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

A Critical Review of Noninvasive Brain Stimulation Technologies in Alzheimer's Dementia and Primary Progressive Aphasia

Multiple pharmacologic agents now have been approved in the United States and other countries as treatment to slow disease and clinical progression for Alzheimer's disease. Given these treatments have not been proven to lessen the cognitive deficits already manifested in the Alzheimer's Clinical Syndrome (ACS), and none are aimed for another debilitating dementia syndrome identified as primary progressive aphasia (PPA), there is an urgent need for new, safe, tolerable, and efficacious treatments to mitigate the cognitive deficits experienced in ACS and PPA. Noninvasive brain stimulation has shown promise for enhancing cognitive functioning, and there has been interest in its potential therapeutic value in ACS and PPA. This review critically examines the evidence of five technologies in ACS and PPA: transcranial direct current stimulation (tDCS), transcranial alternating current stimulation (tACS), transcranial random noise stimulation (tRNS), repetitive transcranial magnetic stimulation (rTMS), and noninvasive vagus nerve stimulation (nVNS). Many randomized controlled trials of tDCS and rTMS report positive treatment effects on cognition in ACS and PPA that persist out to at least 8 weeks, whereas there are few trials for tACS and none for tRNS and nVNS. However, most positive trials did not identify clinically meaningful changes, underscoring that clinical efficacy has yet to be established in ACS and PPA. Much is still to be learned about noninvasive brain stimulation in ACS and PPA, and shifting the focus to prioritize clinical significance in addition to statistical significance in trials could yield greater success in understanding its potential cognitive effects and optimal parameters.

The effects of transcranial random noise stimulation on motor function: A comprehensive review of the literature

The present review considers all papers published on the topic up to the end of the year 2022. Transcranial random noise stimulation (tRNS) is a non-invasive neuromodulation technique introduced about 15 years ago whose use is becoming increasingly widespread in neuroscience. It consists of the application over the scalp of a weak, white noise-like current, through electrodes having a surface of several square centimetres, for a duration ranging from seconds to minutes. Despite its relatively low spatial and temporal resolution, tRNS has well defined effects on central motor excitability, which critically depend on stimulation parameters. These effects seem to be chiefly based on an effect on neuronal membrane sodium channels and can last much longer than the stimulation itself. While the effects at the cellular level in the motor cortex are becoming progressively clear, much more studies are needed to understand the effects of tRNS on motor behaviour and performance, where initial research results are nevertheless promising, in both basic and applied research.

Mechanisms of Action of Noninvasive Brain Stimulation with Weak Non-Constant Current Stimulation Approaches

Objective: Non-constant current stimulation (NCCS) is a neuromodulatory method in which weak alternating, pulsed or random currents are delivered to the human head via scalp or earlobe electrodes. This approach is widely used in basic and translational studies. However, the underlying mechanisms of NCCS, which lead to biological and behavioral effects in the brain, remain largely unknown. In this review, we characterize NCCS techniques currently being utilized in neuroscience investigations, including transcranial alternating current stimulation (tACS), transcranial pulsed current stimulation (tPCS), transcranial random noise stimulation (tRNS), and cranial electrotherapy stimulation (CES). Method: We unsystematically searched all relevant conference papers, journal articles, chapters, and textbooks on the biological mechanisms of NCCS techniques. Results: The fundamental idea of NCCS is that these low-level currents can interact with neuronal activity, modulate neuroplasticity and entrain cortical networks, thus, modifying cognition and behavior. We elucidate the mechanisms of action for each NCCS technique. These techniques may cause microscopic effects (such as affecting ion channels and neurotransmission systems) and macroscopic effects (such as affecting brain oscillations and functional connectivity) on the brain through different mechanisms of action (such as neural entrainment and stochastic resonance). Conclusion: The appeal of NCCS is its potential to modulate neuroplasticity noninvasively, along with the ease of use and good tolerability. Promising and interesting evidence has been reported for the capacity of NCCS to affect neural circuits and the behaviors under their control. Today, the challenge is to utilize this advancement optimally. Continuing methodological advancements with NCCS approaches will enable researchers to better understand how NCCS can be utilized for the modulation of nervous system activity and subsequent behaviors, with possible applications to non-clinical and clinical practices.

Using noise for the better: The effects of transcranial random noise stimulation on the brain and behavior

Van der Groen, O., Potok, W., Wenderoth, N., Edwards, G., Mattingley, J.B. and Edwards, D. Using noise for the better: The effects of transcranial random noise stimulation on the brain and behavior. NEUROSCI BIOBEHAV REV X (X) XXX-XXX 2021.- Transcranial random noise stimulation (tRNS) is a non-invasive electrical brain stimulation method that is increasingly employed in studies of human brain function and behavior, in health and disease. tRNS is effective in modulating perception acutely and can improve learning. By contrast, its effectiveness for modulating higher cognitive processes is variable. Prolonged stimulation with tRNS, either as one longer application, or multiple shorter applications, may engage plasticity mechanisms that can result in long-term benefits. Here we provide an overview of the current understanding of the effects of tRNS on the brain and behavior and provide some specific recommendations for future research.