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A wide body of literature suggests that transcranial direct current stimulation (tDCS) administered over the prefrontal cortex can improve executive function - including decision-making and inhibitory control - in healthy young adults. However, the effects of tDCS in older adults are largely unknown. Here, using a double-blind, sham-controlled approach, changes in a combined perceptual decision-making and inhibitory control task were assessed before and after the application of tDCS (1 mA, 20 minute) targeting the right inferior frontal gyrus (rIFG) or pre-supplementary motor area (preSMA) in 42 young (18-34 years) and 41 older (60-80 years) healthy adults. Compared to sham stimulation, anodal tDCS over the preSMA improved decision-making speed for both age groups. Furthermore, the inhibitory control performance of older and younger adults was improved by preSMA and rIFG stimulation, respectively. This study provides evidence that tDCS can improve both perceptual decision-making and inhibitory control in healthy older adults, with the causal role of the preSMA and rIFG regions in cognitive control appearing to vary as a function of healthy ageing., (Copyright © 2021. Published by Elsevier Inc.)

Functional motor declines that often occur with advancing age-including reduced efficacy to learn new skills-can have a substantial impact on the quality of life. Recent studies using noninvasive brain stimulation indicate that priming the corticospinal system by lowering the threshold for the induction of long-term potentiation-like plasticity before skill training may facilitate subsequent skill learning. Here, we used "priming" protocol, in which we used transcranial direct current stimulation (tDCS) applying the cathode over the primary motor cortex (M1) before the anode placed over M1 during unimanual isometric force control training (FORCE training ). Older individuals who received tDCS with the cathode placed over M1 before tDCS with the anode placed over M1 concurrent with FORCE training showed greater skill improvement and corticospinal excitability increases following the tDCS/FORCE training protocol compared with both young and older individuals who did not receive the preceding tDCS with the cathode placed over M1. The results suggested that priming tDCS protocols may be used in clinical settings to improve motor function and thus maintain the functional independence of older adults., (Copyright © 2016 Elsevier Inc. All rights reserved.)

The ability to coordinate upper and lower limbs--a prerequisite for many everyday activities--is known to decline with age. Here we report 2 experiments in which transcranial magnetic stimulation (TMS) was used to assess corticospinal excitatory and inhibitory processes in younger and older adults during cyclical hand-foot movements. In experiment 1, motor evoked potentials (MEP) and silent period (SP) durations were measured from the active right extensor carpi radialis (ECR) muscle while it executed rhythmic oscillations in conjunction with the right or left foot. Younger adults exhibited increased SP with ipsilateral limb combinations and decreased SP with contralateral limb combinations, relative to a baseline hand only condition. Strikingly, older adults exhibited a reduced SP when ipsilateral limbs moved in opposite directions. This effect was found to be most pronounced in those older adults who exhibited poor coordination performance, suggesting that the inability to regulate inhibitory processes may underlie age-related degradation of task performance. Experiment 2 examined motor evoked potentials and SP duration in the left extensor carpi radialis which maintained a tonic contraction while the coordination task was undertaken by the right arm and right or left foot. For younger adults, coordination of ipsilateral limbs was accompanied by increased inhibition in the ipsilateral motor cortex than during the coordination of contralateral limbs. No differences in SP between conditions were noted for the older adults. In summary, older adults' reduced ability to coordinate upper and lower limbs may be related to the capacity to regulate inhibitory function in both hemispheres. This study suggests for the first time a direct link between age-related differences in interlimb coordination and the control of corticospinal inhibitory processes., (Copyright © 2012 Elsevier Inc. All rights reserved.)