1 Department of Neurobiology and Anatomy, Drexel University College of Medicine;
2 School of Bioengineering and Health Sciences, Drexel University;
3 Biology Department, University of Pennsylvania, ...Philadelphia, Pennsylvania; and
4 Vertex Pharmaceuticals, San Diego, California
Submitted 31 May 2008;
accepted in final form 15 July 2009
ABSTRACT
Spinal circuits may organize trajectories using pattern generators and synergies. In frogs, prior work supports fixed-duration pulses of fixed composition synergies, forming primitives. In wiping behaviors, spinal frogs adjust their motor activity according to the starting limb position and generate fairly straight and accurate isochronous trajectories across the workspace. To test whether a compact description using primitives modulated by proprioceptive feedback could reproduce such trajectory formation, we built a biomechanical model based on physiological data. We recorded from hindlimb muscle spindles to evaluate possible proprioceptive input. As movement was initiated, early skeletofusimotor activity enhanced many muscle spindles firing rates. Before movement began, a rapid estimate of the limb position from simple combinations of spindle rates was possible. Three primitives were used in the model with muscle compositions based on those observed in frogs. Our simulations showed that simple gain and phase shifts of primitives based on published feedback mechanisms could generate accurate isochronous trajectories and motor patterns that matched those observed. Although on-line feedback effects were omitted from the model after movement onset, our primitive-based model reproduced the wiping behavior across a range of starting positions. Without modifications from proprioceptive feedback, the model behaviors missed the target in a manner similar to that in deafferented frogs. These data show how early proprioception might be used to make a simple estimate initial limb state and to implicitly plan a movement using observed spinal motor primitives. Simulations showed that choice of synergy composition played a role in this simplicity. To generate froglike trajectories, a hip flexor synergy without sartorius required motor patterns with more proprioceptive knee flexor control than did patterns built with a more natural synergy including sartorius. Such synergy choices and control strategies may simplify the circuitry required for reflex trajectory construction and adaptation.
Address for reprint requests and other correspondence: S. Giszter, Neurobiology, DUCOM, 2900 Queen Lane, Philadelphia, PA 19129 (E-mail: simon.giszter{at}drexelmed.edu ).
Divine Heiress explores the vital role of the Virgin Mary in the cultural and religious life of Constantinople in late antiquity. It shows how she was transformed from a humble Jewish maiden into a ...divine figure and supernatural protector of Constantinople.Vasiliki Limberis examines the cult of Mary in the context of the religious culture of the Mediterranean world and the imperial Christianity of the Roman Empire. The author looks at all the evidence for the cult but pays particular attention to the early hymns to the virgin. These hymns preserved the strong indigenous goddess traditions of Demeter/Persephone, Isis, Hecate and Athena. By studying them the author places the cult of Mary in its historical and cultural context.
Differentiation of peanut stunt virus isolates in six serotypes Richter, J; Haack, U; Wesemann, M. (Institut fuer Phytopathologie, Aschersleben (German D.R.)) ...
Archiv für Phytopathologie und Pflanzenschutz,
(1987), Letnik:
23, Številka:
2
Journal Article
Recenzirano
An Hand von Sporntesten in Agargel konnten 13 verschiedene Isolate des peanut stunt virus (PSV) folgenden sechs Serotypen zugeordnet werden: V, W, CB, RoM, Ag und P. Hierbei gehoeren fuenf ...Robinien-Isolate aus drei bzw. vier Trifolium-Isolaten aus zwei verschiedenen Laendern jeweils dem gleichen Serotyp (RoM bzw. CB) an. Aus vergleichenden Untersuchungen mit 39 verschiedenen Antiseren gegen die Vertreter der Cucumovirus-Gruppe (PSV , cucumber mosaic virus, tomato aspermy virus) ergaben sich Hinweise auf Unterschiede im Grad der serologischen Verwandtschaft zwischen den sechs Serotypen des PSV
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