Theta-modulated oscillatory transcranial direct current stimulation over posterior parietal cortex improves associative memory

Abstract

Associative memory (AM) reflects the ability to remember and retrieve multiple pieces of information bound together thus enabling complex episodic experiences. Despite growing interest in the use of transcranial direct current stimulation (tDCS) for the modulation of AM, there are inconsistent evidence regarding its benefits. An alternative to standard constant tDCS could be the application of frequency-modulated tDCS protocols, that mimic natural function-relevant brain rhythms. Here, we show the effects of anodal tDCS oscillating in theta rhythm (5 Hz; 1.5 ± 0.1 mA) versus constant anodal tDCS and sham over left posterior parietal cortex on cued recall of face-word associations. In a crossover design, each participant completed AM assessment immediately following 20-min theta-oscillatory, constant, and sham tDCS, as well as 1 and 5 days after. Theta oscillatory tDCS increased initial AM performance in comparison to sham, and so did constant tDCS. On the group level, no differences between oscillatory and constant tDCS were observed, but individual-level analysis revealed that some participants responded to theta-oscillatory but not to constant tDCS, and vice versa, which could be attributed to their different physiological modes of action. This study shows the potential of oscillatory tDCS protocols for memory enhancement to produce strong and reliable memory-modulating effects which deserve to be investigated further.

Transcranial Direct Current Stimulation (tDCS) for Memory Enhancement

“…When it comes to working memory, our results have shown The more advanced protocols such as theta-oscillatory tDCS have been less extensively studied, however the study by Lang and colleagues 26 as well as recent study conducted in our laboratory 27 Appendix. Please click here to download these files.…”

Relationship Between Item and Source Memory: Explanation of Connection-Strength Model

“…The posterior eye field ( Müri et al, 1996 ) and the ratio of posterior-anterior medial temporal lobe volumes can predict the performance of source memory ( Snytte et al, 2020 ). Transcranial direct current stimulation of the parietal cortex decreases false recognition increases item and source memory accuracy compared with the situation with no stimulation ( Pergollzzi and Chua, 2017 ), and improves associative memory ( Vuli et al, 2021 ). The activation of the parietal cortex is associated with our confidence in memory: the activation of the old is larger than the new, and the perceived is larger than the imagined ( King and Miller, 2017 ).…”

Prefrontal Transcranial Direct Current Stimulation Globally Improves Learning but Does Not Selectively Potentiate the Benefits of Targeted Memory Reactivation on Awake Memory Consolidation

“…For instance, anodal tDCS over the primary motor cortex was shown to efficiently increase functional coupling with subcortical thalamus regions [77]. Likewise, theta frequency-modulated oscillatory anodal tDCS over the left posterior parietal cortex before learning [42] improved subsequent performance. In the present case, it can be speculated that increasing brain excitability within prefrontal areas might boost connections with hippocampal areas, thereby increasing the susceptibility of memory traces to be reactivated.…”

“…Similarly, cathodal stimulation of the left DLPFC impairs recognition performance, whereas it tends to be improved by anodal stimulation. Transcranial DCS was also found to be effective on associative memory, either using a single 20 min anodal tDCS session [40,41] or theta frequency-modulated oscillatory anodal tDCS [42] over the left posterior parietal cortex before learning. Besides pre-learning effects, tDCS during actual encoding is also beneficial for memory.…”