Transcranial random noise stimulation mitigates increased difficulty in an arithmetic learning task

• Published in: Neuropsychologia Vol. 81; pp. 255 - 264
• Main Authors: Popescu, Tudor, Krause, Beatrix, Terhune, Devin B., Twose, Olivia, Page, Thomas, Humphreys, Glyn, Cohen Kadosh, Roi
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 29.01.2016; Pergamon Press
• Subjects: Adult; Analysis of Variance; Attention - physiology; Cognitive training; Executive Function - physiology; Female; Humans; Learning - physiology; Male; Mathematical Concepts; Mathematics; Mental arithmetic; Orientation - physiology; Posterior parietal cortex; Prefrontal cortex; Reaction Time - physiology; Task difficulty; Transcranial Direct Current Stimulation; Transcranial random noise stimulation; Young Adult; Task difficulty; Cognitive training; Prefrontal cortex; Mental arithmetic; Posterior parietal cortex; Transcranial random noise stimulation
• ISSN: 0028-3932; 1873-3514
• DOI: 10.1016/j.neuropsychologia.2015.12.028

Proficiency in arithmetic learning can be achieved by using a multitude of strategies, the most salient of which are procedural learning (applying a certain set of computations) and rote learning (direct retrieval from long-term memory). Here we investigated the effect of transcranial random noise stimulation (tRNS), a non-invasive brain stimulation method previously shown to enhance cognitive training, on both types of learning in a 5-day sham-controlled training study, under two conditions of task difficulty, defined in terms of item repetition. On the basis of previous research implicating the prefrontal and posterior parietal cortex in early and late stages of arithmetic learning, respectively, sham-controlled tRNS was applied to bilateral prefrontal cortex for the first 3 days and to the posterior parietal cortex for the last 2 days of a 5-day training phase. The training involved learning to solve arithmetic problems by applying a calculation algorithm; both trained and untrained problems were used in a brief testing phase at the end of the training phase. Task difficulty was manipulated between subjects by using either a large (“easy” condition) or a small (“difficult” condition) number of repetition of problems during training. Measures of attention and working memory were acquired before and after the training phase. As compared to sham, participants in the tRNS condition displayed faster reaction times and increased learning rate during the training phase; as well as faster reaction times for both trained and untrained (new) problems, which indicated a transfer effect after the end of training. All stimulation effects reached significance only in the “difficult” condition when number of repetition was lower. There were no transfer effects of tRNS on attention or working memory. The results support the view that tRNS can produce specific facilitative effects on numerical cognition – specifically, on arithmetic learning. They also highlight the importance of task difficulty in the neuromodulation of learning, which in the current study due to the manipulation of item repetition might have been mediated by the memory system. •tRNS was previously shown to enhance cognitive training in an arithmetical task.•5-day training on Calculation and Drill arithmetic was accompanied by tRNS to PFC&PPC.•Task difficulty was manipulated by including fewer or more problems in training.•tRNS improved Calculation training performance & led to transfer in testing phase.•tRNS effects were seen only in the difficult task condition.