Cerebellum and Brain Stem

The cerebellum receives visual, auditory, vestibular and somatosensory input. It regulates these signals going to and from parts of the body and other parts of the brain. The signals involve movement (orientation in space, volitional movements, fine movements of the hand), thoughts and emotions.

Damage to the cerebellum impairs:

• Standing
• Walking
• Performance of coordinated movements
• Difficulty with coordination of thoughts with motor movements

The Brain stem is usually associated with the basic functions such as breathing, eating, balance, and motor coordination.

People do not usually study the brainstem and cerebellum when looking at autism because many of the behaviors associated with autism, such as language, planning and interpretation of social cues are believed to be controlled by higher level regions of the cerebral cortex and forebrain.

Because of this, researchers believe that the abnormalities in the cerebellum may not be critically important to producing the behavioral manifestations of autism but instead may be neurological markers that indicate the timing of damage during neuronal development.

However, some symptoms of autism such as lack of facial expression, hypersensitivity to touch and sound, sleep disturbances, visual self stimulation and unusual motor coordination, do originate in these basic brain regions and in one case where autopsy was carried out, the brain stem of an autistic adult was shorter than normal. The structures at the junction of the pons and the medulla (the facial nucleus and trapezoid body) were closer to the structures of the lower medulla, as if a band of tissue was missing.

The brain stem of a person with autism also lacks the superior olive and has a smaller than normal facial nucleus. Such changes can only occur in early gestation.

Eric Courchesne found that there was increased activity in the cerebellum when high level cognitive processing tasks were carried out.

He also discovered that

• two areas of the cerebellum, vermal lobules VI and VII were significantly smaller in 78% of the autistic children and
• there are only 10-40% of the normal number of Purkinje cells present in autistic brains (Purkinje cells are essential in the development of the cerebellum's circuitry. These cells are responsible for keeping the actions of other neurons in check; they are inhibitory neurons and each Purkinje cell can connect to 100,000 other cells).

Scientists at York University and the Hospital for Sick Children in Toronto have recently identified an autism related behavior that is much simpler than the array of behaviors that have traditionally been used to diagnose the condition. Susan Bryson found that children with autism respond abnormally to a task involving their reactions to visual stimuli. Because this mental activity is probably mediated by a primitive part of the brain - most likely the brain stem or the cerebellum or both - the discovery has important implications.

In her study, Bryson observed the reactions of two groups of children, those with autism and those without it, as they watched lights flashing on video screens. The children ranged in age from four to seven years. In the first test, each child was placed in front of a three-screen panel and a flashing light appeared on the middle screen. This stimulus prompted all the children to focus their eyes on the flashes. Then the middle screen went blank, and a flashing light appeared on the far right or far left screen of the panel. Both groups of children shifted their eyes to that screen. In the second test, however, the lights on the middle screen kept flashing while the lights appeared on the other screen. The children without autism shifted their eyes to focus on the new stimulus, but the children with autism remained stuck on the first stimulus and failed to turn their eyes to the new one.

Bryson found that children with other kinds of brain damage are perfectly normal in their ability to disengage from one stimulus and focus on another. Children with autism, however, repeatedly fail to disengage from the first stimulus, even if they are highly intelligent. Researchers now suspect that this ability is a low level brain function because it typically appears in infants as early as three to four months after birth, and in children with low IQ's. Animals also orient themselves toward new stimuli, so scientists could conceivably use a similar test in animal studies to verify whether genetic manipulations or toxicologic exposures have produced this symptom of autism.