A fundamental task of the brain is to choose the right action at the right time and properly execute the chosen action. The posterior parietal cortex (PPC) is critically involved in both selection and execution of actions, but it remains unknown whether these two functions are served by the same input and output pathways of PPC. We addressed this issue in mice, focusing on PPC neurons projecting to the dorsal striatum (PPC→STR) and the posterior secondary motor cortex (PPC→pM2). Retrograde labeling showed that PPC→STR and PPC→pM2 represent largely distinct subpopulations. Two-photon calcium imaging during a decision-making task revealed that the PPC→STR population encodes history-dependent choice bias more strongly than PPC→pM2 or general PPC populations. Furthermore, optogenetic inactivation of PPC→STR, somas in PPC or their terminals in STR, decreased history-dependent bias. In contrast, inactivation of PPC→pM2 disrupted movement kinematics. This double dissociation indicates that PPC→STR biases action selection while PPC→pM2 contributes to motor control. Lastly, projection-specific, retrograde monosynaptic tracing revealed that the two output pathways receive differential long-range inputs with PPC→STR receiving stronger inputs from association areas and PPC→pM2 receiving stronger sensorimotor inputs. Together, these results indicate that PPC supports action selection and execution via separate input and output pathways, suggesting pathway-specific functional division in PPC. 


Dr. EunJung Hwang is an associate project scientist in Dr. Takaki Komiyama’s Lab at the University of California, San Diego. Her long-term research interest is the neural mechanisms underlying action selection and execution. Dr. Hwang received her Ph.D. in biomedical engineering from Johns Hopkins University. Her thesis research in Dr. Reza Shadmehr’s lab investigated the coding mechanisms of kinematic variables for motor control in humans. Subsequently, she was a postdoctoral fellow in Dr. Richard Andersen’s Lab at Caltech, studying the macaque posterior parietal cortex in motor control and brain machine interfaces. Her current project in the Komiyama lab investigates action selection and execution circuits in mouse motor and parietal cortices.

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