Primary Supervisor: Dr Tom Matheson, Department of Neuroscience, Psychology and Behaviour
Secondary Supervisor: Dr Swidbert R. Ott
PhD project title: Neuronal and biomechanical mechanisms underlying the control and plasticity of aimed limb movements
University of Registration: University of Leicester
Most animal movements are driven by muscle contractions controlled by the nervous system, but there is now considerable evidence that passive forces, originating in muscles, tendons or other tissues, interact with active forces to generate limb movements in both vertebrates and invertebrates (Page et al. 2008). We developed a neuromechanical model (simulation) of the locust hind leg that predicted an important role for passive forces in generating aimed limb movements, and have now shown experimentally that meaningful movements can indeed be generated by passive forces. Very surprisingly, some of these forces arise within joints themselves and not in the muscles or tendons (Ache & Matheson, 2013). These passive joint forces move the leg in the absence of motor control (and even in the absence of muscles). Across species, where antagonist muscles have different strengths, passive joint forces support the weaker muscle. We therefore suggest that passive joint forces are shaped by evolutionary adaptation and form an important component of effective motor control.
In related work we have shown that locusts 'recalibrate' their aimed limb movements following experimental disruption of joint proprioceptors. This plasticity allows animals to regain accurate movements in the face of sensory loss. Young adult locusts can similarly adjust their movements following the loss of part of a limb. Older adults do not readjust their movements after such injury, indicating that the ability to express plastic changes in motor control varies with age. This is extremely interesting in light of our demonstration that during swarm formation (when locusts undergo remarkable plastic changes in morphology and behaviour collectively known as ‘phase change’) there are marked alterations of walking gait and posture (Blackburn et al. 2010).
This PhD project will merge these strands of research to seek the mechanisms governing plasticity of motor control. The student will measure active and passive limb forces in a range of species to test further our hypothesis that passive joint forces are matched to active forces acting at the same joint. The project will investigate changes in passive forces in animals that learn new movement strategies to deal with limb damage. Is neuronal plasticity matched by plasticity in biomechanical properties? Do passive biomechanical properties change during development? Do our new results generalise across different limb joints? How does inhibitory motor control (Calas-List et al. 2014) bias passive muscle properties? Does the induction of phase change induce motor plasticity in older adult locusts? Limb morphology and function will be investigated using micro CT-scanning coupled with finite element analysis if time permits.
In this multidisciplinary project the student will be trained in both in vivo electrophysiological techniques and in behavioural/kinematic methods. There may be opportunities to develop mathematical modelling skills supported through a longstanding collaboration with Prof Volker Dürr in the Department of Biological Cybernetics at the University of Bielefeld, and a new collaboration with Jingzhe Pan in the College of Science and Engineering. The project will thus use analysis techniques drawn from distinct behavioural, engineering and neurobiological disciplines to address fundamental questions in limb motor control, viewed from a comparative (evolutionary) functional perspective.
- Ache JM and Matheson T (2013) Passive joint forces are tuned to limb use in insects and drive movements without motor activity. Current Biology 23: 1418-1426. doi: 10.1016/j.cub.2013.06.024
- Blackburn LM, Ott SR, Matheson T, Burrows M and Rogers SM (2010) Motor neurone responses during a postural reflex in solitarious and gregarious desert locusts. Journal of Insect Physiology 56: 902-910. DOI:10.1016/j.jinsphys.2010.04.011
- Calas-List D, Clare AJ, Komissarova A, Nielsen TA and Matheson T (2014) Motor inhibition affects the speed but not accuracy of aimed limb movements in an insect. Journal of Neuroscience 34: 7509 - 7521. doi: 10.1523/JNEUROSCI.2200-13.2014.
BBSRC Strategic Research Priority: Understanding the Rules of Life: Neuroscience and Behaviour
Techniques that will be undertaken during the project:
- In vivo electrophysiology
- Muscle force measurements
- Limb kinematics
- Animal behaviour
Possible further techniques:
- Micro-CT (X-ray micro-computed tomography)
- Finite Element Analysis
- Biomechanical modelling
Contact: Dr Tom Matheson, University of Leicester