by Sarah Hansen
Difficulties with social interaction, communication, and motor control are hallmarks of autism. It’s also true that many individuals on the autism spectrum demonstrate average or above-average intelligence, and the intelligence of others can be masked by difficulties initiating speech and movement. This is why at Hussman, we always “presume competence” in individuals with autism. Just because they sometimes struggle to turn their thoughts into spoken words, doesn’t mean they have nothing to say.
Scientists are working hard to understand the autistic brain in order to discover the neurological basis behind these differences in behavior, communication, and social interaction.
“In recent years, we’ve seen converging lines of evidence from genetic, anatomical, and neuroimaging studies that the differences we see in autism may be driven by differences in how the brain forms circuits, particularly those that orchestrate long-range connections,” says John P. Hussman, executive director of the Hussman Institute for Autism.
For example, in a 2004 study, a team led by Marcel Just from Carnegie Mellon University (Pittsburgh, PA) and the University of Pittsburgh School of Medicine revealed one possible mechanism for the differences in communication and comprehension among people with autism—the “underconnectivity theory”—and subsequent papers have provided further evidence.
First, Just’s team found higher activity in a brain region that is responsible for understanding individual words (“Wernicke’s area”) in individuals with autism, but lower activity in a region responsible for more complex sentence comprehension (“Broca’s area”) during a sentence-comprehension task. The participants on the autism spectrum also had less activity in brain areas involved in visualization, suggesting their neurotypical peers might be visualizing the sentences to aid comprehension to a greater extent. This difference might help to explain why directly providing visual supports to people with autism can often assist their comprehension.
The researchers also found less “functional connectivity” between pairs of brain regions involved in the comprehension task in the participants with autism. Of 186 paired brain regions, 10 had statistically significant lower synchronization of activity in individuals with autism. Thirteen additional pairs were nearly statistically significant, and 79 percent of all paired brain regions showed a trend of lower synchronization in people on the spectrum. Synchronization of activity between brain regions indicates communication between those regions, so this result suggests that brain regions in individuals with autism may do less communicating with each other than in neurotypical brains.
The team used functional magnetic resonance imaging (fMRI) to collect the data. fMRI generates images representing brain activity by detecting magnetic changes caused by blood flow. When neurons are active, more oxygen-rich blood flows to that area of the brain.
In 2009, Marjorie Solomon and colleagues investigated brain connectivity in adolescents. Their results indicated a reduction in connectivity between the frontal and parietal lobes of the brain in individuals with autism. These participants also demonstrated less integration than neurotypical individuals across several areas of the brain during a task that required them to press a button on their right after just seeing an arrow that pointed left. This provides a neural basis for the reduction in “cognitive control” seen in autism.
In a 2011 review, Sam Wass discussed studies providing a variety of forms of evidence that suggest long-distance under-connectivity in autism, and the somewhat weaker—but growing—body of evidence for short-range over-connectivity. This paper corroborates Just and colleagues’ 2004 results that individual brain areas are capable of average or above-average function, but tasks that require integration across areas can be difficult for people with autism.
Individual brain areas are capable of average or above-average function, but tasks that require integration across areas can be difficult for people with autism.
In another review, Stewart Mostofsky and Joshua Ewen (2011) emphasized the connection between motor challenges and social challenges in autism because of the reliance of these activities on functional connectivity among brain regions. Mostofsky and Ewen bring together studies of both behavior and neuroanatomy, helping to support the connection between brain underconnectivity and challenges in motor and social abilities.
Recent large-scale genomic research by John P. Hussman and colleagues at the University of Miami further strengthens the link between autism and brain connectivity at a genetic level. The researchers found that a significant proportion of genes associated with autism were involved in pathways that regulate the growth and guidance of neurites, the extensions from neurons that connect them to other neurons in order to form circuits in the brain (see ‘Recent genetic analyses help focus future autism research on neuronal connectivity pathways’).
Taken together, these publications contribute to an explanation for the combination of strengths and difficulties seen in individuals with autism. While tasks that require integration of information from several brain areas can pose a challenge, tasks that rely primarily on one brain area are often completed by individuals on the spectrum just as easily as by their neurotypical peers.
Because social interactions are such complex events, requiring many brain areas, it makes sense that this is where individuals with autism struggle. Tasks like recalling the meanings of individual words or doing mental math, however, require fewer brain areas and, not coincidentally, are tasks at which individuals on the spectrum often excel.
Differences in connectivity may also contribute to movement differences seen in autism. “Generally speaking, our skilled movements are ‘stored’ in the parietal area at the rear of the brain, but our choices are directed by the frontal area. Reduced long-range connectivity could help to explain the difficulties in ‘praxis’—the smooth execution of speech and movement sequences—that are so prevalent in autism,” Hussman said.
Understanding these cognitive differences between neurotypicals and those on the autism spectrum should make it even easier to “presume competence” and help people on the spectrum find appropriate, fulfilling roles in their communities. Learning more about the way our different brains work can help us all interact in ways that bring out each other’s cognitive strengths and support each other’s weaknesses, no matter where we are on the neurodiversity continuum.
The original articles are published here:
Just MA, Cherkassky VL, Keller TA, & Minshew NJ. 2004. Cortical activation and synchronization during sentence comprehension in high-functioning autism: evidence of underconnectivity. Brain. 127:1811-1821.
Wass S. 2011. Distortions and disconnections: Disrupted brain connectivity in autism. Brain and Cognition. 75:18-28.
Solomon M, Ozonoff SJ, Ursu S, Ravizza S, Cummings N, Ly S, & Carter CS. 2009. The neural substrates of cognitive control deficits in autism spectrum disorders. Neuropsychologia. 47:2515-2526.
Mostofsky SH & Ewen JB. 2011. Altered connectivity and action model formation in autism is autism. The Neuroscientist. 17(4):437-448.
Griswold AJ, Dueker ND, Van Booven D, Rantus JA, Jaworski JM, Slifer SH, Schmidt MA, Hulme W, Konidari I, Whitehead PL, Cuccaro ML, Martin ER, Haines JL, Gilbert JR, Hussman JP, Pericak-Vance MA. 2015. Targeted massively parallel sequencing of autism spectrum disorder-associated genes in a case control cohort reveals rare loss-of-function risk variants. Molecular Autism, 6:43. DOI: 10.1186/s13229-015-0034-z