Abstract
BackgroundPrevious studies show that activity in the posterior default mode network (pDMN), including the posterior cingulate cortex and the precuneus, is correlated with the success of long-term episodic memory retrieval. However, the role of the anterior DMN (aDMN) including the medial prefrontal cortex is still unclear. Some studies show that activating the medial prefrontal cortex improves memory retrieval while other studies show deactivation of the medial prefrontal cortex in successful retrieval of episodic memories, suggesting a possible functional dissociation between the aDMN and pDMN. ObjectiveIn the current study, we aim to causally explore this probable dissociation using high-definition transcranial direct current stimulation (HD-tDCS). MethodsWe perform a randomised double-blinded two-visit placebo-controlled study with 84 healthy young adults. During Visit 1 they learn 75 Swahili-English word-associations. Seven days later, they randomly receive either anodal, cathodal or sham HD-tDCS targeting the pDMN or aDMN while they recall what they have previously learned. ResultsWe demonstrate that anodal stimulation of the pDMN and cathodal stimulation of the aDMN, equally improve the percentage of Swahili-English word-associations recalled 7 days after learning. ConclusionsModulating the activity in the aDMN and pDMN causally affect memory retrieval performance. HD-tDCS of the aDMN and pDMN shows that anodal stimulation of the pDMN and cathodal stimulation of the aDMN increases memory retrieval performance one week after the learning phase. Given consistent evidence, it is highly likely that we are increasing the activity in the pDMN with anodal pDMN stimulation. However, it is not clear if cathodal HD-tDCS targetting aDMN works via decoupling from the pDMN or via indirectly disinhibit pDMN.
Highlights
Recalling memories is a basic survival instinct
The current study explores whether polarity-specific neuromodulation of the anterior default mode network (DMN) (aDMN) and posterior default mode network (pDMN) both result in improved performance during episodic memory retrieval in young, non-cognitively impaired adults
Our results revealed that all groups learned the same amount of words on average during the word-association task on the first visit, but participants that received anodal highdefinition transcranial direct current stimulation (HD-tDCS) targeting the pDMN or cathodal HD-tDCS targeting the aDMN during the second visit were able to perform better in comparison to the control conditions
Summary
Recalling memories is a basic survival instinct. At a molecular level, memories are stored in cells called engrams and retrieved (aDMN) includes prefrontal areas such as the medial prefrontal cortex (mPFC), whereas the posterior DMN (pDMN) includes the posterior cingulate cortex (PCC) and precuneus [6,8]. The pDMN was highly activated and the aDMN was strongly deactivated [18] Other research corroborated this evidence by showing that decoupling of the mPFC from the rest of the DMN benefits schema memory [19]. These studies suggest that the aDMN and pDMN may have diametrically opposing functionalities during episodic memory retrieval. During Visit 1 they learn 75 Swahili-English word-associations Seven days later, they randomly receive either anodal, cathodal or sham HD-tDCS targeting the pDMN or aDMN while they recall what they have previously learned. Results: We demonstrate that anodal stimulation of the pDMN and cathodal stimulation of the aDMN, improve the percentage of Swahili-English word-associations recalled 7 days after learning. It is not clear if cathodal HD-tDCS targetting aDMN works via decoupling from the pDMN or via indirectly disinhibit pDMN
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