Sensorimotor control of object manipulation following middle cerebral artery (MCA) stroke

AbstractCurrent bedside diagnostics used for the assessment of the loss of hand function post-stroke examine limited aspects of motor performance. Further, they are not sensitive to subtle changes that can cause deficits in everyday object manipulation tasks. Efficiently lifting an object is a complex neurological event which entails a prediction of required forces based on intrinsic features of the object (sensorimotor integration), short-term updates in the forces required to lift objects that are poorly predicted (sensorimotor memory), as well as the ability to modulate distal fingertip forces. Unfortunately, this complexity is not represented by the existing assessment tools used in clinics for both diagnostic and rehabilitative purposes. The presented research examined these three critical components of skilled object manipulation—production of finely graded muscular forces, sensorimotor integration, and sensorimotor memory—in a heterogeneous population of 60 chronic, unilateral middle cerebral artery stroke participants. Performance was compared to age-matched control participants in each of the three tasks. To examine control of distal fingertip forces, a force-matching task was utilized. To examine sensorimotor integration, participants were presented with familiar objects –large wood or brass blocks—following lifting trials of small and medium sized blocks from the same size-weight families. To accurately predict the weight of the larger blocks, sensorimotor integration of object size and apparent material is required during the first lifts of the large blocks. To examine sensorimotor memory, participants were required to lift a series of size-weight blocks of different colors. One color signified an inverse size-weight relationship that required the modification of short-term sensorimotor memory to efficiently lift. Most post-stroke participants performed below control levels in at least one of the tasks. Importantly, post-stroke participants presented with several different combinations of deficits in each of the tasks performed. The presented research demonstrates MCA stroke patients may have deficits in one or more components required for the successful manipulation of hand-held objects. Further, this information may be used in future studies to aid efforts that target rehabilitation regimens to a stroke survivor’s specific pattern of deficits.