Transcranial direct current stimulation (tDCS) of the left dorsolateral prefrontal cortex modulates declarative memory

doi:10.1016/j.brs.2011.06.007

Brain Stimulation

Volume 5, Issue 3, July 2012, Pages 231-241

https://doi.org/10.1016/j.brs.2011.06.007 Get rights and content

Background

Previous studies have claimed that weak transcranial direct current stimulation (tDCS) induces persisting activity changes in the human motor cortex and working memory, but to date no studies have evaluated the effects of tDCS on declarative memory.

Objective

Our aim was to determine whether anodal and cathodal transcranial direct current stimulation would differentially modify performance in a word memorization task during encoding or recognition when administered over the left dorsolateral prefrontal cortex (DLPFC).

Methods

In two experiments, 32 participants underwent a series of word memorization tasks. This task was performed during sham, anodal, and cathodal stimulation applied over the left DLPFC. Moreover, participants in the first experiment performed the same task with anodal tDCS of the primary motor cortex (M1).

Results

During encoding, anodal stimulation of the left DLPFC improved memory, whereas cathodal stimulation of the same area impaired memory performance in later recognition. Anodal stimulation of M1 had no effect on later recognition. During recognition cathodal stimulation of the left DLPFC impaired recognition compared with sham stimulation of the same area and anodal stimulation had a trend toward improving the recognition.

Conclusions

The results indicated that active stimulation of the left DLPFC leads to an enhancement or impairment of verbal memorization depending on the polarity of the stimulation. Furthermore, this effect was specific to the site of stimulation.

Section snippets

Participants

In total 32 participants (mean age 22.46, standard deviation [SD] 2.31, 19 females) took part in the study comprising of two separates experiments: stimulation during encoding (n = 16) and stimulation during recognition (n = 16). All participants were university students enrolled at the University of London. All participants were naïve to the study, fluent English speakers, and right-handed yielding a laterality quotient of at least +50 on the Edinburgh Handedness Inventor.⁶⁹ All participants

Results

All participants tolerated the stimulation well and there was no complaint of pain or discomfort during the stimulation. Explicit questioning at the end of the last session showed that they did not realize that in one session they were stimulated only for the first 30 seconds.

Discussion

The results showed that tDCS of the left DLPFC can significantly modulate verbal memory performance while administered during encoding (first experiment) or recognition (second experiment) and its effects were location specific and polarity dependent. The results of the first experiment showed that anodal stimulation of the left DLPFC during the encoding phase enhanced the memory performance in a later recognition task. Cathodal stimulation, however, impaired the later recognition of stimuli.

Acknowledgments

We thank Ryota Kanai, Leun Otten, and Sophie Scott for help on designing the experiment and Martin Donovan and Lambert Dean for technical support.

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