Spectral Power and Coherence Correlations During Flash VEP for Typical and Autistic Children

Background: Children with autism have long been recognized to have atypical sensory perception with hypersensitivity to many external stimuli. They have also been shown to have decreased functional connectivity, which has been hypothesized to underlie the predominant perceptual-cognitive style termed weak “central coherence”. We previously showed that children with autism spectrum disorders (ASD) had increased occipital spectral power compared to age-matched controls on flash-induced visual evoked potentials (VEP), which appears to be a biological measure for a hypersensitive visual system. This increase in power during activation was associated with a simultaneous decrease in inter-hemispheric synchrony (coherence). We supposed that this increased power/activation might be correlated with the decrease in inter-hemispheric coherence. Such a correlation would suggest a basic neurophysiologic tenet or rule: that power and coherence are driven by related underlying neural mechanisms, and possibly that poorly gated sensory processing undermines inter-hemispheric synchrony. Objectives: This investigation was undertaken to test the hypothesis that cortical activation as measured by spectral power in response to flash VEP would be inversely correlated with functional connectivity as measured by inter-hemispheric occipital synchrony (coherence) in both autistics and controls. Methods: Flash VEPs were previously recorded from children (ages 5 to 8 yr) with ASD (n = 6) and from age-matched controls (n = 8) using high-density EEG recording. VEP power spectra (per channel) and coherence (per pair of channels) were computed for 1s epochs (100ms pre-stimulus). Regional analysis focused on primary visual areas showed increased power and decreased coherence (p<0.05) across the frequency spectrum in ASD compared to controls, most significant in the alpha band (p<0.01). Correlation analysis (Pearson) was performed for average power (right and left hemisphere combined) and coherence in the alpha band. Results: We found an inverse correlation between power and coherence in typicals such that increased VEP alpha power predicted decreased alpha coherence (r value: -0.79, p = 0.02). The correlation coefficient for the autistics as a group was poor (r value: -0.18, p = 0.73). However, the distribution of autistics suggested three subgroups: those whom when included with typicals strengthen the correlation between power and coherence, (n=3, r value: -0.88, p = 0.0004), and those above (n = 1) and below (n = 2) the regression line. Conclusions: Our results support the hypothesis that spectral power and coherence are highly inversely correlated in the typical brain and in a substantial subset of children with ASD. Some ASD children appear to follow a different set of “neurophysiologic rules” with either better or worse than expected power : coherence relationships. This finding, if it holds up in a larger data set, may help parse autistics as 1) operating within a typical neurophysiologic model or 2) operating outside typical models. The potential future significance of these observations lies in the value of parsing individual neurophysiologic profiles for intervention and treatment trials.