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Ariel Sarver
IST 8A Term Paper
12/09/06
Autism and Abnormalities in Brain Structure and Function
Autism, or “selfism,” from the Greek autos, is a condition that affects half a percent of
American children.i The late Bernard Rimland, one of the pioneers of modern analysis and
treatment of the condition, reported incidences of autism to have increased from the four in
10,000 births observed by Leo Kanner in 1943 when he first named the disease to a current
rate of one in every 175 children.ii Of those who show the effects of the disease, there are
four times as many males as females.iii The condition, often termed “autism spectrum
disorder” due to the large range of symptoms and severity seen in patients, has provided one
of the largest mysteries for modern medicine.
What causes the characteristic lack of empathy, discomfort with normal social
interaction, lack of eye contact, and lack of facility with language that afflicts so many of our
children? The first theory on the cause of autism, now widely discredited, was that
disengaged “refrigerator mothers” forced their children into the condition by mistreating them
and not showering them with love. It was believed that children withdrew into themselves as
a result of abnormal social and emotional stimulus from their parents. However since the
1960s, behavioral and medical studies have reevaluated the condition and decreed it the
“result of a fundamental biochemical defect underlain, perhaps, by defective genes but
ultimately triggered by environmental assaults.”iv Current theories on the cause of autism
center on abnormalities in the structure of the brain, including abnormalities observed in the
cerebellum, the amygdaloid complex, and the brain stem, abnormalities in the firing of
“mirror neurons” which enable empathy and visceral reactions to the observed actions of
others, psychological impairments to the ability to create a “theory of other minds,”
distortions to the salience landscape, and negative effects from mercury in childhood vaccines
administered around the age of 18 months.v In this paper I will focus on the abnormalities in
brain structure and the mirror neuron and salience landscape theories believed to cause
autism.
When examining autism, one runs into difficulty determining what is causal and what
is caused by the defect. What is known is that autism is at least in part a result of the
interaction between genetics and environmental risk factors. In looking at physical
characteristics of autistic children, main differences in brain structure are visible in the
cerebral cortex, in the cerebellum, responsible for voluntary muscle movement, in the
amygdala, responsible for feelings of fear and anger and split-second emotional processing
prior to reasoned judgment, and in the brain stem. In general, autistics have abnormally high
levels of grey matter, or neuronal cell bodies, in the cerebral cortex.vi They do not undergo
the normal progressions of explosive growth of grey matter followed by pruning of
unnecessary synapses. Autistic individuals also show unusual structuring in their
cerebellums, where lobules VI and VII are either shrunken (hypoplasia) or abnormally large
(hyperplasia) and Purkinje cell counts are low. This has been hypothesized to lead to inability
to shift attention quickly and abnormal serotonin levels affecting emotional regulation.vii
However, the likelihood that autism is directly caused by the cerebellum is low because
cerebellar damage caused by childhood strokes does not lead to autistic behavior, and autistic
children do not exhibit the difficulties in motion seen in child stroke victims.viii What is more
likely is that cerebellar abnormalities are a side effect of the genes that cause autism.
Another region in which brain structure abnormalities are often observed in autistic
patients is the amygdala. In doctoral studies at the University of California at Davis in 2005,
Cynthia Mills Schumann observed that autistic boys between the ages of seven and twelve
have larger amygdalas than their normal contemporaries. Where normal children underwent a
growth in the volume of their amygdalas between 7 and 18 years of age, the autistic test
subjects showed no growth during this period. The study discovered that “the amygdala
appears to undergo an abnormal pattern of development that includes precocious early
enlargement and a decreased number of neurons in adulthood.”ix Again in this case there is
the potential for this to be a result of, and not cause for, autism, as Schumann acknowledges
with the phrase “the reduction in the number of neurons may occur early in development, and
therefore early enlargement is due to concurrent pathology, or the loss of neurons may be due
to a degenerative process later in life.”x
Despite question of which brain structure abnormalities cause autism, there are proven
correlations between certain genetic conditions and the disease. Studies have shown that
identical twins are more likely to both be autistic than fraternal twins are, and that “the
likelihood that autism will occur twice in the same family is 50 to 100 times greater than
would be expected by chance alone.”xi Autism is often accompanied by mental retardation
(one study showed 86% of children with IQs below 19 to be autistic), suggesting that damage
to the brain due to genetics, an early childhood injury, or epileptic seizures is directly causal
of the condition.xii More than one third of children with autism showed signs of temporal lobe
epilepsy, which may have caused degradation in the connection between the visual cortex and
the amygdala. Certain genes predispose children to the viral infections most likely to lead to
temporal lobe seizures, reinforcing the theory that autism is a result of combined genetic and
environmental factors.xiii
Another promising avenue for autism research has been the mirror neuron theory,
discovered “by accident” by researchers at the University of Parma in studies on the motor
cortex of macaque monkeys during the early 1990s. What the research team discovered was
that the same motor neurons that fired when monkeys picked up fruit would fire when the
monkeys witnessed a researcher picking up fruit. Eventually the researchers were able to
establish that a network of so-called “mirror neurons,” which fire in response to others’
actions and allow empathy and comprehension, exists throughout the premotor and parietal
cortices. Not only do the mirror neurons fire when someone is observed committing the
action for which the neurons are responsible, they also fire when the activity is implied or
imagined. Tests in which the monkeys were only exposed to the sounds of actions or were
witness to an action that was taking place behind a screen through which they could not see
showed that subsets of audiovisual mirror neurons will still fire in response to this type of
stimuli. Tests of this sort committed on human subjects have established that Homo sapiens
have a mirror neuron network as well, with activations mainly witnessed in the superior
temporal sulcus, the inferior parietal lobule, and the inferior frontal gyrus. According to
Scientific American, “mirror neurons provide an understanding of intention by distinguishing
between similar actions with different goals.” Different activations are recorded in monkeys
when they grasp a piece of fruit to eat than when they grasp it to place in a box, and human
neurons fire differently when they see the same grasping motions in different contexts.
Behaviorally, the mirror neuron structure allows for “direct experiential understanding.”
When people observe others receiving pain or disgust stimuli, regions of their own brains
such as the anterior insula (for olfactory responses) fire, allowing them to gain the survival
knowledge to avoid these potentially harmful substances.xiv
Defects in the mirror neuron system may potentially lead to autism, as the abilities
most linked to this system’s function are those most dysfunctional in autistic individuals. The
mirror system enables learning of new skills by mimicry, absolutely crucial to language and
social skills acquisition in early childhood. The mirror neuron system allows visual
information to be converted to motor skills, and provides “an understanding of other people’s
actions, intention, and emotions.” According to Scientific American, “lack of emotional
mirroring appears to be a hallmark of autism,” suggesting that autism is a result of
malfunctioning or under-activation of the mirror neuron system.xv Autistic children often
have difficulties with communication, showing muteness or delay in speech production,
repeating phrases over and over again, and having issues interpreting body language. Broca’s
area, one of the human language centers, is part of the mirror neuron system. Perhaps autistic
children have language delays because they lack the benefits of learning by mimicry, both
physical and aural. Newborn humans and monkeys show the ability to mimic actions such as
sticking out their tongues when their mothers do, something autistic children often cannot do.
Perhaps autistics cannot understand connections between actions they see completed by others
and the same actions they do themselves, leading to physical and mental isolation from the
outside world and difficulties creating friendships and emotional connections with others. In
addition, the mirror neuron network is invaluable in enabling children to transform “auditory
signals in the hearing centers of the brain’s temporal lobes into verbal output from the motor
cortex,” and in letting them respond to verbal stimuli from parents and other children.xvi
The widely observed inability of autistic children to understand metaphors and their
lack of imagination in playing and understanding intentions may also be traced to a
dysfunctional mirror neuron system. As evinced by the bouba/kiki effect, discovered by
Wolfgang Kohler, children with autism have difficulties making connections across domains,
such as connecting the sounds of words to drawings of shapes they are meant to represent.
This has been postulated to be a result of malfunctions in mirror neuron connections. Based
on the bouba/kiki test and autistics’ difficulties with metaphors, research is being done into
mirror neuron deficiencies in the angular gyrus as causal of the condition.xvii Another test, the
Sally-Anne test, demonstrates further autistic children’s’ inability to make connections
between reality and others’ emotions and beliefs. After seeing a play in which one character
put a marble in a basket and then left the room, at which point the other character moved the
marble to a box, 16 of 20 children predicted that the first character would immediately look
for her marble in the box upon reentry to the room. This demonstrated that they were
incapable of accepting that the character could believe an untruth.xviii This is demonstrated
also in autistic individuals’ attachment to facts and savant abilities. Perhaps due to inability to
connect feelings and senses of things to cold hard facts, autistics tend to have an affinity for
strict routines and to avoid unusual or unclear situations.
The behavioral evidence to support the mirror neuron theory of autism is
supplemented by extensive clinical research. Electroencephalogram measurements show that
when neurons are activated by voluntary muscle movements or by observation of others doing
these movements, mu waves in the brain are interrupted. So-called mu-wave suppression has
been used as a means to experiment with the function of mirror neurons in autistic children.
When autistic and normal control children performed simple voluntary muscle movements,
the expected mu-wave suppression was visible. However, abnormally, children with autism
did not exhibit mu-wave suppression when they saw a video of someone opening and closing
their hand. From these results came the conclusion that the autistic children’s motor control
systems were intact but their mirror neuron systems were deficient.xix Similar results have
been obtained from experiments done with magnetoencephalography and fMRI. Transcranial
magnetic stimulation-induced muscle movements show far less increase in response to
observation of others committing the same action in autistic individuals than they do in
normal individuals. Consistently people with autism are seen to have far fewer, if any,
activations of the mirror neuron system than controls of healthy individuals of their same age
and gender.
New theories of the origin of autism such as the mirror neuron theory and the research
that has been done to test this theory have already led to new methods for treatment of the
disease to supplement traditional behavioral training treatments. Mu-wave suppression as a
means to trace autism leads to much hope for the future. Doctors are hopeful that someday
multimedia therapy can help teach autistic children to mechanically suppress the proper mu
waves in their minds when they see others committing actions, allowing them better
empathetic and reciprocal faculty.xx Surprisingly, the drug ecstasy is showing potential as a
means to stimulate the release of neuromodulators to activate mirror neurons and “foster
emotional closeness and communication.”xxi
Another revolutionary theory on the cause and prevention of autism is the salience
landscape theory. A salience landscape can be defined as “a map that details the emotional
significance of everything in the individual’s environment,” the compilation of sensory input
by the amygdala and its transmission to the rest of the limbic system and the autonomic
nervous system. The theory that distorted salience landscapes may lead to many of the
secondary symptoms of autism is well-supported by the data discovered by Cynthia
Schumann on abnormal amygdala size in autistic patients and the high occurrence of temporal
lobe epilepsy in autistic infants, which may cause “altered connections between the cortical
areas that process sensory input and the amygdala or between the limbic structures and the
frontal lobes that regulate the resulting behavior.”xxii Studies have shown that autistic
children generally record much higher levels of arousal of the autonomic nervous system, as
measured by perspiration levels, than normal children do. A malfunction in the autonomic
system leading to autism may also explain why the condition can be less noticeable when
children have a high fever or why autistic children may engage in seemingly destructive selfstimulation such as single-minded repetition of a phrase or action to shut out autonomic overstimulation.
Even long before its official scientific acknowledgement by Leo Kanner and Hans
Asperger in the early 1940s, autism was a threat to the children of our nation. What is most
sobering is that during the 20th century its occurrence showed such a marked rise. We do not
know exactly what caused the increase of cases or what we can do to combat it, but hopefully
improving technology and medical innovation will allow us to protect future generations from
this disease characterized by the triad of impairment in communication, imagination, and
socialization.xxiii Whether its root is in malfunctions in the mirror neuron system, in distorted
salience landscapes caused by impaired connections in the autonomic nervous system, or in
abnormal shape and sizing of brain structures such as the amygdala, the condition is nearly
within our grasp for treatment and prevention. Hopefully someday soon the amazing
capabilities of idiot-savants shall be freed from the disastrous social paralysis and the lack of
empathy characteristic of their condition, and we will be able to celebrate genius without
worrying that amazing endowments in one sector of mental processing can come only at the
huge cost of deficiencies in other areas.
i
Ramachandran, 63
Maugh, 1
iii
Fombonne (Schumann, 1)
iv
Maugh, 1
v
Rimland, 2
vi
BBC, 1
vii
Edelson, 1
viii
Ramachandran, 64
ix
Schumann, iii
x
Schumann, iii
xi
Frith, 232
xii
Frith, 232-233
xiii
Ramachandran, 69
xiv
Rizzolatti, 54-61 (Citation for entire paragraph)
xv
Rizzolatti, 61
xvi
Ramachandran, 65
xvii
Ramachandran, 67
xviii
Frith, 235
xix
Ramachandran, 67
xx
Ramachandran, 68
xxi
Ramachandran, 68
xxii
Ramachandran, 69; Frith, 232
xxiii
Frith, 232
ii