Characterizing age-related changes in supplementary motor area-primary motor cortex connectivity
Vallence AM, Rurak BK and Drummond PD
1. School of Psychology and Exercise Science, Murdoch University, Perth, Australia
Cortico-cortical connectivity between motor areas is important for motor control. The supplementary motor area (SMA) is densely connected with the primary motor cortex (M1) (1); these two regions are important for bilateral motor control (2). Connectivity within the cortical motor network declines with advancing age (3), therefore, age-related changes in SMA-M1 connectivity might underlie age-related decline in bilateral motor control.
First, we examined the reliability of facilitatory interactions between SMA-M1 measured using transcranial magnetic stimulation (TMS): we hypothesized good test re-test reliability for SMA-M1 facilitation. Second, we measured SMA-M1 facilitation in younger and older adults, and investigated associations between SMA-M1 facilitation and bilateral motor control: we hypothesized less SMA-M1 facilitation in older than younger adults, and positive associations between SMA-M1 facilitation and bilateral motor control.
Dual-coil TMS was used to measure SMA-M1 facilitation (and preSMA-M1 as a control): a conditioning TMS pulse to SMA preceded a test TMS pulse to M1 by 7 ms. The Purdue Pegboard and four square step test were used to measure bilateral motor control of upper and lower limbs, respectively.
An intra-class correlation coefficient of 0.74 showed good test re-test reliability of SMA-M1 facilitation. SMA-M1 facilitation was reduced in older compared to younger adults, and SMA-M1 facilitation was positively associated with task performance.
Findings suggest that SMA-M1 facilitation can be reliably measured with TMS, and that reduced SMA-M1 facilitation with age might play a role in age-related decline in bilateral movement control.
1. Dum, RP & Strick, PL (2002) Physiol Behav 77, 677-682
2. Nachev, P et al. (2008) Nat Rev Neurosci 9, 856-869
3. Seidler, RD et al. (2010) Neurosci Biobehav Rev 34, 721-733