Biology subjects

Grier, H.

Publications and source records attributed to Grier, H..

3 recordsLinked to original sources

bioRxiv2025

Routing of task-relevant information in mouse PPC during continuousvisuomotor control

Posterior Parietal Cortex (PPC) exhibits tuning to many variables, including strong representations of visual information, movement, and behavioral biases. Whether PPC communicates all these variables to other areas is less clear. We examined PPC activity in mice performing a novel, closed-loop, 2D visuomotor joystick task that required animals to act exclusively on a task-relevant axis of visual motion. To determine what components of PPCs representation were sent to M1, we performed two-photon calcium imaging of layer 2/3 neurons in contralateral PPC of expert mice with PPC-M1 projection neurons identified via retrograde tracing. Consistent with previous results, PPC neurons exhibited random mixed selectivity and were typically most strongly modulated by joystick movement. Most of the visually responsive neurons were more strongly modulated by task-relevant than task-irrelevant visual motion. Encoding in labeled PPC-M1 neurons was similar to encoding in unlabeled neurons, with one major exception: unlike the task-relevant visual enrichment in unlabeled PPC neurons, task-relevant and task-irrelevant visual motion were encoded at similarly weak levels in PPC-M1 neurons. This argues that although PPC encodes a mix of visual, movement and other information, the PPC-M1 pathway is dominated by movement information and does not propagate PPCs learned enrichment of task-relevant visual signals.

neuroscience↗

bioRxiv2025

Neural activity profiles reveal overlapping, intermingled subpopulations spanning area borders in mouse sensorimotor cortex

Cortical control of movement is a distributed computation spanning multiple densely-interconnected regions. Although we have rich anatomical atlases and a coarse understanding of how function maps to areas and subregions, we lack a detailed account of how behaviorally-relevant activity is organized across the cortical sheet. Here, we trained head-fixed mice to perform a 15-target reach-to-grasp task while we performed cellular-resolution, two-photon calcium imaging across five regions of sensorimotor cortex (>39,000 layer 2/3 neurons). We characterized each neurons trial-averaged peri-event activity with interpretable metrics and mapped these response properties across areas, revealing large-scale spatial structure. Neuronal response profiles often shifted abruptly at anatomical borders: motor areas showed sharper tuning and more linear relationships with target location, whereas somatosensory areas displayed more heterogeneous response patterns. Neural response properties also differed according to somatotopic representation. Nonlinear dimensionality reduction of the neural feature matrix revealed that areas varied in their average response profiles, but that areas did not have well-separated feature distributions; instead, each area contained subpopulations. Neurons in each subpopulation had characteristic response profiles and were distributed across multiple cortical areas. The spatial distributions of the subpopulations overlapped, with neurons from different subpopulations salt-and-pepper intermingled in the overlap zones. Together, these results describe novel activity structure across sensorimotor cortex and identify several distinct but spatially-overlapping subpopulations with characteristic activity patterns during reach-to-grasp behavior.

neuroscience↗

bioRxiv2025

Mouse sensorimotor cortex reflects complex kinematic details during reaching and grasping

Coordinated forelimb actions, such as reaching and grasping, rely on motor commands that span a spectrum from abstract target specification to detailed instantaneous muscle control. The sensorimotor cortex is central to controlling these complex movements, yet how the detailed command signals are distributed across its numerous subregions remains unclear. In particular, in mice it is unknown if the primary motor (M1) and somatosensory (S1) cortices represent low-level joint angle details in addition to high-level signals like movement direction. Here, we combine high quality markerless tracking and two-photon imaging during a reach-to-grasp task to quantify movement-related activity in the mouse forelimb M1 (M1-fl) and forelimb S1 (S1-fl). Linear decoding models reveal a strong representation of proximal and distal joint angles in both areas, and both areas support joint angle decoding with comparable fidelity. Despite shared low-level encoding, the time course of high-level target-specific information varied across areas. M1-fl exhibited early onset and sustained encoding of target-specific signals while S1-fl was more transiently modulated around lift onset. These results reveal both shared and unique contributions of M1-fl and S1-fl to reaching and grasping, implicating a more distributed cortical circuit for mouse forelimb control than has been previously considered.

neuroscience↗