Brittany Rurak: Moderate test re-test reliability of supplementary motor area-primary motor cortex connectivity measured using dual-site TMS in younger and older adults  

Thanks for the presentation. How do you measure the SMA-M1 ratio or the connectivity? Is it the ratio of MEP amplitude in the conditioned TMS pulse to the unconditioned MEP pulse?

Thanks, William

@wdedoncker - thanks for your question. SMA-M1 connectivity was quantified by expressing the mean dual-site MEP amplitude as a ratio of the mean single-pulse MEP amplitude (as you mentioned) :).

@bkrurak my question then is, what effect does a conditioning pulse to the SMA have an MEP elicited within M1? assuming a healthy population. And why is that the case?

@wdedoncker - good question! When a conditioning pulse delivered to SMA precedes a test pulse to M1 by short intervals (6-7 ms), the amplitude of the MEP is increased when compared to the amplitude of the MEP elicited by a single-pulse to M1. The increase of the MEP amplitude from dual stimuli is thought to be due to the activation of glutamatergic excitatory interactions between SMA and M1. However, future research is required to establish the validity and responsiveness of dual-site TMS measures of SMA-M1 connectivity to better understand the neurophysiological mechanisms being measured. Does this answer your question? Please let me know if it does not. 

Hi Brittany, Great presentation. I have a couple of questions

1) I wanted to ask your thoughts on differential effect of PAS on SMA-M1 connectivity in younger and older population

2) How do you think this might be extended to other cortical areas that are for example involved in cognition

Thanks