RESUMO
BACKGROUND: Stimulus-related γ-band oscillations, which may be related to perceptual binding, are reduced in people with autism spectrum disorders (ASD). The purpose of this study was to examine auditory transient and steady-state γ-band findings in first-degree relatives of people with ASD to assess the potential familiality of these findings in ASD. METHODS: Magnetoencephalography (MEG) recordings in 21 parents who had a child with an autism spectrum disorder (pASD) and 20 healthy adult control subjects (HC) were obtained. Gamma-band phase locking factor (PLF), and evoked and induced power to 32, 40 and 48 Hz amplitude-modulated sounds were measured for transient and steady-state responses. Participants were also tested on a number of behavioral and cognitive assessments related to the broad autism phenotype (BAP). RESULTS: Reliable group differences were seen primarily for steady-state responses. In the left hemisphere, pASD subjects exhibited lower phase-locked steady-state power in all three conditions. Total γ-band power, including the non-phase-locked component, was also reduced in the pASD group. In addition, pASD subjects had significantly lower PLF than the HC group. Correlations were seen between MEG measures and BAP measures. CONCLUSIONS: The reduction in steady-state γ-band responses in the pASD group is consistent with previous results for children with ASD. Steady-state responses may be more sensitive than transient responses to phase-locking errors in ASD. Together with the lower PLF and phase-locked power in first-degree relatives, correlations between γ-band measures and behavioral measures relevant to the BAP highlight the potential of γ-band deficits as a potential new autism endophenotype.
RESUMO
BACKGROUND: Studies investigating the effect of rods on unique hue loci in the peripheral retina generally obtain measures at two time points associated with the dark adaptation function - the cone plateau and the rod plateau. In comparison, this study used a color-naming procedure to identify the loci of unique green and unique yellow as a function of time associated with the entire dark adaptation function. The unique hue loci derived by this procedure were then compared to those obtained directly with a staircase procedure. METHOD: Hue-scaling functions were obtained for monochromatic stimuli for four observers using the '4 + 1' procedure. Data were collected every 4 min following extinction of a bleaching stimulus. These hue-scaling functions were then converted to uniform appearance diagrams (UADs) to derive unique green and unique yellow loci. Unique green and unique yellow loci were also obtained from the same observers via a staircase procedure at 4-9 min post-bleach (minimal rod input) and after 28 min dark adaptation (maximal rod input). Measurements were made in the peripheral retina at 10° temporal retinal eccentricity and at the fovea. RESULTS: Unique green loci derived from UADs are at longer wavelengths compared to those measured directly with the staircase procedure. In addition, unique green loci derived from UADs show a progressive shift to longer wavelengths as time post-bleach increases; whereas, unique green loci obtained from the staircase procedure differ little between the rod-bleach and no-bleach conditions. Unique yellow loci are similar across both experimental procedures. CONCLUSION: Unique green loci derived from UADs are not the same as those measured with traditional psychophysical procedures. These differences may be due to the different response criteria used by observers in the color-naming and staircase procedures. The unique green loci obtained from UADs indicate that rod signals shift unique green loci to longer wavelengths as time post-bleach increases. More direct methods need to be employed to determine if this rod effect is valid.
