Sensorimotor Control of Grasping: Physiology and Pathophysiology

Stroke results in irreversible brain damage, with the type and severity of symptoms dependent upon the location and the amount of injured brain tissue. The most common neurological impairment caused by stroke is partial weakness, called paresis, reflecting a reduced general ability to voluntarily activate spinal motoneurons. In conjunction with the reduced ability to voluntarily activate spinal motoneurons, there is often a reduced ability to selectively activate the spinal motoneurons pools, i.e. turn on some neurons while no turning on others. Together, these mechanisms result in altered movement control of many muscles, especially the contralesional hand and arm muscles used for grasping. Because of the altered muscle control, a variety of kinematic and kinetic alterations are observed during grasping in people with paresis post stroke. Impairments in grasping are related to the inability to use the hand for functional activities during daily life. In rarer instances, stroke affects the posterior parietal lobe, resulting in distinct grasping deficits that are substantially different from grasping deficits seen after corticospinal system damage. Future studies investigating grasping post stroke could include the examination of both kinematic and kinetic aspects of grasping in the same subject samples, the examination of different types of grasping (e.g. palmar, precision), and the examination of different time points post stroke. General information about stroke Stroke is an acute, neurological event that is caused by an alteration in blood flow to the brain. The alteration in blood flow can be either a deprivation of blood to the brain tissue (ischemic stroke) or a spilling of blood (hemorrhagic stroke) onto the brain tissue. Ischemic strokes account for about 85% of all strokes. Stroke is a major health problem. More than 700,000 new strokes occur each year in the United States, and stroke is the leading cause of adult disability (Kelly-Hayes et al., 1998). Stroke results in irreversible brain damage, with the type and severity of symptoms dependent upon the location and the amount of injured brain tissue. The most common neurological impairment caused by stroke is partial weakness, often called paresis, reflecting a reduced ability to activate spinal motoneurons voluntarily. Total paralysis, or plegia, is the most severe form of paresis, reflecting a complete inability to activate motoneurons voluntarily. Post stroke paresis or plegia most dramatically affects the side of the body contralateral to the damaged brain tissue. Typically, the entire contralateral half of the body is weak or paralyzed (hemiparesis or hemiplegia), although occasionally smaller strokes weaken only the contralateral arm or only the leg (monoparesis or monoplegia). Note that paresis can result from a wide range