Study shows link between cerebellum and body's ability to sense movement and limb position

Researchers at the Kennedy Krieger Institute announced today study findings showing, for the first time, the link between the brain's cerebellum and proprioception, or the body's ability to sense movement and joint and limb position. Published in The Journal of Neuroscience, the study uncovers a previously unknown perceptual deficit among cerebellar patients, suggesting that damage to this portion of the brain can directly impact a person's ability to sense the position of their limbs and predict movement. This discovery could prompt future researchers to reexamine physical therapy tactics for cerebellar patients, who often have impaired coordination or appear clumsy.

The sense of proprioception arises from the brain's readout of signals from receptors in muscles, joints and ligaments, but also from the brain's predictions of how motor commands will move the limb. The latter can only contribute to proprioception when a person actively moves their own body. To date, researchers and neurologists believed that proprioception did not occur in the cerebellum, and thus, damage to the cerebellum did not affect proprioception.

"Proprioception was previously not considered a factor in the therapy or recovery of cerebellar patients. In fact, previous research has shown that individuals with cerebellum damage and no other clinical neurological impairments have normal proprioception when their limbs are moved passively in a clinical setting," says Amy J. Bastian, Ph.D., PT, director of the Motion Analysis Laboratory at Kennedy Krieger Institute. "However, when these patients move their limbs actively, they exhibit significant proprioceptive impairment."

Additionally, researchers found that proprioception in healthy subjects was impaired when unpredictable dynamics, or small disturbances to the cerebellum, were incorporated into active movement. This suggests that muscle activity alone is likely insufficient to improve perception of limb placement, and proprioception should be taken into consideration when determining therapeutic practices for cerebellar patients.

Study Results and Methodology
The study compared 11 healthy people (control group) to 11 patients with cerebellar damage (caused by spinocerebellar ataxia, sporadic cerebellar ataxia or autosomal-dominant cerebellar ataxia type III) but no evidence of white matter damage, spontaneous nystagmus or atrophy to the brainstem. None of the patients included in the study had sensory loss assessed by conventional clinical measures of proprioception and tactile sensation.

Participants were compared in three psychophysical tasks designed to assess passive proprioception, active proprioception with simple dynamics, and active proprioception with complex, unpredictable dynamics designed to disrupt the cerebellum. All tasks relied on proprioceptive sense without vision.

Results showed that:
•Cerebellar patients had no deficits in passive proprioception
•Unlike control subjects, cerebellar patients did not show an improvement between passive and active proprioception with simple dynamics
•Control patients performed similarly to patients in an active proprioception task with unpredictable, small disruptions to their movement.

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