Transcranial direct current stimulation (tDCS) has become a valuable tool in cognitive neuroscience research as it enables causal inferences about neural underpinnings of cognition. However, studies using tDCS to modulate cognitive functions often yield inconsistent findings. Hence, there is an increasing interest in factors that may moderate the effects, one of which is the participants’ beliefs of the tDCS condition (i.e., real or sham) they received. Namely, whether participants’ correct guessing of sham condition may lead to false-positive tDCS effects. In this study, we aimed to explore if participants’ beliefs about received stimulation type (i.e., the success of blinding) impacted their task performance in tDCS experiments on associative (AM) and working memory (WM). We analyzed data from four within-subject, sham-controlled tDCS memory experiments (N = 83) to check if the correct end-of-study guess of sham condition moderated tDCS effects. We found no evidence that sham guessing moderated post-tDCS memory performance in experiments in which tDCS effects were observed as well as in experiments that showed null effects of tDCS. The results suggest that the correct sham guessing (i.e., placebo-like effect) is unlikely to influence the results in tDCS memory experiments. We discuss the results in light of the growing debate about the relevance and effectiveness of blinding in brain stimulation research.

Non-invasive brain stimulation (NIBS) methods have gained increased interest in research and therapy of associative memory (AM) and its impairments. However, the one-size-fits-all approach yields inconsistent findings, thus putting forward the need for electroencephalography (EEG)-guided personalized frequency-modulated NIBS protocols to increase the focality and the effectiveness of the interventions. Still, extraction of individual frequency, especially in the theta band, turned out to be a challenging task. Here we present an approach to extracting the individual theta-band frequency (ITF) from EEG signals recorded during the AM task. The method showed a 93% success rate, good reliability, and the full range of variability of the extracted ITFs. This paper provides a rationale behind the adopted approach and critically evaluates it in comparison to the alternative methods that have been reported in the literature. Finally, we discuss how it could be used as an input parameter for personalized frequency-modulated NIBS approaches—transcranial alternating current stimulation (tACS) and transcranial oscillatory current stimulation (otDCS) directed at AM neuromodulation.

Non-invasive brain stimulation (NIBS) has gained increased interest in research and therapy of associative memory (AM) and its impairments. However, the one-size-fits-all approach yields inconsistent findings, thus putting forward the need for the development of personalized frequency-modulated NIBS protocols to increase the focality and the effectiveness of the interventions. There have been only a few attempts to deliver theta frequency-personalized tES. The current study explores the feasibility of determining dominant individual theta-band frequency (ITF) based on AM task-evoked EEG activity. In a sample of 42 healthy young adults, we extracted the frequencies (2-15 Hz, in 0.5 Hz steps) with the highest event-related spectral perturbation from the EEG recorded during successful encoding in the AM task. The developed method for extraction of the dominant theta-band frequency based on the AM-evoked EEG changes is able to reliably determine the AM-related ITF and can be used for personalization of the oscillatory NIBS techniques.

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