Long-latency reflexes account for limb biomechanics through several supraspinal pathways.
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2015 Jan 29;8:99. doi: 10.3389/fnint.. eCollection
2014.Long-latency reflexes account for limb biomechanics through several supraspinal pathways.1.1Department of Biomedical Sciences, New York Institute of Technology - College of Osteopathic Medicine Old Westbury, NY, USA.AbstractAccurate control of body posture is enforced by a multitude of corrective actions operating over a range of time scales. The earliest correction is the short-latency reflex (SLR) which occurs between 20-45 ms following a sudden displacement of the limb and is generated entirely by spinal circuits. In contrast, voluntary reactions are generated by a highly distributed network but at a significantly longer delay after stimulus onset (greater than 100 ms). Between these two epochs is the long-latency reflex (LLR) (around 50-100 ms) which acts more rapidly than voluntary reactions but shares some supraspinal pathways and functional capabilities. In particular, the LLR accounts for the arm's biomechanical properties rather than only responding to local muscle stretch like the SLR. This paper will review how the LLR accounts for the arm's biomechanical properties and the supraspinal pathways supporting this ability. Relevant experimental paradigms include clinical studies, non-invasive brain stimulation, neural recordings in monkeys, and human behavioral studies. The sum of this effort indicates that primary motor cortex and reticular formation (RF) contribute to the LLR either by generating or scaling its structured response appropriate for the arm's biomechanics whereas the cerebellum scales the magnitude of the feedback response. Additional putative pathways are discussed as well as potential research lines.KEYWORDS:
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Evoked muscle activity to limb displacement and proposed neural circuitry. (A) The left panel depicts an example of joint angle displacement following an applied step torque. The right panel depicts an example of muscle activity evoked by joint displacement. Vertical lines bracket the short-latency reflex (SLR), long-latency reflex (LLR), and Voluntary reaction (Vol) epochs. Pink, purple, and green horizontal bars depict the neural process that contribute to the different epochs. Note the neural contributions continue throughout the perturbation and overlap in time. (B) Simplified diagram of neural contributors to the different epochs of evoked activity. Colored boxes correspond to colored bars in panel above. Note that several pathways may be involved for a particular epoch.Front Integr Neurosci. .Testing whether shoulder responses are linked to local muscle stretch or multi-muscle stretch. (A) Torque perturbations applied to the arm, a shoulder flexor torque (see the red arm) and an elbow extensor torque (see the blue arm). (B) Change in joint angle from the starting posture. Solid and dashed lines denote the change in shoulder and elbow angle, respectively. Red and blue indicate motion resulting from shoulder flexor torque and elbow extensor torque, respectively. 0 ms is perturbation onset. Shoulder motion is nearly identical for the two conditions, flexion is positive. (C) Predicted shoulder muscle response to the shoulder torque and elbow torque perturbations if the neural processes only utilized local muscle stretch. (D) Predicted shoulder muscle responses if the neural processes integrated stretch from shoulder and elbow muscles appropriate to counter the underlying torque. (E) Torque perturbations applied to the arm, a shoulder-elbow flexor torque (see the red arm) and a shoulder-elbow extensor torque (see the blue arm). (F) Change in joint angle from the starting posture. Same format as (B). The initial joint motion is almost entirely restricted to the elbow. (G) Predicted shoulder muscle response to the shoulder torque and elbow torque perturbations if the neural processes only utilized local muscle stretch. (H) Predicted shoulder muscle responses if the neural processes integrated stretch from shoulder and elbow muscles appropriate to counter the underlying torque. (A,B), (E,F) modified with permission from Kurtzer et al. ().Front Integr Neurosci. .Shoulder muscle responses to perturbations causing selective joint motion. (A) Group average of shoulder extensor muscle activity evoked by two perturbations during postural maintenance. Red and blue traces denote activity during shoulder flexor torque and elbow extensor torque perturbations, respectively (Figures ). (B) Group average of shoulder extensor muscle activity evoked by same two perturbations applied during unperturbed pattern of muscle activity has been removed. (C) Group average of shoulder extensor muscle activity evoked by two perturbations during postural maintenance. Red and blue traces denote activity during combined flexor and combined extensor torque perturbations which cause elbow flexion and extension, respectively (Figures ). (D) Group average of shoulder extensor muscle activity evoked by same two perturbations applied during unperturbed pattern of muscle activity has been removed. (A,B) modified with permission from Kurtzer et al. (). (C,D) modified with permission from Kurtzer et al. ().Front Integr Neurosci. .Applied joint torques and joint motion to test adaptation of LLRs. (A) Configuration of the arm at the starting position and at the final position when reaching to three targets. A force field applied loads which resisted elbow motion, torque proportional to elbow velocity. The target on the left required shoulder flexion a resistive load at the elbow applied a flexion torque. The target in the middle only requi there was no load applied to the elbow as there was no elbow motion. The target on the right re a resistive load at the elbow applied an extension torque. (B) Deviation of the handpaths from a straight line when reaching
black, red, and blue denote the movement errors before, during, and after the application of the elbow resistive load. (C) Activity of elbow flexor muscle when reaching to the three targets before, during, and after introducing the resistive loads at the elbow. (D) Evoked activity of the elbow flexor muscle when reaching to the target requiring only shoulder motion. Data is shown for before, during, and after introducing the resistive load at the elbow. Figure modified with permission from Cluff and Scott ().Front Integr Neurosci. .Evoked muscle activity to perturbation torques and transcranial magnetic stimulation. (A) Torque perturbations applied to the arm, a shoulder flexion torque which displaced the shoulder joint (left cartoon) and shoulder + elbow flexion torque which only displaced the elbow (right cartoon). (B) Evoked activity of the shoulder extensor muscle during shoulder displacement (left panel) and pure elbow displacement (right panel), 0 ms is perturbation onset. Data from a representative subject (C) Evoked activity in the shoulder extensor to a single TMS pulse, 0 ms is TMS onset. (D) TMS pulse timed to occur during the SLR with shoulder displacement (left panel) and pure elbow displacement (right panel). Orange trace is the observed muscle activity to t black trace is the predicted response, summed activity to the separate perturbation and TMS stimuli. (E) TMS pulse timed to occur during the LLR. Same format as above. (F) Group data for the two shoulder muscles. Data normalized to predicted response so values equal to 1 equal linearity whereas values above 1 indicate superlinearity and evidence of a common cortical circuit. Figure modified with permission from Pruszynski et al. ().Front Integr Neurosci. .Task-dependent change in LLR. (A) Cartoon of subject responding to an imposed shoulder torque. Maintaining the hand within a small target requires a vigorous response and is analogous to a “resist” the black trace depicts the small displacement of the hand to the perturbation. Maintaining the hand within a large target requires a weak response and is analogous to a “yield” the gray trace depicts the large displacement of the hand to the perturbation. (B) Evoked shoulder activity while the muscle had a high level of background activity from countering a co black and gray traces correspond to the small and large target conditions, respectively. (C) Evoked shoulder activity while the muscle had a low level of background activity as its antagonist countered a constant opposing load. Figure modified with permission from Kurtzer et al. ().Front Integr Neurosci. .Testing which component of the LLR utilizes knowledge of limb dynamics. (A) Left panel depicts a simple model of LLR comprised of two functional component: an automatic component scaled by background muscle activity and a task-dependent component scaled by target size. Right panel depicts expected pattern of LLR if only the automatic component utilized an internal model of limb dynamics. Expression of that information (i.e., a differential response to the pair of perturbations) would be evident during high background activity of the muscle but would not change with target size. (B) If only the task-dependent component utilized an internal model of limb dynamics than expression of that information would be evident with a small target requiring a vigorous response and not change with background activity of the muscle. (C) If both the automatic and task-dependent components utilized an internal model of limb dynamics than expression of that information would co-vary with background activity and target size. Figure modified with permission from Kurtzer et al. ().Front Integr Neurosci. .Modulation of LLR to target size and background muscle activity. (A) Torque perturbations applied to the arm, a shoulder flexor torque (red arm) and an elbow extensor torque (blue arm). Red and blue traces show exemplar hand paths resulting from the two torque perturbations during presentation of a small target or large target. (B) Group average of shoulder extensor muscle activity evoked by the shoulder flexor torque (red) and elbow extensor torque (bue). The four panels display data during the four combinations of background muscle activity and target size. (C) Differential activity of the LLR to the pair of perturbations (shoulder flexor torque and elbow extensor torque) given the four combinations of target size+background muscle activity (compare to predictions in Figure ). (D) Torque perturbations applied to the arm, a shoulder + elbow flexor torque (red arm) and a shoulder + elbow extensor torque (blue arm). Red and blue traces show hand paths resulting from the perturbations, same format as above. (E) Group average muscle activity evoked by the shoulder + elbow flexor torque (red) and shoulder + elbow extensor torque (bue). (F) Differential activity of the LLR to the pair of perturbations (shoulder flexor+elbow flexor torque and shoulder extensor+elbow extensor torque) given the four combinations of target size+background muscle activity (compare to predictions in Figure ). Figure modified with permission from Kurtzer et al. ().Front Integr Neurosci. .Long-latency reflexes during cerebellar damage. (A) Cartoon of evoked activity from the shoulder extensor by healthy subjects. Panels on the left indicate responses to shoulder displacement caused by a shoulder flexor torque (red) and an elbow extensor torque (blue). Panels on the right indicate responses to elbow displacement caused by a shoulder + elbow flexor torque (red) and an shoulder + elbow extensor torque (blue). (B) Cartoon of predicted shoulder muscle activity if cerebellar damage eliminates the ability to integrate multi-joint muscle. (C) Group average of shoulder extensor muscle activity by a group of healthy subject. (D) Group average of shoulder muscle activity by a group of subjects suffering cerebellar damage. Figure modified with permission from Kurtzer et al. ().Front Integr Neurosci. .Publication typeGrant supportFull Text Sources
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):1137-51.[Reaction mechanism of mammalian molecular chaperones]. [Article in Japanese]1.1Department of Material-process Engineering and Applied Chemistry for Environment, Akita University, Faculty of Engineering and Resource Science, Akita City, Japan.PMID:
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