April 4, 2013 – Neuroscientists at Georgetown University Medical Center (GUMC) have discovered a brain anomaly that explains why some people diagnosed with autism cannot easily recognize faces.
The problem has been linked to impairments in social interactions considered by many to be a hallmark of the disorder.
In a study published March 15 in the journal NeuroImage: Clinical, the scientists say that, in some people with autism spectrum disorders, neurons in a brain area that processes faces are too broadly “tuned” to discriminate between facial features of different people.
They made the discovery using a form of functional magnetic resonance imaging (fMRI) to look at that part of the brain, called the fusiform face area or FFA. The FFA is about the size of a blueberry.
Too Broadly Tuned
“When your brain is processing faces, you want neurons to respond selectively so that each is picking up a different aspect of individual faces,” says senior study investigator Maximilian Riesenhuber, an associate professor of neuroscience at GUMC.
“The neurons need to be finely tuned to understand what is dissimilar from one face to another,” he explains. “What we found in our 15 adult participants with autism is that in those with more severe face perception deficits, the neurons are more broadly tuned, so that one face looks more like another, as compared with the fine tuning seen in the FFA of typical adults.”
“We found that the reduced selectivity in FFA neurons can well predict behavioral deficits in everyday facial recognition in theses participants,” the study’s lead author, Georgetown neuroscientist Xiong Jiang, says.
“If your neurons cannot tell different faces apart, it makes it more difficult to tell who is talking to you or understand the facial expressions that are conveyed, which limits social interaction,” Riesenhuber explains.
Social Dysfunction Roots?
He adds that there is huge variation in the ability of individuals diagnosed with autism to discriminate among faces, and that some autistic people have no problem with facial recognition at all.
“But for those that do have this challenge, it can have substantial ramifications – some researchers believe deficits in face processing are at the root of social dysfunction in autism,” he says.
Neuroscientists have used traditional fMRI studies in the past to probe the neural bases of behavioral differences in people with autism, but these studies have produced conflicting results, Riesenhuber says .
Hope for The ‘Face-Blind’
The team developed a novel brain imaging analysis technique, called local regional heterogeneity analysis, or Hcorr, for the study.
“Hcorr has several significant advantages,” says Jiang. “It can estimate neuronal selectivity from short scans, even while participants close their eyes, which makes the technique suitable also for individuals that cannot perform complicated tasks in the scanner.”
After the study was completed, the researchers attempted to improve facial recognition skills in an autistic participant.
They showed the participant pairs of faces that were very dissimilar at first, but became increasingly similar, and found that FFA tuning improved along with behavioral ability to tell the faces apart.
“This suggests high-level brain areas may still be somewhat plastic in adulthood,” says Riesenhuber.
The study was funded by a grant from the National Institute of Mental Health (R01MH076281), a grant from the National Science Foundation (0449743), National Institutes of Health grants (IDDRC P30HD40677 and GCRC M01-RR13297).