THE BASAL GANGLIA: FOCUSED SELECTION AND INHIBITION OF COMPETING MOTOR PROGRAMS
Section snippets
INTRODUCTION
Participation of the basal ganglia in the control of movement is an old idea dating back to the early part of this century when S.A. Kinnier Wilson described a disease characterized by muscular rigidity, tremor, and weakness with pathological changes in the liver and basal ganglia (hepatolenticular degeneration) (Wilson, 1912). Wilson noted that several features usually associated with damage to the pyramidal tracts were not present in this disease and postulated that the motor abnormalities
ANATOMY OF THE BASAL GANGLIA
It useful to consider a overview of the basal ganglia connections before discussing each connection in detail (Fig. 1). The basal ganglia may be viewed as two primary input structures, two primary output structures, and two intrinsic nuclei. The input structures of the basal ganglia are the striatum (caudate and putamen) and the subthalamic nucleus (STN). The striatum receives excitatory inputs from virtually all areas of cerebral cortex and STN receives excitatory inputs from motor areas of
ACTIVITY OF THE BASAL GANGLIA DURING MOVEMENT
Although the anatomic organization of the basal ganglia provides the infrastructure for their function, any inference of function from anatomy can only be speculative. One way to obtain direct information about the function of a structure is to measure its activity during behavior. Several methods have been used to measure the activity of different components of the basal ganglia including single unit recording, 2-deoxyglucose (2-DG) autoradiography, and positron emission tomography (PET). The
THE EFFECT OF BASAL GANGLIA DAMAGE
Some important clues to the function of the basal ganglia have come from recording the activity of single neurons during behavior. However, other methods are required to demonstrate a causal relationship between the discharge of neurons and the behavioral variable of interest. One way to determine the function of a structure is to selectively remove it from an otherwise intact system. With modern techniques, small focal lesions can be made in one structure with minimal effect on surrounding
FOCUSED SELECTION AND INHIBITION OF COMPETING MOTOR PROGRAMS: AN HYPOTHESIS OF BASAL GANGLIA FUNCTION
The results of anatomical, physiological and lesion studies can be integrated into an overall hypothesis of what the basal ganglia contribute to movement. This hypothesis states that the tonically active inhibitory output of the basal ganglia acts as a “brake” on motor pattern generators (MPGs) in the cerebral cortex (via thalamus) and brainstem. When a movement is initiated by a particular MPG, basal ganglia output neurons projecting to competing MPGs increase their firing rate, thereby
CONCLUSION
When voluntary movement is generated, motor areas in the cerebral cortex send a corollary signal to the subthalamic nucleus which causes widespread excitation of GPi and SNpr and subsequent inhibition of motor pattern generators for competing postures and movements. Simultaneously, motor and other areas of cerebral cortex send signals to striatum which filters and transforms those signals in a context-dependent manner and then focally inhibits GPi and SNpr to remove tonic inhibition from motor
Acknowledgements
I thank my mentor, W.T. Thach, for his support and contribution to the development of these ideas.
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