PROCESSING OF LINEAR FORCE INTO TILT &TRANSLATION

University Of Rochester, Rochester NY

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Abstract

Individuated movementsDthose in which one or more body parts move relatively independently of the movement or posture of other body partsDimpart a rich flexibility to the human behavioral repertoire. The individuated movements used in many forms of cognitive expression, such as speaking, dancing, or playing a musical instrument, contrast significantly with the phylogenetically older movements of the same body parts used, respectively, in eating, walking or grasping. In neurologic patients, individuated movements are the first lost and last recovered when lesions of any sort injure the motor cortex or corticospinal tract. Given the importance of individuated finger movements in so many aspects of human functionDfrom buttoning buttons to playing the pianosurprisingly few studies have quantitatively examined the ability of normal humans to individuate finger movements, or to recover this ability after nervous system injury. This reflects an underlying assumption that humans make perfectly independent movements of each finger, with any lack of independence being attributable to connections between the tendons to different fingers. Independent finger movements are assumed to be controlled by different parts of the primary motor cortex (Ml), and produced by separatemuscles moving each finger. Recent studies in non-human primates have shown, however, that individuated finger movements are controlled by overlapping neuronal populations in Ml, and are produced by multitendoned extrinsic muscles that put tension on more than one finger at a time. In humans, recent evidence indicates: (i) that Ml territories controlling different fingers overlap extensively; (ii) that motoneurons in different human finger muscles receive common input from the same premotor neurons; and (iii) that human multitendoned finger musclesDsuch as flexor digitorum profundusDmay not have separate functional subdivisions for each finger.