A new study shows how motion-induced postural reflexes in stick insects are modified under different loading conditions. A team of scientists from the University of Cologne (Germany) and Ohio University (USA) tracked the load and movement signals from the sensory organs in the insect’s leg through the neuronal network to the motor neurons and muscles that generate the reflex. This allowed them to reveal a mechanism that changes the movement reflexes in the legs of stick insects, depending on the load. The study was published in the journal Current Biology.
When asked to close their eyes and point to the foot, most people would have no problem with that, wherever the foot was. While this may seem simple, it is an extremely difficult task for the nervous system, requiring it to constantly monitor, solely through internal sensory pathways, the posture and position of the body and all its limbs.
This sense of our physical self is called proprioception. Proprioception is so fundamentally a part of our existence that we are rarely aware of it. An example of proprioception that most people are familiar with is the knee-jerk reflex: the tapping under the kneecap by a doctor and the resulting extension of the leg. In normal behavior (eg walking), this reflex helps stabilize the knee angle and is one of many proprioceptive mechanisms by which animals and humans can stand, run, swim or dance ballet.
The response to proprioceptive input must be modified in a context-dependent manner. For example, the reflex reflex helps stabilize the body after jumping, but is suppressed during running. Context-dependent regulation requires nervous systems to integrate input from movement, load, and position senses. How this integration occurs at the neural level has long been an open question.
dr. Corinna Gebehart and Professor Dr. Ansgar Büschges of the Institute of Zoology of the University of Cologne (Germany), and Professor Dr. Scott L. Hooper of the Department of Biological Sciences at Ohio University, Athens (USA), recently published in Current Biology a mechanism by which loading changes the movement reflexes in the legs of stick insects. As in mammals, the “knee joint” of insect legs, the femur-tibia joint, has a stabilizing reflex. When this joint is bent by an external disturbance, the nervous system responds by stretching it reflexively. This effect is mediated by a neural network in the insect’s ventral nerve cord, the insect equivalent of the mammalian spinal cord.
The scientists tracked proprioceptive signals of load and movement from their senses in the walking insect through the neural network that combines them in the ventral nerve cord with the motor neurons and muscles that produce the reflex. “We were able to show that leg loading reduced movement reflex strength through a neuronal mechanism called presynaptic afferent inhibition,” says Dr. Corinna Gebehart, lead author of the new study. “This mechanism altered information processing in the neural network of the nerve cord and thereby reduced the response of the motor neurons and muscles to motion input.”
The behavioral importance of this interaction of load and movement can be appreciated by considering that a light load is applied to the animal – a leaf landing on it – in which case a resistance reflex must occur to keep the leg position constant and the animal upright. to leave. However, if the load applied is greater than what the leg muscles can withstand – a branch pressing on the animal – the resistance reflex must be reduced, the joint must flex and the animal’s body must yield to the greater load, to avoid damage. avoid to the leg.
Proprioception, its integration by the nervous system, and the resulting motor reflexes are surprisingly similar in mammals and insects. The stick insect findings thus shed light on potentially general mechanisms by which nervous systems combine different types of proprioceptive signals to form a coherent internal image of their bodies, and how these processing pathways can be modified depending on the animal’s behavioral context.
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Corinna Gebehart et al, Nonlinear multimodal integration in a distributed premotor network regulates proprioceptive reflex amplification in the insect paw, Current Biology (2022). DOI: 10.116/j.cub.2022.07.005
Provided by the University of Cologne
Quote: New insights into the regulation of intuitive and reflexive body perception in insects (2022, July 27) retrieved July 27, 2022 from https://phys.org/news/2022-07-insights-intuitive-reflexive-body-perception.html
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