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How Does Autism Occur In The Brain

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Understanding Autisms Effects On The Brain

Autism Study Shows Link to Brain Overgrowth

Autism is a disorder of the brain that affects how people with the condition interact with others and the world around them. Autisms effects on the brain vary greatly depending on the individual as well as the severity of the disorder.

Autism is not a static condition. It occurs on a spectrum, with severe impairment on one end and a high level of functioning on the other. People with severe autism often do not speak very much in some cases, they are completely nonverbal. They can have debilitating intellectual and cognitive impairments.

On the other hand, some people with high-functioning forms of autism have average IQs, even above average IQs, and can communicate verbally. Despite certain strengths, they may struggle to read nuance, body language, sarcasm, or subtext.

People with autism generally struggle in social situations. Their interests in certain topics can appear to be obsessive, to the exclusion of other interests and interactions with other people. When they become overwhelmed, they often perform repetitive behaviors to soothe themselves. Sometimes, these behaviors can be disruptive or even dangerous.

Brain Connectivity In Asd

The brain is a structural and functional system that has features of complex networks . Early brain imaging studies have focused on region specific differences in activity however, accumulated data implicate an important role of brain network activity in the brain function . Brain connectivity can be divided into functional and structural connectivity: temporal similarities of brain activity in multiple regions and physical connections between the brain regions. A number of studies using the brain imaging techniques such as fMRI and diffusion tensor image identified abnormal brain connectivity in individuals with ASD. Long-range cortical hypo-connectivity theory has been largely supported by many investigators , even there are some opposite reports to show hyper-connectivity in ASD . Other investigators also demonstrated that local-range hyper-connectivity , however, these results are controversial and the agreement on terminology, local- and long-range, is still lacking.

Thus, below we mainly focused on the global connectivity depending on the developmental stage.

Increased Miscommunication For Autistic Brains

Too many brain connections may be at the root of autism was Science Dailys summary of a study from the Washington University School of Medicine. Researchers found a defective gene that influenced how neurons connect to and communicate with each other. Studies on animals that lacked the gene also showed too many connections existing between those key brain neurons and difficulties with learning and memory.

The findings led the Washington University researchers to suggest that the symptoms of autism may be the result of problems in how cells in the brain communicate with each other specifically that there may be too many synapses in the brains of patients with autism. The senior author of the study explained that instead of more synapses making the brain work better, the higher number results in increased miscommunication between neurons. This leads to impairments with learning, but the mechanisms of this problem arent fully understood.

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Total Brain Volume Size Of The Brain Is Bigger In Younger Children With Asd

In early childhood, from approximately two to four years of age, children with ASD are found to have accelerated brain volume growth as compared to children without ASD. Children with ASD often have greater brain volume when they are young but then do not show differences in brain volume when they are older as compared to typically developing peers .

The increased brain volume in young children with ASD seems most commonly associated with differences in the volume of the frontal lobe, which has to do with motor movements and language as well as executive functioning and attention and the temporal lobe which has to do with auditory, olfactory, vestibular, visual and linguistic functioning .

When youth with ASD enter their adolescent years, they may experience less differences in brain volume as compared to typically developing peers. So, from around age ten to fifteen, children with ASD dont have as much difference in brain volume growth.

Brain volume differences in youth with ASD may be due to accelerated surface area growth of the cortical region of the brain, which is the outermost part of the brain.

Infants Toddlers And Children


Social communication and social interaction

Language development is a critical neurobiological process to communicate each other. Delayed language development is one of the early warning signs of ASD . Children with ASD commonly show impaired language development that leads to social communication deficits. Some fMRI studies have examined the neurobiological differences of impaired language development between children with ASD and TD children . Wang et al. used fMRI to examine the neurobiological deficits in understanding irony in high-functioning children with ASD. In contrast to previous studies showing hypo-activation of regions involved in understanding the mental states of others, children with ASD showed hyper-activation than TD children in the right IFG as well as in bilateral temporal regions. Greater activity children with ASD fell within the network recruited in the TD children and this may reflect more efforts needed to interpret the intention of a word. They concluded that children with ASD have impairments interpreting the communicative intention of others’. These results also indicated that children with ASD can recruit regions activated as part of the normative brain circuitry when task requires some degree of explicit attention to socially relevant cues .

Restricted and repetitive patterns of behavior, interests, or activities

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Is Autism Spectrum Disorder Hereditary

Autism arises froma complex interplay of genes and the environment. Genetics plays a role in ASD, but scientists still dont know precisely how risk for the disorder is inherited. While some genes and gene variations are known to raise susceptibility to the condition, the genes presence doesnt necessarily mean that an individual will develop ASD. Even when one identical twin has autism, the other twin has only a 60 percent chance of receiving the same diagnosis.

Although environmental factors are almost certainly partly to blame for the development of autism, a recent study has suggested that as much as 80% of the disorders risk comes from genetics.

How Is Autism Spectrum Disorder Diagnosed

No lab test, blood work, or imaging exams are used to diagnose ASD. Pediatricians usually doan assessment at a childs 18- and 24-month checkups to look for the disorders developmental signs.

Doctors observe the childs behavior and talk to parents. If concerns arise, an autism specialist may be recommended to evaluate a childs behavior and development to make a diagnosis.

If ASD is suspected, healthcare professionals will work through a checklist of questions to pursue a diagnosis. Some of these questions might include:

  • Are the childs behaviors odd or repetitive?
  • Does the child have trouble making eye contact?
  • Does the child interact with other people?
  • Does the child respond to someones voice?
  • Is the child sensitive to light, noise, or temperature?
  • Does the child have sleep or digestive problems?
  • Does the child seem irritable or angry?


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Defining Autism Spectrum Disorder

Autism Spectrum Disorder is a developmental disorder that usually emerges in the first three years and persists throughout the individuals life. Though the key symptoms of ASD fall into three general categories , each person with ASD exhibits symptoms in these domains in different ways and to varying degrees. This phenotypic heterogeneity reflects the high degree of variability in the genes underlying ASD . Though we have identified genetic differences associated with individual cases of ASD, each accounts for only a small number of the actual cases, suggesting that no single genetic cause will apply in the majority of people with ASD. There is currently no biological test for ASD.

Autism is in the category of pervasive developmental disorders, which includes Asperger’s disorder, childhood disintegrative disorder, autistic disorder, and pervasive developmental disorder – not otherwise specified. These disorders, together, are labeled autism spectrum disorder . ASD is defined by the presence of profound difficulties in social interactions and communication combined with the presence of repetitive or restricted interests, cognitions and behaviors. The diagnostic process involves a combination of parental report and clinical observation. Children with significant impairments across the social/communication domain who also exhibit repetitive behaviors can qualify for the ASD diagnosis. There is wide variability in the precise symptom profile an individual may exhibit.

Head Circumference And Total Brain Volume

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Atypical head circumference growth curve in the first two years of life is a phenotypical risk indicator for autism . In the case of autism, head circumference that is normal or near normal size at birth follows an accelerated growth pattern at about four months . It has been shown that 37% of autistic children between the ages of two and four meet the criteria for developmental macrocephaly .

The hypothesis has been put forward that unusual brain growth curves lead to an abnormal pattern of changes in cortico-cortical connections. Changes in the brain during development adversely affect the development and persistence of growth curves among short-and long-haul connections. It has been suggested that the growth rate of brain size is less than the normal rate where developmental disorders are concerned, which leads to an increase in long-haul connections. Moreover, if brain size is larger than normal in developmental disorders such as autism, leads to a reduction in long-distance structural and functional connections .

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Brain Structure Changes In Autism Explained

by Angie Voyles Askham / 15 October 2020
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Autism is a neurodevelopmental condition. Although it is diagnosed based on the presence of two core behaviors restricted interests and repetitive behaviors, as well as difficulties with social interactions and communication those traits are thought to arise because of alterations in how different parts of the brain form and connect to one another.

No research has uncovered a characteristic brain structure for autism, meaning that no single pattern of changes appears in every autistic person. Studies of brain structure often turn up dissimilar results there is great variety across individuals in general. But some trends have begun to emerge for subsets of autistic people. These differences might one day provide some insight into how some autistic peoples brains function. They may also point to bespoke treatments for particular subtypes of autism.

Here is what we know about how brain structure differs between people with and without autism.

Which brain regions are known to be structurally different betweenautistic and non-autistic people?Studies that make use of a brain-scanning technique called magnetic resonance imaging have highlighted a few brain regions that are structurally distinct in people with autism.

Other structural differences, such as the rate of brain growth and amount of cerebrospinal fluid, appear similar between the sexes6,9.


References And Further Reading:

  • American Psychiatric Association: Diagnostic Manual of MentalDisorders , 4th Edition, Washington, D.C., AmericanPsychiatric Association, 1994.
  • Griffiths, D. 5-Minute Clinical Consult, Baltimore: Williamsand Wilkins, Inc., 1999.
  • Kaplan, H.I. and Sadock, B.J., Comprehensive Textbook ofPsychiatry, 6th Edition, Baltimore: Williams and Wilkins, 1995.
  • Kates, W.R. et al., Neuroanatomical and neurocognitive differences ina pair of monozygous twins discordant for strictly defined autism, Ann.Neurol., 43:782-791, 1998.
  • Rapin, I. Autism in search of a home in the brain. Neurology,52:902-904, 1999.
  • Rowland, L.P., Merritt’s Textbook of Neurology, 9th Edition,Malvern: Williams and Wilkins, 1995.
  • Autism Informationfrom the National Institute of Child Health and Human Development
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    What Role Do Genes Play

    Twin and family studies strongly suggest that some people have a genetic predisposition to autism. Identical twin studies show that if one twin is affected, then the other will be affected between 36 to 95 percent of the time. There are a number of studies in progress to determine the specific genetic factors associated with the development of ASD. In families with one child with ASD, the risk of having a second child with the disorder also increases. Many of the genes found to be associated with autism are involved in the function of the chemical connections between brain neurons . Researchers are looking for clues about which genes contribute to increased susceptibility. In some cases, parents and other relatives of a child with ASD show mild impairments in social communication skills or engage in repetitive behaviors. Evidence also suggests that emotional disorders such as bipolar disorder and schizophrenia occur more frequently than average in the families of people with ASD.

    Brain Development And Autism

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    The brain develops differently in autistic children compared with typically developing children.

    In young children, the brain is developing all the time. Every time a child does something or responds to something, connections in the brain are reinforced and become stronger.

    Over time, the connections that arent reinforced disappear theyre pruned away as theyre not needed. This pruning is how the brain makes room for important connections those needed for everyday actions and responses, like walking, talking or understanding emotions.

    In autistic children, the brain tends to grow faster than average during early childhood, especially during the first three years of life. The brains of autistic babies appear to have more cells than they need, as well as poor connections between the cells.

    Also, pruning doesnt seem to happen as much in autistic children. This means that information might be lost or sent through the wrong connections. The lack of pruning might also explain why the brain seems to be growing faster in autistic children than in typically developing children.

    Its not yet clear what causes this difference in brain development.

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    Symptoms And Effects Of Asd

    Autism is a spectrum disorder, meaning that not everyone experiences it in the same way. There is wide variability in the symptoms and behaviors of people with a condition on the autism spectrum.

    Symptoms of ASD can include:

    • Problems with verbal and nonverbal communication, including spoken language, gestures, facial expressions, tone of voice, and eye contact
    • Expressing and recognizing emotions in self and others
    • Anxiety in social situations
    • Intense interest in narrow subjects
    • Need for routines or rules to follow

    Other characteristics of ASD may include:

    • Autism is associated with repetitive behavior patterns, such as arm flapping and rocking from side to side. Difficulties appear early in development, generally by age three.
    • Up to 40% of people with autism also suffer from anxiety.
    • People with autism often struggle to understand social nuances.
    • People with autism often suffer from gastrointestinal problems, seizures, sleep disturbances, attention-deficit/hyperactivity disorder , and phobias.
    • Despite these challenges, some individuals with ASD show unique strengths in problem-solving and attention to detail.
    • Children with the high-functioning form of ASD sometimes display extraordinary abilities with memory, music, or mathematics.

    What Is Autism Spectrum Disorder

    Autism spectrum disorder refers to a group of complex neurodevelopment disorders characterized by repetitive and characteristic patterns of behavior and difficulties with social communication and interaction. The symptoms are present from early childhood and affect daily functioning.

    The term spectrum refers to the wide range of symptoms, skills, and levels of disability in functioning that can occur in people with ASD. Some children and adults with ASD are fully able to perform all activities of daily living while others require substantial support to perform basic activities. The Diagnostic and Statistical Manual of Mental Disorders includes Asperger syndrome, childhood disintegrative disorder, and pervasive developmental disorders not otherwise specified as part of ASD rather than as separate disorders. A diagnosis of ASD includes an assessment of intellectual disability and language impairment.

    ASD occurs in every racial and ethnic group, and across all socioeconomic levels. However, boys are significantly more likely to develop ASD than girls. The latest analysis from the Centers for Disease Control and Prevention estimates that 1 in 68 children has ASD.

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    How Is Asd Diagnosed

    ASD symptoms can vary greatly from person to person depending on the severity of the disorder. Symptoms may even go unrecognized for young children who have mild ASD or less debilitating handicaps.

    Autism spectrum disorder is diagnosed by clinicians based on symptoms, signs, and testing according to the Diagnostic and Statistical Manual of Mental Disorders-V, a guide created by the American Psychiatric Association used to diagnose mental disorders. Children should be screened for developmental delays during periodic checkups and specifically for autism at 18- and 24-month well-child visits.

    Very early indicators that require evaluation by an expert include:

    • no babbling or pointing by age 1
    • no single words by age 16 months or two-word phrases by age 2
    • no response to name
    • excessive lining up of toys or objects
    • no smiling or social responsiveness

    Later indicators include:

    • impaired ability to make friends with peers
    • impaired ability to initiate or sustain a conversation with others
    • absence or impairment of imaginative and social play
    • repetitive or unusual use of language
    • abnormally intense or focused interest
    • preoccupation with certain objects or subjects
    • inflexible adherence to specific routines or rituals

    What Does Autism Look Like In The Brain

    Amazing Things Happen – Explaining the brain of those with autism.

    People on the autism spectrum often dislike exposure to unexpected stimuli, but why is that? New research takes a look at what happens in the brain, and how that relates to a persons ability to tolerate exposure to various stimuli.

    People with autism do not like unexpected stimuli, and it may be because brains are not as efficient at rapidly shifting between ideas or thoughts, notes Dr. Jeff Anderson, a professor in Radiology at the University of Utah Health in Salt Lake City.

    Recently, Dr. Anderson and colleagues decided to try and gain a better understanding as to why individuals with autism may experience some of their symptoms.

    To do so, they directed their attention to the complex circuitry of the human brain. We wondered if we could see how local circuits in the brain react in patients with autism, explains the researcher.

    The research team reports the

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