Social skills – the ability to hold a conversation, interpret an expression or decode body language – spring from activity within various, scattered hubs in the brain. But autism researchers are taking aim at certain hot spots to learn how people acquire, or fail to acquire, this important set of abilities.
They have found that many of these skills involve a long groove on the brain’s bumpy surface that runs along each side of the head, over the ears. The groove is called the superior temporal sulcus (STS) and is the home of numerous differences in function between people with autism and typically developing individuals.
The STS is attuned to socially meaningful stimuli, such as a person’s tone of voice, facial expression or body movements. By capturing such information, it plays a role in perceiving another person’s thoughts and feelings and predicting their actions. It is also involved in processing language. Autism typically affects all of these abilities.
…Researchers are exploring how the STS could help them gauge the response to autism treatments.
“I think as we gain a better understanding of the STS, we could possibly use its pattern of activation as some kind of indication of treatment effectiveness,” says Elizabeth Redcay, director of the Developmental Social Cognitive Neuroscience Lab at the University of Maryland, College Park.
Increasing activity in the area, scientists say, might even enhance the efficacy of some behavioral interventions.
A river runs through it:
Scientists have traced the anatomy of the STS from just inside the temple to behind the ear and then up slightly, toward the crown of the head. The STS collects streams of information from neurons on its banks the way a river collects tributaries.
Much of what is known about this river of data comes from functional magnetic resonance imaging (fMRI) studies that track which parts of the brain light up in response to images, sounds or other stimuli. In people with autism, the STS doesn’t respond as strongly or preferentially to social stimuli as it does in controls. For example, the groove’s upper bank is typically more sensitive to voices than to other kinds of sounds. But this preference is missing in people with autism1.
“Across a number of different kinds of social tasks, there is this reduced specialisation,” Redcay says.
In one study, which remains particularly influential after more than a decade, researchers showed participants a video of a character who looks either toward or away from a flickering checkerboard that appears briefly in a corner of the screen. Controls show more and longer-lasting activity in the STS when the character looks away from the checkerboard, as if their brains are puzzling out the unexpected response. But those with autism show equal STS activity regardless of the character’s gaze2.
…According to one study, the STS in people with autism shows diminished activity during joint attention compared with controls, and enhanced activity during solo pursuits4.
Tangled bank:
Studies of brain connectivity also support the notion that the STS is under-specialized in people with autism. The most socially responsive parts of the STS cluster at the back of the groove, around its upward bend. This area is known as the posterior superior temporal sulcus, or pSTS. Researchers have found that the pSTS in people with autism shows enhanced ‘intrinsic functional connectivity,’ a measure of which regions of the brain activate in sync when a person is not engaged in any particular task5.
…studies have also uncovered associations between STS abnormalities and the severity of social deficits in individuals with autism.
But it is unclear what the alterations in STS function seen in people with autism mean. “We don’t really know if they’re a cause or a consequence of having autism,” Redcay says.
Most researchers suspect the latter. But to prove it, they need a better understanding of the normal organization and function of the STS, how it develops during childhood, and how that development differs in people with autism.
One area of controversy concerns whether the STS consists of a fine-grained series of functionally specialized areas, or is more integrated along its length. Some research has identified what appear to be small, specialized patches of cortex in the STS region.
…But other studies finger less sharply defined regions in the STS. Unpublished data from Redcay’s lab show that an area involved with language processing overlaps with one attuned to gestures.
Even more puzzling, some research supports both hypotheses. A study published last year shows that different functions, such as face or biological motion processing, occur in the same order along the STS and in roughly the same spot in different people.
…Another piece of the picture is how STS activity changes and develops as a child grows. Mueller and his colleagues found that the functional connections involving three locations along the STS become increasingly specific with age. But this specialisation doesn’t occur to the same degree in children with autism.
There are also a few oblique hints about how STS development may play into autism. Infant siblings of children with autism, or ‘baby sibs’, show weak STS function. But after about age 4, weak STS activity separates children with autism from both unaffected siblings and controls with no family history of the condition…
Researchers say boosting STS activity could increase the effectiveness of behavioral interventions for autism by priming a child to pay attention to social information. Both transcranial magnetic stimulation and neurofeedback training – in which people learn to control their brain waves through feedback – could target the STS…