Descending Corticospinal Control of Intersegmental Dynamics

Pigeon P, DiZio P, Lackner JR. Immediate compensation for variations in self-generated Coriolis torques related to body dynamics and carried objects. J Neurophysiol 110: 1370 -1384, 2013. First published July 3, 2013 doi:10.1152/jn.00104.2012We have previously shown that the Coriolis torques that result when an arm movement is performed during torso rotation do not affect movement trajectory. Our purpose in the present study was to examine whether torso motion-induced Coriolis and other interaction torques are counteracted during a turn and reach (T&R) movement when the effective mass of the hand is augmented, and whether the dominant arm has an advantage in coordinating intersegmental dynamics as predicted by the dynamic dominance hypothesis (Sainburg RL. Exp Brain Res 142: 241-258, 2002). Subjects made slow and fast T&R movements in the dark to just extinguished targets with either arm, while holding or not holding a 454-g object. Movement endpoints were equally accurate at both speeds, with either hand, and in both weight conditions, but subjects tended to angularly undershoot and produce more variable endpoints for targets requiring greater torso rotation. There were no changes in endpoint accuracy or trajectory deviation over repeated movements. The dominant right arm was more stable in its control of trajectory direction across targets, whereas the nondominant left arm had an improved ability to stop accurately on the target for higher levels of interaction torques. The trajectories to more eccentric targets were straighter when performed at higher speeds but slightly more deviated when subjects held the weight. Subjects did not slow their torso velocity or change the timing of the arm and torso velocities when holding the weight, although there was a slight decrease in their hand velocity relative to the torso. The delay between the onsets of torso and finger movements was almost twice as large for the right arm than the left, suggesting the right arm was better able to account for torso rotation in the arm movement. Holding the weight increased the peak Coriolis torque by 40% at the shoulder and 45% at the elbow and, for the most eccentric target, increased the peak net torque by 12% at the shoulder and 34% at the elbow. In accordance with Sainburg's dynamic dominance hypothesis, the right arm exhibited an advantage for coordinating intersegmental dynamics, showing a more stable finger velocity in relation to the torso across targets, decreasing error variability with movement speed, and more synchronized peaks of finger relative and torso angular velocities in conditions with greater joint torque requirements. The arm used had little effect on the movement path and the magnitude of the joint torques in any of the conditions. These results indicate that compensations for forthcoming Coriolis torque variations take into account the dynamic properties of the body and of external objects, as well as the planned velocities of the torso and arm. reaching movement kinematics; coordination; interaction torques...

Section: Subjectsmentioning

confidence: 84%

Immediate compensation for variations in self-generated Coriolis torques related to body dynamics and carried objects

Pigeon

DiZio

Lackner

2013

“…Later, it was established that M1 also contains neurons tuned to joint motions and muscle torque power (Caminiti et al 1991;Scott et al 2001). Increasing evidence supports the involvement of M1 in computations related to the internal model of limb's intersegmental dynamics (Gritsenko et al 2011;Scott 2004). However, these computations may be not limited to M1.…”

Section: Discussionmentioning

confidence: 99%

A preferred pattern of joint coordination during arm movements with redundant degrees of freedom

Dounskaia

Wang

2014

“…The primary motor cortex (M1) is known to be a key region contributing to voluntary movements and long-latency responses (Evarts and Tanji 1975;Matthews 1991;Porter and Lemon 1993;Scott 2004). In particular, it has been shown recently that corticospinal excitability correlates with interaction torques at the elbow during voluntary reaching movements (Gritsenko et al 2011). As well, studies using single-unit recordings in the monkey and transcranial magnetic stimulation in humans have recently demonstrated that M1 resolves the ambiguous torque-motion relationship induced by multijoint perturbations (Pruszynski et al 2011b).…”

Section: Discussionmentioning

confidence: 99%

Fast corrective responses are evoked by perturbations approaching the natural variability of posture and movement tasks

Crevecoeur

Kurtzer

Scott

2012

Crevecoeur F, Kurtzer I, Scott SH. Fast corrective responses are evoked by perturbations approaching the natural variability of posture and movement tasks. J Neurophysiol 107: 2821-2832, 2012. First published February 22, 2012 doi:10.1152/jn.00849.2011.-A wealth of studies highlight the importance of rapid corrective responses during voluntary motor tasks. These studies used relatively large perturbations to evoke robust muscle activity. Thus it remains unknown whether these corrective responses (latency 20 -100 ms) are evoked at perturbation levels approaching the inherent variability of voluntary control. To fill this gap, we examined responses for large to small perturbations applied while participants either performed postural or reaching tasks. To address multijoint corrective responses, we induced various amounts of single-joint elbow motion with scaled amounts of combined elbow and shoulder torques. Indeed, such perturbations are known to elicit a response at the unstretched shoulder muscle, which reflects an internal model of arm intersegmental dynamics. Significant muscle responses were observed during both postural control and reaching, even when perturbation-related joint angle, velocity, and acceleration overlapped in distribution with deviations encountered in unperturbed trials. The response onsets were consistent across the explored range of perturbation loads, with short-latency onset for the muscles spanning the elbow joints (20 -40 ms), and long-latency for shoulder muscles (onset Ͼ 45 ms). In addition, the evoked activity was strongly modulated by perturbation magnitude. These results suggest that multijoint responses are not specifically engaged to counter motor errors that exceed a certain threshold. Instead, we suggest that these corrective processes operate continuously during voluntary motor control. feedback control; internal models; long-latency reflex; motor variability; upper limb