Reflex reversal and positive feedback in the generation of walking motor patterns
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1
Georgia State University, Neuroscience Institute, United States
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2
University of Bordeaux 1 and Bordeaux 2, Centre de Neurosciences Integratives et Cognitives, France
Rhythmic behaviors like walking depend on a dynamic interplay between sensory feedback and central pattern generation. In the walking legs of crayfish, rhythmic levation and depression are controlled by pools of levator and depressor motor neurons that receive sensory feedback from a stretch receptor, the coxabasal chordotonal organ (CBCO). In vitro preparations of the ventral nerve cord with the nerves of the fifth walking leg intact are generally quiescent and exhibit resistance reflexes that oppose imposed movements. Following application of oxotremorine (OXO), a muscarinic agonist, the motor neurons begin to burst rhythmically with long (15s to 60s) periods and their resistance reflexes reverse to become assistance reflexes that are synergistic with imposed forces. While the neural circuitry of the levation-depression reflexes and CPG has been described, the manner in which CBCO reafference modulates the CPG remains unknown. Here we show that reafference is able both to speed and stabilize the walking rhythm of an in vitro ventral nerve cord preparation when it is made part of a neuromechanical hybrid system. An electronic interface enables the recorded spikes of levator and depressor motor neurons to evoke muscle contractions and leg movements of a computational model of the crayfish body and leg in real time. It also enables the resulting movements of a model CBCO to evoke identical movements of the real CBCO, and so create a sensory-motor feedback loop. We found that a tonically active preparation in closed loop produced resistance reflexes in response to imposed leg lifts, but after exposure to OXO, these became assistance reflexes or sequential levator/depressor (lev/dep) bursts. Irregular, low frequency (<1/30s) lev/dep bursts in open loop became regular, higher frequency (1/10s) bursts in closed loop. While the durations of the lev/dep bursts were unchanged in closed loop, the interval between bursts decreased. This occurred because the levator assistance reflex triggered the levator burst in closed loop but not open loop. A computational neuromechanical model replicated these results, and showed that activation of the Assistance Reflex Interneurons. (ARINs) by OXO enabled the assistance reflex and created a positive feedback loop that increased the walking frequency.
Acknowledgements
NSF Research Grant IOS-1120291
Keywords:
computational model,
CpG,
crayfish,
hybrid system,
neuromechanics,
reafference,
Sensory feedback,
Walking
Conference:
Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012.
Presentation Type:
Poster (but consider for Participant Symposium)
Topic:
Motor Systems
Citation:
Edwards
DH,
Chung
B and
Cattaert
D
(2012). Reflex reversal and positive feedback in the generation of walking motor patterns.
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00254
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Received:
30 Apr 2012;
Published Online:
07 Jul 2012.
*
Correspondence:
Dr. Donald H Edwards, Georgia State University, Neuroscience Institute, Atlanta, United States, 30303, United States, dedwards@gsu.edu