Does primary motor cortex plasticity parallel adaptive modification to human walking?

Walking in a novel environment, such as with resistance, has been associated with changes in muscle activity (Lam, Anderschitz & Dietz, 2006), limb position (Lam et al., 2006; 2008) and cortical spinal activity (Capaday, Lavoie, Barbeau, Schneider & Bonnard, 1999; Bonnard, Camus, Coyle & Pailhous, 2002) compared to baseline walking measurements. Previous literature on locomotor adaptation, suggests that the nervous system has the ability to adapt to task demands. The location and mechanisms of these physiological and kinematic changes are still unknown. The purpose of the current study was to verify that corticospinal (CS) excitability is altered by resisted walking. Second, we explored whether CS changes are modulated by attention and lastly whether changes in excitability are muscle specific. Locomotor adaptations were induced in 40 healthy participants using a robotic gait-assisted treadmill (Lokomat). Velocity-dependent resistance was applied against hip and knee movements during walking. CS excitability was assessed by quantifying motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation immediately before and after adaptation to both resisted and nonresisted walking. Recruitment curves were collected by stimulating at increments of 5% from 105-145%AMT. To determine whether adaptation is muscle specific, MEPs were measured through random assignment of either the biceps femoris (BF) or rectus femoris (RF). To evaluate the impact of attention on adaptive walking, half the participants attended to their walking pattern via a visual feedback tracking task (post_cog). The other half watched a controlled visual stimulus (post_nocog). Results demonstrated a significant increase in MEP amplitude in the BF and not the RF following resisted walking. The post_cog condition adaptations did not reveal an increase in MEP amplitude compared the post_nocog condition. Results suggest that locomotor adaptations result in an increase in CS excitability that is muscle specific. Focused attention to motor adaptation may not be an important modulator of movement and motor learning as has been reported in past work. The current study is the first to consider both the role of the CS system in adaptations during walking and the impact of attention on CS excitability and parallels previous findings on muscle specific locomotor adaptations.Medicine, Faculty ofGraduat