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The mystery of autism has long enthralled both scientists and individuals. Over time, researchers have proposed various theories of the condition from the diametric mind to the extreme male brain to the social motivation hypothesis and many others. All hope to weave the unique features of autism—such as social challenges, savant syndrome, or the sex difference in diagnoses—into a coherent framework with which to understand the condition.

The Diametric Mind

The diametric model of the mind and mental illness holds that autism and psychosis exist on opposite ends of a spectrum. Autism leads to an understanding of the world in literal, mechanistic terms, and a limited ability to understand others’ intentions and perspectives. Psychosis, in contrast, results in the “overinterpretation” of other’s intentions, misreading minds to such a degree that paranoia and delusion result.

What is the diametric mind theory?

In this theory, there is a spectrum between hypomentalism, which manifests as autism, and hypermentalism, which manifests as psychosis. Between these poles are more common thinking styles that range from mechanistic to mentalistic. 

The theory has its roots in how one’s genes are expressed: Autism results from greater paternal gene expression, and psychosis results from greater maternal gene expression.

What is the imprinted brain theory?

Imprinted genes refer to genes expressed from one parent rather than from both. According to the imprinted brain theory, paternal gene expression may cause a child to have a larger brain, develop more quickly, and demand more from the mother. Maternal gene expression may cause a baby to have a smaller brain, develop more slowly, and demand less from the mother.

The Extreme Male Brain

Autism has historically been diagnosed four times more often in men than in women. There are also certain cognitive domains that vary by sex: Women tend to excel at empathizing and men tend to excel at systemizing. These two principles form the foundation of psychologist Simon Baron-Cohen’s theory that autism represents an “extreme” form of the male brain.

Research from Baron-Cohen’s team suggests that people with autism may be exposed to more testosterone in utero, which could affect brain development. Other research, however, calls that hypothesis into question.

What do “systemizing” and “empathizing” mean?

Systemizing is the tendency to organize the world into systems or develop rules or principles to understand complex systems. Empathizing refers to social skills, understanding others’ emotions, and feeling sympathy and empathy.

Who developed the extreme male brain theory?

British psychologist Simon Baron-Cohen began developing the idea in the 1990s. He conceived of the systemizing-empathizing spectrum, assessed people with autism for those traits, and identified a potential biological cause, exposure to testosterone in utero. He formally published the idea in a 2002 journal article.

Previously Baron-Cohen had focused on theory of mind as it related to autism and published the book Mindblindness: An Essay on Autism and Theory of Mind in 1995.

The Social Motivation Hypothesis

The social motivation hypothesis proposes that autism may be due to differences in the brain’s reward system. Neurotypical individuals find social interactions, such as eye contact and conversation, inherently valuable. Autistic individuals find social interactions difficult or uninteresting. Some research supports this hypothesis: Children with autism show less reward-related brain activity when anticipating social information than do neurotypical children.

The theory also helps explain why people with autism have restricted interests, as research suggests that narrow, deep focus and expertise, as well as non-social stimuli, are more rewarding to those with ASD than are social stimuli. Autism may emerge from the brain’s reward circuitry developing differently, but future research will need to investigate further.

The Intense World Hypothesis

The intense world theory is that people with autism have increased brain activity, which makes it hard to selectively pay attention to certain things and not others. They may experience the world as more intense or overwhelming than neurotypical people. For example, at a party it may be difficult for a neurotypical individual to focus on the one person they’re speaking to and ignore everyone else. For someone with autism, the sound of an air-conditioner could feel grating or a sweater could feel itchy.

This idea would mean that two core features of autism—social challenges and sensory sensitivity—may both be rooted in overactive brain responses. Research suggests that the prefrontal cortex and the amygdala may be more active in people with autism than neurotypical people.

The Mirror Neuron Hypothesis

Mirror neurons help us understand and predict the actions of others. These brain cells are activated by actions we take and by watching others take those same actions. Mirror neurons are involved in imitation and may help translate other’s actions so that we understand their intentions.

The mirror neuron hypothesis of autism proposes that social challenges are due to differences in mirror neuron activity. Research suggests that mirror neuron activity may be diminished in those on the spectrum. They therefore don’t have the same ability to predict and understand the “why” behind others’ behaviors.

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