The Effect of Transcranial Direct-Current Stimulation of Right Anterior Superior Temporal Sulcus in Adults Related to Autism Traits

The direction of the eye gaze provides important information about the focus of attention of other persons, their mental states, private thoughts, goals and desire. It is a fundamental mechanism involved in social communication and social interaction, and it is modulated by a lot of factors, such as expectation, head direction or emotional face expressions. In contrast with most animals for which the direct gaze is perceived as a threat, for humans the mutual gaze is often considered as positive attitude. As a matter of fact, a lot of studies have focused on the usefulness of eye gaze and its mechanisms. Infants of 2 days show a preference for direct gaze, preferring to look at face with a direct gaze compared to face with averted gaze, confirming the relevance of eye gaze perception in humans.
The brain area which is more related to the perceptual coding of another’s gaze is the anterior superior temporal sulcus (aSTS). Numerous studies in macaques and humans identified an involvement of aSTS in gaze processing, in particular in coding specific gaze directions, across different cues, such as head orientation. For example, functional imaging studies has shown that superior temporal sulcus is activated during the perception of changeable features of faces, such as the angles at which the eyes are oriented, and during the view of both still pictures and moving images. One of the most common disorder which involved a deficit in eye – gaze processing is the Autism Spectrum Disorder (ASD). This is a neurodevelopmental disorder which affect a broad range of abilities and behaviors. In particular the social and relational sphere is primary affected. Autistic people have difficult to recognize others’ emotions and feeling, which limited their ability to communicate with people. This relational problem can be due in part to the abnormal eye – gaze processing which is present in autistic people. In fact numerous studies have highlighted that autistic people tend to avoid the eyes of a person in front of them and look more frequently the lower part of the face. This caused a limited ability to use the eyes and the eye – gaze as a source of information, necessary to communicate and establish social interactions.