.. Participants were fitted with a breathable swimming

cap and disposable electrodes (Ambu, Glen Burnie, MD) placed over the belly of the ECR longus muscle of each forearm to record muscle electrical activity. Electromyographic (EMG) signals were amplified and high-(1000 Hz) and low-pass (0.3 Hz) filtered online (Grass Technologies, Astro-Med, Inc., West Warwick, RI) before being converted Inhibitors,research,lifescience,medical into digital signals through a Powerlab™ data collection unit (ADInstruments, New South Wales, Australia), and monitored and stored on a computer. Transcranial magnetic stimuli (TMS) and sham TMS were applied in each trial with a Magstim 2002 stimulator (Magstim™, Whitland, Wales; see 1977 section below). Experimental task Participants’ capacity for torque generation about the wrist was measured by recording the largest torque produced in three successive maximal voluntary Inhibitors,research,lifescience,medical 5FU contractions (MVCs) of the wrist extensor muscles. In all subsequent trials, the target endpoint force level was set to 5 ± 1% MVC. Participants were provided with a visual display of wrist extension torque along with the target torque range (see Fig. 1A). Wrist extension perturbations and magnetic stimuli were delivered when the target torque had been maintained for 1 sec. In this

experiment, we evaluated the role of the contralateral Inhibitors,research,lifescience,medical and ipsilateral primary motor cortex in Inhibitors,research,lifescience,medical regulating the amplitude of the long-latency reflex in the ECR longus muscle to cope with changes

in environmental stability. To do this we elicited LLSRs during a period of cortical suppression induced by TMS (Kimura et al. 2006; Shemmell et al. 2009). Reflexes were elicited in each participant with perturbations of the left (nondominant) wrist that were 45° in amplitude and occurred with a velocity of 450°/sec. The duration of each perturbation was therefore 100 msec, sufficient to elicit consistent long-latency responses Inhibitors,research,lifescience,medical in other upper limb muscles (Lewis et al. 2005). Twenty perturbations were applied in each of two task conditions: a condition in which subjects interacted with a stiff mechanical environment Florfenicol (stiff) and received an instruction of “Do not intervene” with the perturbation, and a mechanical environment with reduced stiffness (compliant) with the same instruction. In addition, TMS and sham TMS were applied over the motor cortical representations of the ECR muscle in both the contralateral (contra) and ipsilateral (Ipsi) cerebral hemispheres. In each trial, TMS (or sham TMS) was applied 50 msec before the wrist perturbation. The order of task conditions was randomized for each participant. During each block of 20 perturbations participants were provided with visual feedback of wrist torque, along with the target torque level (equivalent to 5 ± 1% MVC).