Neural noise in Autism Spectrum Conditions (ASC)

Increased neural noise is proposed to be a potential endophenotype of Autism Spectrum Conditions (ASC), capturing disrupted neural synchrony dynamics inherent to the condition. Nevertheless, the neural noise hypothesis of ASC has not been previously examined systematically. Using Electroencephalography (EEG), the present thesis investigates neural noise by measuring the degree of phase angle alignment of neural oscillations between experimental trials through the Inter-trial Phase Coherence (ITPC) metric and the steepness of 1/f noise slope of Power Spectral Density (PSD), a variable quantifying broadband changes in power spectra as a function of temporal frequency in a visual task-based and a resting state condition. The present thesis comprises of four studies: a) an investigation of neural noise in clinical samples of adults with ASC and ADHD b) the presentation of a new accessible method of studying brain activity of autistic individuals at home, using mobile EEG technology, c) a study of neural noise in a large sample of children with ASC (n=67) and d) an investigation of the relationship between neural noise and behavioural symptoms associated with the ASC phenotype. In the present thesis it was established that increased neural variability in the form of low ITPC occurs only in a group of children with ASC. Although levels of ITPC differed significantly between children with and without ASC at a group level, low ITPC could not differentiate participants with ASC from participants without ASC with adequately high accuracy to be considered a biomarker of ASC, as proposed in the literature (David et al., 2016). In addition, it was demonstrated that ITPC, as measured in response to visual stimulation, is not linked to primary phenotypic expressions of ASC but is associated with anomalous visual experiences and visual distortions, a group of visuoperceptual symptoms shown to manifest with varying prevalence in individuals with ASC and other people in the general population. Finally, it was established that 1/f noise power spectral dynamics, measured during processing of simple visual stimuli and during rest, were intact in the ASC and ADHD samples tested, providing evidence against the pathological undercoupling hypothesis proposed by Voytek & Knight (2015).