MEG signals reveal arm posture coding and intrinsic movement plans in parietofrontal cortex

Movement planning processes must account for body posture to accurately convert sensory signals into movement plans. While movement plans can be computed relative to the world (extrinsic), intrinsic muscle commands tuned for current limb posture are ultimately needed to execute spatially accurate movements. The whole-brain topology and dynamics of this process are largely unknown. Here, we use high spatiotemporal resolution magnetoencephalography (MEG) in humans combined with a Pro-/Anti-wrist pointing task with 2 opposing forearm postures to investigate this question. First, we computed cortical source activity in 16 previously identified bilateral cortical areas (Alikhanian, et al., Frontiers in Neuroscience 2013). We then contrasted oscillatory activity related to opposing wrist postures to find posture coding and test when and where extrinsic and intrinsic motor codes occurred. We found a distinct pair of overlapping networks coding for posture (predominantly in γ band) vs. posture-specific movement plans (α and β). Some areas (e.g., pIPS) only showed extrinsic motor coding, and others (e.g., AG) only showed intrinsic coding, but the majority showed both types of codes. In the latter case, intrinsic codes appeared slightly before extrinsic codes and persisted in parallel across different cortical areas. These findings are consistent with two cortical networks for 1) direct feed-forward sensorimotor transformations to intrinsic muscle coordinates (for rapid control) and 2) computations of extrinsic spatial coordinates, possibly for use in higher-level aspects of visually-guided action, such as spatial updating and internal performance monitoring.