Characterization of Torque-Related Activity in Primary Motor Cortex During a Multijoint Postural Task

2007 ◽  
Vol 97 (4) ◽  
pp. 2887-2899 ◽  
Author(s):  
Troy M. Herter ◽  
Isaac Kurtzer ◽  
D. William Cabel ◽  
Kirk A. Haunts ◽  
Stephen H. Scott
Keyword(s):  
Motor Cortex ◽  
Primary Motor Cortex ◽  
Bimodal Distribution ◽  
Joint Torque ◽  
Neural Responses ◽  
Joint Activities ◽  
Baseline Activity ◽  
Arm Muscles ◽  
Postural Task

The present study examined neural activity in the shoulder/elbow region of primary motor cortex (M1) during a whole-limb postural task. By selectively imposing torques at the shoulder, elbow, or both joints we addressed how neurons represent changes in torque at a single joint, multiple joints, and their interrelation. We observed that similar proportions of neurons reflected changes in torque at the shoulder, elbow, and both joints and these neurons were highly intermingled across the cortical surface. Most torque-related neurons were reciprocally excited and inhibited (relative to their unloaded baseline activity) by opposing flexor and extensor torques at a single joint. Although coexcitation/coinhibition was occasionally observed at a single joint, it was rarely observed at both joints. A second analysis assessed the relationship between single-joint and multijoint activity. In contrast to our previous observations, we found that neither linear nor vector summation of single-joint activities could capture the breadth of neural responses to multijoint torques. Finally, we studied the neurons' directional tuning across all the torque conditions, i.e., in joint-torque space. Our population of M1 neurons exhibited a strong bimodal distribution of preferred-torque directions (PTDs) that was biased toward shoulder-extensor/elbow-flexor (whole-limb flexor) and shoulder-flexor/elbow-extensor (whole-limb extensor) torques. Notably, we recently observed a similar bimodal distribution of PTDs in a sample of proximal arm muscles. This observation illustrates the intimate relationship between M1 and the motor periphery.

Nonuniform Distribution of Reach-Related and Torque-Related Activity in Upper Arm Muscles and Neurons of Primary Motor Cortex

2006 ◽  
Vol 96 (6) ◽  
pp. 3220-3230 ◽  
Author(s):  
Isaac Kurtzer ◽  
Troy M. Herter ◽  
Stephen H. Scott
Keyword(s):  
Motor Cortex ◽  
Primary Motor Cortex ◽  
Muscular Activity ◽  
Elbow Flexion ◽  
Bimodal Distribution ◽  
The Body ◽  
Related Activity ◽  
Upper Arm ◽  
Reaching Task ◽  
Arm Muscles

The present study examined the activity of primate shoulder and elbow muscles using a novel reaching task. We enforced similar patterns of center-out movement while the animals countered viscous loads at their shoulder, elbow, both joints, or neither joint. Accordingly, we could examine reach-related activity during the unloaded condition and torque-related activity by comparing activity across load conditions. During unloaded reaching the upper arm muscles exhibited a bimodal distribution of preferred hand direction. Maximal reach-related activity occurred with hand movements mostly toward or away from the body. Arm muscles also exhibited a bimodal distribution of their preferred torque direction. Maximal torque-related activity typically occurred with shoulder-extension/elbow-flexion torque or shoulder-flexion/elbow-extension torque. Similar biases in reach-related and torque-related activity could be reproduced by optimizing a global measure of muscle activity. These biases were also observed in the neural activity of primary motor cortex (M1). The parallels between M1 and muscular activity demonstrate another link between motor cortical processing and the motor periphery and may reflect an optimization process performed by the sensorimotor system.

Perturbation-evoked responses in primary motor cortex are modulated by behavioral context

2014 ◽  
Vol 112 (11) ◽  
pp. 2985-3000 ◽  
Author(s):  
Mohsen Omrani ◽  
J. Andrew Pruszynski ◽  
Chantelle D. Murnaghan ◽  
Stephen H. Scott
Keyword(s):  
Motor Cortex ◽  
Primary Motor Cortex ◽  
Initial Perturbation ◽  
Motor Task ◽  
Initial Response ◽  
Mechanical Perturbation ◽  
Population Activity ◽  
Motor Action ◽  
Central Target ◽  
Postural Task

Corrective responses to external perturbations are sensitive to the behavioral task being performed. It is believed that primary motor cortex (M1) forms part of a transcortical pathway that contributes to this sensitivity. Previous work has identified two distinct phases in the perturbation response of M1 neurons, an initial response starting ∼20 ms after perturbation onset that does not depend on the intended motor action and a task-dependent response that begins ∼40 ms after perturbation onset. However, this invariant initial response may reflect ongoing postural control or a task-independent response to the perturbation. The present study tested these two possibilities by examining if being engaged in an ongoing postural task before perturbation onset modulated the initial perturbation response in M1. Specifically, mechanical perturbations were applied to the shoulder and/or elbow while the monkey maintained its hand at a central target or when it was watching a movie and not required to respond to the perturbation. As expected, corrective movements, muscle stretch responses, and M1 population activity in the late perturbation epoch were all significantly diminished in the movie task. Strikingly, initial perturbation responses (<40 ms postperturbation) remained the same across tasks, suggesting that the initial phase of M1 activity constitutes a task-independent response that is sensitive to the properties of the mechanical perturbation but not the goal of the ongoing motor task.

scholarly journals Independent representations of ipsilateral and contralateral limbs in primary motor cortex

eLife ◽  
2019 ◽  
Vol 8 ◽  
Author(s):  
Ethan A Heming ◽  
Kevin P Cross ◽  
Tomohiko Takei ◽  
Douglas J Cook ◽  
Stephen H Scott
Keyword(s):  
Motor Cortex ◽  
Primary Motor Cortex ◽  
Contralateral Side ◽  
The Body ◽  
Motor Output ◽  
Neural Responses ◽  
Related Activity ◽  
Contralateral Limb ◽  
Mechanical Loads ◽  
Contralateral Motor

Several lines of research demonstrate that primary motor cortex (M1) is principally involved in controlling the contralateral side of the body. However, M1 activity has been correlated with both contralateral and ipsilateral limb movements. Why does ipsilaterally-related activity not cause contralateral motor output? To address this question, we trained monkeys to counter mechanical loads applied to their right and left limbs. We found >50% of M1 neurons had load-related activity for both limbs. Contralateral loads evoked changes in activity ~10ms sooner than ipsilateral loads. We also found corresponding population activities were distinct, with contralateral activity residing in a subspace that was orthogonal to the ipsilateral activity. Thus, neural responses for the contralateral limb can be extracted without interference from the activity for the ipsilateral limb, and vice versa. Our results show that M1 activity unrelated to downstream motor targets can be segregated from activity related to the downstream motor output.

Comparison of Neural Responses in Primary Motor Cortex to Transient and Continuous Loads During Posture

2009 ◽  
Vol 101 (1) ◽  
pp. 150-163 ◽  
Author(s):  
Troy M. Herter ◽  
Tereza Korbel ◽  
Stephen H. Scott
Keyword(s):  
Steady State ◽  
Motor Cortex ◽  
Primary Motor Cortex ◽  
Reciprocal Inhibition ◽  
Elbow Flexor ◽  
The Other ◽  
Rapid Responses ◽  
Steady State Responses ◽  
Directional Preference ◽  
Arm Muscles

The present study examined whether neurons in primary motor cortex (M1) exhibit similar responses to transient and continuous loads applied during posture. Rapid responses to whole-limb perturbations were examined by transiently applying (300 ms) flexor and extensor torques to the shoulder and/or elbow during postural maintenance. Over half of M1 neurons responded to these transient loads within 80 ms and many responded within 20–40 ms. These rapid responses exhibited a broad continuum of modulation patterns across load directions. At one extreme, neurons exhibited reciprocal increases and decreases in activity for opposing loads. At the other extreme, neurons (particularly those with onset times of 20–40 ms) displayed relatively uniform increases in activity for all loads. Activity of proximal arm muscles displayed a narrower distribution of modulation patterns characterized by broadly tuned excitation combined with little or no reciprocal inhibition. Both neurons and muscles showed a directional preference for whole-limb flexor and whole-limb extensor torques (flexor at one joint and extensor at the other). Most neurons with rapid responses also showed steady-state responses to continuous loads, although these responses generally displayed reciprocal increases and decreases in activity for opposing loads. Importantly, the preferred-torque directions were quantitatively similar across tasks. For example, a neuron with a maximal rapid response to a transient elbow flexor torque tended to exhibit a maximal steady-state response to a continuous elbow flexor torque. Activity of proximal arm muscles also showed this preservation of directional tuning. These results illustrate that M1 neurons respond rapidly to transient multijoint loads and their patterns of activity share some, but not all, features related to continuous multijoint loads applied during posture.

scholarly journals Reward modulates behaviour and neural responses in motor cortex during action observation

2019 ◽  
Author(s):  
Andreea Loredana Cretu ◽  
Rea Lehner ◽  
Rafael Polania ◽  
Nicole Wenderoth
Keyword(s):  
Motor Cortex ◽  
Primary Motor Cortex ◽  
Response Times ◽  
Contextual Information ◽  
Action Observation ◽  
Neural Responses ◽  
Motor Resonance ◽  
Neural Representations ◽  
Attentional Engagement ◽  
Physiological Outcomes

AbstractTranscranial magnetic stimulation (TMS) studies demonstrated that observing the actions of other individuals leads to action-specific facilitation of primary motor cortex (M1) (i.e., “motor resonance”). Motor resonance is modulated by contextual information accompanying others’ actions, however, it is currently unknown whether action value influences behavioural and physiological outcomes during action observation in humans. Here we tested whether response times (RT) and muscle-specific changes of M1 excitability are modulated by the value an observer assigns to the action executed by another agent and whether this effect can be distinguished from attentional engagement. We show that observing highly-valued actions leads to a significant decrease in RT variability and a significant strengthening of action-specific neural representations in M1. This “sharpening” of behavioural and neural responses was observed over and beyond a control task requiring similar attentional engagement but did not include any rewards. Our finding that reward influences action specific representations in human M1 even if no motor response is required is new, suggesting that reward influences the transformation of action stimuli from the perceptual to the motor domain. We suggest that premotor areas are important for mediating the observed effect, most likely by optimizing grasp-specific PMv-M1 interactions which cause muscular facilitation patterns in M1 to be more distinct for rewarded actions.

scholarly journals Oscillatory Activity in Mouse Lemur Primary Motor Cortex During Natural Locomotor Behavior

2021 ◽  
Vol 15 ◽  
Author(s):  
Banty Tia ◽  
Fabien Pifferi
Keyword(s):  
Motor Cortex ◽  
Primary Motor Cortex ◽  
Small Diameter ◽  
Cortical Activity ◽  
Mouse Lemur ◽  
Oscillatory Activity ◽  
Half Cycle ◽  
Substrate Orientation ◽  
Baseline Activity ◽  
Mouse Lemurs

In arboreal environments, substrate orientation determines the biomechanical strategy for postural maintenance and locomotion. In this study, we investigated possible neuronal correlates of these mechanisms in an ancestral primate model, the gray mouse lemur. We conducted telemetric recordings of electrocorticographic activity in left primary motor cortex of two mouse lemurs moving on a branch-like small-diameter pole, fixed horizontally, or vertically. Analysis of cortical oscillations in high β (25–35 Hz) and low γ (35–50 Hz) bands showed stronger resting power on horizontal than vertical substrate, potentially illustrating sensorimotor processes for postural maintenance. Locomotion on horizontal substrate was associated with stronger event-related desynchronization than vertical substrate, which could relate to locomotor adjustments and/or derive from differences in baseline activity. Spectrograms of cortical activity showed modulation throughout individual locomotor cycles, with higher values in the first than second half cycle. However, substrate orientation did not significantly influence these variations. Overall, these results confirm that specific cortical mechanisms are solicited during arboreal locomotion, whereby mouse lemurs adjust cortical activity to substrate orientation during static posture and locomotion, and modulate this activity throughout locomotor cycles.

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