22. Autism

12 01neurLecture 22; November 28, 2013Autism

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Book recommendations

An Anthropologist on Mars Oliver Sacks Far From the Tree Andrew Solomon


Introduction to the autism spectrum It seems that autism spectrum disorders have

always existed, though they were not recognized as a distinct clinical entity until somewhat recently.

The word autism was first coined by Eugen Bleuler (recall that he also coined the term schizophrenia) as a symptom of schizophrenia. In its original meaning, autism referred to a morbid

self-absorption. From autos self (G.).

The modern sense of the word autism was first used in the late 1930s/early 1940s by Hans Asperger and Leo Kanner. Both of these psychiatrists described syndromes in

children reminiscent of modern-day autism spectrum disorders.

Hans Asperger (1906-1980)

Leo Kanner (1986-1981)


Prevalence, and the autism spectrum Every mental illness is believed to exist on a

continuum (see ADHD lecture). However, the idea of a continuum is especially central to our current understanding of autism.

The behavioral and neurobiological traits of autism represent one extreme of the autism spectrum. It is possible to have moderate or intermediate

levels of dysfunction. In this case, one is said to have an autism spectrum disorder.

The prevalence of autism may be as high as 1 in every 500 births. Autism spectrum disorders as a whole have a prevalence of around 1 in every 110 births. The prevalence of autism spectrum disorders

seems to have increased in recent years, but this is likely due to more refined diagnostic practices. Previously, children with autism may have been diagnosed with a learning disability or neurological impairment.


The autism spectrum Up until the DSM5, individuals on the extreme

end of the autism spectrum were diagnosed with autistic disorder. Those with higher levels of function were diagnosed with Aspergers syndrome.

In the DSM5, this scheme has changed. Aspergers has been folded into Autism Spectrum Disorder, which is now given a numerical grade based on the functional impairment. Grades range from 3 Requires very substantial

support to 1 Requires support.

Thus high-functioning autism and Aspergers syndrome are now diagnosed as dierent levels of Autism Spectrum Disorder.


Clinical description Autism spectrum disorders typically appear in early

childhood, often being first recognized during the second year of life. Not surprisingly, this is around the same time social behavior

is supposed to begin developing.

Parents often report a roughly normal pattern of development up to the 12 month mark, followed by a startling decline in function in following years. This pattern of development has given rise to many

superstitious theories of autism, for example the putative link to vaccines (the delivery of which coincides with sudden declines in function).

The autism spectrum disorders are characterized by three major areas of diculty: Impaired communication Impaired social interactions Restricted behavior, interests, and activities


Social interactions Children with autism do not tend to develop the types of

social relationships expected for their age.

This may manifest as a lack of apparent social interest, or as unusual social interactions. Children may interact with others only insofar as they are useful

to their needs.

Children with autism have limited abilities in social-emotional reciprocity they cannot engage with others and share thoughts or feelings.

Deficits in social function can be observed in very young children, often before the onset of more obvious symptoms. Children with autism have reduced eye contact with parents,

and seem to focus on non-social stimuli. Children with autism are insensitive to social cues that other

children can detect effortlessly.


Communication People with autism nearly always have

problems or delays in communication. Language skill can vary widely, with some

individuals showing extremely high levels of function.

On average, about 1/3 of people with autism never acquire speech at all.

For those who develop speech, the pattern of communication is often quite unusual. Echolalia repeating the speech and

intonation of others is common. Children may possess an odd combination

of verbal abilities, for example knowing the alphabet but not their own name.

Individuals may have an overly literal understanding of language may have difficulties understanding analogies and metaphors.


Restricted behavior Individuals with autism often exhibit

repetitive, apparently pointless behaviors called stereotypies. Since these behaviors seem to be

concerned with sensory self-stimulation, the practice is also called stimming.

Example stereotypies include: rocking, hand flapping, yelling etc.,

These can often be self-injurious.

Autism is associated with an intense preference for the status quo individuals like things to stay the same.

Ritualistic behaviors may also be apparent, for example lining up ones blocks in order from largest to smallest.


Genetics of autism Autism has a clear genetic component. It has

been known for some time that autism, and autism spectrum traits seem to run in families. Families that have one child with autism have a

5-10% risk of having another child with the disorder.

Twin studies have suggest that heritability of autism spectrum disorders range from 37% to 90%. However, scientists know of few genes that can

reliably be linked with autism.

Autism spectrum disorders are four times more common in males than in females. However, females are over-represented in low-IQ

cases of autism. Higher-IQ variants of autism seem to be more common among males.


Genetics of autism Not only do the autism spectrum disorders themselves

run in families, so do traits that seem to be linked to that spectrum.

One characteristic trait of individuals on the autism spectrum is the tendency to systematize, organize, and classify. Individuals on the spectrum are also known to develop

eccentric, often obsessive interests in unusual topics.

When these traits are concentrated in a single individual, they can be quite a burden. But in smaller doses, they might be very well suited to certain professions.

University students studying mathematics, engineering and physics are more likely to have relatives with autism (Baron-Cohen 1997).

Similarly, fathers and grandfathers of children with autism are over-represented in fields such as engineering (Baron-Cohen 1997).


The mirror neuron system

Mirror neurons are neurons that will fire both when an individual performs a certain action, and when they observe that action being performed by someone else. Mirror neurons can be found in a variety of places throughout the cortex,

though they were first discovered in the premotor cortex.Illustration from J.P.J. Pinel, Biopsychology. Allyn & Bacon, 2011


Frontal lobe!

Insula!

The mirror neuron system The mirror neuron system may provide a

neurobiological basis for social cognition. Social cognition is the knowledge of the perceptions,

ideas, and intentions of others (an ability that is notably absent or deficient in individuals on the autism spectrum).

Mirror neurons respond to the understanding of an action, not to some superficial aspect of it. For example: if you had discovered a mirror neuron that

responded to picking up a certain object, it would only fire in response to that object. Moreover, it would fire not only when the action is directly seen, but also when it is implied but hidden (say behind a screen).

Mirror neurons have also been found in the cingulate cortex, and the insula. These neurons may play a role in empathy.

It seems that many of the deficits seen in autism are precisely those skills that are controlled by mirror neurons.

Illustration from Kolb & Wishaw, An Introduction to Brain and Behavior. Sinauer, 2014


Mirror neurons in autism The function of mirror neurons cannot be directly

studied in humans, as doing so requires the use of brain surgery and invasive electrophysiological recording equipment.

Nevertheless, it is possible to infer the activity of mirror neurons through EEG recordings.

The mu wave is a an EEG wave that can be observed in the premotor cortex. It is suppressed both when an individual carries out a behavior, and when the individual views the same behavior in someone else.

Unlike healthy control children, children with autism do not show suppression of the mu wave when observing others carrying out a behavior. This suggests a problem with the function of their

mirror neuron systems.


The role of prenatal testosterone Autism spectrum disorders are much more

common in males. When these disorders appear in females, they are often present quite dierently.

Simon Baron-Cohen and others have suggested that exposure to testosterone during prenatal brain development may play a role in the development of autism.

This is a rather interesting hypothesis, because it suggests that the autistic brain is actually an over-masculinized brain. By extension, autistic cognitive and social traits

are simply exaggerated versions of how those traits normally work in males.


The role of prenatal testosterone

Testosterone levels produced by the fetus spike mid-gestation. It is during this period that much of the body and brains sexually dimorphic features develop. Sexual dimorphisms are anatomical or physiological characteristics that are substantially different

between males and females. They often develop under the influence of hormones, not genetics.


Prenatal testosterone As you may recall from the eating

disorder lecture, prenatal testosterone aects the digit ratio the ratio of the lengths of the ring and index fingers. Males have lower digit ratios (~0.947)

than females (~0.965).

The digit ratio is substantially lower in males with autism as compared to control males. This implies that they were exposed to

more testosterone than usual in the womb.

You can measure your own digit ratio. Measure the index and ring fingers from the basal crease to the tip, then divide the index finger by the ring finger (2D/4D).


Prenatal testosterone Numerous subtle psychological traits are

correlated with prenatal testosterone.

Eye contact at 12 months of age is correlated with prenatal testosterone. Males naturally make less eye contact than

females, and this is exacerbated by excess prenatal testosterone. Interestingly, this is also a trait on the autism spectrum.

Prenatal testosterone also seems to reduce performance at mind-reading tasks. These are experimental tasks where

children are asked to look at a picture of a person, and guess what that persons emotional state may be.

Example stimulus from a mind-reading task. Can you tell what emotion this face is expressing?


Treatment Autism spectrum disorders have no easily defined

neurochemical underpinning. For that reason, the search for pharmacotherapies has yielded little. Autism spectrum disorders can, however, be made more

manageable by treating secondary conditions such as depression, anxiety, aggression, tantrums and stereotypic behaviors.

Clinical trials with oxytocin are showing promise. Recall that this hormone is involved in social cognition, bonding, and cooperativeness, and can easily be administered intranasally to humans. There is also some evidence that individuals with autism spectrum

disorders have lower levels of plasma oxytocin, but this doesnt necessarily reflect the levels of oxytocin in the brain.

A recent clinical trial of intravenous oxytocin to adults with

autism showed promising reductions in stereotypic behavior.

Intranasal oxytocin was also shown to improve emotion recognition in young children with autism. This suggests that oxytocin may be useful in treating some of the

core symptoms of autism spectrum disorders

22. Autism

Documents

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highfunctioning autism

aspergers syndrome

autistic disorder

higher levels of function

hans asperger

leo kanner

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