Objectives: The aim of this study was to test oscillatory synchrony in the gamma range in a visual simultaneity task in a group of high-functioning ASD patients versus age-matched and IQ-matched typically developing subjects (TD).
Methods: 17 ASD (mean age = 24; ADI-R and ADOS-confirmed) and 17 TDC (mean age = 26) were recruited with appropriate ethical approval. Individuals participated in a visual simultaneity task in the magnetoencephalography (MEG) scanner at the Oxford Human Brain Activity centre at the University of Oxford and were presented with three conditions on a screen: a simultaneous condition (two vertical bars appearing on a screen at the same time); a short condition (17 ms delay of appearance for the second bar); and a long condition (117 ms delay; not reported here). Participants judged the stimuli as simultaneous or asynchronous with a response cue of 1500 ms and completed 4 experimental blocks consisting of 60 trials each. Time-frequency analyses were performed on individual epochs.
Results: Our behavioural data show that ASD individuals significantly discriminate between the short and simultaneous conditions (p<0.05) compared to TD subjects, who perceive both conditions as being similar. Our time-frequency analyses show a burst of phase-locked gamma-band activity between 40 and 60Hz in the short condition during early visual processing between 50 and 80ms after stimulus onset in the TDCs. However, ASD individuals show no gamma-band activity for this condition (p<0.001). This localises to the occipital pole. In the simultaneous condition, gamma-band activity was similar between both groups.
Conclusions: Discrimination of the timing of events in ASD individuals during early visual processes might suggest a cognitive strategy that does not involve oscillatory synchrony in the gamma range over the occipital pole. Although gamma-band bursts are thought to support visual binding processes, ASD individuals still have an enhanced access to early visual processing of perceptual simultaneity, which may not involve synchrony in the gamma range.
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See more of: Brain Structure & Function