Entraining theta oscillations in the dorsolateral prefrontal and posterior parietal cortices (DLPFC-PPC) and attention networks in ADHD: a tACS study

Theta oscillations are critical for cognitive functions, yet whether and how their entrainment in the frontoparietal network enhances attentional networks in ADHD remains unknown. Using 6 Hz transcranial alternating current stimulation (tACS), we entrained theta oscillations in the left dorsolateral prefrontal cortex (lDLPFC) and right posterior parietal cortex (rPPC) unilaterally or bilaterally (in synchronized and desynchronized modalities), and evaluated three attentional networks in adults with and without ADHD. Thirty participants (15 with ADHD, 15 healthy controls) completed a randomized, sham-controlled, within-subjects study with five weekly tACS protocols (2 mA intensity, 20 min duration, 5 × 5 cm electrodes): individual rPPC entrainment (P4), individual lDLPFC entrainment (F3), synchronized (in-phase) rPPC-lDLPFC entrainment (F3-P4), desynchronized (anti-phase) rPPC-lDLPFC entrainment (F3-P4), and sham. The Attentional Network Test was administered during each session. In adults with ADHD, the unilateral rPPC tACS enhanced the alerting network compared with the healthy controls, but not vs. sham, while healthy controls exhibited significantly higher alerting scores during lDLPFC vs. rPPC unilateral tACS. For the executive domain, no group×stimulation interaction was found, although unilateral lDLPFC tACS improved the executive network vs. sham (regardless of group). No effects were observed on the orienting domain. Bilateral entrainment (in‑phase or anti‑phase) of lDLPFC-rPPC yielded no effects on attentional networks. These results suggest that targeted, region‑specific theta entrainment in the rPPC and lDLPFC may selectively improve alerting in ADHD and overall executive control regardless of group, whereas simultaneous rPPC-lDLPFC entrainment showed no benefit under the present parameters. Given the modest sample and exploratory design, findings require replication in larger, clinically well‑characterized cohorts.