Static and dynamic γ‐motor output to ankle flexor muscles during locomotion in the decerebrate cat

Taylor, Anthony R.; Durbaba, Rade; Ellaway, P H; Rawlinson, S.

doi:10.1113/jphysiol.2005.101634

Cited by 43 publications

(42 citation statements)

References 35 publications

(58 reference statements)

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“…For example, by pulling the foot forward, the force field changed the expected muscle elongation/shortening pattern. This likely changed spindles afferent discharge (Taylor et al 2006). In addition, by pulling the foot up, the force field tended to reduce loading of the experimental leg and to shift body weight to the other leg more rapidly at the end of stance.…”

Section: Initial Exposure To the Force Fieldmentioning

confidence: 99%

Timing-Specific Transfer of Adapted Muscle Activity After Walking in an Elastic Force Field

Blanchette¹,

Bouyer²

2009

Journal of Neurophysiology

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Blanchette A, Bouyer LJ. Timing-specific transfer of adapted muscle activity after walking in an elastic force field. J Neurophysiol 102: 568 -577, 2009. First published May 6, 2009 doi:10.1152/jn.91096.2008. Human locomotion results from interactions between feedforward (central commands from voluntary and automatic drive) and feedback (peripheral commands from sensory inputs) mechanisms. Recent studies have shown that locomotion can be adapted when an external force is applied to the lower limb. To better understand the neural control of this adaptation, the present study investigated gait modifications resulting from exposure to a position-dependent force field. Ten subjects walked on a treadmill before, during, and after exposure to a force field generated by elastic tubing that pulled the foot forward and up during swing. Lower limb kinematics and electromyographic (EMG) activity were recorded during each walking period. During force field exposure, peak foot velocity was initially increased by 38%. As subjects adapted, peak foot velocity gradually returned to baseline in Յ125 strides. In the adapted state, hamstring EMG activity started earlier (16% before toe off) and remained elevated throughout swing. After force field exposure, foot velocity was initially reduced by 22% and returned to baseline in 9 -51 strides. Aftereffects in hamstring EMGs consisted of increased activity around toe off. Contrary to the adapted state, this increase was not maintained during the rest of swing. Together, these results suggest that while the neural control of human locomotion can adapt to force field exposure, the mechanisms underlying this adaptation may vary according to the timing in the gait cycle. Adapted hamstring EMG activity may rely more on feedforward mechanisms around toe off and more on feedback mechanisms during the rest of swing.

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Section: Initial Exposure To the Force Fieldmentioning

confidence: 99%

Timing-Specific Transfer of Adapted Muscle Activity After Walking in an Elastic Force Field

Blanchette¹,

Bouyer²

2009

Journal of Neurophysiology

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“…These components resemble the dynamic and static ␥-motor firing patterns, respectively, of a fusimotor response (Taylor et al 2006). The onset of the tonic signal, which reflects the position of the eye in the orbit, is masked by the phasic component during a saccade task, making it difficult to determine when area 3a has access to stable eye position information.…”

mentioning

confidence: 99%

The time course of the tonic oculomotor proprioceptive signal in area 3a of somatosensory cortex

Wang

Peck

et al. 2011

Journal of Neurophysiology

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A proprioceptive representation of eye position exists in area 3a of primate somatosensory cortex (Wang X, Zhang M, Cohen IS, Goldberg ME. Nat Neurosci 10: 640-646, 2007). This eye position signal is consistent with a fusimotor response (Taylor A, Durbaba R, Ellaway PH, Rawlinson S. J Physiol 571: 711-723, 2006) and has two components during a visually guided saccade task: a short-latency phasic response followed by a tonic response. While the early phasic response can be excitatory or inhibitory, it does not accurately reflect the eye's orbital position. The late tonic response appears to carry the proprioceptive eye position signal, but it is not clear when this component emerges and whether the onset of this signal is reliable. To test the temporal dynamics of the tonic proprioceptive signal, we used an oculomotor smooth pursuit task in which saccadic eye movements and phasic proprioceptive responses are suppressed. Our results show that the tonic proprioceptive eye position signal consistently lags the actual eye position in the orbit by ~60 ms under a variety of eye movement conditions. To confirm the proprioceptive nature of this signal, we also studied the responses of neurons in a vestibuloocular reflex (VOR) task in which the direction of gaze was held constant; response profiles and delay times were similar in this task, suggesting that this signal does not represent angle of gaze and does not receive visual or vestibular inputs. The length of the delay suggests that the proprioceptive eye position signal is unlikely to be used for online visual processing for action, although it could be used to calibrate an efference copy signal.

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“…It was observed that static gamma activity formed a fusimotor template of intended movement (Taylor et al, 2006), and may carry kinematic information of joint angles. In the periphery, direct recording of Ia afferents from the dorsal ganglion cells of decerebrated cats suggested a similar conclusion that Ia afferents carried joint angle information (Stein et al, 2004).…”

Section: Discussionmentioning

confidence: 99%

Fusimotor control of spindle sensitivity regulates central and peripheral coding of joint angles

Lan¹,

He²

2012

Front. Comput. Neurosci.

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Proprioceptive afferents from muscle spindles encode information about peripheral joint movements for the central nervous system (CNS). The sensitivity of muscle spindle is nonlinearly dependent on the activation of gamma (γ) motoneurons in the spinal cord that receives inputs from the motor cortex. How fusimotor control of spindle sensitivity affects proprioceptive coding of joint position is not clear. Furthermore, what information is carried in the fusimotor signal from the motor cortex to the muscle spindle is largely unknown. In this study, we addressed the issue of communication between the central and peripheral sensorimotor systems using a computational approach based on the virtual arm (VA) model. In simulation experiments within the operational range of joint movements, the gamma static commands (γs) to the spindles of both mono-articular and bi-articular muscles were hypothesized (1) to remain constant, (2) to be modulated with joint angles linearly, and (3) to be modulated with joint angles nonlinearly. Simulation results revealed a nonlinear landscape of Ia afferent with respect to both γs activation and joint angle. Among the three hypotheses, the constant and linear strategies did not yield Ia responses that matched the experimental data, and therefore, were rejected as plausible strategies of spindle sensitivity control. However, if γs commands were quadratically modulated with joint angles, a robust linear relation between Ia afferents and joint angles could be obtained in both mono-articular and bi-articular muscles. With the quadratic strategy of spindle sensitivity control, γs commands may serve as the CNS outputs that inform the periphery of central coding of joint angles. The results suggest that the information of joint angles may be communicated between the CNS and muscles via the descending γs efferent and Ia afferent signals.

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Static and dynamic γ‐motor output to ankle flexor muscles during locomotion in the decerebrate cat

Cited by 43 publications

References 35 publications

Timing-Specific Transfer of Adapted Muscle Activity After Walking in an Elastic Force Field

Timing-Specific Transfer of Adapted Muscle Activity After Walking in an Elastic Force Field

The time course of the tonic oculomotor proprioceptive signal in area 3a of somatosensory cortex

Fusimotor control of spindle sensitivity regulates central and peripheral coding of joint angles

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