Electrical Brain Stimulation During a Retrieval-Based Learning Task Can Impair Long-Term Memory
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ORIGINAL RESEARCH
Electrical Brain Stimulation During a Retrieval-Based Learning Task Can Impair Long-Term Memory Wesley Pyke 1 & Athanasios Vostanis 2 & Amir-Homayoun Javadi 1,3,4 Received: 19 April 2020 / Accepted: 11 November 2020 # The Author(s) 2020
Abstract Anodal transcranial direct current stimulation (tDCS) to the left dorsolateral prefrontal cortex (DLPFC) has been shown to improve performance on a multitude of cognitive tasks. These are, however, often simple tasks, testing only one cognitive domain at a time. Therefore, the efficacy of brain stimulation for complex tasks has yet to be understood. Using a task designed to increase learning efficiency, this study investigates whether anodal tDCS over the left DLPFC can modulate both learning ability and subsequent long-term memory retention. Using a within-subject design, participants (N = 25) took part in 6 training sessions over consecutive days in which active or sham stimulation was administered randomly (3 of each). A computer-based task was used, containing flags from countries unknown to the participants. Each training session consisted of the repetition of 8 pairs of flag/country names. Subsequently, in three testing sessions, free, cued, and timed cued recall, participants were assessed on all 48 flags they had learnt. No difference in learning speed between active and sham tDCS was found. Furthermore, in the timed cued recall phase, flags learnt in the sham tDCS sessions were recalled significantly better than flags learnt in the active tDCS sessions. This effect was stronger in the second testing session. It was also found that for the flags answered incorrectly; thus, meaning they were presented more frequently, subsequent long-term retention was improved. These results suggest that for a complex task, anodal tDCS is ineffective at improving learning speed and potentially detrimental to long-term retention when employed during encoding. This serves to highlight the complex nature of brain stimulation, providing a greater understanding of its limitations and drawbacks. Keywords Memory impairment . Long-term memory . Anodal stimulation . Transcranial direct current stimulation (tDCS) . Transcranial electrical brain stimulation (tES) . Retrieval-based learning . Dorsolateral prefrontal cortex (DLPFC)
Introduction Cognitive enhancement using transcranial electrical brain stimulation has received much interest in the past decade, with a wide variety of methods showing improvements for memory (Javadi & Walsh, 2012; Katz et al., 2017), reaction time (Hill, Fitzgerald, & Hoy, 2016; Loftus, Yalcin, Baughman, * Amir-Homayoun Javadi [email protected] 1
School of Psychology, Keynes College, University of Kent, Canterbury CT2 7NP, UK
2
The Tizard Centre, University of Kent, Canterbury, UK
3
Institute of Behavioural Neuroscience, University College London, London, UK
4
School of Rehabilitation, Tehran University of Medical Sciences, Tehran, Iran
Vanman, & Hagger, 2015), and motor learning (Antal et al., 2004; Nitsche et al., 2003). The tasks u
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