歩行中の感覚運動統合における内側無顆粒皮質の役割：げっ歯類脳卒中モデルからの洞察

In the rodent motor cortex, limb movements are primarily governed by the lateral agranular cortex (AGl), whereas the medial agranular cortex (AGm) has been proposed to contribute to higher-order aspects of motor control. However, its independent contribution to sensory-motor integration has not been established. Previous studies have shown that infarcts encompassing both the AGl and AGm cause contralateral motor impairments, suggesting, but not proving, that the AGm might participate in movement control. In this study, we specifically tested whether focal lesions restricted to the AGm impair skilled locomotion. Using the ladder rung walking task, which requires precise paw placement based primarily on somatosensory cues with additional visual contributions, we examined mice with focal photothrombotic infarcts centered within the AGm at +2.0, +1.5, +1.0, or +0.5 mm anterior to bregma. To enable objective assessment, we developed an automated analysis pipeline using DeepLabCut^TM (v2.2.0.4), a markerless pose-detection machine learning Python package, that computed forelimb and hindlimb foot-fault rates from multi-view videos. Foot-fault rates for both limbs did not increase under either regular or irregular rung patterns across pre- and postoperative sessions. By isolating the functional contribution of the AGm from that of the AGl, our results refine previous interpretations and demonstrate that AGm lesions alone do not impair visually and somatosensorily guided limb movements. Within the sensitivity of this assay, these findings indicate that the AGm is not required for executing such movements on this task. Together with prior evidence, these findings support the view that the AGm contributes primarily to the higher-order modulation of motor behavior, likely through spatial attention, rather than to direct motor execution.