@phdthesis{20735,
  abstract     = {Left–right alternation is a defining feature of spinal locomotor circuits, yet the level of neuronal
detail required to generate and maintain this pattern remains unclear. This thesis investigates how
models spanning multiple levels of abstraction—from biophysically detailed Hodgkin–Huxley (HH)
neurons to adaptive integrate–and–fire (I&F) formulations and synfire-chain modules—can account
for the generation of fictive swimming in the spinal cord of the Xenopus laevis tadpole. The guiding
hypothesis is that a small set of neuronal mechanisms is sufficient to reproduce the essential features
of rhythmic alternation, and that moving between modeling scales helps distinguish core principles
from biological detail.
A minimal bilateral HH network comprising only four canonical neuron classes—excitatory
descending interneurons (dINs), inhibitory commissural interneurons (cINs), ipsilateral inhibitory
interneurons (aINs) and motoneurons—served as a biophysical proof of concept. Tuned to reproduce
experimentally observed firing modes, the model demonstrated that rebound-prone dIN excitability,
contralateral inhibition and modest electrical coupling are sufficient to generate stable alternating
activity, even in very small networks. These results motivated the transition to simpler models
capable of efficient analysis and scaling.
Adaptive exponential I&F (AdEx) neurons were calibrated to physiological recordings using
simulation-based inference, yielding tonic and phasic/rebound templates that preserved the key
dynamical signatures of the HH model. Phase-plane analysis clarified the mechanisms underlying
single-spike responses and rebound firing in dINs. At network level, the I&F models robustly
reproduced left–right alternation, while highlighting constraints on synaptic kinetics and adaptation
needed to avoid multi-spike responses.
Finally, a synfire-chain framework provided a complementary, timing-centric perspective, demonstrating how precise spike synchrony, synaptic delays and minimal inhibitory coupling can generate
alternating left–right sequences in a feedforward setting. Together, these approaches converge on a
common conclusion: rebound-prone ipsilateral excitation combined with precisely timed contralateral inhibition constitutes a sufficient substrate for alternating spinal rhythms.
By integrating bottom-up and top-down modeling strategies, this thesis provides a unified, extensible framework for studying spinal pattern generation. The results show that essential locomotor
dynamics can be captured across multiple abstraction levels, offering both mechanistic insight and
practical tools for future data-driven investigations of spinal circuit development, robustness and
modulation.},
  author       = {Wilson, Alexia C},
  issn         = {2791-4585},
  pages        = {110},
  publisher    = {Institute of Science and Technology Austria},
  title        = {{Modelling the spinal cord of a tadpole : Exploring different ways to model the spinal cord in the Xenopus frog}},
  doi          = {10.15479/AT-ISTA-20735},
  year         = {2025},
}

@article{13097,
  abstract     = {Vertebrate movement is orchestrated by spinal inter- and motor neurons that, together with sensory and cognitive input, produce dynamic motor behaviors. These behaviors vary from the simple undulatory swimming of fish and larval aquatic species to the highly coordinated running, reaching and grasping of mice, humans and other mammals. This variation raises the fundamental question of how spinal circuits have changed in register with motor behavior. In simple, undulatory fish, exemplified by the lamprey, two broad classes of interneurons shape motor neuron output: ipsilateral-projecting excitatory neurons, and commissural-projecting inhibitory neurons. An additional class of ipsilateral inhibitory neurons is required to generate escape swim behavior in larval zebrafish and tadpoles. In limbed vertebrates, a more complex spinal neuron composition is observed. In this review, we provide evidence that movement elaboration correlates with an increase and specialization of these three basic interneuron types into molecularly, anatomically, and functionally distinct subpopulations. We summarize recent work linking neuron types to movement-pattern generation across fish, amphibians, reptiles, birds and mammals.},
  author       = {Wilson, Alexia C and Sweeney, Lora Beatrice Jaeger},
  issn         = {1662-5110},
  journal      = {Frontiers in Neural Circuits},
  publisher    = {Frontiers},
  title        = {{Spinal cords: Symphonies of interneurons across species}},
  doi          = {10.3389/fncir.2023.1146449},
  volume       = {17},
  year         = {2023},
}