Background: One of the great challenges in psychiatry is finding reliable biomarkers that may allow for more accurate diagnosis and treatment of patients. In this context the topic of neural variability received scientific attention in recent years. Altered neural variability was found in different cohorts of patients with autism spectrum disorder (ASD) using both functional magnetic resonance imaging (fMRI) and electroencephalography (EEG). These findings lead to the neural noise hypothesis of ASD. The number of studies focusing on neural variability is, however, yet small and the reported effects are controversial and poorly understood.
Methods: In the present study we compared different temporal and structural aspects of variability in visually evoked EEG activity in a cohort of 16 adult participants with Asperger Syndrome (AS) and 19 matched neurotypical (NT) controls. Participants performed a visual oddball task using fine and coarse checkerboard stimuli.
Results: We investigated various measures of neural variability and found effects on multiple time scales. (1) As opposed to some of the previous studies, we found reduced inter-trial variability in the AS group compared to NT. (2) This effect builds up over the entire course of a 5-minute experiment and (3) seems to be based on smaller variability of neural background activity in patients compared to NTs.
Limitations: The present study is exploratory in nature with a hypothesis generating character. Further studies with a new and larger set of participants are thus mandatory to verify or falsify our findings.
Conclusion: The here reported variability effects come with considerably large effect sizes, making them promising candidates for potentially reliable biomarkers in psychiatric diagnostics. The observed pattern of universality across different time scales and stimulation conditions indicates trade like effects. The inconsistency of our findings with previous reports from the literature, on the other hand, rather points towards state-like effects, specific to the current stimulus material and/or experimental paradigm.