Individuated movements are those in which one or more body parts are moved independent of the movement or posture of other contiguous body parts. Loss of individuated movements, particularly those of the fingers, is one of the earliest and most severe impairments for human patients affected by lesions of the motor cortex or corticospinal tract. Though prior studies indicate that the motor cortex is crucial in executing individuated movements and that area 6 may contribute to their selection and preparation, exactly how neuronal activity in these area performs these functions remains unknown. The long term objective of this research ,therefore, is to understand the neuronal mechanisms underlying the selection and execution of individuated movements. To this end, monkeys are trained to perform isolated movements of each digit of the right hand, of the wrist, and of the shoulders. They are trained as well to perform combined movement of one or more digits. These movements are performed both in a reaction- time paradigm and in a delayed response paradigm. Once trained, cortical areas 4 (motor cortex) and 6 (arcuate premotor area, premotor cortex, supplementary motor area) are studied in three ways. First, single neuron recording is used to study neuronal activity during isolated and combined individuated movements. Each neuron's activity is analyzed in terms of its somatic motor field, defined as those digits and more proximal joints which when moved are associated with discharge of that neuron. Changes in the somatic motor field over the reaction time or the delay period are examined to study how individuated movements are selected and executed. Second, active cortical areas are temporarily inactivated by focal injection of the GABA agonist, muscimol. Changes in individuated movements observed during focal inactivation of a particular area are compared with features of neuronal activity observed in that area during normal function. Third, each monkey is studied terminally with 14C-2-deoxyglucose to survey the brain for other areas that may be important in the performance of individuate movement tasks.
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