Exploring the neuronal basis for why people with autism have impaired social attention

Lay Summary

Exploring the neuronal basis for why people with autism have impaired social attention

One of the most striking alterations in people with autism spectrum disorder (ASD) is their atypical pattern of social attention.  As early as infancy, and confirmed somewhere between ages two to five, children with ASD evidence characteristic social and communicative behaviors. They pay less attention to faces and other social stimuli (such as human voices and hand gestures) while tending instead to fixate on objects such as gadgets, devices, vehicles, electronics.   Scientists do not yet know the neuronal basis for these atypical social attention preferences, but research suggests that the brain’s amygdala may be involved.

The amygdala is thought to play a major role in what people determine is salient—what they notice and pay attention to—as reflected in their eye movements, learning, and behavior. Studies using fMRI in people with ASD have shown that abnormal signaling in the amygdala is correlated with abnormalities in the way they attend to faces. This correlation might be due to problems with the neurons in the amygdala or with the neurons’ connections to the visual or prefrontal cortex. The investigators plan to determine which is the case, using electrodes placed on the brain to record the signaling of individual neurons, based on their prior animal model studies.

This electrical recording, in combination with fMRI, is possible to do because ASD occurs in about 20 percent of people with epilepsy, some of whom require surgery to treat their seizures. These patients have depth electrodes placed in their brains prior to surgery to determine which brain tissues are vital and must not be surgically removed to control their seizures. The electrodes record signaling from individual neurons. The investigators anticipate that about eight out of 40 of their epilepsy patients needing surgical treatment also will have ASD and will participate in the study.

In these eight people, the investigators will probe the neuronal basis for their atypical visual attention patterns. Electrical recordings will investigate the neuronal basis for two behavioral deficits in autism: a bottom-up and a top-down attentional deficit, both of which differ from findings in healthy volunteers. The bottom-up deficit: when viewing natural scenes, people with ASD compared to healthy volunteers tend to focus on the image’s center regardless of what objects are in the periphery. They also pay less attention to faces and locations.  The top-down deficit: contrary to the way healthy volunteers show an efficient search strategy to locate a target object or face, the search strategies by people with ASD are far less efficient, especially when searching for faces.

The electrophysiological recordings are expected to provide a key missing ingredient from fMRI data. They will help to discern signaling patterns in attentional deficits that are bottom-up (involving the visual cortex) and top-down (involving the prefrontal cortex). Since amygdala neurons connect to both the prefrontal and visual cortices, the findings will test a key function of the amygdala in representing saliency in the brain in ASD.

Significance: This initial information on the specific brain processes that may be abnormal in autism would then need to be confirmed in larger-scale studies, and ultimately may lead to new interventions, such as deep brain stimulation, to prevent or treat ASD.