The nematode Caenorhabditis elegans offers a uniquely tractable model for studying the
relationships between neuronal activity, connectivity, and behavior. Despite its simplicity, key
questions remain about how information flows through its nervous system and how neural
activity is transformed to generate behavior. Sensory neurons relay information through firstand
second-layer interneurons to command interneurons and motor neurons, forming a
largely feedforward network. Along this pathway, neuronal activity transitions from closely
mirroring environmental stimuli at the sensory level to correlating strongly with behavior at
the motor level. Interneurons, particularly those in the second layer such as RIA, RIB, and RIM,
exhibit more complex dynamics, integrating both external sensory inputs and internal signals.
The functional role of these interneurons in encoding and transmitting behaviorally relevant
information remains incompletely understood. To address this, we employed simultaneous
neuronal and behavioral recordings, combined with advanced deep learning tools, to gain
deeper insights into how second-layer interneurons encode concurrent and future behaviors
during chemotaxis
A key technological contribution of this work is the development of Targettrack, a novel analysis
pipeline for segmenting and tracking neuronal activity in freely moving animals. Traditional
convolutional neural networks (CNNs) for neuron tracking require extensive manual annotations
of diverse brain postures, which becomes infeasible for highly deformable brains,
such as in C. elegans. Targettrack introduces "targeted augmentation," a method that learns
internal brain deformations fromlimited ground-truth annotations and uses this information
to generate synthetic annotations for diverse postures. This drastically reduces the need
for manual annotation and proofreading while maintaining high accuracy. Implemented
as an end-to-end pipeline with a graphical interface, Targettrack enables the segmentation
and tracking of neurons as 3D volumes or points acrossmultiple animals and experimental
conditions.
Using Targettrack, we investigated interneuronal dynamics in freelymoving C. elegans exposed
to periodic chemosensory stimuli. We observed increasing coordination among interneurons,
with stronger correlations at larger temporal scales, suggesting synchronization mechanisms
that may facilitate encoding of sustained behavioral states. RIA and RIB interneurons exhibited
particularly strong correlations, with RIA axonal segments reflecting RIB activity, suggesting
the potential for functional relationship between these two interneurons. Furthermore, regres
sion analyses revealed that RIM and RIB activities collectively predict the worm's current and
future locomotion speed, with RIB alone emerging as a stronger predictor across individuals.
These findings suggest complementary roles for RIA, RIB, and RIMin encoding sensory and
behavioral dynamics.