For centuries, the brain has been a source of endless fascination. From exploring its
structure to mapping neural connections, researchers have made remarkable strides in understanding how our brains function. Developmental neuroscience examines how the brain changes throughout life, focusing on the mechanisms that drive structural and neurological shifts (Jessell & Sanes, 2000). Thanks to advancements in this field, we now know that brain development follows fairly consistent and predictable stages, both in the womb and beyond (Stiles & Jernigan, 2010). However, in some cases, these stages may take a different course of development, leading to behavioural differences. When this occurs, a neurodevelopmental condition may be identified. One of these conditions, which has been heavily researched over the years, is Autism Spectrum Disorder (ASD).
Explaining brain diversity in autistic individuals has long been a complex and debated topic (Picci et al., 2016). Some theories propose common patterns of brain diversity in ASD (e.g., Just et al., 2012), yet findings often prove challenging to replicate, leaving the field with a mix of conflicting results. It can often feel like research has reached a standstill in recent years. However, there's hope—and a possible reason behind these discrepancies. In this blog post, we’ll delve into what current research reveals about brain diversity in ASD, explore the factors contributing to conflicting findings, and highlight the latest insights and future directions in this fascinating yet intricate area of study!
Did you know? Many researchers and clinicians are adopting more positive language to describe brain diversity in neurodevelopmental conditions. This shift reflects a deeper understanding that these conditions are natural variations in human development rather than limitations. While "Autism Spectrum Disorder" remains the correct term, words like "diversity" or "differences" are now favoured over terms like "abnormalities" or "problems" This language highlights that autistic brains aren’t "wrong"—they’re simply unique. And that’s something to celebrate!
What is ASD?
ASD is a neurodevelopmental condition characterized by challenges in social communication and interaction, as well as repetitive or restrictive behaviors, interests, or activities (American Psychiatric Association, 2022). ASD is highly heterogeneous, meaning it exists on a spectrum with a wide range of presentations; the ways in which autistic individuals experience and express these behaviours can vary significantly from person to person (Lord, 2019). The Diagnostic and Statistical Manual of Mental Disorders – Fifth Edition (DSM-5) defines ASD with three levels of support needs (American Psychological Association, 2013):
Level 1: Requiring Support – Individuals may have noticeable challenges with social interactions and communication, and can function with minimal support. Social engagement and managing routines may be challenging but are generally manageable.
Level 2: Requiring Substantial Support – Individuals show more pronounced challenges in social interactions and communication, and repetitive behaviors that are more evident. Support is needed to navigate social situations, and overstimulation may lead to distress.
Level 3: Requiring Very Substantial Support – Individuals experience significant challenges in social interactions, communication, and may exhibit very evident repetitive behaviours. They may experience extreme distress from sensory overstimulation and typically require assistance for daily living and basic needs.
Additionally, ASD can be diagnosed with or without language and cognitive impairments, which can also influence how the condition presents itself in individuals. This variability highlights the need for a careful understanding of ASD, as each person's profile can lead to different experiences. Recognizing these differences fosters a more inclusive perspective on the diverse experiences of those on the autism spectrum. Keep this in the back of your mind—we’ll revisit this idea at the end of the blog!
What does research tell us about brain structure in ASD?
Over the past decade, numerous studies have suggested that the brains of autistic individuals are connected differently from those of non-autistic people. A significant review by Just et al. (2012) highlights this, finding that autistic individuals tend to have reduced communication between the frontal and posterior (i.e., back) areas of the brain. In simpler terms, this research proposes that there is less “bandwidth” or connectivity between these brain areas, which could impact both brain function and everyday experiences. They attribute this reduced connectivity to early developmental differences in the brain.
One key process thought to be involved is synaptic pruning, where the brain "cleans up" extra neural connections to help synchronize brain regions (Casey et al., 2005). Just et al. (2012) suggests that synaptic pruning may not work as effectively in autistic children, leading to “noisy” communication between brain areas and lower connectivity.
Additional research supports this idea, finding that microglia—the brain cells responsible for pruning—might not function properly in autistic individuals (Hu et al., 2022; Luo & Wang, 2024). These microglia are also involved in other critical processes, like guiding neural connections (called axonal pathfinding) and insulating brain pathways (known as myelination), both of which may be affected in ASD (Luo & Wang, 2024; Santos & Fields, 2021). Studies also show that these disruptions could influence white matter density, which affects communication between different brain areas, especially in pathways like the corpus callosum and longitudinal fasciculus (Andrews et al., 2021; Rane, 2015; Tung et al., 2021). These neural pathways have even been seen to be smaller in autistic individuals.
Additionally, Just et al. (2012) suggests that autistic brains not only have reduced long-range connections but also exhibit heightened local connectivity, particularly in sensory-processing areas. This implies that certain brain regions may be hyperconnected, which could account for sensory hypersensitivity in individuals with ASD.
Did you know? Synaptic pruning plays a key role in how our brains develop. It might sound strange, but this process involves the brain breaking down some of its neural connections to make itself more efficient. To understand this, think of synaptic pruning like cleaning up a messy room. When there are too many items cluttering the space, it becomes hard to move around and find what you need. By getting rid of the unnecessary stuff, you create more room and make it easier to use the space effectively. Similarly, when the brain prunes away less-used connections, it strengthens the important ones, helping it function better. The brain is so smart that it actually cleans itself up! In the case of ASD, research suggests that this pruning process may not happen quite as it does in non-autistic individuals, leading to some connections remaining stronger or weaker than they are typically.
Why are the findings so inconsistent?
The research findings we've discussed are interesting and worth paying attention to. However, it's important to keep an open mind and think critically about them. There are some reasons to believe these findings might not apply to everyone or every situation. Other studies have shown inconsistent results, which underscores the complexity of this topic (Picci et al., 2016).
So, why is this the case? Here are a few potential reasons for these inconsistencies (Picci et al., 2016; Vasa et al., 2016):
Movement: Most of the research to date uses functional Magnetic Resonance Imaging (fMRI), a technique commonly used to map brain connections. However, one downside of fMRI is that it can be easily affected by head movement (Maknojia et al., 2019). Even the slightest movement can distort the data, leading to misinterpretation of brain connections. Given that motor-related challenges can be present in autistic individuals (Zampella et al., 2021), even with efforts to remain still, some studies may obtain inaccurate results due to movement during imaging.
Differences in Methodology: There are various ways to measure brain connections, such as fMRI, Electroencephalography (EEG), and Magnetoencephalography (MEG). While it’s great that modern medicine offers so many different methods, it can make comparisons between studies challenging. For instance, fMRI measures blood flow in the brain but can’t distinguish between different types of neural activity. In contrast, EEG and MEG can measure electrical activity and magnetic fields in the brain (Khan et al., 2016). Therefore, when comparing studies, it’s essential to consider how the data was collected, as they may be fundamentally different.
The third reason will be explained in the final part of our blog post and is likely the most significant factor!
Our Current Understanding and Steps Forward
The third and final reason to consider is something I asked you to remember earlier: ASD is highly diverse. Each person with ASD has their own unique mix of behaviours, feelings, and physical characteristics, and the severity of these traits can vary widely. This makes it hard for researchers to agree on a single explanation for the differences in brain connections seen in autistic individuals (Lenroot & Yeung, 2013).
It wouldn’t be right for neuroscience researchers to assume that all autistic people have the same brain connectivity patterns. Such a belief overlooks the rich variety within the autism spectrum and risks oversimplifying the condition. This could lead to support methods that aren’t effective for everyone. Remember, the DSM-5-TR, which is the latest tool used by psychologists to diagnose ASD, divides the spectrum into three levels, with varying presentations of cognitive and language impairments. If this tool acknowledges that each person's experience is different, how can we expect to come up with just one explanation for how the brains of autistic individuals are connected?
This leads to a situation where researchers keep producing studies with different and sometimes conflicting results. Some scientists suggest that we should not think of ASD as a simple label. Instead, we should view autism as a diverse range of presentations and approach ASD neuroscience research with an open and exploratory mindset to discover individualized patterns of neural connectivity (Tang et al., 2020).
Think of it like this: Just as a recipe needs a mix of ingredients to create a dish, we cannot understand ASD by looking at each ingredient on its own. We need to see it as a unique combination of different elements that come together to form the whole recipe. This means more research is needed to understand the complexities of ASD and identify the various “ingredients” that shape each individual’s unique experience and brain makeup.
Conclusion
You might feel like this conclusion doesn’t really wrap things up neatly, and that’s okay. The key takeaway is this: Even though the research on differences in brain connections of individuals with Autism Spectrum Disorder can seem inconsistent, that doesn’t mean it’s not important. Instead, it shows just how complex ASD is and why we need to take a broader view. The variable and unique ways ASD can present itself suggests that various brain connectivity patterns could lead to different behaviours and experiences for each person. Rather than seeing these inconsistencies as failures, we should view them as chances for deeper exploration and understanding. While researchers may not yet agree on the exact ways brain connectivity differs in ASD, they do agree that these differences exist. The clear answer to this question may be hard to find, but an important step forward is to approach ASD neuroscience research with an open mind. By embracing this complexity, we can gain better insights into the unique experiences of autistic individuals and work towards more effective support and interventions.
If you would like to inquire about an ASD assessment for you or your child, please feel free to reach out to Onyx Assessments at (587) 415-0482 or info@onyxassessments for more information!
References
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