Functional and Neurophysiological correlates of Corticospinal Function in Human Aging

Acknowledgments First and farmost, I would like to thank my thesis supervisor Dr. François Tremblay for his time and guidance throughout my research project. Thanks to him I was not only able successfully complete my project, but also have the opportunity to develop as a researcher by participating at various conferences. I extend my gratitude to Sabah Master for her help in data collection as well as her company, guidance and suggestions throughout my whole research project. I would also like to acknowledge Marielle Young-Bernier help with data collection. University of Ottawa for their financial support. They provided a master's graduate study scholarship and a research trainee fellowship respectively, towards the completion and presentation of this project. AMT active motor threshold ANOVA analysis of variance ANCOVA analysis of covariance cm centimetre CM corticomotor cSP contralateral silent period CST corticospinal tract DTI duration of transcallosal inhibition EMG electromyogram FA fractional anisotropy FDI first dorsal interosseous FTT simple finger tapping test GABA gamma-aminobutyric acid GPT grooved pegboard test HAROLD hemispheric asymmetry reduction in older adults IHI interhemispheric inhibition ISI inter-stimulus interval iSP ipsilateral silent period iSParea area under the curve during the ipsilateral silent period kg kilogram Latency fac Latency facilitated during active contraction Latency 120 MEP latency at 120% RMT iv LTI latency of transcallosal inhibition MEP motor evoked potential MEP fac facilitated motor evoked potential amplitude MEP 120 MEP elicited at 120% RMT ms milliseconds MovT reaction/movement time MT motor threshold mV millivolt MVC maximal voluntary contraction M1 primary motor cortex PFC prefontral cortex RC recruitment curve RMT resting motor threshold sqrtRC Squareroot transformed slope of the recruitment curve s second SRT simple reaction time TES transcranial electric stimulation TMS transcranial magnetic stimulation µV microvolt v Summary Healthy normal aging is characterized by a series of progressive changes observed throughout the body, such as those at the neurological and musculoskeletal level. However, few studies have examined the link that exists between age-related alteration in neurophysiology and hand function. In this study, we used transcranial magnetic stimulation (TMS) to investigate age-related effects on intracortical excitability and interhemispheric inhibition, including how changes in these measures could predict hand function. Participants consisted of young (n=13) and senior (n=17) healthy, right-handed individuals. Participants underwent a series of stimulations to determine their intracortical excitability and interhemispheric inhibition of each hemisphere. The former was evaluated by measuring the resting motor threshold (RMT), recruitment curve (RC) and …