Electromyography of superficial cervical muscles with exertion in the sagittal, coronal and oblique planes.
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The purpose of the current study was twofold: (1) to determine the isometric force and electromyographic (EMG) relationship of the sternocleidomastoid, splenii and trapezii muscles bilaterally in graded and maximal exertions in the sagittal, coronal and oblique planes. and (2) to develop regression equations to predict force based on the EMG scores. A newly designed and validated cervical isometric strength testing device was used to measure the cervical muscle isometric strength and force/EMG relationship in cervical flexion, extension, bilateral lateral flexion, bilateral anterolateral flexion, and bilateral posterolateral extension, all beginning with an upright seated neutral posture. A group of 40 healthy subjects were asked to exert their cervical motions in the directions of interest, while the force output and EMG from the sternocleidomastoids, splenii, and trapezii were sampled bilaterally at 1 kHz. ANOVA, correlation, and regression analyses were carried out. The force and EMG scores were significantly different between the directions of effort (P<0.01). All regressions were significant (P<0.01). All subjects registered the highest forces in pure extension and the lowest in pure flexion, showing a gradual decrease from the posterior to anterior direction. There was a modest correlation between EMG of the investigated muscles and force (r=0.15-0.76, P<0.01). EMG output was, for example, approximately 66% higher in flexion than in extension (while force output was roughly 30% less in flexion than extension) - thus relatively more muscle activity was required in flexion than extension to generate a given force. The intermediate positions (i.e. anterolateral flexion) revealed force/EMG ratio scores that were intermediate in relation to the force/EMG ratios for pure flexion and pure extension. The cervical muscle strength and cervical muscle EMG are therefore dependent on the direction of effort. (+info)
Mechanical power output during running accelerations in wild turkeys.
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We tested the hypothesis that the hindlimb muscles of wild turkeys (Meleagris gallopavo) can produce maximal power during running accelerations. The mechanical power developed during single running steps was calculated from force-plate and high-speed video measurements as turkeys accelerated over a trackway. Steady-speed running steps and accelerations were compared to determine how turkeys alter their running mechanics from a low-power to a high-power gait. During maximal accelerations, turkeys eliminated two features of running mechanics that are characteristic of steady-speed running: (i) they produced purely propulsive horizontal ground reaction forces, with no braking forces, and (ii) they produced purely positive work during stance, with no decrease in the mechanical energy of the body during the step. The braking and propulsive forces ordinarily developed during steady-speed running are important for balance because they align the ground reaction force vector with the center of mass. Increases in acceleration in turkeys correlated with decreases in the angle of limb protraction at toe-down and increases in the angle of limb retraction at toe-off. These kinematic changes allow turkeys to maintain the alignment of the center of mass and ground reaction force vector during accelerations when large propulsive forces result in a forward-directed ground reaction force. During the highest accelerations, turkeys produced exclusively positive mechanical power. The measured power output during acceleration divided by the total hindlimb muscle mass yielded estimates of peak instantaneous power output in excess of 400 W kg(-1) hindlimb muscle mass. This value exceeds estimates of peak instantaneous power output of turkey muscle fibers. The mean power developed during the entire stance phase increased from approximately zero during steady-speed runs to more than 150 W kg(-1) muscle during the highest accelerations. The high power outputs observed during accelerations suggest that elastic energy storage and recovery may redistribute muscle power during acceleration. Elastic mechanisms may expand the functional range of muscle contractile elements in running animals by allowing muscles to vary their mechanical function from force-producing struts during steady-speed running to power-producing motors during acceleration. (+info)
Role of arcuate frontal cortex of monkeys in smooth pursuit eye movements. I. Basic response properties to retinal image motion and position.
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Anatomical and physiological studies have shown that the "frontal pursuit area" (FPA) in the arcuate cortex of monkeys is involved in the control of smooth pursuit eye movements. To further analyze the signals carried by the FPA, we examined the activity of pursuit-related neurons recorded from a discrete region near the arcuate spur during a variety of oculomotor tasks. Pursuit neurons showed direction tuning with a wide range of preferred directions and a mean full width at half-maximum of 129 degrees. Analysis of latency using the "receiver operating characteristic" to compare responses to target motion in opposite directions showed that the directional response of 58% of FPA neurons led the initiation of pursuit, while 19% led by 25 ms or more. Analysis of neuronal responses during pursuit of a range of target velocities revealed that the sensitivity to eye velocity was larger during the initiation of pursuit than during the maintenance of pursuit, consistent with two components of firing related to image motion and eye motion. FPA neurons showed correlates of two behavioral features of pursuit documented in prior reports. 1) Eye acceleration at the initiation of pursuit declines as a function of the eccentricity of the moving target. FPA neurons show decreased firing at the initiation of pursuit in parallel with the decline in eye acceleration. This finding is consistent with prior suggestions that the FPA plays a role in modulating the gain of visual-motor transmission for pursuit. 2) A stationary eccentric cue evokes a smooth eye movement opposite in direction to the cue and enhances the pursuit evoked by subsequent target motions. Many pursuit neurons in the FPA showed weak, phasic visual responses for stationary targets and were tuned for the positions about 4 degrees eccentric on the side opposite to the preferred pursuit direction. However, few neurons (12%) responded during the preparation or execution of saccades. The responses to the stationary target could account for the behavioral effects of stationary, eccentric cues. Further analysis of the relationship between firing rate and retinal position error during pursuit in the preferred and opposite directions failed to provide evidence for a large contribution of image position to the firing of FPA neurons. We conclude that FPA processes information in terms of image and eye velocity and that it is functionally separate from the saccadic frontal eye fields, which processes information in terms of retinal image position. (+info)
Action-perception dissociation in response to target acceleration.
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The purpose of this study was to investigate whether information about the acceleration characteristics of a moving target can be used for both action and perception. Also of interest was whether prior movement experience altered perceptual judgements. Participants manually intercepted targets moving with various acceleration, velocity and movement time characteristics. They also made perceptual judgements about the acceleration characteristics of these targets either with or without prior manual interception experience. Results showed that while aiming kinematics were sensitive to the acceleration characteristics of the target, participants were only able to perceptually discriminate the velocity characteristics of target motion, even after performing interceptive actions to the same targets. These results are discussed in terms of a two channel (action-perception) model of visuomotor control. (+info)
Vestibuloocular reflex dynamics during high-frequency and high-acceleration rotations of the head on body in rhesus monkey.
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For frequencies >10 Hz, the vestibuloocular reflex (VOR) has been primarily investigated during passive rotations of the head on the body in humans. These prior studies suggest that eye movements lag head movements, as predicted by a 7-ms delay in the VOR reflex pathways. However, Minor and colleagues recently applied whole-body rotations of frequencies < or =15 Hz in monkeys and found that eye movements were nearly in phase with head motion across all frequencies. The goal of the present study was to determine whether VOR response dynamics actually differ significantly for whole-body versus head-on-body rotations. To address this question, we evaluated the gain and phase of the VOR induced by high-frequency oscillations of the head on the body in monkeys by directly measuring both head and eye movements using the magnetic search coil technique. A torque motor was used to rotate the heads of three Rhesus monkeys over the frequency range 5-25 Hz. Peak head velocity was held constant, first at +/-50 degrees /s and then +/-100 degrees /s. The VOR was found to be essentially compensatory across all frequencies; gains were near unity (1.1 at 5 Hz vs. 1.2 at 25 Hz), and phase lag increased only slightly with frequency (from 2 degrees at 5 Hz to 11 degrees at 25 Hz, a marked contrast to the 63 degrees lag at 25 Hz predicted by a 7-ms VOR latency). Furthermore, VOR response dynamics were comparable in darkness and when viewing a target and did not vary with peak velocity. Although monkeys offered less resistance to the initial cycles of applied head motion, the gain and phase of the VOR did not vary for early versus late cycles, suggesting that an efference copy of the motor command to the neck musculature did not alter VOR response dynamics. In addition, VOR dynamics were also probed by applying transient head perturbations with much greater accelerations (peak acceleration >15,000 degrees /s(2)) than have been previously employed. The VOR latency was between 5 and 6 ms, and mean gain was close to unity for two of the three animals tested. A simple linear model well described the VOR responses elicited by sinusoidal and transient head on body rotations. We conclude that the VOR is compensatory over a wide frequency range in monkeys and has similar response dynamics during passive rotation of the head on body as during passive rotation of the whole body in space. (+info)
Constraints on the source of short-term motion adaptation in macaque area MT. II. tuning of neural circuit mechanisms.
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Neurons in area MT, a motion-sensitive area of extrastriate cortex, respond to a step of target velocity with a transient-sustained firing pattern. The transition from a high initial firing rate to a lower sustained rate occurs over a time course of 20-80 ms and is considered a form of short-term adaptation. In the present paper, we compared the tuning of the adaptation to the neuron's tuning to direction and speed. The tuning of adaptation was measured with a condition/test paradigm in which a testing motion of the preferred direction and speed of the neuron under study was preceded by a conditioning motion: the direction and speed of the conditioning motion were varied systematically. The response to the test motion depended strongly on the direction of the conditioning motion. It was suppressed in almost all neurons by conditioning motion in the same direction and could be either suppressed or enhanced by conditioning motion in the opposite direction. Even in neurons that showed suppression for target motion in the nonpreferred direction, the adaptation and response direction tuning were the same. The speed tuning of adaptation was linked much less tightly to the speed tuning of the response of the neuron under study. For just more than 50% of neurons, the preferred speed of adaptation was more than 1 log unit different from the preferred response speed. Many neurons responded best when slow motions were followed by faster motions (acceleration) or vice versa (deceleration), suggesting that MT neurons may encode information about the change of target velocity over time. Finally, adaptation by conditioning motions of different directions, but not different speeds, altered the latency of the response to the test motion. The adaptation of latency recovered with shorter intervals between the conditioning and test motions than did the adaptation of response size, suggesting that latency and amplitude adaptation are mediated by separate mechanisms. Taken together with the companion paper, our data suggest that short-term motion adaptation in MT is a consequence of the neural circuit in MT and is not mediated by either input-specific mechanisms or intrinsic mechanisms related to the spiking of individual neurons. The circuit responsible for adaptation is tuned for both speed and direction and has the same direction tuning as the circuit responsible for the initial response of MT neurons. (+info)
Otolith and semicircular canal inputs to single vestibular neurons in cats.(63/829)
Control and modulation of canal driven vestibulo-ocular reflex.
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It has been well known that the canal driven vestibulo-ocular reflex (VOR) is controlled and modulated through the central nervous system by external sensory information (e.g. visual, otolithic and somatosensory inputs) and by mental conditions. Because the origin of retinal image motion exists both in the subjects (eye, head and body motions) and in the external world (object motion), the head motion should be canceled and/or the object should be followed by smooth eye movements. Human has developed a lot of central nervous mechanisms for smooth eye movements (e.g. VOR, optokinetic reflex and smooth pursuit eye movements). These mechanisms are thought to work for the purpose of better seeing. Distinct mechanism will work in appropriate self motion and/or object motion. As the results, whole mechanisms are controlled in a purpose-directed manner. This can be achieved by a self-organizing holistic system. Holistic system is very useful for understanding human oculomotor behavior. (+info)