New information on the effects of transcranial direct current stimulation on n-back task performance
The n-back task is prototypical tool widely used to evaluate working memory (WM) abilities in healthy and clinical populations. Previous studies finding beneficial effects of transcranial direct current stimulation (tDCS) over the dorsal lateral prefrontal cortex (DLPFC) on n-back task performance were limited by the number of n-back “memory loads” utilized and the assessment of performance only immediately following stimulation. Our aims were to investigate both the immediate and lasting effects of six sessions of bilateral tDCS over the DLPFC on n-back performance. We used a 1-, 2-, 3-, and 4-back shaped WM task at three time points: pre-stimulation (T1), immediately following a final (6th) stimulation (T2), and 1 month following the final stimulation (T3). Twenty-five right-handed participants were randomly assigned to active or sham stimulation. Performance was evaluated by percentage hits, false alarms, and reaction times (RTs) for correct responses. Results showed lack of improvement in all outcome measures for both groups at T2. Except for general faster RT in the active group, no lasting effect on percentage hits and false alarms was found for all memory loads among both groups at T3. However, lenient analysis indicated improvement in RT for the 1-back memory load among the active group from T1 to T3. These results question the previously found effectiveness of tDCS over the DLPFC in improving short-term n-back performance and cast doubt on its long-term effectiveness.
KeywordsBilateral stimulation n-Back task tDCS Lasting effect Working memory
The authors would like to thank Shira Chana Bienstock for her thorough editorial review of this manuscript.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee, and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
- Hill AT, Fitzgerald PB, Hoy KE (2016) Effects of anodal transcranial direct current stimulation on working memory: A systematic review and meta-analysis of findings from healthy and neuropsychiatric populations. Brain Stimul 9:197–208. https://doi.org/10.1016/j.brs.2015.10.006 CrossRefGoogle Scholar
- Kasahara K, Tanaka S, Hanakawa T, Senoo A, Honda M (2013) Lateralization of activity in the parietal cortex predicts the effectiveness of bilateral transcranial direct current stimulation on performance of a mental calculation task. Neurosci Lett 545:86–90. https://doi.org/10.1016/j.neulet.2013.04.022 CrossRefGoogle Scholar
- Keeser D, Padberg F, Reisinger E, Pogarell O, Kirsch V, Palm U, Karch S et al (2011) Prefrontal direct current stimulation modulates resting EEG and event-related potentials in healthy subjects: A standardized low resolution tomography (sLORETA) study. Neuroimage 55(2):644–657. https://doi.org/10.1016/j.neuroimage.2010.12.004 CrossRefGoogle Scholar
- Kim JH, Kim DW, Chang WH, Kim YH, Kim K, Im CH (2014) Inconsistent outcomes of transcranial direct current stimulation may originate from anatomical differences among individuals: Electric field simulation using individual MRI data. Neurosci Lett 564:6–10. https://doi.org/10.1016/j.neulet.2014.01.054 CrossRefGoogle Scholar
- Lifshitz Ben Basat A, Gvion A, Vatine J-J, Mashal N (2016) Transcranial direct current stimulation to improve naming abilities of persons with chronic aphasia: a preliminary study using individualized based protocol. J Neurolinguist 38:1–13. https://doi.org/10.1016/j.jneuroling.2015.09.004 CrossRefGoogle Scholar
- Mulquiney PG, Hoy KE, Daskalakis ZJ, Fitzgerald PB (2011) Improving working memory: exploring the effect of transcranial random noise stimulation and transcranial direct current stimulation on the dorsolateral prefrontal cortex. Clin Neurophysiol 122:2384–2389. https://doi.org/10.1016/j.clinph.2011.05.009 CrossRefGoogle Scholar
- Nitsche MA, Paulus W (2000) Excitability changes induced in the human motor cortex by weak transcranial direct current stimulation. J Physiol 527:633–639. https://doi.org/10.1111/j.1469-7793.2000.t01-1-00633.x CrossRefGoogle Scholar
- Rodriguez-Jimenez R, Avila C, Garcia-Navarro C, Bagney A, Aragon AM, Ventura-Campos N et al (2009) Differential dorsolateral prefrontal cortex activation during a verbal n-back task according to sensory modality. Behav Brain Res 205:299–302. https://doi.org/10.1016/j.bbr.2009.08.022 CrossRefGoogle Scholar
- Seibt O, Brunoni AR, Huang Y, Bikson M (2015) The pursuit of DLPFC: non-neuronavigated methods to target the left dorsolateral pre-frontal cortex with symmetric bicephalic transcranial direct current stimulation (tDCS). Brain Stimul 8(3):590–602. https://doi.org/10.1016/j.brs.2015.01.401 CrossRefGoogle Scholar
- Zaehle T, Sandmann P, Thorne JD, Jäncke L, Herrmann CS (2011) Transcranial direct current stimulation of the prefrontal cortex modulates working memory performance: Combined behavioural and electrophysiological evidence. BMC Neurosci 12:2. https://doi.org/10.1186/1471-2202-12-2 CrossRefGoogle Scholar