Physiology “brown-bag” lunchtime seminars are normally held on selected WEDNESDAYS at noon in Applied Physiology Building, room 1253 (or as indicated). Special seminar dates/times outside of the regular schedule are indicated as such.
Contact Dr. Boris Prilutsky, boris.prilutsky@biosci.gatech.edu, to be considered as a future speaker, added to the e-mail distribution list, if you would like to meet with a speaker, or for other seminar-related inquiries.
For directions: Applied Physiology
SEMINAR: Wednesday, March 15, 2023
Role of proprioceptive feedback in control of cat and mouse locomotion
Seyed Mohammad Ali Rahmati, PhD
School of Biological Sciences
Georgia Institute of Technology
Abstract
Quantitative analysis of proprioceptive feedback during functional movements is required to understand fully motor control and to design effective rehabilitation methods and neuroprosthetic devices to help patients with severe motor disorders. Recording proprioceptive neural activity of quadruped animals during their daily movements faces prohibitive challenges. Alternatively, the role of motion-dependent proprioceptive feedback (activity of group Ia, Ib and II afferents) in feline locomotion can be estimated using neuromechanical modeling and motion analysis, whereas genetically modified mouse models allow for selective removal of proprioceptive feedback. In this presentation, I will show results of two ongoing collaborative studies looking at the role of forelimb muscle morphology in muscle sensorimotor function during cat locomotion and at the effects of removal of proprioception on lateral locomotor stability in mice.
To compute proprioceptive feedback from cat forelimb muscles during walking and investigate the effects of forelimb morphology on proprioceptive feedback, I used morphological characteristics of 40 forelimb muscles from 4 adult cats measured in the groups of Drs. Thomas Burkholder and T. Richard Nichols. These characteristics included 3D coordinates of muscle attachments, muscle physiological cross-sectional area (PCSA), muscle fiber and sarcomere length, etc. Using recorded cat full-body locomotor mechanics, EMG activity of forelimb muscles, and the regression equations for computing activity of group Ia, Ib and II afferents, developed by Prochazka and Gorassini (1998), I calculated motion-dependent sensory signals during cat walking and mapped them onto the corresponding cervical spinal segments. The obtained results indicate that muscle morphology (e.g., muscle moment arms and PCSA) contributes strongly to the estimated motor and sensory functions of forelimb muscles. I identified forelimb muscles that likely trigger the swing-to-stance (spinodeltoideus, teres major) and stance-to-swing (supraspinatus, biceps brachii, extensor carpi radialis) transitions based on their length-dependent afferent activities. Similar to the hindlimb, these muscles cross mainly proximal limb joints.
In the second study, I computed measures of lateral stability of wild-type mice and genetically modified mice without proprioceptive feedback during locomotion using machine learning analysis of biplanar video recordings of locomoting mice obtained in the group of Dr. Turgay Akay. Preliminary results demonstrate a substantial increase of step width and margins of lateral stability in response to removal of proprioception.
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Bio: Dr. Seyed Mohammad Ali Rahmati received his MSc in biomedical engineering-biomechanics at Iran University of Science & Technology, investigating motor control of snatch weightlifting. He then completed his PhD in the same field at Amirkabir University of Technology, studying the neuro-musculoskeletal modeling of human locomotion and its application to the optimal design of the foot prosthesis for unilateral transtibial amputees. He then moved to Georgia Tech as a post-doctoral fellow with Dr. Boris Prilutsky, where he initiated studies on the feline forelimb neuromechanics and neuromechanical modeling of quadrupedal cat locomotion. He also has contributed to several other projects investigating the role of proprioception in lateral locomotor stability in mice and the optimal muscle activation strategies in walking cats. |
Host: Boris I. Prilutsky, PhD
Time: 12:00 – 1:00 PM
Location: 555 14th street NW, Atlanta 30318; Applied Physiology Building, room 1253; Zoom Link
SEMINAR: Wednesday, March 29, 2023
Contribution of forelimb movements to the modulation of hindlimb locomotion in intact and spinal cord-injured cats
Jonathan Harnie, PhD
Department of Pharmacology and Physiology
University of Sherbrooke, Québec
Abstract
Locomotion after complete spinal cord injury (spinal transection) in animal models is usually evaluated in a hindlimb-only condition with the forelimbs placed on a stationary platform or with the body in a vertical position in small rodents and compared with quadrupedal locomotion in the intact state. However, because of the quadrupedal nature of movement in these animals, the forelimbs can play an important role in modulating the hindlimb pattern and vice-versa. This raises the question: whether changes in the hindlimb pattern after spinal transection are due to the state of the system (intact versus spinal) or because the locomotion is hindlimb-only. To test this hypothesis, we recorded kinematic and electromyographic data before and after spinal transection during quadrupedal and hindlimb-only locomotion in the intact state and hindlimb-only locomotion in the spinal state (Harnie et al., 2022). We also recorded hindlimb cutaneous reflexes during these different locomotor conditions. We find that some changes in the hindlimb pattern (e.g., improper coordination of ankle and hip joints, a switch in the timing of knee flexor and hip flexor EMG bursts, modulation of EMG burst durations with speed, etc.) depended on to the spinal state. Alternatively, some changes relate to the hindlimb-only nature of the locomotion (e.g., paw placement relative to the hip at contact, magnitude of knee and ankle yield, burst durations of some muscles and their timing). Overall, we show greater similarity in spatiotemporal and EMG variables between the two hindlimb-only conditions, suggesting that the more appropriate pre-spinal control is hindlimb-only rather than quadrupedal locomotion.
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Bio: Dr. Jonathan Harnie received his master’s degree (2015-2017) at the Université of Nantes (France) in human motor control under the supervision of Prof. M. Jubeau and Prof. T. Cattagni. He received his PhD degree (2017-2021) and subsequent postdoctoral training under the supervision of Prof. Alain Frigon at the Université de Sherbrooke (Québec). The topic of his PhD and postdoctoral work was the control and reactivation of locomotion by somatosensory feedback after spinal cord injury in the cat. Currently, Jonathan Harnie investigates the control of spinal and intra-spinal cord stimulation by a haptic glove in collaboration with Prof. Alain Frigon and Dr Christian Iorio-Morin. |
Host: Boris I. Prilutsky, PhD
Time: 12:00 – 1:00 PM
Location: 555 14th street NW, Atlanta 30318; Applied Physiology Building, room 1253; Zoom Link