EM retention. Thirty-six healthy adults were randomly assigned to the tACS or sham-control groups. On day 1, participants completed three sessions consisting of a word-learning task followed by a recognition test. Subsequently, 40 Hz tACS (1.5 mA) was delivered for 20 min after the learning phases. Recognition performance was assessed based on hit ratio, false alarm ratio, and d-prime on days 1, 7, and 28. Results showed significant differences in the tACS group compared to the sham stimulation control group for hit ratio on day 28 (p = 0.01), as well as for false alarm ratio on day 7 (p = 0.02) and day 28 (p < 0.01). Furthermore, d-prime were significantly higher on day 7 (p = 0.01) and day 28 (p < 0.01). These findings suggest that administering tACS during the highly plastic and labile immediate post-learning window may promote long-term memory consolidation.