What Happens in Brain with Autism: Uncovering the Autistic Brain

Autism

Explore what happens in the brain with autism, from genetic factors to altered brain structures.

Steven Zauderer

June 27, 2024

8 min read

min read

Brain Connectivity in Autism

In the quest to understand what happens in the brain with autism, one area that researchers have focused on is the patterns of brain connectivity. In individuals with Autism Spectrum Disorder (ASD), there are observed differences in brain connectivity, specifically, short-range over-connectivity and long-range under-connectivity. These differences can impact various functions, including social interactions and complex motor tasks.

Short-Range Over-Connectivity

Short-range over-connectivity refers to increased connections within proximal or nearby regions of the brain. This over-connectivity is often seen within the frontal lobe, a region associated with cognitive functions such as problem-solving, memory, and language. Some studies suggest that this hyper-connectivity may contribute to the restricted and repetitive behaviors seen in individuals with ASD. For instance, research has found that in high-risk infants who were later diagnosed with ASD, the degree of hyper-connectivity in frontal regions at 14 months strongly correlated with the severity of restricted and repetitive behaviors at 3 years.

Long-Range Under-Connectivity

On the other hand, long-range under-connectivity refers to reduced connections between distal or distant areas of the brain. Often, this is observed between areas such as the frontal and parietal lobes. These areas are crucial for tasks related to social functions and complex motor tasks. Lower connectivity in these networks can potentially contribute to the social and behavioral challenges often experienced by individuals with ASD [1].

However, it's important to note that the understanding of brain connectivity in autism is still evolving. Studies have reported varied results due to differences in factors such as the experiment and its components, the type of functional brain data used, the age of the patients examined, the anatomical regions examined, and the time interval and frequency bands in which connectivity was analyzed. These variables underscore the complexity of ASD and highlight the need for continued research to further our understanding of this condition.

Neuroanatomy and Autism

A deeper look into the neuroanatomy and the brain structure of individuals with Autism Spectrum Disorder (ASD) reveals significant differences compared to the general population. These differences underscore the impact of autism on the brain and contribute to the unique cognitive and behavioral characteristics associated with the condition.

Altered Brain Structure

Studies have found that the brain structure of individuals with autism is altered, with significantly more folding in certain regions. This increased cortical folding impacts the connectivity within the brain and affects language production. It is one of the key factors that account for the unique cognitive and behavioral characteristics observed in individuals with ASD [1].

Additionally, research has shown that children and adolescents with autism often have an enlarged hippocampus, the part of the brain responsible for forming and storing memories. However, it remains unclear whether this difference persists into adolescence and adulthood.

It's also worth noting that autistic individuals have been found to have decreased amounts of brain tissue in parts of the cerebellum. This part of the brain was previously thought to mainly coordinate movements but is now understood to play a role in cognition and social interaction as well.

Language Lateralization

One of the intriguing facets of how autism impacts the brain pertains to language lateralization. Neuroanatomy studies have found that individuals with ASD tend to have reduced leftward language lateralization. This is observed as a higher rate of left-handedness compared to the general population [1].

Language lateralization refers to the phenomenon where one hemisphere of the brain (typically the left hemisphere in right-handed individuals) is more dominant in language-related tasks. In individuals with ASD, this dominance is less pronounced, leading to potentially unique patterns of brain activity during language processing.

In understanding 'what happens in the brain with autism', it is crucial to consider these neuroanatomical differences. They not only offer insight into the unique cognitive and behavioral characteristics of individuals with ASD but also pave the way for future research and therapeutic strategies.

Genetic and Environmental Factors

Delving into the factors that contribute to the neurological characteristics of autism, one must consider the impact of both genetic and environmental elements. These factors can interact in complex ways to influence brain development and function, ultimately contributing to the unique neural signature of autism.

Prenatal Neurotoxin Exposure

Research suggests that exposure to neurotoxins during prenatal or perinatal periods may play a role in the development of autism. These compounds might interfere with neurotransmitters, the chemical messengers in the brain, potentially disrupting normal brain development and function.

Neurotoxins can come from a variety of sources, including certain medications, environmental pollutants, and substances found in some foods and beverages. The timing, duration, and intensity of the exposure can all influence the risk of developing autism.

It's important to note that while these findings provide valuable insights into the potential environmental triggers of autism, they do not establish a direct causal link. Instead, they highlight the complex interplay between genetics and environment in determining individual susceptibility to autism.

Brain Development and Autism Risk

Genetic factors also play a crucial role in the development of autism. Recent research has uncovered significant differences in the behavior of genes involved in inflammation, immune response, and neural connectivity in the brains of people with autism. These differences begin in childhood and evolve over time, affecting neuronal communication and interactions.

A study identified 194 significantly different genes in the brains of individuals with autism. Of these, 143 genes produced more mRNA (upregulated) and 51 produced less (downregulated) compared to neurotypical brains. Downregulated genes were primarily linked to brain connectivity, potentially indicating less efficient neuronal communication in autistic individuals [4].

Moreover, autistic brains showed increased mRNA expression for heat-shock proteins, which respond to stress and activate immune response and inflammation. This could potentially contribute to the aging of the brain in individuals with autism [4].

Several immune and inflammation-related genes were strongly upregulated in autistic brain tissues, indicating immune dysfunction that may worsen with age. Additionally, age-related alterations were found in genes involved in GABA signaling, a neurotransmitter that helps regulate neuronal hyperactivity in anxiety and stress.

These findings provide valuable insights into the genetic factors that may contribute to the development of autism. Further research is required to fully understand the complex interplay between these factors and how they shape the autistic brain.

Brain Regions in Autism

Understanding what happens in the brain with autism necessitates a closer look at specific regions of the brain that show alterations in individuals with autism. In this section, we will delve into the cerebellum and the hippocampus, two brain areas that exhibit distinct changes in autistic individuals.

Cerebellum Alterations

The cerebellum, a part of the brain that was once thought to mainly coordinate movements, is now understood to play a role in cognition and social interaction as well. Autistic individuals have been observed to have decreased amounts of brain tissue in parts of the cerebellum. This alteration could potentially shed light on the unique cognitive and social patterns seen in individuals with autism.

Additionally, alterations in white matter, the bundles of long neuron fibers that connect brain regions, have been inferred from diffusion MRI studies in individuals with autism. Preschoolers with autism have shown significant differences in the structure of multiple white-matter tracts, and these alterations are also seen in autistic toddlers and adolescents [3].

Hippocampus Enlargement

The hippocampus, the brain region responsible for forming and storing memories, is often found to be enlarged in children and adolescents with autism. However, it remains unclear if this difference persists into adolescence and adulthood. Such alterations in the hippocampus could influence the way individuals with autism process and store information.

Furthermore, recent studies have hinted at sex differences in the brain structures of people with autism. For instance, autistic girls may have more affected amygdalae, leading to more severe emotional problems compared to autistic boys. Also, the changes in white-matter observed in preschoolers with autism differ by sex.

In summary, distinct alterations in the cerebellum and hippocampus contribute to the unique brain functioning seen in individuals with autism. These findings offer critical insights into the neural underpinnings of autism and provide a foundation for further exploration and understanding of this complex condition.

Sensory Processing in Autism

Sensory processing is a critical aspect of understanding how autism affects the brain. Autistic individuals often experience variations in their sensory perception, leading to both over- and under-sensitivity to stimuli. This section explores the concept of sensory overload and the different sensory sensitivities that those with autism may experience.

Sensory Overload

Autistic individuals may experience sensory overload, a state where they find it challenging to process everyday sensory information. This can result in stress, anxiety, and possibly physical pain, leading to withdrawal, distressed behavior, or meltdowns. Changes to the environment and creating a sensory profile may help in such situations.

Sensory overload can occur across various senses. For instance, those with hypersensitivity to sound may find noise magnified and distorted, leading to difficulties concentrating. They may even hear conversations in the distance. Strategies to help include preparing the person before going to noisy places and providing earplugs and music for distraction.

Sensory Sensitivities

Sensory sensitivities in autism can manifest in both over- and under-sensitivity to various senses such as sight, sound, smell, taste, touch, balance, and body awareness. These affect their daily experiences, feelings, and actions.

For instance, some autistic individuals with over-sensitivity to smell may find odors intense and overpowering, causing toileting problems or disliking strong scents like perfumes. Strategies to help include using unscented products and creating a fragrance-free environment.

Moreover, autistic individuals with under-sensitive touch may enjoy heavy objects on them, smear feces, and chew on everything. Creating alternative sensory activities like offering different textures can help in these situations.

Atypical sensory-based behaviors are a common feature of autism spectrum disorders (ASD), with over 96% of children with ASD reporting hyper and hypo-sensitivities in multiple domains. These sensory behavioral differences can range from mild to severe and can persist into adulthood.

In conclusion, sensory processing in autism is a complex issue, with autistic individuals exhibiting a wide range of sensory sensitivities. Understanding these sensitivities and finding appropriate coping strategies is crucial for helping those with autism navigate their environment.

Neurotransmitters in Autism

Understanding what happens in the brain with autism involves exploring the role of neurotransmitters. Neurotransmitters are chemical messengers that transmit signals across a synapse from one neuron to another. In autism, research suggests that alterations in neurotransmitter systems such as GABA, glutamate, serotonin, and dopamine contribute to the condition.

GABA and Glutamate

Alterations in the GABA (gamma-aminobutyric acid) and glutamate systems, which are responsible for the balance between neuronal excitability, are potential mechanisms for autistic behaviors and neurodevelopmental disorders. Magnetic resonance spectroscopy studies have shown reductions in GABA and glutamate levels in individuals with Autism Spectrum Disorder (ASD), leading to abnormal information processing.

Moreover, both hypoglutamatergic and hyperglutamatergic states have been proposed as hypotheses for the role of glutamate in ASD. Reduced glutamate signaling and AMPA receptor levels have been observed in cerebellum tissue of ASD patients, supporting the hypoglutamatergic hypothesis. Conversely, higher glutamate levels in certain brain regions of individuals with ASD suggest a hyperglutamatergic state.

Serotonin and Dopamine

In addition to GABA and glutamate, serotonin and dopamine also play significant roles in the autistic brain. Hyperserotonemia, or increased blood serotonin levels, has been observed in 25 to 50% of individuals with ASD. Given serotonin's critical role in the development of social skills and behavior regulation, abnormalities in the serotonergic pathway have been linked to ASD. Low brain serotonin levels have also been observed in individuals with ASD, supporting the hyposerotonergic hypothesis.

Simultaneously, dopaminergic dysfunction, particularly in the mesocorticolimbic pathway, has been linked to social cognition and behaviors in ASD. Alterations in the dopamine system, including reduced dopamine release and neural response, have been observed in individuals with ASD. Dopamine receptor blockers, such as risperidone and aripiprazole, have been approved for the treatment of irritability and repetitive behaviors in ASD [8].

In conclusion, the neurotransmitter systems of GABA, glutamate, serotonin, and dopamine play key roles in the development and regulation of the brain, and dysfunction in these systems is thought to be responsible for Autism Spectrum Disorder (ASD). Understanding these neurotransmitter systems can provide valuable insights into the neurobiological mechanisms underlying autism and pave the way for new therapeutic interventions.