In this talk (part 4 of it) I explain how "functional targeting" supports boosting of ongoing plasticity by tDCS. And how 'functional targeting' modulates ongoing oscillations. All part of a conceptual framework of "tDCS of cortical columns". https://www.youtube.com/watch?v=vBO_1AwcWqg
More recent work enhances these ideas including @lcparra showing 'functional targeting' down to the synapse level as "tDCS boosts Hebb". https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6989352/
@MaromBikson @lcparra have you or others found out how to reliably produce sleep onset like imagery through tDCS? cf. Gorgoni and Galbiati - 2022 - Non-REM sleep electrophysiology in REM sleep behavhttps://doi.org/10.1016/j.neubiorev.2020.04.003