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

Abstract

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 (IPI ) or 30 (IPI ) mins. For each IPI, the first (priming) PAS block was either PAS (N20 latency + 2 ms) or PAS (N20 latency - 10 ms), while the second (test) PAS block was always PAS . 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 PAS -primed PAS was significantly greater than the response produced by PAS -primed PAS . Furthermore, the effects of PAS priming on PAS were significantly greater for IPI . 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.

Long-lasting forms of plasticity through patterned ultrasound-induced brainwave entrainment

“…These results highlight the importance of timing for “priming” stimulation in facilitating motor skill learning (Fig. 4E), consistent with studies using TMS and transcranial electrical stimulation (TES) for M1 priming stimulation to improve subsequent motor skill acquisition ( 52 ). To rule out the possibility that the reduced success rate in the contralateral cTBUS group was due to reduced motor activity, similar to the case of motor cortex injury ( 53 ), we examined the number of reaching attempts per minute.…”

Test-Retest Reliability of Homeostatic Plasticity in the Human Primary Motor Cortex

“…Consistent with the BCM theory, studies exploring homeostatic plasticity using repetitive tetanic stimulation [ 5 , 33 – 35 ] and noninvasive brain stimulation [ 3 , 4 , 36 – 38 ] have shown that neuronal activity is modified based on the level of postsynaptic activity [ 39 – 41 ]. For example, studies have shown that two blocks of anodal tDCS produce effects on M1 that follow a time-dependent rule consistent with homeostatic mechanisms [ 9 ].…”

Metaplastic neuromodulation via transcranial direct current stimulation has no effect on corticospinal excitability and neuromuscular fatigue

“…These markings were continuously monitored throughout the protocol. Active motor threshold (AMT) was defined as the lowest TMS stimulus intensity necessary to elicit a MEP discernible from background EMG signal in 3 out of 5 trials (Sidhu et al, 2017). TMS intensity was set at 120 % of AMT for all measurement blocks (55 ± 10 % of maximum stimulator output) to ensure effective activation of the FDI during the experiment.…”