Brain-Wide Activations Related to Forepaw Force Control Identified by Behaving Mouse FMRI.

Abstract

Control of upper limb force is crucial for motor skill acquisition. Rodent models have been instrumental in elucidating the behavioral and neural mechanisms underlying skilled movements. Integrating these models with advanced neuroimaging approaches, such as awake functional magnetic resonance imaging (fMRI) in behaving mice, enables whole-brain mapping of motor activity. However, experimental paradigms supporting awake fMRI during upper limb motor behavior in mice remain limited. Here, we developed an MRI-compatible head-fixation system that enables male and female mice to perform a unilateral forepaw force control task for water reward during ultrahigh-field (11.1 T) fMRI. Mice successfully acquired the task, as evidenced by increased rewarded presses, convergence of force output toward the rewarded threshold, and reduced force variability. Significant activation clusters related to forepaw force were identified across multiple cortical regions, including the primary and secondary motor cortex, anterior cingulate cortex, and primary somatosensory cortex. Activation extended to subcortical structures, including the cerebellum, striatum, hypothalamus, and thalamus (ventrolateral and ventroposterior nuclei). Analysis of limb kinematics from synchronized video recordings revealed strong spatial correspondence between forepaw-related and force-dependent activation maps. Region-of-interest analyses further identified engagement of medullary structures, specifically the lateral rostral medulla and caudal medulla (CauM), in forepaw force control. Notably, the cerebellum and CauM exhibited later peak responses relative to cortical regions. Together, these results establish a robust framework for awake fMRI during forelimb motor tasks and provide a comprehensive map of cortical, subcortical, and brainstem circuits underlying forelimb force control in mice.