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189. Bimanuelle Koordination und Händigkeit

Author

Uttner, I, primary, Hermsdörfer, J, additional, Nowak, D, additional, Krey, P, additional, Müller, F, additional, Philipp, J, additional, Zierdt, A, additional, and Kraft, E, additional

Published
2004
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193. Moving weightless objects

Author

Hermsdörfer, J., primary, Marquardt, C., additional, Philipp, J., additional, Zierdt, A., additional, Nowak, D., additional, Glasauer, S., additional, and Mai, N., additional

Published
2000
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196. Preserved and Impaired Aspects of Feed-Forward Grip Force Control After Chronic Somatosensory Deafferentation.

Author

Hermsdörfer, J., Elias, Z., Cole, J. D., Quaney, B. M., and Nowak, D. A.

Abstract

Background. Although feed-forward mechanisms of grip force control are a prerequisite for skilled object manipulation, somatosensory feedback is essential to acquire, maintain, and adapt these mechanisms. Objective. Individuals with complete peripheral deafferentation provide the unique opportunity to study the function of the motor system deprived of somatosensory feedback. Methods. Two individuals (GL and IW) with complete chronic deafferentation of the trunk and limbs were tested during cyclic vertical movements of a handheld object. Such movements induce oscillating loads that are typically anticipated by parallel modulations of the grip force. Load magnitude was altered by varying either the movement frequency or object weight. Results. GL and IW employed excessive grip forces probably reflecting a compensatory mechanism. Despite this overall force increase, both deafferented participants adjusted their grip force level according to the load magnitude, indicating preserved scaling of the background grip force to physical demands. The dynamic modulation of the grip force with the load force was largely absent in GL, whereas in IW only slower movements were clearly affected. Conclusions. The authors hypothesize that the deafferented patients may have utilized visual and vestibular cues and/or an efferent copy of the motor command of the arm movement to scale the grip force level. Severely impaired grip force-load coupling in GL suggests that sensory information is important for maintaining a precise internal model of dynamic grip force control. However, comparably better performance in IW argues for the possibility that alternative cues can be used to trigger a residual internal model. [ABSTRACT FROM AUTHOR]

Published
2008
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197. Digit cooling influences grasp efficiency during manipulative tasks.

Author

Nowak, Dennis A., Hermsdörfer, Joachim, Nowak, D A, and Hermsdörfer, J

Subjects
PHYSIOLOGICAL effects of cold temperatures, SENSES, FINGERS, SENSORY evaluation, AFFERENT pathways, SENSE organs
Abstract

A commonly experienced effect of cold is a sensation of numbness and loss of sensibility in the fingers. Intact tactile sensibility of the grasping digits is essential for the efficient scaling of grip force level during the manipulation of hand-held objects. We investigated whether or not cooling of the grasping digits affects scaling of the grip force magnitude in relation to the loads resulting from continuous vertical arm movements performed with a grasped instrumented object. Maxima and minima of load force occurred at the lower and upper turning point of the movement cycle, respectively, and were accompanied by maximum and minimum peaks in grip force occurring close in time prior to and following digit cooling, respectively. Thus, digit cooling did not influence the ability to adjust the grip force profile in anticipation of movement-induced fluctuations in load force. However, subjects established significantly higher grip forces against the hand-held object following digit cooling and generated a 10-70% higher ratio between grip and load forces at the upper and lower turning points of the movement cycle. It is thought that the impaired economical scaling of grip force level is the result of reduced sensory feedback from the grasping fingers during digit cooling. The results provide further evidence to support the suggestion that cutaneous afferent input plays a subordinate role in the predictive temporal regulation of the grip force profile, but is used to adapt economically the force level to the actual loading requirements during dynamic object manipulation. [ABSTRACT FROM AUTHOR]

Published
2003
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