THE BRAIN GUIDE
The human brain has many parts and functions. This is a brief look only at two structures known to be abnormal in opsoclonus-myoclonus.
Located at the back of the brain and beneath the cerebral hemispheres, the cerebellum is a small but important structure. It helps us sit, stand, walk, and talk. It also exerts some control over the eyes. The main motor functions of the cerebellum are:
The cerebellum consists of two halves called cerebellar hemispheres. Each
controls one side of the body.
In opsoclonus-myoclonus, cerebellar dysfunction causes many problems including:
We also know the cerebellum has more than just motor functions. It is involved in learning and behavior. These are crucial issues in opsoclonus-myoclonus.
A puzzle: Children with opsoclonus-myoclonus usually have a normal looking cerebellum on imaging studies such as the CT or MRI scan. Many parents ask how that could be possible when symptoms of cerebellar dysfunction are so clear. Appearances can be deceiving. Cerebellar function or metabolism may still be impaired. Problems with synapses or with small populations of cells do not show up on these scans. We have been using other techniques to evaluate cerebellar dysfunction.
The brainstem connects the higher brain with the spinal cord. It contains many tracts going between the two and vital cells that help control the eyes, swallowing, breathing, blood pressure, pupil size, alertness, and sleep.
In opsoclonus-myoclonus, the brainstem and cerebellum probably interact to produce:
The brain center that allows us to quickly look at something (saccades) is in the pons, which lies just below the cerebellum. Opsoclonus is an excess of saccades. It is more erratic and sudden than nystagmus, with which it is sometimes confused. Unlike nystagmus, the movements are in all directions.
One brain center for myoclonus is the medulla, the part of the brainstem just above the spinal cord. Muscle jerks during rapid eye movement (REM) sleep come from the lower brainstem. In children with opsoclonus myoclonus, these jerks may be increased and disrupt sleep.
Brainstem dysfunction in opsoclonus-myoclonus also may contribute to:
A puzzle: Do the brainstem and cerebellum account for all the abnormal brain function in opsoclonus-myoclonus? Parents are often most concerned about learning and behavior problems. We are investigating other brain areas that may be dysfunctional in children with opsoclonus-myoclonus. We must keep these in mind because both the brainstem and cerebellum have so many connections to other brain areas. These research studies should help define the extent of brain injury.
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