A shift to randomness of brain oscillations in people with autism.
BACKGROUND
Resting-state functional magnetic resonance imaging (fMRI) enables investigation of the intrinsic functional organization of the brain. Fractal parameters such as the Hurst exponent, H, describe the complexity of endogenous low-frequency fMRI time series on a continuum from random (H = .5) to ordered (H = 1). Shifts in fractal scaling of physiological time series have been associated with neurological and cardiac conditions.


METHODS
Resting-state fMRI time series were recorded in 30 male adults with an autism spectrum condition (ASC) and 33 age- and IQ-matched male volunteers. The Hurst exponent was estimated in the wavelet domain and between-group differences were investigated at global and voxel level and in regions known to be involved in autism.


RESULTS
Complex fractal scaling of fMRI time series was found in both groups but globally there was a significant shift to randomness in the ASC (mean H = .758, SD = .045) compared with neurotypical volunteers (mean H = .788, SD = .047). Between-group differences in H, which was always reduced in the ASC group, were seen in most regions previously reported to be involved in autism, including cortical midline structures, medial temporal structures, lateral temporal and parietal structures, insula, amygdala, basal ganglia, thalamus, and inferior frontal gyrus. Severity of autistic symptoms was negatively correlated with H in retrosplenial and right anterior insular cortex.


CONCLUSIONS
Autism is associated with a small but significant shift to randomness of endogenous brain oscillations. Complexity measures may provide physiological indicators for autism as they have done for other medical conditions.
Lai
Meng-Chuan
MC
Autism Research Centre, Department of Psychiatry, University of Cambridge, United Kingdom. mcl45@cam.ac.uk
Lombardo
Michael V
MV
Chakrabarti
Bhismadev
B
Sadek
Susan A
SA
Pasco
Greg
G
Wheelwright
Sally J
SJ
Bullmore
Edward T
ET
Baron-Cohen
Simon
S
Suckling
John
J
D000328:Adult; D001321:Autistic Disorder / Q000503:physiopathology*; D001921:Brain / Q000503:physiopathology*; D058256:Brain Waves / Q000502:physiology*; D017709:Fractals; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D017711:Nonlinear Dynamics