Imaging study ties brain connection to sociability

Scientists have linked a person’s social ability with the strength of a specific connection between two areas deep within the brain.

The study, published in the August issue of the American Journal of Psychiatry¹, is noteworthy as one of the first to investigate the brain circuits gone awry in autism by focusing on the range of autism-related traits within the general population.

The work was based on brain scans of adults who do not have autism, but whose social skills span the normal range — such as comfortably interacting with others, showing appropriate facial expressions, or recognizing when a scenario is unfair — as judged by their spouse or someone else who knows them well.

The researchers found that compared with participants who are good at reading and responding to social cues, those who are somewhat aloof have a weaker connection between the pregenual anterior cingulate cortex (ACC) — a region that’s active when thinking about the beliefs of others — and a part of the anterior insula, a region involved in understanding the emotions of others.

These results are intriguing because the brains of those with autism also exhibit patterns of underconnectivity², say the researchers.

“Now we have a new candidate connection to explore for autism,” says Adriana Di Martino, associate research scientist at the New York University Child Study Center.

The correlation between brain connectivity and social skills came to light through the use of the Social Responsiveness Scale (SRS), a questionnaire that, when tallied, results in a single number to describe social abilities, rather than simply labeling people with a categorically defined social disorder, such as autism or Asperger’s syndrome.

Child psychiatrist John Constantino developed the SRS with the idea that even people without autism can exhibit autism-related behaviors — such as being awkward in turn-taking interactions, or having a tendency to focus on parts of things rather than the whole picture — but to a milder degree than someone diagnosed with the disorder.

Since its commercial release in 2005, the SRS has been used in genetic studies of autism, but the new report is one of the first to apply it to brain scans.

“I’m definitely not surprised to see a neural correlate of the SRS,” says Constantino, professor of psychiatry and pediatrics at Washington University in St. Louis. “We know that what the SRS measures is an inherited trait. So the issue of what is the neural structure of that inherited trait is obviously of intense interest.”

Firing together:

The study used ‘resting- state’ functional magnetic resonance imaging (fMRI), a technique in which participants’ brains are scanned while they are resting in the MRI machine, not engaged in any particular task.

Resting- state fMRI takes advantage of the fact that, even at rest, the brain hums with electrical activity. Over the past decade, scientists have realized that the patterns of this spontaneous activity can reveal how the brain is organized³.

“The signal at rest is not noise, and it is not random, but actually in fact it represents functionally organized networks,” Di Martino says.

When two brain regions activate simultaneously, this suggests they are connected. Di Martino and colleagues looked for brain regions that co-activated with the pregenual ACC because it consistently turns on during a wide range of social tasks⁴, and because it is under-activated in autism⁵.

After scanning 25 healthy adults, the team discovered that the pregenual ACC lights up at the same time as some parts of the insula, a region that is often overlooked because it is tucked in between folds of the brain, says Di Martino. The front part of the insula strongly co-activates with the pregenual ACC in all study participants, indicating a robust connection between the two; on the back end of the insula, however, there is no sign of such a connection.

In between, activity fluctuates: For some participants, this middle region shows strong connectivity with the pregenual ACC, whereas others have weak connectivity.

The SRS helped the scientists decipher this variability. Activation in this middle region — which is implicated in showing empathy — varies according to each person’s SRS score. The more socially adept, the stronger the connection, and the more socially awkward, the weaker . The continuous correlation between connectivity and SRS scores would never have been revealed by simply categorizing people into two groups and comparing them.

“The SRS is potentially a more sensitive tool, and this study is a good demonstration of its usefulness,” says Daniel Kennedy, a post doctoral scholar in neuroscience at the California Institute of Technology, who wrote a commentary about the new study⁶.

Di Martino is now exploring whether this ‘cingulo-insular’ neural connection is further degraded in people with autism, who score poorly on the SRS.

The social deficits of autism could also stem from abnormalities in other brain regions. These possibilities are not mutually exclusive, she says. “To develop autism, you might need two hits, meaning you might need to have the abnormal cingulo-insular connectivity pattern plus something else.”

Because the resting-state paradigm only requires a person to lie quietly for about six minutes, Di Martino’s study can include a wide range of people with autism who vary in social and cognitive abilities. Typical fMRI studies require a person to do a task, which often limits researchers to high-functioning people with autism.

But the success of the resting-state approach in delineating patterns of connectivity doesn’t mean that it’s time to throw out the traditional task-based approach.

“A lot of our interpretations of what these resting fluctuations mean come from task-based studies,” says Rasmus Birn, assistant professor of psychiatry at the University of Wisconsin –Madison, who has looked in depth at what causes changes in functional connectivity, including those found in people with autism⁷. “It’s still valid to look at both approaches.”

References: