UCSF

An important goal of neuroscience is to establish principles that can guide comparative studies across species. If we specifically compare rodents and macaques, there are fundamental differences in motor network anatomy. From a functional perspective, there are also a growing number of studies which indicate that in rodents, extensive skill training can lead to a ‘disengagement’ of M1 from movement control; after a period of initial deficits, movements appeared to be identical and relied only on subcortical structures. However, classic studies indicate that cortical networks are essential for prehension and perhaps less important for proximal control. However, the exact amount of task training was not clear and detailed kinematics were not performed. Thus, it remains unclear precisely how gross and fine motor control might change with a M1 lesion in primates. Here we aimed to measure changes in skilled gross and fine motor control after a M1 lesion in both macaques and mice. In macaques, we ensured that animals were well trained; we also independently measured performance in a gross motor skill and a reach-to-grasp skill. In mice, we also performed long-term monitoring of layer 5 M1 projection neurons, i.e., pathways we know are more likely to reflect movement control signals from M1. Across species, we performed detailed kinematic monitoring to quantify changes in performance, kinematic variability and transitions between sub-movements. Together, our results indicate that there is a common and preserved functional principle after the loss of M1. Even in primates, there is rapid restoration of gross movement control after a period of deficits; strikingly similar to what is reported for rodents. In contrast, for a task involving prehension, we noted prolonged deficits in prehension and changes in the transition reliability of reach to grasp. Lastly, we also do not find any evidence of neural disengagement when considering layer 5 projection neurons, pathways that are known to be critical for reach to grasp skills. Interestingly, the shared trajectory post-lesion across the two species underscores a commonality in the disruption of smooth transition probabilities that is replaced by a mosaic of fragmented movements during a task that is comprised of reaching and prehension.