The Effect of Transcranial Random Noise Stimulation on Cognitive Training Outcome in Healthy Aging

Michela Brambilla; Lars Dinkelbach; Annelien Bigler; Joseph Williams; Nahid Zokaei; Roi Cohen Kadosh; Anna-Katharine Brem

doi:10.3389/fneur.2021.625359

The Effect of Transcranial Random Noise Stimulation on Cognitive Training Outcome in Healthy Aging

Front Neurol. 2021 Mar 9:12:625359. doi: 10.3389/fneur.2021.625359. eCollection 2021.

Authors

Michela Brambilla^{1

2}, Lars Dinkelbach^{1

3}, Annelien Bigler^{1

4}, Joseph Williams^{1

5}, Nahid Zokaei¹, Roi Cohen Kadosh¹, Anna-Katharine Brem^{1

6}

Affiliations

¹ Department of Experimental Psychology, University of Oxford, Oxford, United Kingdom.
² Biomedical and Clinical Sciences Department, Center for Research and Treatment on Cognitive Dysfunctions, "Luigi Sacco" Hospital, University of Milan, Milan, Italy.
³ Department of Neurology, Institute of Clinical Neuroscience and Medical Psychology, Heinrich Heine University, Duesseldorf, Germany.
⁴ Department of Experimental Psychology, Ghent University, Ghent, Belgium.
⁵ Medical Sciences Division, University of Oxford, Oxford, United Kingdom.
⁶ Department of Neurology, Berenson-Allen Center for Noninvasive Brain Stimulation and Division for Cognitive Neurology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, United States.

Abstract

Background and Objective: Aging is associated with a decline in attentional and executive abilities, which are linked to physiological, structural, and functional brain changes. A variety of novel non-invasive brain stimulation methods have been probed in terms of their neuroenhancement efficacy in the last decade; one that holds significant promise is transcranial random noise stimulation (tRNS) that delivers an alternate current at random amplitude and frequency. The aim of this study was to investigate whether repeated sessions of tRNS applied as an add-on to cognitive training (CT) may induce long-term near and far transfer cognitive improvements. Methods: In this sham-controlled, randomized, double-blinded study forty-two older adults (age range 60-86 years) were randomly assigned to one of three intervention groups that received 20 min of 0.705 mA tRNS (N = 14), 1 mA tRNS (N = 14), or sham tRNS (N = 19) combined with 30 min of CT of executive functions (cognitive flexibility, inhibitory control, working memory). tRNS was applied bilaterally over the dorsolateral prefrontal cortices for five sessions. The primary outcome (non-verbal logical reasoning) and other cognitive functions (attention, memory, executive functions) were assessed before and after the intervention and at a 1-month follow-up. Results: Non-verbal logical reasoning, inhibitory control and reaction time improved significantly over time, but stimulation did not differentially affect this improvement. These changes occurred during CT, while no further improvement was observed during follow-up. Performance change in logical reasoning was significantly correlated with age in the group receiving 1 mA tRNS, indicating that older participants profited more from tRNS than younger participants. Performance change in non-verbal working memory was significantly correlated with age in the group receiving sham tRNS, indicating that in contrast to active tRNS, older participants in the sham group declined more than younger participants. Interpretation: CT induced cognitive improvements in all treatment groups, but tRNS did not modulate most of these cognitive improvements. However, the effect of tRNS depended on age in some cognitive functions. We discuss possible explanations leading to this result that can help to improve the design of future neuroenhancement studies in older populations.

Keywords: cognitive enhancement; cognitive training; executive functions; healthy aging; transcranial random noise stimulation.