Investigating the influence of paired-associative stimulation on multi-session skill acquisition and retention in older adults.

OBJECTIVE: Priming non-invasive brain stimulation (NIBS) can improve motor learning in the elderly, but it remains unclear how benefits observed in a single training session translate to multiple training sessions. The current study therefore examined the influence of priming NIBS on acquisition and retention of a novel motor skill over sequential training days in older adults. METHODS: In 30 older adults (68.2 ± 5.3 years, 14 females), paired-associative stimulation (PAS) was applied prior to visuomotor training on 3 consecutive days. The interstimulus interval used for PAS was either 10 ms (PASLTD) or 100 ms (PASControl) and long-term retention was assessed by quantifying motor performance 7 days after the final training session. RESULTS: During training, skill progressively increased across sessions (P < 0.0001), but this was not different between PASLTD and PASControl (P > 0.1). In contrast, the magnitude of skill retained 7 days after training was significantly greater in the PASLTD group (P = 0.02), suggesting significantly greater long-term retention of the trained skill. CONCLUSIONS: PASLTD over multiple sessions may represent an effective tool to help maintain newly learned motor skills in older adults. SIGNIFICANCE: While multisession priming with PAS can influence long-term skill retention, improving skill acquisition requires investigation of alternative protocols.

Preconditioning cathodal transcranial direct current stimulation facilitates the neuroplastic effect of subsequent anodal transcranial direct current stimulation applied during cycling in young adults.

The study aimed to examine the effect of a pre-conditioning cathodal transcranial direct current stimulation (ctDCS) before subsequent anodal-tDCS (atDCS) was applied during low workload cycling exercise on the corticospinal responses in young healthy individuals. Eleven young subjects participated in two sessions receiving either conditioning ctDCS or sham stimulation, followed by atDCS while cycling (i.e. ctDCS-atDCS, sham-atDCS) at 1.2 times their body weight (84 ±â€¯20 W) in a counterbalanced double-blind design. Corticospinal excitability was measured with motor evoked potentials (MEPs) elicited via transcranial magnetic stimulation with the intensity set to produce an MEP amplitude of 1 mV in a resting hand muscle at baseline (PRE), following pre-conditioning tDCS (POST-COND) and post atDCS combined with cycling exercise (POST-TEST). There was a significant interaction between time and intervention (P < 0.01) on MEPs. MEPs increased from PRE (1.0 ±â€¯0.06 mV) to POST-TEST (1.3 ±â€¯0.06 mV) during ctDCS-atDCS (P < 0.001) but did not change significantly across time during sham-atDCS (P > 0.7). Furthermore, MEPs were higher in ctDCS-atDCS compared to sham-atDCS (both P < 0.01) at POST-COND (ctDCS-atDCS: 1.1 ±â€¯0.06 mV, sham-atDCS: 1.0 ±â€¯0.06 mV) and POST-TEST (ctDCS-atDCS: 1.3 ±â€¯0.06 mV, sham-atDCS: 1.0 ±â€¯0.06 mV). These outcomes demonstrate that pre-conditioning cathodal tDCS can enhance subsequent corticospinal excitability changes induced by anodal tDCS applied in combination with cycling exercise. The findings have implications for the application of tDCS in combination with cycling exercise in rehabilitation and sporting contexts.

Older Adults Differentially Modulate Transcranial Magnetic Stimulation-Electroencephalography Measures of Cortical Inhibition during Maximal Single-joint Exercise.

The effects of muscle fatigue are known to be altered in older adults, and age-related changes in the brain are likely to be a contributing factor. However, the neural mechanisms underlying these changes are not known. The aim of the current study was to use transcranial magnetic stimulation combined with electroencephalography (TMS-EEG) to investigate age-related changes in cortical excitability with muscle fatigue. In 23 young (mean age ±â€¯SD: 22 ±â€¯2 years) and 17 older (mean age ±â€¯SD: 68.3 ±â€¯5.6 years) adults, single-pulse TMS-EEG was applied before, during and after the performance of fatiguing, intermittent isometric abduction of the index finger. Motor-evoked potential (MEP) measures of cortical excitability were increased during (estimated mean difference, 123.3%; P < 0.0001) and after (estimated mean difference, 117.5%; P = 0.001) fatigue and this was not different between groups (P > 0.5). For TMS-EEG, the amplitude of the P30 and P180 potentials were unaffected by fatigue in older participants (P > 0.05). In contrast, the amplitude of the N45 potential in older adults was significantly reduced both during (positive cluster: mean voltage difference = 0.7 µV, P < 0.005; negative cluster: mean voltage difference = 0.9 µV, P < 0.0005) and after (mean voltage difference = 0.5 µV, P < 0.005) fatiguing exercise, whereas this response was absent in young participants. These results suggest that performance of maximal intermittent isometric exercise in old but not young adults is associated with modulation of cortical inhibition likely mediated by activation of gamma-aminobutyric acid type A receptors.

Increasing motor cortex plasticity with spaced paired associative stimulation at different intervals in older adults.

The ability of priming non-invasive brain stimulation (NIBS) to modulate neuroplasticity induction (i.e. metaplasticity) within primary motor cortex (M1) may be altered in older adults. Previous studies in young subjects suggest that consecutive NIBS protocols interact in a time-dependent manner and involve homoeostatic metaplasticity mechanisms. This was investigated in older adults by assessing the response to consecutive blocks of paired-associative stimulation (PAS) separated by different inter-PAS intervals (IPIs). Fifteen older (62-82 years) subjects participated in four sessions, with each session involving two PAS blocks separated by IPIs of 10 (IPI10 ) or 30 (IPI30 ) mins. For each IPI, the first (priming) PAS block was either PASLTP (N20 latency + 2 ms) or PASLTD (N20 latency - 10 ms), while the second (test) PAS block was always PASLTP . Changes in M1 excitability were assessed by recording motor evoked potentials from a muscle of the right hand. For both IPIs, the response produced by PASLTD -primed PASLTP was significantly greater than the response produced by PASLTP -primed PASLTP . Furthermore, the effects of PASLTD priming on PASLTP were significantly greater for IPI30 . These findings suggest that priming PAS can increase plasticity induction in older adults, and this occurs through mechanisms involving homoeostatic metaplasticity. They also demonstrate that the timing between priming and test NIBS is a crucial determinant of this effect, with a 30-min interval being most effective. Providing a 30-min delay between priming NIBS and motor training may improve the efficacy of NIBS in augmenting motor performance and learning in the elderly.