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The effects of digital anaesthesia on predictive grip force adjustments during vertical movements of a grasped object

Authors

  • Dennis A. Nowak,

    1. Department of Neurology, Ludwig-Maximilians-Universität München, Klinikum Großhadern, Marchioninistraße 23, D-81377 München, Germany
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    • *

      Present address: Abteilung für Neurologie, Städtisches Krankenhaus Bogenhausen, Englschalkingerstraße 77, D-81925 München, Germany.

  • Joachim Hermsdörfer,

    1. Clinical Neuropsychology Research Group, Krankenhaus München-Bogenhausen, Technische Universität München, Dachauerstraße 164, D-80992 München, Germany
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  • Stefan Glasauer,

    1. Department of Neurology, Ludwig-Maximilians-Universität München, Klinikum Großhadern, Marchioninistraße 23, D-81377 München, Germany
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  • Jens Philipp,

    1. Department of Neurology, Ludwig-Maximilians-Universität München, Klinikum Großhadern, Marchioninistraße 23, D-81377 München, Germany
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  • Ludger Meyer,

    1. Department of Surgery, Ludwig-Maximilians-Universität München, Klinikum Großhadern, Marchioninistraße 23, D-81377 München, Germany
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  • Norbert Mai

    1. Department of Neurology, Ludwig-Maximilians-Universität München, Klinikum Großhadern, Marchioninistraße 23, D-81377 München, Germany
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    • Deceased.


: Dr Joachim Hermsdörfer, as above.
E-mail: joachim.hermsdoerfer@extern.lrz-muenchen.de

Abstract

Grip force adjustments to fluctuations of inertial loads induced by vertical arm movements with a grasped object were analysed during normal and impaired finger sensibility. Normally grip force is modulated in a highly economical way in parallel with fluctuations of load force. Two subjects performed vertical up and down movements of a grasped object, both with normal finger sensibility and then cutaneously anaesthetized finger sensibility. Short breaks were taken in between single movements, during which the object was held stationary. After digital anaesthesia was applied to the grasping fingers, both subjects substantially increased the grip force. The grip force amplitude and timing still anticipated changes in load force, although the established grip force had already overcome movement-induced load force peaks. This implies that the increase of grip force and consequently the elevated force ratio between maximum grip and maximum load force are not processed to alter the feedforward system of grip force control. Cutaneous afferent information from the grasping digits appears to be necessary for economic scaling of the grip force level, but it plays a subordinate role in the precise anticipatory temporal coupling of grip and load forces during voluntary object manipulation.

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