Neural decoding reveals specialized kinematic tuning after an abrupt cortical transition.

The primary motor cortex (M1) exhibits a protracted period of development, including the development of a sensory representation long before motor outflow emerges. In rats, this representation is present by postnatal day (P) 8, when M1 activity is "discontinuous." Here, we ask how the representation changes upon the transition to "continuous" activity at P12. We use neural decoding to predict forelimb movements from M1 activity and show that a linear decoder effectively predicts limb movements at P8 but not at P12; instead, a nonlinear decoder better predicts limb movements at P12. The altered decoder performance reflects increased complexity and uniqueness of kinematic information in M1. We next show that M1's representation at P12 is more susceptible to "lesioning" of inputs and "transplanting" of M1's encoding scheme from one pup to another. Thus, the emergence of continuous M1 activity signals the developmental onset of more complex, informationally sparse, and individualized sensory representations. [Display omitted] • In P8 rats, a linear decoder reliably predicts limb movements from M1 activity • At P12, M1 activity is continuous, and a nonlinear decoder is required • M1 activity is more sensitive to "lesions" and encoding scheme "transplants" at P12 • P12 marks the onset of more sparse and individualized M1 movement representations Cortical activity transitions from discontinuous to continuous around postnatal day 12 in rats. Glanz et al. use neural decoding to assess this transition's effect on sensory representations of limb kinematics in the primary motor cortex (M1). After the transition, M1 activity is more informationally dense, and its encoding scheme is more individualized. [ABSTRACT FROM AUTHOR]