Single neuron recording, combined with focal ablation and with anatomical methods, will be used to study and compare cortical motor areas (areas 4 and subdivisions of area 6) in trained monkeys performing individuated movements. Rhesus monkeys will place the fingers of one hand in a specially designed manipulandum which will monitor the flexion/extension movements of each digit. Selected proximal joints will be monitored as well. During movements, percutaneously inserted wire electrodes will be used to record electromyographic activity. Via a specially designed, wide-field recording chamber, Pt-Ir microelectrodes will be inserted into both the motor cortex and different subdivisions of area 6 to record the activity of single neurons. Three individuated movement tasks will be used to characterize neuronal activity in different cortical motor areas. First, monkeys will perform isolated movements on single digits or more proximal joints to determine which body parts when moved are associated with a single neuron's discharge, thereby defining that neuron's somatic motor field. Second, monkeys will perform tasks consisting of simultaneous, sequential, or repetitive individuated movements of two or more body parts. Neurons found to be active will be tested further to determine whether individual neurons are related to particular movement complexes per se, or to discrete components of those complexes. Third, monkeys will move two or more different body parts in a delayed response paradigm. During the delay period, single neuron activity will be examined to determine whether anticipatory discharge is related specifically to that body-part which the monkey is about to move. Further experiments will use a two-part foreperiod delay to investigate the interactions between body-part set and directional set. In each of the three tasks, once neuronal activity has been characterized in normal animals, motor cortex neurons will be restudied during reversible or permanent dysfunction of different subdivisions of area 6 to define more clearly each subdivision's contribution to individuated movements. Also, cortico-cortical connections between area 4 and area 6 will be studied by anterograde transport of tritiated amino acids to permit direct comparison of anatomic connections with physiologic maps in individual hemispheres. These experiments will further elucidate the normal roles of cortical motor areas in the generation and use of individuated movements, and the motor deficits resulting from cortical destruction.
| Schieber, M H (1991) Individuated finger movements of rhesus monkeys: a means of quantifying the independence of the digits. J Neurophysiol 65:1381-91 |
