Abstract
Healthy aging limits the activities of daily living and personal independence. Furthermore, cognitive-motor interference in dual-task (e.g., walking while talking) appears to be more pronounced in the elderly. Transcranial direct current stimulation (tDCS), a form of the non-invasive brain stimulation technique, is known to modify cortical excitability and has been investigated as a tool for enhancing motor and cognitive performance in health and disease. The present study examined whether tDCS targeting the dorsolateral prefrontal cortex (DLPFC) could improve dual-task performance in healthy older adults. The effects of tDCS, among other factors, depend on stimulation polarity (anodal vs. cathodal), electrode setup (unilateral vs. bilateral) and the time of application (off-line vs. on-line). We therefore explored the effects of unilateral and simultaneous bilateral tDCS (anodal and cathodal) of left DLPFC while performing (on-line) the Grooved Pegboard Test (GPT) and Serial Seven Subtraction Test (SSST) alone or together (dual-tasking). The number of pegs and the number of correct subtractions were recorded before, during and 30 min after tDCS. The dual-task performance was measured as the percent change from single- to the dual-task condition (dual-task cost DTC). Only bilateral, anode left tDCS, induced a significant increase in subtracted numbers while dual-tasking, i.e., it reduced the DTC of manual dexterity (GPT) to a cognitive task. Significant changes 30 min after the stimulation were only present after bilateral anode right (BAR) tDCS on GPT dual-task costs. These findings suggest that anodal tDCS applied on-line interacts with a dual-task performance involving demanding cognitive and manual dexterity tasks. The results support the potential use of non-invasive brain stimulation for improvement of cognitive functioning in daily activities in older individuals.
Highlights
It is widely recognized that in normal aging brain undergoes complex structural and functional changes, giving rise to age-related deterioration of cognitive, perceptual, and motor abilities, affecting activities of daily living, independence, and overall quality of life (Craik and Bialystok, 2006)
The present study examined whether Transcranial direct current stimulation (tDCS) targeting the dorsolateral prefrontal cortex (DLPFC) could improve dual-task performance in healthy older adults
Changes in the raw performance on single Seven Subtraction Test (SSST) and Grooved Pegboard Test (GPT) tasks and the simple reaction time (SRT) across all experimental sessions are shown in Table 1 There was no main effect of stimulation montage on SRT (F(4,84) = 1.416, p = 0.236) before (PRE), during (DUR; F(4,84) = 1.088, p = 0.368) and after tDCS (POST; F(4,84) = 1.032, p = 0.395) suggesting that tDCS did not influence SRT irrespective of the arrangement of DLPFC stimulation
Summary
It is widely recognized that in normal aging brain undergoes complex structural and functional changes, giving rise to age-related deterioration of cognitive, perceptual, and motor abilities, affecting activities of daily living, independence, and overall quality of life (Craik and Bialystok, 2006). A single tDCS session targeting PFC increased standing postural sway complexity with concurrent non-postural cognitive tasks (Zhou et al, 2015). All of these studies examined unilateral tDCS, where an active electrode is placed over the region of interest over the left or the right hemisphere and the return electrode is placed over the contralateral supraorbital area or an extracephalic area (Nasseri et al, 2015). Unlike in unilateral stimulation in bilateral tDCS anodal and cathodal stimulation are simultaneously applied over homologous cortical brain regions aiming to enhance the excitability in one region, while at the same time reducing the excitability in the opposite hemisphere (To et al, 2018). Applying tDCS during task performance (on-line design) aims to facilitate motor performance by enhancing the activity of task-related networks and strengthening of relevant synaptic connections (e.g. Oldrati et al, 2018)
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