Social difficulties in autism are hypothesized to result, in part, from impaired face processing and social context integration. Similar functional impairments are also apparent in amygdala lesion patients. Converging evidence thus suggests that the amygdala plays an important role in processing the socially relevant information that might be disrupted in autism. How the amygdala neurons respond to faces, or other social stimuli, and how these responses might differ in people with autism, is poorly understood.
Having a rare opportunity to obtain intracranial recordings from patients with intractable epilepsy, we have designed an extensive battery of behavioral paradigms to address several questions related to the role of the amygdala in processing social stimuli, precisely aimed at identifying putative disparities in the activity elicited by social stimuli in autism. Given the high co-morbidity of autism and epilepsy, up to 20% of our patients are diagnosed with autism, offering a unique opportunity to record single unit activity in the amygdala of patients with autism.
We record single neuron activity while the participants are viewing images from four relevant categories, selected based on results from studies on restricted interests in autism: a high-autism interest category (clocks, trains, cars); a low-autism interest category (furniture, clothes); a social category (people); and a specific interest category (reported by the participant). We compare activity in the amygdala neurons in response to social versus non-social stimuli, as well as in response to stimuli of interest to the participant versus non-interesting ones.
To investigate the sensitivity of amygdala neurons to emotional faces and parts of faces we are presenting partially masked emotional faces in an emotion discrimination task. This approach is optimal for an unbiased sampling of the face in an emotion judgment, and we are simultaneously acquiring eye-tracking data to confirm the areas in the face that are fixated by the eyes.
In addition, we investigate putative amygdala activity modulation in response to the direction of gaze in photographs of faces, in computer-generated faces, and in a real person.
We assess the role of the amygdala in social context integration by presenting bi-stable emotional faces in an emotion discrimination task in which we manipulate the perceived social context of each image with a short preceding text.
Preliminary results show that there are strong and reliable responses in the amygdala to a variety of emotional stimuli, including faces, parts of faces, and emotional scenes. We are in the process of obtaining a fuller inventory in a larger sample of participants. So far, we have indications that responses to parts of faces differ significantly among patients who have a diagnosis of autism, versus those who do not. Eye-tracking studies confirm that these differences cannot be attributed to differential eye movements, but instead are likely to arise from central processing of the stimuli.
There are single neurons in the amygdala responding to a variety of social stimuli, suggesting that this brain region plays a pivotal role in extracting emotion information from faces, possibly differently in autism.
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