Thesis
The influence of the conditioning stimulus intensity on supplementary motor area and primary motor cortex connectivity in younger than older adults using dual-site transcranial magnetic stimulation
Honours, Murdoch University
2022
Abstract
Ageing is associated with a decline in voluntary motor control and a reduction in the integrity and volume of white matter tissue, causing reduced effective connectivity throughout the motor network, such as between the supplementary motor area (SMA) and primary motor cortex (M1). Dual-site transcranial magnetic stimulation (TMS) assesses connectivity by examining the change in motor evoked potentials (MEPs) caused by M1 excitation following an initial conditioning stimulus (CS) pulse to the SMA. The current study aimed to (1) replicate previous dual-site TMS research showing greater SMA-M1 facilitation in younger than older adults with a CS intensity of 140% active motor threshold (AMT) and (2) investigate whether younger adults required a lower CS intensity to facilitate MEPs in M1 compared to older adults. Dual-site TMS was used to deliver six SMA conditioning stimulus (CS) intensities ranging from 100 to 150% AMT (differing by 10% increments) in independent samples of younger (n = 15) and older adults (n = 23). Findings show that with a CS intensity of 140% AMT, younger adults showed more substantial SMA-M1 facilitation than older adults, implying that direct excitatory connections between SMA and M1 were more effective in the younger group. Furthermore, for the first time, no significant facilitation was observed in either age group at any of the other intensities, suggesting that SMA activation may not be a graded response to the CS intensity. These findings contribute to our current understanding of the methodological factors that may contribute to SMA-M1 connectivity and may help guide future research to further define the optimal parameters for SMA-M1 stimulation and the development of TMS interventions to improve bilateral and bimanual motor control.
Details
- Title
- The influence of the conditioning stimulus intensity on supplementary motor area and primary motor cortex connectivity in younger than older adults using dual-site transcranial magnetic stimulation
- Authors/Creators
- Shari Manansala
- Awarding Institution
- Murdoch University; Honours
- Identifiers
- 991005779522007891
- Murdoch Affiliation
- School of Psychology
- Resource Type
- Thesis
Metrics
21 File views/ downloads
34 Record Views