Topics and Speakers John H. Martin, Ph.D.
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Synopsis
The cerebellum, which means little brain, plays a major role in motor learning and adaptation. However, as Professor John H. Martin discusses in his lecture, much about the organization and function of the cerebellum remains mysterious. Although the cerebellum provides the major inputs into virtually all the motor systems, cerebellar damage does not result in motor weakness. Similarly, the cerebellum receives information from all the sensory modalities, and yet cerebellar damage does not cause cognitive impairments. This mismatch between the function, as suggested by neural connections, and the dysfunction resulting from damage to those connections is one of the mysteries researchers are working to solve.
The lecture provides a comprehensive overview of the cerebellum's place within the hierarchy of the motor system. Martin first discusses the general functional anatomy of the cerebellum, including the general organization of neural pathways in and out of the cerebellum. By tracing the neural circuits that connect the cerebellum down to the spinal cord and up to the cortex, Martin provides an anatomical explanation for how the cerebellum exerts its influence on motor adaptation.
The cerebellum receives sensory information from bodily receptors in the skin and muscle, which allows it to monitor how a movement is executed. In addition, the cerebellum also receives information from the cerebral cortex as it sends control signals to the spinal cord. This intermediate position enables the cerebellum to compare the intended movement signaled by the cortex to the actual movement executed by the body. When the executed movement fails to match the intended, the cerebellum may send an error signal that will improve performance the next time the movement is attempted.
In addition to comparing intention to execution, the cerebellum also has an anticipatory, feed-forward control function that also aids motor learning. Martin describes several experiments that have investigated this feed-forward control. Subjects attempt to learn a new motor task through practice. Over time researchers found that the cerebellum learns to anticipate the next movement required by associating particular sensory inputs with the required motor outputs. This anticipatory control does not merely improve performance of a motor task; it is utterly critical for effective navigation through the world.
