Narjes Soltani Dehaghani - Institute for Cognitive and Brain Sciences, Shahid Beheshti University, Tehran, Iran.
Burkhard Maess - Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany
Reza Khosrowabadi - Institute for Cognitive and Brain Sciences, Shahid Beheshti University, Tehran, Iran.
Mojtaba Zarei - Institute for Medical Sciences and Technology, Shahid Beheshti University, Tehran, Iran.

Pre-stimulus oscillation could affect post-stimulus activities during face processing 1. It is unclear if this interaction is intact in individuals with autism who often have difficulty in this function 2. Here we study the impact of pre-stimulus oscillations on post-stimulus evoked activities associated with face and non-face stimuli in two participants with autism.Method Responses to face and non-face stimuli in two autistic participants were recorded using MEG system. In each trial, two sequentially presented stimuli from the same category (face or motorbike) were displayed and participants had to identify pairs of identical images. We calculated pre-stimulus alpha power in stimuli selective regions including occipital face area (OFA), fusiform face area (FFA), superior temporal sulcus (STS) and lateral occipital complex (LOC) per trial and made a median split of trials based on the achieved values per stimulus type. Between trial cluster-based permutation 3 were calculated to compare group of trials with low pre-stimulus alpha vs. the group of trials with high pre-stimulus alpha in each participant. This was done in the stimuli selective regions along with intra-parietal sulcus (IPS) and frontal eye field (FEF) in the post-stimulus interval. Results Pre-stimulus alpha power in LOC yielded a significant difference between the two groups in FFA and OFA for faces in one participant. This effect was observed from 198ms to 239ms after stimulus onset (p=0.037). Figure 1 shows the event-related activities of the two groups in FFA, averaged over the trials in each group. Evoked power is shown in the inset. There was no significant effect for motorbikes in this subject and no significant effect was found for the other participant.Conclusions Our results suggest that pre-stimulus modulation of post stimulus processing is present in autism. This is likely to be an inhibitory mechanism, in the sense that higher activation of stimulus unspecific regions during pre-stimulus intervals leads to larger post-stimulus activity in stimulus selective regions.