Effects of reversible blockade of basal ganglia on a voluntary arm movement.

1. The effects of a reversible blockade of basal ganglia were examined in two monkeys trained to perform a visually guided, step-tracking arm movement around the elbow joint. To block glutamatergic excitation, kynurenate (a glutamate antagonist) was locally injected into the putamen and the external segment (GPe) and the internal segment (GPi) of the globus pallidus contralateral to the arm tested. Muscimol [a gamma-aminobutyric acid (GABA) agonist] was also used to suppress neuronal activity in these structures. The drugs were injected in the arm area of the putamen, which was identified by microstimulation or by recording neural activity. For the GPe and GPi, injections were made into the area medioventral to the arm area of the putamen. 2. The blockade of the putamen caused abnormal braking of the arm movements. The first step of the movement became hypometric, and multiple steps were necessary to reach the target. The electromyographic (EMG) analysis revealed an increase of burst activity in the antagonist muscles and a decrease of that in the agonist muscles at the fast movements. The tonic activity increased in the extensor muscles during a holding period. 3. The blockade of the GPi caused dysmetric movements. Amplitude and peak velocity of the first step of movement largely fluctuated among trials. It became difficult for the animal to brake and adjust its arm onto the target. 4. The blockade of the GPe caused a flexion posture at the elbow joint of the contralateral arm. The tonic activity of the flexor muscles increased. Cocontraction of the agonist and antagonist muscles was also observed. 5. These results suggest that the putaminopallidal system of the basal ganglia contributes to both of two motor functions: 1) static control to maintain the posture with tonic muscle activity, and 2) dynamic control to enable fast movements.