An exploration of SSVEPs across development and autism spectrum conditions

This thesis contains an experimental investigation of networks dynamics across development and autism spectrum disorders (ASD). The interplay between functional segregation and integration within functional cortical networks was investigated based on the hypothesis that it plays a key role in development and ASD. Functional segregation refers to the synchronization between adjacent brain areas and functional integration indicates the synchronization between distributed brain regions. Steady-state visual evoked potentials (SSVEPs) to high contrast (90%) luminance and isoluminant chromatic (red-green) vertical gratings with two spatial frequencies (2.8 and 6 cpd) at 7.5 Hz (luminance) and 3.3 Hz (chromatic) were recorded in individuals with and without ASD. SSVEPs were analysed in the frequency and time domains to carrying out a detailed analysis of the dynamic functional connectivity elicited by perception of simple and complex visual stimuli.
The first research study explored aged-related changes in networks dynamics. Participants were 30 children aged 7 to 17 and 11 adults from the typical population. Our results suggest functional reorganization from local to distributed networks across development, and that networks underpinning medium spatial frequency change would be a useful biomarker of typical brain function. The second research study explored potential changes in networks dynamics between children with and without ASD. Participants were 20 children aged 7 to 17 (10 with ASD and 10 age-matched typically developing). The result of this study is a potential EEG biomarker to characterize atypical brain function in autism. Our results suggest a direct relationship between functional segregation and functional integration during visual perception; atypical functional connectivity in lower processing mechanisms might contribute to the disruption in long-range functional integration reported in ASD, because both abnormalities occur in concert in the autistic brain.
Overall this exploratory research shows that SSVEPs can elicit different functional networks involving local and distributed cortical brain systems, and can also show segregated and overlapping functional networks underlying neural mechanisms at early stages of visual processing during development and ASD. Therefore, SSVEPs would be a potentially useful technique to identify differences in the brains of people with and without autism.