A study of about 400 children has found that brain activity linked to recognizing faces is less distinct in children with autism than in neurotypical children. Published in Nature Mental Health, the research used EEG recordings from across the scalp to show that face-processing responses develop differently in autism and that these differences may begin earlier than the commonly studied N170 brain signal.
Some autistic people look at faces less often, make less eye contact, or have difficulty remembering faces and interpreting facial expressions. Scientists have studied the brain activity associated with these differences for decades. In the early 2000s, for example, researchers at Yale University reported lower activity in a brain region involved in face processing among people with autism than among people without autism.
Dr. James McPartland, Harris Professor at the Children’s Research Center and director of the Center for Brain and Mental Health, uses electroencephalography (EEG) to study how autistic people process faces. EEG records electrical activity in the brain, but earlier research often examined signals from only a limited area rather than analyzing activity across the entire scalp.
Mapping face processing across the brain
To obtain a more complete picture, McPartland and his colleagues analyzed electrical signals recorded across the scalps of about 400 autistic and neurotypical children. The researchers found that activity associated with face recognition was less clearly distinguishable in the autistic participants. They also identified differences in development: in neurotypical children, responses to faces became more specialized with age, while children with autism did not show the same pattern.
“This is the first time that we have taken full advantage of the extremely rich information provided by EEG recordings to understand facial perception and autism,” McPartland said.
McPartland compares traditional studies of face recognition to trying to understand traffic across an entire city by monitoring a single downtown street.
“Most of the research on face processing to date has been successful in this way,” McPartland said.
The new method offers a broader view, more like using satellite imagery to observe traffic across a city. The researchers analyzed data collected through the Autism Biomarker Clinical Trials Consortium (ABC-CT), which included autistic and neurotypical children from various age groups.
During the experiment, participants viewed pictures of faces and everyday objects while an EEG machine recorded their brain activity. Instead of concentrating on a small number of recording sites, the researchers examined signals from all 128 electrodes placed around each participant’s scalp.
They then used machine-learning techniques to determine whether patterns in the recordings could indicate what each child was viewing.
The results showed that the brain activity of neurotypical children more clearly indicated when they were looking at faces than did the activity of children with autism. In other words, the autistic participants showed less distinct electrical signals associated with viewing faces.
“The neural activity that we measure at the scalp is less clear in children with autism,” said lead author Dr. Jason Griffin, an assistant professor of psychology at the University of Houston. Griffin previously worked as a postdoctoral researcher in McPartland’s lab.
The researchers also found that neurotypical participants became better at distinguishing what they were viewing from their brain activity as they grew older. This age-related improvement was not observed in the autistic children, suggesting that neural responses to faces develop along different trajectories.
“Face-specific processing doesn’t follow the same trajectory,” Griffin said.
Differences may emerge before the N170 signal
The study identifies not only differences in brain activity but also clues about when those differences emerge during face recognition.
Recognizing a person involves several stages of neural processing. The sequence begins when visual information enters the eye and continues as the brain interprets that information until a face is recognized.
Much previous research on autism and facial perception has focused on the N170, a measurable change in electrical activity that typically occurs about 170 milliseconds after a person looks at a face. Earlier studies found that autistic people tend to have slower N170 responses.
By examining a wider range of brain activity, the researchers found evidence that differences in face processing begin before the N170 appears. The finding suggests that autism-related differences may occur at earlier stages of visual processing than previously established.
“But if we look at face processing with a more comprehensive approach across the temporal range, we find that autism differences occur even earlier,” McPartland said.
Implications for support and diagnosis
The findings could eventually influence how researchers approach autism diagnosis and develop supportive interventions.
Historically, some clinicians tried to address difficulties with facial recognition by requiring autistic people to maintain eye contact. Subsequent research has shown that forcing eye contact is not an effective solution. A better understanding of how face processing develops in the brain may help identify approaches that are more useful and appropriate.
A continuing challenge in autism research is distinguishing neurological differences associated with autism from changes that may result from living with autism. The researchers say the patterns in this study suggest that differences in facial processing are related to underlying developmental characteristics of autism, rather than simply reflecting accumulated life experiences.
“If we see the sophistication and specialization that we would expect from non-autistic people, we see reduced developmental variation in autistic people,” McPartland explained.
Because these differences emerge during development, the findings also raise the possibility that support designed to help autistic children interpret facial emotions could be particularly beneficial when introduced early in childhood.
However, autism does not necessarily cause difficulties that require intervention. Many neurodivergent people experience little or no disability associated with autism and may not need or want additional support. Difficulty recognizing faces and interpreting facial expressions can also make some everyday social interactions more challenging.
“Imagine life when you have difficulty recognizing information in other people’s faces, from navigating around the playground to navigating a job interview,” McPartland said. “This is one of the key areas that causes difficulty for many autistic people.”
Another potential application is the development of more objective ways to assess autism. Clinicians currently diagnose autism primarily through behavioral assessment because reliable biological tests are not yet available for routine diagnosis.
Scientists are investigating several potential biomarkers—measurable biological characteristics that could improve diagnostic evaluation or help distinguish between groups within the autism spectrum.
The newly identified patterns of face-related brain activity could contribute to that effort. By examining how these neural signals vary among individuals, researchers may eventually develop additional diagnostic tools or better identify autistic people who are likely to benefit from particular forms of support, such as social skills therapy.
Further research is needed before the findings can be translated into clinical practice. The study nevertheless provides a new way to investigate how the autistic brain processes faces and how those responses change throughout childhood.
“This is the first step in introducing new biomarkers,” McPartland said.
Source: www.sciencedaily.com
