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The Musical Brain
Music and the Cerebellum
The cerebellum lies below the cerebral hemispheres and is connected to the rest of the brain and spinal cord. Like the cerebrum, the cerebellum has two hemispheres and a cortex with gyri and sulci. The cerebellum is involved in producing smooth, coordinated movements by regulating muscle tone and the rate, range, and force of muscle contraction. Dysfunction is expressed as disorders of movement and equilibrium.
It has an extensive cortical surface with dense connections to and from the cerebral cortex. The basal ganglia and cerebellum work together to control movement. A simple schema would have the motor cortex sending signals to both, with feedback via the thalamus. The output of the cerebellum is excitatory. The basal ganglia are inhibitory. Correct balance between the two systems produces coordinated movements. Disturbances in either system will cause movement disorders.
The neurological understanding of the cerebellum focused on movement, balance and muscle tone. Disease and damage to the cerebellum can lead to: 1) loss of coordination of motor movement (asynergia), 2) impaired movement tracking (dysmetria), 3) the inability to perform rapid alternating movements (adiadochokinesia), 4) tremors (action tremor), 5) staggering, wide based walking (ataxic gait), 6) falling, 7) weak muscles (hypotonia), 8) slurred speech (ataxic dysarthria), and 9) abnormal eye movements (nystagmus).
The cerebellum is essential to learning and implementing motor skills. New skills require effort and much practice to acquire and then become automatic. Since all interactions with the outside world are movements, the cerebellum assumes great importance. Movements include speaking, singing, using tools, playing musical instruments, writing and reading are all key components of acquired cognitive skills. The role of the cerebellum in cognition and emotion is a research priority and Springer is publishing a journal devoted to cerebellar neuroscience.
Brown et al studied human dance to music processes in the brain investigated with positron emission tomography to identify what systems were involved. They suggested that three hypotheses of cerebellar function were pertinent to their findings: 1. The cerebellum embodies internal forward-inverse model pairs needed to integrate the sensory aspects of movement, the movements per se and perception of the auditory beat. 2. The cerebellum generates timing processes in the preparation and coordination of motor responses (vermal and anterior cerebellum) and the sensory perception of duration on the order of hundreds of milliseconds (lateral cerebellum). 3. The cerebellum optimizes the acquisition of sensory data to synchronize the execution of movement with the auditory rhythm.
The basal ganglia and cerebellum receive input from and send output to the cerebral cortex forming multisynaptic loops. Bostana et al identified communication between the basal ganglia and cerebellum. Projections from the subthalamic nucleus (STN) go to the cerebellar cortex and the dentate nucleus of the cerebellum projects to the striatum. The anatomy suggests an integrated functional network involving cerebellum, basal ganglia and cerebral cortex. They suggested that abnormal increases in cerebellar activity are found in Parkinson's Disease patients; stimulation of the STN improves the motor signs and normalizes cerebellar activation. Resting tremors can be stopped by stimulating or lesioning the ventral intermediate nucleus of the thalamus, a main target of cerebellar efferents.
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