Venue: CARF
Language of the defense: english
IINS
Thesis dierctor: Frédéric Gambino
Title
Cortico-cortical circuits of perceptual decision-making
Abstract
Animals continuously use sensory information to guide actions toward their goals. A fundamental problem in this process is determining whether an intended action is physically attainable given both the geometry of the environment and the animal’s own biomechanical capabilities. In rodents, the whisker-related primary somatosensory cortex (wS1, barrel cortex) and secondary motor cortex (wM2) are key components of the sensorimotor network supporting whisker-guided active sensing. However, much of our understanding of these regions comes from highly controlled tasks in head-restrained animals, leaving their roles during continuous, self-generated perceptual decisions poorly understood. In this thesis, we combined freely moving gap-crossing behavior, quantitative whole-body tracking, cortical lesions, and longitudinal electrophysiological recordings from wS1 and wM2 to investigate the behavioral and neural mechanisms underlying attainability judgments.
We first developed a gap-crossing paradigm in which freely moving mice actively explored a target platform before deciding whether to cross. Quantitative analysis of continuous behavior allowed us to decompose this process into distinct behavioral subprocesses and identify candidate perceptual and decisional windows as well as different perception-action categories. We next investigated the causal contribution of the barrel cortex by lesioning it either before or after animals learned the task. Mice were able to acquire the task without wS1 and recovered within a few days when the lesion was performed after learning, demonstrating that barrel cortex is not strictly required for gap-crossing behavior. However, its contribution depended on previous experience. Animals lesioned before learning favored perception-action strategies characterized by a greater reliance on integrated sensorimotor processes and fewer overt perceptual epochs. Conversely, animals lesioned after learning exhibited an increased prevalence of overt perceptual epochs before committing to crossing. Thus, wS1 contributes to the organization of perception-action coupling rather than simply determining whether the task can be performed, with its role shaped by previous experience. Finally, we recorded electrophysiological activity in wS1 and wM2 to examine the cortical dynamics accompanying these behavioral processes. Both regions showed task-related activity during sensory exploration and movement preparation, but with distinct temporal profiles. Neither region exhibited a categorical activity pattern that distinguished trials in which the target platform was reachable, detectable but unreachable, or absent. Instead, lesion experiments revealed interactions between the two cortical areas. Removal of wS1 altered the temporal organization of layer 5 wM2 activity associated with movement preparation, whereas removal of wM2 increased and temporally broadened layer 5 wS1 activity beyond periods of likely tactile contact. Disrupting either region therefore reorganized task-related activity in the remaining cortex rather than abolishing it.
Together, these findings show that gap-crossing decisions emerge from continuous, embodied sensorimotor computations in which mice relate sensory estimates of environmental geometry to their own biomechanical capabilities. They identify wS1 not as an obligatory substrate for this behavior, but as a contributor to the temporal organization of perception and action, and reveal wS1 and wM2 as components of an interacting cortical network capable of functional reorganization following perturbation. More broadly, this work demonstrates how studying self-generated and uninstructed behavior can reveal neural and behavioral mechanisms of perceptual decision-making that are difficult to capture in highly constrained experimental paradigms.
Keywords: perceptual decision-making, freely moving, gap-crossing, attainability judgment, wS1-wM2 circuit, in vivo electrophysiological recordings, excitotoxic lesion.
Jury
Sami El-Boustani: spokesperson
Isabelle Férézou: spokesperson
Marion Rivalan: examinator
Mathieu Wolff: examinator