What’s Going On?
BODY SENSES AND MOTOR
What role might the brain stem nuclei play in
causing or contributing to autism?
If we go by the assumption that autism is
caused by sensory impulses not completing the full processing circuit, so that
they are not properly integrated into coherent, meaningful perceptions, it
stands to reason that the earlier these impulses are interrupted in the
processing circuit, the more basic the information that is going to be
sacrificed. The most basic information the brain receives is from our skin.
Sensations of touch, temperature, texture, pain and pressure are conveyed from
skin receptors through the peripheral nerves to the spinal cord and up to the
At the brain stem, these sensations feed into
the reticular core or formation; a tangled web of nuclei that acts as an arousal
center for the nervous system. When stimulated these nuclei wake, calm, alert
and excite us. They send messages on to the hypothalamus to regulate heartbeat,
breathing and digestion. They also send messages up to the cortex, signaling it
to shift our attention from one thing to another. If a person’s reticular
processes are not operating smoothly, focusing
attention and maintaining control would be very difficult.14
Sensations of touch also feed into another even
more complex and critical network of nuclei at the brain stem level. These
vestibular nuclei have interconnections with almost every part of our brain and
body. They process and coordinate sensations from the gravity and movement
receptors in our inner ears with information from all our other sense receptors.
This processing determines our basic relationship to gravity and the physical
world, and this gravitational security serves as a reference point for our
interpretation of all sensory experience.15
A child who feels uncertain about
his connection to the earth is likely to feel uncertain and insecure about just
about everything else.16
If the vestibular nuclei are not functioning
properly, the registration and integration of all sensory messages would be “off.”
The soothing sensations from normal mother-child bonding, from holding, cuddling
and snuggling, would be sabotaged before they could wend their way to the limbic
system, so that the basic connections that inspire kindness and empathy would
never have a chance to develop.
Sensations from the eyes and ears would not be
processed into clear-cut perceptual information if that input was not properly
integrated with basic body information at the brain stem-vestibular level. A
child who is uncertain about what he sees and hears because he is missing some
relevant visual, spatial or auditory clue would find it very difficult to attend
to either words or deeds in a typical manner.
How might the poor modulation of sensory input
impact vestibular function in autism?
If certain inhibitory neurotransmitters are not
doing their job of inhibiting and certain excitatory neurotransmitters are not
doing their job of facilitating, the vestibular nuclei cannot do their job of
integrating and passing along organized, modulated sensory information to all
the body and brain systems and structures that need it. Because of too little
facilitation, information from the vestibular receptors does not flow smoothly
to the spinal cord and muscles, undermining balance and muscle tone and making a
child gravitationally insecure, thereby insuring that the operation of all
sensory processes will be out of sync with the normal state.17
Because of too
little inhibition, rather than being eliminated, the disorganized sensory
impulses that pass through the vestibular nuclei are fed into the reticular
arousal system and the brain becomes overstimulated.
How might the thalamus contribute to autism?
After leaving the brain stem, sensory impulses
move on to another cluster of nuclei within the thalamus. Located in the core of
the brain, these nuclei control what and how impulses are transmitted and
integrated beyond the brain stem level. They are differentiated and specialized
to correspond with and relay information reciprocally to and from the sensory
lobes and association areas of the cortex.
This two-way connection network is not a
genetic given. In fact, we are born into a state where the sensory areas of the
brain are “cross-wired.” As we develop, our growing experience and
consciousness separates and straightens out this crucial wiring.18
But if that
experience is lagging, the specialized sensory wiring of either the cortex or
thalamus might remain skewed, skewing their crucial two-way interconnections and
causing problems with input registration.
Or, the specialized nuclei in the
thalamus might act on their own to suppress or selectively pass along sensory
input and cortical feedback. Thalamic nuclei working in a particularly selective
mode would account for the failure of many autistic children to attend to the
things that normal children readily notice. If the thalamus is acting in its
gatekeeping role to suppress some sensory impulses while exaggerating the
importance of others, then not only would autistic attention be limited and
selective, but it would likely be odd as well. The brain would have a hard time
knowing what information was important and what was not.
How are sensory impulses transformed into motor
Tactile impulses from the hands, fingers and
mouth and proprioception from the muscles and joints wend their way from the
brain stem, through the thalamus, to the somatosensory cortex in the parietal
lobe, where details about the type of touch we feel or movement our muscles make
enter our conscious awareness.19
Once we become aware of sensations from our
body, we must decide what to do about them. This is the job of the association
cortex. The association nuclei send signals to the basal ganglia and to the
cerebellum, where precise motor commands are formulated and passed on to the
thalamus. The thalamus receives these signals, coordinates them with incoming
sensory information and forwards messages up to the motor cortex, where the
commands are executed.20
The motor cortex actually consists of two neural strips
located atop and down the sides of the brain’s frontal lobes, with different
sized patches or sections devoted to specific body parts according to their
degree of sensitivity. The left motor cortex controls the muscles on the body’s
right side and the right one those on the body’s left side. The hands, feet
and mouth have the largest cortical patches, affording us greater precision in
the control of these muscles.21
What might go awry in the carrying out of motor
Once a movement is begun it is continuously
monitored by the cerebellum, which receives instructions from the motor cortex
and proprioceptive feedback from the muscles and joints. The cerebellum compares
and assesses this information and sends signals to the motor cortex to modify or
fine tune the movement.22
If the nuclei in the cerebellum are not operating to
full capacity, information relayed to the motor cortex might be vague or
The movement process might be further complicated if proprioceptive
feedback is weak because muscles and joints are not receiving a healthy flow of
input from the vestibular nuclei to keep them toned. Also, if tactile sensations
from the mouth and hands fail to register in the somatosensory cortex as intact,
clearly defined perceptions, the result would be a diminished sense of oral
awareness and tactile discrimination, which would make the planning and carrying
out of the movements involved in speech and fine motor tasks difficult.
The bottom line, if the sensations in a child’s
brain aren’t feeding him back good, precise information about his body, he
will have a poorly developed sense of self overall.
How does stimulating the body help to develop
and organize the brain?
Every time the cerebellum actively plans and
sends out a motor command, the tactile, vestibular and proprioceptive input that
feeds back into the brain as a result of this intentional movement adds
information to the ‘strip’ map of the motor cortex. The more information fed
into each patch, the more detailed and accurate this motor map or body percept
will become. And, the more accurate and detailed a person’s body percept, the
better he will be at learning and carrying out other intentional movements.
Stimulating a body physically, either through
exercise or sensory integrative therapy, forms and stimulates synapses. When
synapses are stimulated, used repeatedly for sensori-motor functions, neural
memories of those functions are created.23
Neural memories are the basis for all
learning, both mental and physical. On the physical side of the equation, neural
memories translate into motor skills; actions that no longer require planning or
A child with many motor skills is able to do many things
without thinking about them, while one with fewer motor skills has to think a
lot about everything he does and consequently doesn’t find doing many things
Why do autistic children often have so little
motivation or interest in doing new things?
One explanation is that many autistic children
have a paucity of motor skills causing them to have a difficult time figuring
out how to do things, and because of this they have little desire to try
anything new or different. But the problem probably originates in the association cortex; the primary response
planning region of the brain.
In the autistic brain, sensory impulses flow
unimpeded until they reach the nuclear networks in the brain stem where, if
either network is malfunctioning but particularly the vestibular one, they begin
to unravel, to scatter or fragment. Those impulses that do make it on to the
thalamus are filtered further through selective registration or through skewed
interconnections to the cerebral cortex. The result is that fewer intact
sensations actually make it all the way to the final association phase where a
decision can be made to act upon them.
Because their developing brains are only
fully registering and integrating a selected portion of the sensations that pass
through them, autistic children are not fully capable of making a well
considered decision to do or not to do something. The shortcircuiting of
cerebral neural impulses not only results in a lack of inner drive, it also
causes an inability to think things through; to consider all factors of a
decision before taking action. Hence their predisposition to impulsivity.
Even if the association cortex in an autistic
brain does make a decision to do something, plans an action or response, there
is a good chance that the message it sends on to the cerebellum and the
cerebellum sends on to the motor cortex will be obfuscated by being routed
through skewed thalamic synapses. And, if a motor command is initiated at the
cortical level, the message still has to pass through the brain stem en route to
the spinal cord and muscles, so there is further likelihood that it could get
fouled up. In short, autistic children lack an inner drive because they lack an
intact, fully functioning sensory processing system.
How does their restrictive thought pattern
affect the play style of autistic children?
Because they cannot register the meaning or
potential use of toys, young children with autism have little incentive to
explore or play with them. They generally find activities that challenge them to
experience new sensations and develop new skills confusing and off-putting. They
would rather be left alone to do nothing in particular or to stick to the
familiar, repetitive actions and routines that they know can’t hurt them and
won’t overwhelm them.
The trouble is that the limited “play” strategies
they come up with -- strategies that include holding, gazing at, twirling,
mouthing or lining up toys -- do hurt them because they do not challenge them to
learn anything. By not trying to figure out more sophisticated or purposeful
ways to manipulate their toys autistic children set themselves further behind
developmentally by failing to process the necessary sensations and develop the
neural connections that would help to better organize their brains.25
What is the critical Catch-22 situation in
which young people with autism find themselves?
Because the synapses in the brains of autistic
children are not working efficiently or effectively, fewer intact perceptions
reach the association or planning processing areas, causing them to have less
motivation or inner drive. Consequently, they plan and carry out less
intentional actions, resulting in the formation of fewer neural memories and
motor skills. This further impedes the growth of the crucial neural
interconnections that would help to develop and organize their brains so that
they could properly process sensations into the perceptions or adaptive
responses that would make learning -- planning and carrying out actions or
thinking meaningful thoughts -- easier for them.