Effects of Transcranial Direct Current Stimulation on Neural Networks in Young and Older Adults

Transcranial direct current stimulation (tDCS) may be a viable tool to improve motor and cognitive function in advanced age. However, although a number of studies have demonstrated improved cognitive performance in older adults, other studies have failed to show restorative effects. The neural effects of beneficial stimulation response in both age groups is lacking. In the current study, tDCS was administered during simultaneous fMRI in 42 healthy young and older participants. Semantic word generation and motor speech baseline tasks were used to investigate behavioral and neural effects of uni- and bihemispheric motor cortex tDCS in a three-way, crossover, sham tDCS controlled design. Independent components analysis assessed differences in task-related activity between the two age groups and tDCS effects at the network level. We also explored whether laterality of language network organization was effected by tDCS. Behaviorally, both active tDCS conditions significantly improved semantic word retrieval performance in young and older adults and were comparable between groups and stimulation conditions. Network-level tDCS effects were identified in the ventral and dorsal anterior cingulate networks in the combined sample during semantic fluency and motor speech tasks. In addition, a shift toward enhanced left laterality was identified in the older adults for both active stimulation conditions. Thus, tDCS results in common network-level modulations and behavioral improvements for both age groups, with an additional effect of increasing left laterality in older adults.

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Focality-Oriented Selection of Current Dose for Transcranial Direct Current Stimulation

Journal of Personalized Medicine ◽

10.3390/jpm11090940 ◽

2021 ◽

Vol 11 (9) ◽

pp. 940

Author(s):

Rajan Kashyap ◽

Sagarika Bhattacharjee ◽

Ramaswamy Arumugam ◽

Rose Dawn Bharath ◽

Kaviraja Udupa ◽

...

Keyword(s):

Older Adults ◽

Direct Current ◽

Current Density ◽

Transcranial Direct Current Stimulation ◽

Age Groups ◽

Average Current Density ◽

Peak Region ◽

Direct Current Stimulation ◽

Reference Space ◽

The Brain

Background: In transcranial direct current stimulation (tDCS), the injected current becomes distributed across the brain areas. The objective is to stimulate the target region of interest (ROI) while minimizing the current in non-target ROIs (the ‘focality’ of tDCS). For this purpose, determining the appropriate current dose for an individual is difficult. Aim: To introduce a dose–target determination index (DTDI) to quantify the focality of tDCS and examine the dose–focality relationship in three different populations. Method: Here, we extended our previous toolbox i-SATA to the MNI reference space. After a tDCS montage is simulated for a current dose, the i-SATA(MNI) computes the average (over voxels) current density for every region in the brain. DTDI is the ratio of the average current density at the target ROI to the ROI with a maximum value (the peak region). Ideally, target ROI should be the peak region, so DTDI shall range from 0 to 1. The higher the value, the better the dose. We estimated the variation of DTDI within and across individuals using T1-weighted brain images of 45 males and females distributed equally across three age groups: (a) young adults (20 ≤ x ˂ 40 years), (b) mid adults (40 ≤ x ˂ 60 years), and (c) older adults (60 ≤ x ˂ 80 years). DTDI’s were evaluated for the frontal montage with electrodes at F3 and the right supraorbital for three current doses of 1 mA, 2 mA, and 3 mA, with the target ROI at the left middle frontal gyrus. Result: As the dose is incremented, DTDI may show (a) increase, (b) decrease, and (c) no change across the individuals depending on the relationship (nonlinear or linear) between the injected tDCS current and the distribution of current density in the target ROI. The nonlinearity is predominant in older adults with a decrease in focality. The decline is stronger in males. Higher current dose at older age can enhance the focality of stimulation. Conclusion: DTDI provides information on which tDCS current dose will optimize the focality of stimulation. The recommended DTDI dose should be prioritized based on the age (>40 years) and sex (especially for males) of an individual. The toolbox i-SATA(MNI) is freely available.

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Transcranial Direct Current Stimulation Enhances Episodic Memory in Healthy Older Adults by Modulating Retrieval-Specific Activation

Neural Plasticity ◽

10.1155/2020/8883046 ◽

2020 ◽

Vol 2020 ◽

pp. 1-11

Author(s):

Lijuan Huo ◽

Zhiwei Zheng ◽

Jia Huang ◽

Rui Li ◽

Jin Li ◽

...

Keyword(s):

Older Adults ◽

Prefrontal Cortex ◽

Episodic Memory ◽

Direct Current ◽

Transcranial Direct Current Stimulation ◽

Anterior Cingulate ◽

Controlled Study ◽

Healthy Older Adults ◽

Sham Stimulation ◽

Direct Current Stimulation

Memory decline has become an issue of major importance in the aging society. Anodal transcranial direct current stimulation (atDCS) is a viable tool to counteract age-associated episodic memory deterioration. However, the underlying neural mechanisms are unclear. In this single-blind, sham-controlled study, we combined atDCS and functional magnetic resonance imaging to assess the behavioral and neural consequences of multiple-session atDCS in older adults. Forty-nine healthy older adults received either 10 sessions of anodal or sham stimulation over the left dorsolateral prefrontal cortex. Before and after stimulation, participants performed a source memory task in the MRI scanner. Compared to sham stimulation, atDCS significantly improved item memory performance. Additionally, atDCS significantly increased regional brain activity around the stimulation area in the prefrontal cortex and extended to the bilateral anterior cingulate cortex. Neural changes in the prefrontal cortex correlated with memory gains. Our findings therefore indicate that multiple-session offline atDCS may improve memory in older adults by inducing neural alterations.

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Can Transcranial Direct Current Stimulation Enhance Functionality in Older Adults? A Systematic Review

Journal of Clinical Medicine ◽

10.3390/jcm10132981 ◽

2021 ◽

Vol 10 (13) ◽

pp. 2981

Author(s):

Andrés Pino-Esteban ◽

Álvaro Megía-García ◽

David Martín-Caro Álvarez ◽

Hector Beltran-Alacreu ◽

Juan Avendaño-Coy ◽

...

Keyword(s):

Systematic Review ◽

Older Adults ◽

Direct Current ◽

Transcranial Direct Current Stimulation ◽

Randomized Clinical Trials ◽

Scientific Evidence ◽

Healthy Older Adults ◽

Sham Stimulation ◽

Direct Current Stimulation ◽

Potential Benefits

Transcranial direct current stimulation (tDCS) is a non-invasive, easy to administer, well-tolerated, and safe technique capable of affecting brain excitability, both at the cortical and cerebellum levels. However, its effectiveness has not been sufficiently assessed in all population segments or clinical applications. This systematic review aimed at compiling and summarizing the currently available scientific evidence about the effect of tDCS on functionality in older adults over 60 years of age. A search of databases was conducted to find randomized clinical trials that applied tDCS versus sham stimulation in the above-mentioned population. No limits were established in terms of date of publication. A total of 237 trials were found, of which 24 met the inclusion criteria. Finally, nine studies were analyzed, including 260 healthy subjects with average age between 61.0 and 85.8 years. Seven of the nine included studies reported superior improvements in functionality variables following the application of tDCS compared to sham stimulation. Anodal tDCS applied over the motor cortex may be an effective technique for improving balance and posture control in healthy older adults. However, further high-quality randomized controlled trials are required to determine the most effective protocols and to clarify potential benefits for older adults.

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Effects of transcranial direct current stimulation combined with listening to preferred music on memory in older adults

Scientific Reports ◽

10.1038/s41598-021-91977-8 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Ricky Chow ◽

Alix Noly-Gandon ◽

Aline Moussard ◽

Jennifer D. Ryan ◽

Claude Alain

Keyword(s):

Older Adults ◽

Working Memory ◽

Recognition Memory ◽

Direct Current ◽

Transcranial Direct Current Stimulation ◽

Digit Span ◽

Recognition Task ◽

Music Listening ◽

Subsequent Performance ◽

Direct Current Stimulation

AbstractListening to autobiographically-salient music (i.e., music evoking personal memories from the past), and transcranial direct current stimulation (tDCS) have each been suggested to temporarily improve older adults’ subsequent performance on memory tasks. Limited research has investigated the effects of combining both tDCS and music listening together on cognition. The present study examined whether anodal tDCS stimulation over the left dorsolateral prefrontal cortex (2 mA, 20 min) with concurrent listening to autobiographically-salient music amplified subsequent changes in working memory and recognition memory in older adults than either tDCS or music listening alone. In a randomized sham-controlled crossover study, 14 healthy older adults (64–81 years) participated in three neurostimulation conditions: tDCS with music listening (tDCS + Music), tDCS in silence (tDCS-only), or sham-tDCS with music listening (Sham + Music), each separated by at least a week. Working memory was assessed pre- and post-stimulation using a digit span task, and recognition memory was assessed post-stimulation using an auditory word recognition task (WRT) during which electroencephalography (EEG) was recorded. Performance on the backwards digit span showed improvement in tDCS + Music, but not in tDCS-only or Sham + Music conditions. Although no differences in behavioural performance were observed in the auditory WRT, changes in neural correlates underlying recognition memory were observed following tDCS + Music compared to Sham + Music. Findings suggest listening to autobiographically-salient music may amplify the effects of tDCS for working memory, and highlight the potential utility of neurostimulation combined with personalized music to improve cognitive performance in the aging population.

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