Research Abstract
The spinal cord appears, at least in part, to structure movement through combining a limited number of
stereotyped ‘motor modules’. Module structure and combination is often dysfunctional in motor system
diseases, such as spinal cord injury (SCI). The long-term goal of this research is to identify mechanisms of
motor module structure and recruitment, to enable artificial activation or restoration to ameliorate maladaptive
motor control. The objective of this proposal is to determine how spinal motor modules are activated in the
spinal cord and how these modules then recruit motoneurons from the motor pools in the simpler spinal
bullfrog model. The central hypothesis is that motor modules are partially independent, generate both rhythm
and pattern, and recruit particular motoneurons across coactivated motor pools in turn. The rationale
underlying this proposal is that frogs have unique physiology allowing chronic survival despite destruction of
supraspinal centers, permitting the intrinsic capacities of the spinal cord to be studied within the intact
musculature over an extended period of time. This proposal builds off historical research which activated motor
modules through electrical stimulation or excitatory neurotransmitters. I will test the central hypothesis through
two specific aims: 1) Evaluating independence of module activation during manipulation of spinal state,
and 2) Discerning the granularity of recruitment of motor pools contributing to motor modules. I utilize
two innovative methods to refine these investigations: 1) a new type of electrode which can record from many
single motor units simultaneously and 2) a new mathematical tool to identify state-dependent effects between a
spiking neuron with continuous signals, such as muscle activity. The proposed research is significant as it will
bridge modularity research in the spinal wiping reflexes with hierarchical models of spinal motor pattern
generation (e.g. locomotion). A more refined understanding of motor module organization may clarify muscle
and motor pool recruitment in higher species, including humans, where direct analysis is often obscured or
impossible due to increased complexity. The expected outcome of this work is an understanding of how
modules are activated by the spinal cord and their capacity to be flexibly combined. This work will have a
further positive impact by validating new tools and techniques for experimental use, and lay the groundwork for
proactively activating motor modules in a task-dependent fashion in neuroprostheses. Towards this end, I have
finished my neuroscience coursework and proposed cross-disciplinary training in biomedical engineering
through Drexel University’s neuroengineering initiative to increase his quantitative skills to better pursue these
questions. This training plan will combine the historically-strong program of spinal cord biology and motor
control within the Department of Neurobiology and Anatomy with the quantitative rigor of formal mathematics
and engineering, further equipping me to accomplish these aims and pursue a successful career as an
independent research scientist.
