scholarly journals Task-dependent coordination of rapid bimanual motor responses

2012 ◽  
Vol 107 (3) ◽  
pp. 890-901 ◽  
Author(s):  
Michael Dimitriou ◽  
David W. Franklin ◽  
Daniel M. Wolpert
Keyword(s):  
Sensory Information ◽  
Optimal Feedback Control ◽  
Single Trial ◽  
Mechanical Perturbation ◽  
Contralateral Limb ◽  
Motor Responses ◽  
Bimanual Task ◽  
Rapid Responses ◽  
Long Latency ◽  
Long Latency Reflex

Optimal feedback control postulates that feedback responses depend on the task relevance of any perturbations. We test this prediction in a bimanual task, conceptually similar to balancing a laden tray, in which each hand could be perturbed up or down. Single-limb mechanical perturbations produced long-latency reflex responses (“rapid motor responses”) in the contralateral limb of appropriate direction and magnitude to maintain the tray horizontal. During bimanual perturbations, rapid motor responses modulated appropriately depending on the extent to which perturbations affected tray orientation. Specifically, despite receiving the same mechanical perturbation causing muscle stretch, the strongest responses were produced when the contralateral arm was perturbed in the opposite direction (large tray tilt) rather than in the same direction or not perturbed at all. Rapid responses from shortening extensors depended on a nonlinear summation of the sensory information from the arms, with the response to a bimanual same-direction perturbation (orientation maintained) being less than the sum of the component unimanual perturbations (task relevant). We conclude that task-dependent tuning of reflexes can be modulated online within a single trial based on a complex interaction across the arms.

Influence of the behavioral goal and environmental obstacles on rapid feedback responses

2012 ◽  
Vol 108 (4) ◽  
pp. 999-1009 ◽  
Author(s):  
Joseph Y. Nashed ◽  
Frédéric Crevecoeur ◽  
Stephen H. Scott
Keyword(s):  
Muscle Activity ◽  
Motor System ◽  
Optimal Feedback Control ◽  
Motor Responses ◽  
Spatial Properties ◽  
Long Latency ◽  
Circular Target ◽  
Motor Actions ◽  
Behavioral Goal ◽  
Feedback Responses

The motor system must consider a variety of environmental factors when executing voluntary motor actions, such as the shape of the goal or the possible presence of intervening obstacles. It remains unknown whether rapid feedback responses to mechanical perturbations also consider these factors. Our first experiment quantified how feedback corrections were altered by target shape, which was either a circular dot or a bar. Unperturbed movements to each target were qualitatively similar on average but with greater dispersion of end point positions when reaching to the bar. On random trials, multijoint torque perturbations deviated the hand left or right. When reaching to a circular target, perturbations elicited corrective movements that were directed straight to the location of the target. In contrast, corrective movements when reaching to a bar were redirected to other locations along the bar axis. Our second experiment quantified whether the presence of obstacles could interfere with feedback corrections. We found that hand trajectories after the perturbations were altered to avoid obstacles in the environment. Importantly, changes in muscle activity reflecting the different target shapes (bar vs. dot) or the presence of obstacles were observed in as little as 70 ms. Such changes in motor responses were qualitatively consistent with simulations based on optimal feedback control. Taken together, these results highlight that long-latency motor responses consider spatial properties of the goal and environment.

scholarly journals Stabilizing stretch reflexes are modulated independently from the rapid release of perturbation-triggered motor plans

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Hyunglae Lee ◽  
Eric J. Perreault
Keyword(s):  
Motor Response ◽  
Spinal Reflexes ◽  
Reflex Response ◽  
Voluntary Activity ◽  
Motor Responses ◽  
Triggered Reaction ◽  
Triggered Reactions ◽  
Long Latency ◽  
Target Effect ◽  
Long Latency Reflex

Abstract Responses elicited after the shortest latency spinal reflexes but prior to the onset of voluntary activity can display sophistication beyond a stereotypical reflex. Two distinct behaviors have been identified for these rapid motor responses, often called long-latency reflexes. The first is to maintain limb stability by opposing external perturbations. The second is to quickly release motor actions planned prior to the disturbance, often called a triggered reaction. This study investigated their interaction when motor tasks involve both limb stabilization and motor planning. We used a robotic manipulator to change the stability of the haptic environment during 2D arm reaching tasks, and to apply perturbations that could elicit rapid motor responses. Stabilizing reflexes were modulated by the orientation of the haptic environment (field effect) whereas triggered reactions were modulated by the target to which subjects were instructed to reach (target effect). We observed that there were no significant interactions between the target and field effects in the early (50–75 ms) portion of the long-latency reflex, indicating that these components of the rapid motor response are initially controlled independently. There were small but significant interactions for two of the six relevant muscles in the later portion (75–100 ms) of the reflex response. In addition, the target effect was influenced by the direction of the perturbation used to elicit the motor response, indicating a later feedback correction in addition to the early component of the triggered reaction. Together, these results demonstrate how distinct components of the long-latency reflex can work independently and together to generate sophisticated rapid motor responses that integrate planning with reaction to uncertain conditions.

Feedback responses rapidly scale with the urgency to correct for external perturbations

2013 ◽  
Vol 110 (6) ◽  
pp. 1323-1332 ◽  
Author(s):  
F. Crevecoeur ◽  
I. Kurtzer ◽  
T. Bourke ◽  
S. H. Scott
Keyword(s):  
Behavioral Performance ◽  
Small Target ◽  
Motor Responses ◽  
External Perturbations ◽  
Rapid Responses ◽  
Long Latency Responses ◽  
Long Latency ◽  
Linear Regressions ◽  
Explicit Criteria ◽  
Muscle Responses

Healthy subjects can easily produce voluntary actions at different speeds and with varying accuracy requirements. It remains unknown whether rapid corrective responses to mechanical perturbations also possess this flexibility and, thereby, contribute to the capability expressed in voluntary control. Paralleling previous studies on self-initiated movements, we examined how muscle activity was impacted by either implicit or explicit criteria affecting the urgency to respond to the perturbation. Participants maintained their arm position against torque perturbations with unpredictable timing and direction. In the first experiment, the urgency to respond was explicitly altered by varying the time limit (300 ms vs. 700 ms) to return to a small target. A second experiment addresses implicit urgency criteria by varying the radius of the goal target, such that task accuracy could be achieved with less vigorous corrections for large targets than small target. We show that muscle responses at ∼60 ms scaled with the task demand. Moreover, in both experiments, we found a strong intertrial correlation between long-latency responses (∼50–100 ms) and the movement reversal times, which emphasizes that these rapid motor responses are directly linked to behavioral performance. The slopes of these linear regressions were sensitive to the experimental condition during the long-latency and early voluntary epochs. These findings suggest that feedback gains for very rapid responses are flexibly scaled according to task-related urgency.

Rapid Motor Responses Are Appropriately Tuned to the Metrics of a Visuospatial Task

2008 ◽  
Vol 100 (1) ◽  
pp. 224-238 ◽  
Author(s):  
J. Andrew Pruszynski ◽  
Isaac Kurtzer ◽  
Stephen H. Scott
Keyword(s):  
Upper Limb ◽  
Spatial Information ◽  
Target Position ◽  
Target Distance ◽  
Motor Responses ◽  
Target Direction ◽  
Verbal Instructions ◽  
Voluntary Response ◽  
Rapid Responses ◽  
Long Latency

Considerable research has established that rapid motor responses (traditionally called reflexes), can be modified by a subject's voluntary goals. Here, we expand on past observations using verbal instructions by defining the voluntary goal via visual target position. This approach allowed us to objectively enforce task adherence and explore a richer set of variables, such as target direction and distance, metrics that modify voluntary control and that—according to our hypothesis—will influence rapid motor responses. Our first experiment tested whether upper-limb responses are categorically modulated by target direction by placing targets such that the same perturbation could push the hand into one target and out of the other, a spatial analogue to “resist/yield” verbal instructions. Consistent with these classical results, we found that the short-latency rapid response (R1, 20–45 ms) was not modulated by target direction, whereas long-latency rapid responses (R2/R3, 45–105 ms) were modified in a manner approaching the voluntary response (VOL, 120–180 ms). Our second experiment tested whether upper-limb responses are continuously modulated by target distance by distributing five targets along one axis centered on the hand. Here, the long-latency and voluntary response mirrored the task demands by increasing activity in a graded fashion with increasing target distance. Our final experiment explored how upper-limb responses incorporate two-dimensional spatial information by placing targets radially around the hand. Notably, long-latency responses exhibited smooth tuning functions to target direction that were similar to those observed for the voluntary response. Taken together, these results illustrate the flexibility of long-latency rapid responses and emphasize their similarity to later voluntary responses.

Neuromuscular Control of Movement

2018 ◽  
Keyword(s):  
Nervous System ◽  
Sensory Information ◽  
Neuromuscular Control ◽  
Complex Environments ◽  
Locomotor Rhythm ◽  
Motor Responses ◽  
Reflex Pathways ◽  
Local Reflex ◽  
Local Circuits ◽  
And Control

The control of movement is essential for animals traversing complex environments and operating across a range of speeds and gaits. We consider how animals process sensory information and initiate motor responses, primarily focusing on simple motor responses that involve local reflex pathways of feedback and control, rather than the more complex, longer-term responses that require the broader integration of higher centers within the nervous system. We explore how local circuits facilitate decentralized coordination of locomotor rhythm and examine the fundamentals of sensory receptors located in the muscles, tendons, joints, and at the animal’s body surface. These sensors monitor the animal’s physical environment and the action of its muscles. The sensory information is then carried back to the animal’s nervous system by afferent neurons, providing feedback that is integrated at the level of the spinal cord of vertebrates and sensory-motor ganglia of invertebrates.

scholarly journals Long-latency reflexes for inter-effector coordination reflect a continuous state feedback controller

2018 ◽  
Vol 120 (5) ◽  
pp. 2466-2483 ◽  
Author(s):  
Frederic Crevecoeur ◽  
Isaac Kurtzer
Keyword(s):  
Feedback Control ◽  
State Feedback ◽  
Feedback Controller ◽  
State Feedback Control ◽  
Comprehensive Treatment ◽  
State Feedback Controller ◽  
Long Latency ◽  
Continuous State ◽  
Long Latency Reflex ◽  
Long Latency Reflexes

Successful performance in many everyday tasks requires compensating unexpected mechanical disturbance to our limbs and body. The long-latency reflex plays an important role in this process because it is the fastest response to integrate sensory information across several effectors, like when linking the elbow and shoulder or the arm and body. Despite the dozens of studies on inter-effector long-latency reflexes, there has not been a comprehensive treatment of how these reveal the basic control organization that sets constraints on any candidate model of neural feedback control such as optimal feedback control. We considered three contrasting ways that controllers can be organized: multiple independent controllers vs. a multiple-input multiple-output (MIMO) controller, a continuous feedback controller vs. an intermittent feedback controller, and a direct MIMO controller vs. a state feedback controller. Following a primer on control theory and review of the relevant evidence, we conclude that continuous state feedback control best describes the organization of inter-effector coordination by the long-latency reflex.

Re-innervation of axolotl limbs - II. Sensory nerves

1975 ◽  
Vol 190 (1098) ◽  
pp. 59-75 ◽  
Keyword(s):  
Tactile Stimulation ◽  
Receptive Fields ◽  
Sensory Information ◽  
Extracellular Recording ◽  
Sensory Nerves ◽  
Sensory Innervation ◽  
Contralateral Limb ◽  
Innervation Patterns ◽  
Control Limb ◽  
Left And Right

Segmental sensory receptive fields in axolotl hindlimb skin were mapped during extracellular recording of nerve responses to light tactile stimulation. Normally, cutaneous sensory innervation patterns for a given pair of left and right hindlimbs were similar, but there was variability among animals. Individual cutaneous fibres innervated a solitary receptive field whose borders were sharply defined. When spinal nerves were crushed or cut and allowed to regrow the receptive fields re-established were similar to those on the normal contralateral limb. However, many single cutaneous fibres innervated multiple receptive fields. After cutting and interchanging the two major limb nerve branches, regenerating cutaneous nerves tended to innervate skin toward which they were directed, and receptive fields did not resemble the patterns on the control limb skin. This contrasts with the results following the same operations on the motor innervation where patterns of re-innervation do resemble the control. Regenerating cutaneous fibres apparently cannot relocate their respective original cutaneous addresses, but readily re-innervate foreign skin areas. Nerves regenerating after a crush or cut appear to follow mechanical and/or biochemical orienting clues within the nerve trunks for restoration of typical innervation patterns. It is not known how the axolotl central nervous system copes with cutaneous sensory information from mislocated nerve terminals.

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