Negative findings of a combined approach of tRNS and cognitive training in healthy aging

Ageing is associated with a decline in attentional and executive abilities, linked to physiological, structural, and functional brain changes. A wide variety of neuroenhancement methods have been developed in the last decades; one that holds significant promise is transcranial random noise stimulation (tRNS) that delivers an alternate current at random frequency. The aim of the present study was to investigate whether repeated sessions of tRNS applied as an add-on to cognitive training may induce long-term cognitive improvements. We applied tRNS (at two different levels of intensity) or sham stimulation bilaterally over the dorsolateral prefrontal cortices for 5 sessions over two weeks combined with a newly developed computerized cognitive training focusing on executive function. The 39 enrolled older adults were randomly assigned to one of three treatment groups: 0.705 mA tRNS plus CT; Group 1 mA tRNS plus CT, and sham tRNS plus CT. The combination of tRNS with cognitive training did not lead to significant increases in cognitive abilities at post-treatment and at one month follow-up. We believe that this null result is relevant to avoid unsuccessful clinical trials, minimise publication bias, and to improve the design of future neuroenhacement studies.