Meeting Abstract
Sensory feedback is an integral part of the complex closed-loop system of locomotion. Lampreys are model organisms for vertebrate locomotion. Like in all vertebrates, lamprey swimming is driven by a central pattern generator (CPG), a neural circuit located in the spinal cord that produces a pattern of neural activity that activates muscles for swimming. The CPG also responds to proprioceptive inputs that indicate how the body is moving and adjusts its output accordingly. In the lamprey, these proprioceptors are mechanosensory cells called “edge cells”, which are located in the margins of the spinal cord. Our goal is to model the sensory inputs from edge cells to the lamprey CPG in order to complete a closed-loop model of lamprey swimming. To identify the response properties of edge cells, we isolated spinal cords of silver lampreys (Ichthyomyzon unicuspis) and recorded extracellularly from the lateral tracts. We identified cells that responded to mechanical stimuli and used standard spike sorting algorithms to identify separate units. We used ramp bending stimuli that let us examine how edge cells respond differently to bending velocity as compared to static bending angle. Although some edge cells respond to the bending angle, as was previously known, the strongest and most common responses were to bending rate. We also used Gaussian band-limited noise stimuli and system identification techniques to identify the transfer function between bending and edge cell activity. An under-damped harmonic oscillator with phase dependent forcing that depends on the sinusoidal bending captures key features of the experimental data, and thus can be used to represent the signal from the edge cell to the CPG.
