scholarly journals Primary motor cortical discharge during force field adaptation reflects muscle-like dynamics

2013 ◽  
Vol 110 (3) ◽  
pp. 768-783 ◽  
Author(s):  
Anil Cherian ◽  
Hugo L. Fernandes ◽  
Lee E. Miller
Keyword(s):  
Force Field ◽  
Muscle Activation ◽  
Primary Motor Cortex ◽  
Neural Mechanism ◽  
Reaching Movements ◽  
Behavioral Adaptation ◽  
Experimental Session ◽  
Electrode Arrays ◽  
Preferred Direction ◽  
Neural Discharge

We often make reaching movements having similar trajectories within very different mechanical environments, for example, with and without an added load in the hand. Under these varying conditions, our kinematic intentions must be transformed into muscle commands that move the limbs. Primary motor cortex (M1) has been implicated in the neural mechanism that mediates this adaptation to new movement dynamics, but our recent experiments suggest otherwise. We have recorded from electrode arrays that were chronically implanted in M1 as monkeys made reaching movements under two different dynamic conditions: the movements were opposed by either a clockwise or counterclockwise velocity-dependent force field acting at the hand. Under these conditions, the preferred direction (PD) of neural discharge for nearly all neurons rotated in the direction of the applied field, as did those of proximal limb electromyograms (EMGs), although the median neural rotation was significantly smaller than that of muscles. For a given neuron, the rotation angle was very consistent, even across multiple sessions. Within the limits of measurement uncertainty, both the neural and EMG changes occurred nearly instantaneously, reaching a steady state despite ongoing behavioral adaptation. Our results suggest that M1 is not directly involved in the adaptive changes that occurred within an experimental session. Rather, most M1 neurons are directly related to the dynamics of muscle activation that themselves reflect the external load. It appears as though gain modulation, the differential recruitment of M1 neurons by higher motor areas, can account for the load and behavioral adaptation-related changes in M1 discharge.

Kinematic Coordinates In Which Motor Cortical Cells Encode Movement Direction

2000 ◽  
Vol 84 (5) ◽  
pp. 2191-2203 ◽  
Author(s):  
Robert Ajemian ◽  
Daniel Bullock ◽  
Stephen Grossberg
Keyword(s):  
Cellular Response ◽  
Muscle Activation ◽  
Primary Motor Cortex ◽  
Joint Angle ◽  
Movement Direction ◽  
Mathematical Framework ◽  
Coordinate Systems ◽  
Sensorimotor Transformation ◽  
Cortical Cells ◽  
Preferred Direction

During goal-directed reaching in primates, a sensorimotor transformation generates a dynamical pattern of muscle activation. Within the context of this sensorimotor transformation, a fundamental question concerns the coordinate systems in which individual cells in the primary motor cortex (MI) encode movement direction. This article develops a mathematical framework that computes, as a function of the coordinate system in which an individual cell is hypothesized to operate, the spatial preferred direction (pd) of that cell as the arm configuration and hand location vary. Three coordinate systems are explicitly modeled: Cartesian spatial, shoulder-centered, and joint angle. The computed patterns of spatial pds are distinct for each of these three coordinate systems, and experimental approaches are described that can capitalize on these differences to compare the empirical adequacy of each coordinate hypothesis. One particular experiment involving curved motion was analyzed from this perspective. Out of the three coordinate systems tested, the assumption of joint angle coordinates best explained the observed cellular response properties. The mathematical framework developed in this paper can also be used to design new experiments that are capable of disambiguating between a given set of specified coordinate hypotheses.

Impedance Control Balances Stability With Metabolically Costly Muscle Activation

2004 ◽  
Vol 92 (5) ◽  
pp. 3097-3105 ◽  
Author(s):  
David W. Franklin ◽  
Udell So ◽  
Mitsuo Kawato ◽  
Theodore E. Milner
Keyword(s):  
Force Field ◽  
Muscle Activation ◽  
Force Fields ◽  
Impedance Control ◽  
Reaching Movements ◽  
The Novel ◽  
Minimum Level ◽  
Stable Direction ◽  
Endpoint Stiffness ◽  
Unstable Dynamics

Humans are able to stabilize their movements in environments with unstable dynamics by selectively modifying arm impedance independently of force and torque. We further investigated adaptation to unstable dynamics to determine whether the CNS maintains a constant overall level of stability as the instability of the environmental dynamics is varied. Subjects performed reaching movements in unstable force fields of varying strength, generated by a robotic manipulator. Although the force fields disrupted the initial movements, subjects were able to adapt to the novel dynamics and learned to produce straight trajectories. After adaptation, the endpoint stiffness of the arm was measured at the midpoint of the movement. The stiffness had been selectively modified in the direction of the instability. The stiffness in the stable direction was relatively unchanged from that measured during movements in a null force field prior to exposure to the unstable force field. This impedance modification was achieved without changes in force and torque. The overall stiffness of the arm and environment in the direction of instability was adapted to the force field strength such that it remained equivalent to that of the null force field. This suggests that the CNS attempts both to maintain a minimum level of stability and minimize energy expenditure.

scholarly journals Trial-by-Trial Adaptation of Movements during Mental Practice under Force Field

2013 ◽  
Vol 2013 ◽  
pp. 1-11 ◽  
Author(s):  
Muhammad Nabeel Anwar ◽  
Salman Hameed Khan
Keyword(s):  
Nervous System ◽  
Force Field ◽  
Motor Imagery ◽  
Internal Model ◽  
Human Movement ◽  
Mental Practice ◽  
Higher Learning ◽  
Reaching Movements ◽  
Adaptive Compensation ◽  
Human Nervous System

Human nervous system tries to minimize the effect of any external perturbing force by bringing modifications in the internal model. These modifications affect the subsequent motor commands generated by the nervous system. Adaptive compensation along with the appropriate modifications of internal model helps in reducing human movement errors. In the current study, we studied how motor imagery influences trial-to-trial learning in a robot-based adaptation task. Two groups of subjects performed reaching movements with or without motor imagery in a velocity-dependent force field. The results show that reaching movements performed with motor imagery have relatively a more focused generalization pattern and a higher learning rate in training direction.

scholarly journals Statistical assessment of the stability of neural movement representations

2011 ◽  
Vol 106 (2) ◽  
pp. 764-774 ◽  
Author(s):  
Ian H. Stevenson ◽  
Anil Cherian ◽  
Brian M. London ◽  
Nicholas A. Sachs ◽  
Eric Lindberg ◽  
...  
Keyword(s):  
Primary Motor Cortex ◽  
Tuning Curve ◽  
Modulation Depth ◽  
Measurement Noise ◽  
Neural Representation ◽  
Experimental Conditions ◽  
Sensory Stimuli ◽  
Tuning Curves ◽  
Dynamic Tuning ◽  
Preferred Direction

In systems neuroscience, neural activity that represents movements or sensory stimuli is often characterized by spatial tuning curves that may change in response to training, attention, altered mechanics, or the passage of time. A vital step in determining whether tuning curves change is accounting for estimation uncertainty due to measurement noise. In this study, we address the issue of tuning curve stability using methods that take uncertainty directly into account. We analyze data recorded from neurons in primary motor cortex using chronically implanted, multielectrode arrays in four monkeys performing center-out reaching. With the use of simulations, we demonstrate that under typical experimental conditions, the effect of neuronal noise on estimated preferred direction can be quite large and is affected by both the amount of data and the modulation depth of the neurons. In experimental data, we find that after taking uncertainty into account using bootstrapping techniques, the majority of neurons appears to be very stable on a timescale of minutes to hours. Lastly, we introduce adaptive filtering methods to explicitly model dynamic tuning curves. In contrast to several previous findings suggesting that tuning curves may be in constant flux, we conclude that the neural representation of limb movement is, on average, quite stable and that impressions to the contrary may be largely the result of measurement noise.

Abstract TP92: Brain Activity Related To The Effects Of Augmented Feedback On Learning Movements In A Dynamic Environment In Healthy Subjects And Stroke Survivors

Stroke ◽  
2013 ◽  
Vol 44 (suppl_1) ◽  
Author(s):  
Mukul Mukherjee ◽  
Wen-Pin Chang ◽  
Ka-Chun Siu ◽  
Pierre Fayad ◽  
Nicholas Stergiou
Keyword(s):  
Older Adults ◽  
Force Field ◽  
Cognitive Processing ◽  
Visual Feedback ◽  
Brain Activity ◽  
Dynamic Environments ◽  
Reaching Movements ◽  
Stroke Survivors ◽  
Frequency Bands ◽  
Dynamic Task

Augmented visual feedback has been shown to be effective for learning reaching movements in dynamic environments after a stroke. However, the mechanisms behind such changes are not known. In addition, how brain activity changes with age as we learn novel dynamic tasks is also not clear. The purpose of this study was to examine brain activity changes that are observed when healthy younger and older adults and stroke survivors learn reaching movements in dynamic environments using augmented visual feedback. Healthy young and older adults and chronic stroke survivors were randomly assigned to either a control or an experimental group. They all performed reaching movements with the Inmotion2 robotic system (Interactive Motion Tech Inc., MA) using the dominant/affected arm in a velocity-dependent force field. Controls received actual feedback of their movement, while experimental subjects received augmented visual feedback. Electroencephalogram recordings were analyzed to determine Event Related Desynchronization percent (ERD%). The theta, alpha, and beta frequency bands were examined during movement and pre-movement phases. With learning, the absolute power of the frequency bands increased from the baseline to the adaptation condition, which was then washed out when the force field was removed. With age, there was a reduction in ERD% in alpha and beta bands as the motor task was learned. Stroke subjects had a further reduction in the ERD% in comparison to the healthy older adults. In addition, augmented visual feedback led to a significant increase in the ERD% in comparison to controls during the planning and execution stages of the movement. Past studies have shown when novel dynamics are learned, ERD% reduces indicating increased cognitive processing and memory load. We found that with aging, the cognitive processing and memory required for performing the same dynamic task, increased. After a stroke, there was a further increase. However, the utilization of augmented visual feedback may reduce such requirements and lessen the load on higher centers. These results provide mechanistic support for employing augmented visual feedback for stroke rehabilitation specific to reaching movements in dynamic environments.

scholarly journals Role of Interhemispheric Cortical Interactions in Poststroke Motor Function

2019 ◽  
Vol 33 (9) ◽  
pp. 762-774 ◽  
Author(s):  
Jacqueline A. Palmer ◽  
Lewis A. Wheaton ◽  
Whitney A. Gray ◽  
Mary Alice Saltão da Silva ◽  
Steven L. Wolf ◽  
...  
Keyword(s):  
Motor Function ◽  
Muscle Activation ◽  
Primary Motor Cortex ◽  
Silent Period ◽  
Negatively Associated ◽  
Interhemispheric Coherence ◽  
Stroke Group ◽  
Active Condition ◽  
Hand Muscle ◽  
Clinical Measures

Background/Objective. We investigated interhemispheric interactions in stroke survivors by measuring transcranial magnetic stimulation (TMS)–evoked cortical coherence. We tested the effect of TMS on interhemispheric coherence during rest and active muscle contraction and compared coherence in stroke and older adults. We evaluated the relationships between interhemispheric coherence, paretic motor function, and the ipsilateral cortical silent period (iSP). Methods. Participants with (n = 19) and without (n = 14) chronic stroke either rested or maintained a contraction of the ipsilateral hand muscle during simultaneous recordings of evoked responses to TMS of the ipsilesional/nondominant (i/ndM1) and contralesional/dominant (c/dM1) primary motor cortex with EEG and in the hand muscle with EMG. We calculated pre- and post-TMS interhemispheric beta coherence (15-30 Hz) between motor areas in both conditions and the iSP duration during the active condition. Results. During active i/ndM1 TMS, interhemispheric coherence increased immediately following TMS in controls but not in stroke. Coherence during active cM1 TMS was greater than iM1 TMS in the stroke group. Coherence during active iM1 TMS was less in stroke participants and was negatively associated with measures of paretic arm motor function. Paretic iSP was longer compared with controls and negatively associated with clinical measures of manual dexterity. There was no relationship between coherence and. iSP for either group. No within- or between-group differences in coherence were observed at rest. Conclusions. TMS-evoked cortical coherence during hand muscle activation can index interhemispheric interactions associated with poststroke motor function and potentially offer new insights into neural mechanisms influencing functional recovery.

Pallidal Discharge Related to the Kinematics of Reaching Movements in Two Dimensions

1997 ◽  
Vol 77 (3) ◽  
pp. 1051-1074 ◽  
Author(s):  
Robert S. Turner ◽  
Marjorie E. Anderson
Keyword(s):  
Discharge Rate ◽  
Contextual Information ◽  
Two Dimensions ◽  
Reaching Movements ◽  
Linear Component ◽  
Movement Amplitude ◽  
Starting Position ◽  
Preferred Direction ◽  
Component Amplitude ◽  
Behavioral Conditions

Turner, Robert S. and Marjorie E. Anderson. Pallidal discharge related to the kinematics of reaching movements in two dimensions. J. Neurophysiol. 77: 1051–1074, 1997. Movement-related discharge of neurons in the internal and external segments of the globus pallidus (GPi and GPe, respectively) of two monkeys was studied during reaching movements in a two-dimensional workspace. Discharge was studied during movements to targets in eight directions and at three distances from the starting position under three behavioral conditions that manipulated target visibility and movement triggering. A total of 73 neurons (57 in GPe and 18 in GPi) with changes in discharge in concert with arm movements were included in a quantitative analysis. Of these, 83% also changed their discharge during manipulation of the contralateral arm outside of the task. Although 73% of changes in discharge began before the initiation of movement, they seldom preceded the initial activity of the agonist muscles. Decreases in discharge were more common than reported previously, constituting 40% of the changes in discharge detected. In GPi neurons, decreases also tended to begin earlier than increases. Changes in discharge in GPe neurons were of larger magnitude than those in GPi, and increases in discharge were larger than decreases. Onsets of changes in discharge were temporally linked to movement onset in 69% of neurons. Time locking of neural onsets to trigger presentation and movement termination was found in only 30 and 1% of neurons,respectively. Direction of movement influenced the magnitude of changes in discharge in 78% of cells. Directional modulations were broadly tuned and preferred directions were uniformly distributed across the range of directions. When directional modulations were large, preferred directions were consistent for different amplitudes of movement and for different behavioral conditions. Amplitude of movement influenced the magnitude of changes in discharge in 78% of cells, and in 80% of cases that relation had a significant linear component. Amplitude effects were not more common or stronger for movements in directions close to a cell's preferred direction. Linear relations to movement amplitude were more common and accounted for more of the trial-to-trial variance in discharge rate than relations to either average velocity or movement duration. The relation to movement amplitude was consistent for two behavioral conditions when the change in discharge was scaled strongly with movement amplitude. Movement-related changes in discharge of neurons in the skeletomotor portions of both pallidal segments reflect the kinematics of movement. This information, encoded in combination with sensory and contextual information, may play an on-line role in the selective facilitation and suppression of different frontal thalamocortical circuits.

Dynamical Organization of Directional Tuning in the Primate Premotor and Primary Motor Cortex

2003 ◽  
Vol 89 (2) ◽  
pp. 1136-1142 ◽  
Author(s):  
Yoram Ben-Shaul ◽  
Eran Stark ◽  
Itay Asher ◽  
Rotem Drori ◽  
Zoltan Nadasdy ◽  
...  
Keyword(s):  
Motor Cortex ◽  
Primary Motor Cortex ◽  
Hand Movement ◽  
Movement Direction ◽  
Cortical Surface ◽  
Preferred Direction ◽  
Preparation Period ◽  
Direction Of Movement ◽  
The Mean ◽  
Movement Parameters

Although previous studies have shown that activity of neurons in the motor cortex is related to various movement parameters, including the direction of movement, the spatial pattern by which these parameters are represented is still unresolved. The current work was designed to study the pattern of representation of the preferred direction (PD) of hand movement over the cortical surface. By studying pairwise PD differences, and by applying a novel implementation of the circular variance during preparation and movement periods in the context of a center-out task, we demonstrate a nonrandom distribution of PDs over the premotor and motor cortical surface of two monkeys. Our analysis shows that, whereas PDs of units recorded by nonadjacent electrodes are not more similar than expected by chance, PDs of units recorded by adjacent electrodes are. PDs of units recorded by a single electrode display the greatest similarity. Comparison of PD distributions during preparation and movement reveals that PDs of nearby units tend to be more similar during the preparation period. However, even for pairs of units recorded by a single electrode, the mean PD difference is typically large (45° and 75° during preparation and movement, respectively), so that a strictly modular representation of hand movement direction over the cortical surface is not supported by our data.

Comparison of Onset Time and Magnitude of Activity for Proximal Arm Muscles and Motor Cortical Cells Before Reaching Movements

1997 ◽  
Vol 77 (2) ◽  
pp. 1016-1022 ◽  
Author(s):  
Stephen H. Scott
Keyword(s):  
Primary Motor Cortex ◽  
Onset Time ◽  
Relative Magnitude ◽  
Reaching Movements ◽  
Electromyographic Activity ◽  
Cortical Cells ◽  
Motor Patterns ◽  
Direction Of Movement ◽  
Arm Muscles ◽  
Motor Cortical

Scott, Stephen H. Comparison of onset time and magnitude of activity for proximal arm muscles and motor cortical cells before reaching movements. J. Neurophysiol. 77: 1016–1022, 1997. The activity of motor cortical cells and proximal arm muscles during the initiation of planar reaching movements were analyzed to identify whether features of coordinated motor patterns of muscles spanning the elbow and shoulder were evident in the discharge patterns of motor cortical cells. Shoulder and elbow muscles were divided into four groups, flexors and extensors at each joint. Features of the initial agonist activity, onset time and magnitude, at the shoulder and elbow were compared for movements in different spatial directions. As observed for human movements, differences in the onset time and the relative magnitude of electromyographic activity (EMG) of muscles acting about the shoulder and elbow were dependent on the direction of movement. Motor cortical cells were categorized as elbow or shoulder related on the basis of their response to passive movement of the joints. Differences in the onset time and the relative magnitude of activity of cells related to the shoulder and elbow were both dependent on the direction of movement and were similar to those observed for muscles spanning these joints. There was a modest, but significant correlation between the onset time and magnitude of EMG for individual muscles. A similar magnitude-time coupling was observed for individual motor cortical cells. Variations in the discharge pattern of motor cortical cells before movement that mirror those observed for muscles spanning the shoulder and elbow support the potential role of primary motor cortex in the selection, timing, and magnitude of agonist motor patterns at the shoulder and elbow to initiate reaching movements.

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