Dr. Leah R. Bent

My path into academia began in the third year of my Human Kinetics undergraduate degree at the University of Guelph. It was here, during an upper-level neurophysiology course that I became interested in the area of posture and balance control. I was introduced to the concept of spinal reflex loops, central pattern generators and the importance of sensory input in the modulation of how we move. I was intrigued by the extent of our knowledge of how we balance and accommodate as bipedal beings, and how sensory decline can greatly affect successful task achievement. This led me to complete my Masters at the University of Guelph with Drs. Jim Potvin and Bill McIlory, examining the potential for a subcortical substrate for postural control by investigating balance adjustments during reflexive stepping in humans.

My continued interest in postural control got me thinking about the sensory contributors involved in these balance adjustments. As a result, during my Ph.D. with Drs. Tim Inglis and Brad McFadyen I examined vestibular contributions to locomotor tasks, including the integration of vestibular information with other sensory input. Although I felt I was slowly unravelling the puzzle, determining underlying neurophysiological connections using whole body analysis of behaving humans was challenging. My goal during my post-doctoral fellowship was to learn a technique called microneurography. I acquired these skills under the supervision of Dr. Vaughan Macefield in Sydney Australia. Microneurography is a relatively new, and powerful tool used to record from single nerve fibres involved in the transfer of sensory information from the periphery to the spinal cord.

I have set up a microneurography laboratory here at Guelph where I will continue to investigate neural connections between peripheral sensory receptors (skin, muscle, joint) and 1) pathways to the brain, and 2) synapses that generate reflexes responses in muscle. The long-term objective of the work is to identify key sensory interactions in the spinal cord that facilitate balance and locomotion. Ultimately, by testing sensory contributions and interactions, my research program will take steps toward understanding where and how posture is controlled.

B.Sc. - Human Kinetics, University of Guelph
M.Sc. - University of Guelph
Ph.D. - University of British Columbia
Post-Doctorate Prince of Wales Medical Research Institute, Australia

Sensory contributions are intimately related to successful movement. With age and pathology, there is an increase in the difficulties associated with mobility. These changes alter the freedom and independence of the aging population and can largely be attributed to a decline in sensory function. The primary goals of my research program are 1) to understand where posture is controlled 2) to understand what sensory information contributes to successful movement and equilibrium.

By investigating these two key questions I believe we will have a better understanding of how sensory decline contributes to a loss of mobility as we age. Declines in sensory information are often replaced by other sensory modalities through compensation. Does this take place at the level of the spinal cord, or further upstream with changes in cortical plasticity? Are we able to develop facilitatory devices such as shoe insoles to improve cutaneous sensation or visual aids to enhance visual cues?

My research program involves two key areas of study.

• To perform direct recordings from sensory afferents and motor efferents in awake human subjects to investigate sensory contributions to movement, balance control, and reflex responses.
• To elicit balance perturbations to test the function of these reflex loops, and sensory contributions to the maintenance of equilibrium and postural control.

I use several techniques to investigate sensory contributions to standing balance. To perturb the vestibular system I use the technique of Galvanic Vestibular Stimulation (GVS), which alters the firing of peripheral vestibular afferents and changes the perception of vertical. One goal is to establish the role of vestibular input in “setting” the excitatory nature of the spinal cord. In an altered vestibular state do we see changes in other sensory reflexes? For example, does our ability to reflexively respond to a stumble change?

Microneurography is another technique used in my laboratory. This tool enables direct recordings from afferent and efferent nerve fibres in awake humans. The advantage of microneurography is that it enables a level of investigation currently unafforded by other approaches. Our access to single cutaneous afferents, for example, allows us to monitor their involvement in postural responses, functional strategies and their interaction with other sensory input, including vestibular. Many sensory receptors, such as those from the skin and muscle have been shown to degenerate with age and in certain pathological conditions. My work to date has focused on determining how nerves connect in healthy individuals so that we can then apply this knowledge to developing rehabilitation programs for target populations. Isolation of individual cutaneous receptors involved in functional postural responses will serve the purpose of developing more sophisticated and applicable prosthetic devices to facilitate skin input in deficient aged and diabetic populations.

Finally, I am able to examine contributions from cortical areas in the control of movement. To do this I use a technique called transcranial magnetic stimulation (TMS). TMS allows us to probe central contributions to postural reflex loops by enabling us to excite or inhibit descending input from the brain.

Lowrey CR, Perry SD, Strzalkowski ND, Williams DR, Wood SJ, Bent LR. Selective Skin Sensitivity Changes and Sensory Reweighting following Short-Duration Space Flight. J. Appl. Physiol. (1985). 2014; 116(6):683-92.

Bent LR, Sander M, Bolton PS, Macefield VG. The Vestibular System does Not Modulate Fusimotor Drive to Muscle Spindles in Contracting Leg Muscles of Seated Subjects. Exp. Brain Res. 2013; 227(2):175-83.

Bent LR, Lowrey CR. Single Low-Threshold Afferents Innervating the Skin of the Human Foot modulate Ongoing Muscle Activity in the Upper Limbs. J. Neurophysiol. 2013; 109(6):1614-25.

Lowrey CR, Strzalkowski ND, Bent LR. Cooling Reduces the Cutaneous Afferent Firing Response to Vibratory Stimuli in Glabrous Skin of the Human Foot Sole. J. Neurophysiol. 2013; 109(3):839-50.

Thomas KE, Bent LR. Subthreshold Vestibular Reflex Effects in Seated Humans can contribute to Soleus Activation when Combined with Cutaneous Inputs. Motor Control. 2013; 17(1):62-74.

Muise SB, Lam CK, Bent LR. Reduced Input from Foot Sole Skin through Cooling Differentially Modulates the Short Latency and Medium Latency Vestibular Reflex Responses to Galvanic Vestibular Stimulation. Ex. Brain Res. 2012; 218(1):63-71.

Lowrey CR, Strzalkowski ND, Bent LR. Skin Sensory Information from the Dorsum of the Foot and Ankle is necessary for Kinesthesia at the Ankle Joint. Neurosci. Lett. 2010; 485(1):6-10.

Srbely JZ, Dickey JP, Bent LR, Lee D, Lowerison M. Capsaicin-Induced Central Sensitization Evokes Segmental Increases in Trigger Point Sensitivity in Humans. J. Pain. 2010; 11(7):636-43.

• HK*3600 Applied Human Biology
• HK*3100 Human Neuromuscular Physiology
• HHNS*6200 Research Methods in Biomechanics

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