Gaze Perception, Superior Temporal Sulcus and Autism: An rTMS Study

Background: The superior temporal sulcus (STS) is known to be implicated in social perception and social cognition processes, mainly the process of eye gaze information. Previous brain imaging studies have suggested that abnormalities within the STS would be related to social impairments in autism. In a recent study with healthy volunteers, we have shown that it is possible to change gaze pattern by transitory inhibition of the neural activity of the STS using repetitive transcranial magnetic stimulation (rTMS). Indeed, inhibition of the right STS reduced fixations to the eyes of characters during visualization of social movies, as measured with eye-tracking (Saitovitch et al. 2016).

Objectives: In this study in adults with ASD, we investigated changes using eye-tracking changes in gaze perception induced by rTMS stimulation of the right STS.

Methods: Seventeen adults with ASD (mean age = 22.4 ± 2.3) participated in the study. ASD diagnosis was based on DSM IV-R and ADI-R criteria. All subjects underwent a structural MRI for a precise localization of the stimulation target for each individual. Subjects underwent both sham stimulation and excitatory rTMS delivered over the right posterior STS (mean Talairach coordinates: 50 -53 15). The rTMS stimulation was delivered following protocol described by Huang et al., 2005. Stimulation was delivered in 2sec trains every 10sec, a total of 190sec (600 pulses), with an intensity of 90% of the active motor threshold. Fixations to the eyes were measured with a Tobii-120 eye-tracker during passive visualization of social movies at baseline, at 3 time-points (1min, 6min and 12min) after sham and at 3 time-points after TMS (1min, 6min and 12min). Eye-tracking data was processed with Tobii-Studio® software. Individual analysis was performed a posteriori in order to detect individual patterns of response, with a threshold of 12% increase or decrease.

Results: At the group level, no significant results were found in fixations to the eyes after stimulation of the STS. Qualitative analysis of data indicates strong heterogeneity in the response. Therefore, individual analysis of data has allowed to identify three different groups within participants: 3 subjects respond to the stimulation by increasing fixations to the eyes (>12%); 8 participants respond to the stimulation by reducing fixations to the eyes (>12%); 6 participants presented no changes in gaze pattern.

Conclusions: This study shows the feasibility of a TMS protocol in participants with ASD. Preliminary results show that, in line with the heterogeneity of autism itself, response to the TMS varies among individuals. Such heterogeneity could be linked to differences in the lasting effects of the TMS in ASD, as described in previous research (Oberman et al, 2012). A further study will address this issue in the perspective to use TMS as new therapeutic strategy in autism.