Transcranial Direct Current Stimulation and Memory Enhancement

     Transcranial direct current stimulation (tDCS) is a brain stimulation method that uses low direct current via electrodes on the head. Currently, many researchers are investigating the potential of tDCS in many different conditions. tDCS has many advantages as it is non-invasive, it does not pose health risks, and it is cost effective (Bjekić et al., 2021). However, there is an ongoing debate on whether or not tDCS modulates brain activity enough to positively impact patients with neurological disorders (Vanneste et al., 2020). Recently, neuroscientists have been researching the effects of tDCS on memory enhancement. Vanneste el al. researched the effect of tDCS on the brain circuits involved in memory. Bjekić et al. further discusses how tDCS can be used for memory enhancement.

Venneste et al. researched tDCS in relation to its effects on locus coeruleus–noradrenergic (LC-NAc) system and communication between the LC, amygdala, and hippocampus and the lasting effects of memory. In a resting state fMRI experiment, researchers found an increased correlation strength between LC and the right hippocampus (Vanneste et al., 2020). The right hippocampus has been known to play a crucial role in spatial memory. Furthermore, Venneste et al. further discussed tDCS in relation to memory. Researchers gave participants a face-name association memory task. Then, participants were given ON-tDCS during the encoding and consolidation phase of memory. ON-tDCS is occipital nerve transcranial direct current stimulation. The occipital nerve can aid memory as the ascending fibers of the occipital nerve link to the locus coeruleus, which promotes noradrenaline release. The noradrenergic pathway drives hippocampal activity, as it modifies functional connectivity and supports the consolidation of memory (Vanneste et al., 2020). Venneste et al. found that participants were able to recognize more faces from the face-name association memory task after ON-tDCS. These findings show that ON-tDCS positively impacts memory consolidation. 

Bjekić et al. also studied the effects of tDCS on memory enhancement. Bjekić et al.used a weak constant anodal current in order to stimulate targets within the cortico-hippocampal functional network that are engaged in memory processes. Bjekić et al. specifically researched the effects of tDCS on associative memory and working memory using oscillatory tDCS, which mimics “a natural brain rhythm to promote hippocampus-dependent memory functions” (Bjekić et al., 2021). Bjekić et al.’s results show that after 20 minutes of right frontal tDCS, working memory was enhanced. Both verbal and spatial working memory were enhanced. However, when left frontal tDCS was applied, no significant difference in working memory was seen. Furthermore, Bjekić et al.’s results on associative memory further demonstrate the results found by Venneste et al. Bjekić et al. found that after 20 minutes of tDCS on the left posterior parietal cortex, memory for face-word associations were improved.

In conclusion, research done by Venneste et al. and Bjekić et al. emphasize the positive impact that tDCS can have on memory. With this research, more research can be done using tDCS to further understand its impact on memory. Further research may look at the implications of using tDCS as preventative therapy for those at risk for Alzhiemer’s or dementia.

References

Bjekić, J., Živanović, M., Filipović, S. R. Transcranial Direct Current Stimulation (tDCS) for Memory Enhancement. J. Vis. Exp. (175), e62681, doi:10.3791/62681 (2021).

Sven Vanneste, et al.,The peripheral effect of direct current stimulation on brain circuits involving memory. Sci. Adv. 6, eaax9538 (2020). DOI:10.1126/sciadv.aax9538