Modulation of corticospinal excitability during arm cycling in humans

Abstract

Animal studies have shown that the basic pattern for locomotor activities are generated via neural networks found in the spinal cord, referred to as central pattern generators (CPGs) (Grillner, 1981). In humans, accumulating research evidence suggests that primates, including man, have a similar locomotor centre as animals that controlled by CPGs (Petersen et. al., 1998). It’s indicative that CPGs are sufficient to enable locomotion in quadrupeds; however a more extensive cortical input is involved in the production of locomotion and/or cycling in humans (Zehr et. al 2004). Advanced methods such as transcranial magnetic stimulation (TMS) and transmastoid electrical stimulation were implemented to examine supraspinal and spinal excitability, and bridge the gap between animal and human research. Therefore, this thesis set out to determine changes in corticospinal excitability in biceps brachii during different motor outputs, including those generated by spinal CPGs. The major findings from the present study suggest that corticospinal excitability is enhanced, in biceps brachii, during the initiation of the flexion phase of arm cycling when compared to an intensity matched contraction. The results also proposed that spinal mechanisms are the dominant factors which drive task- and phase-dependent modulation of corticospinal excitability during arm cycling.