There is converging evidence for what Kana et al. (in press) refer to as “disrupted cortical connectivity” in autism spectrum disorders (ASD). To date, only a few studies have examined the functional role of the corpus callosum for information transfer in autism, including structural (e.g., DTI; Shukla et al., 2010) and behavioral (Nyden et al., 2004) studies. EEG-based event-related potential (ERP) techniques have high temporal resolution and are ideally suited for research regarding interhemispheric transfer of information across the corpus callosum, including studies of psychiatric samples (Endrass et al., 2002).
We utilized ERP for an interhemispheric transmission time (IHTT) task to examine whether our ASD group would show relatively longer transfer times across the corpus callosum.
Older children and adolescents (ages 10-18) diagnosed with an ASD (n=28; mean ADOS score = 12.8) and healthy controls (n=22) matched on age (M=13.6) and IQ (M=107.3) completed the IHTT task while wearing a 128-electrode geodesic sensor net with an EGI amplifier system. The task involved pairs of letters (either “A” or “B,” which could be either uppercase or lowercase) appearing to either side of a central fixation cross for 60milliseconds. Participants pushed one key with their right hand if the two letters were the same letter (e.g., both “A”) and a separate key with the left hand if they did not match. The IHTT is defined as the difference in latency of the early-occurring evoked potential components between the contralateral and the ipsilateral hemispheres (Endrass et al., 2002). We examined the latency of the N1 deflection using electrodes at parietal sites.
A 2 (visual field) x 2 (hemisphere) x 2 (diagnostic group) ANOVA demonstrated a significant interaction of visual field x hemisphere, F(1,48)=6.9, p<.05, as both groups showed similar, robust differences in contralateral (slower) than ipsilateral trials. There were no significant effects of diagnostic group with hemisphere, visual field, nor importantly for the three-way interaction with diagnostic group, F(1,48)=.22 p=.64.
We show evidence of interhemispheric transmission rates similar in ASD and our typical controls, with both groups showing similar slower rates of early ERP deflections for contralateral vs. ipsilateral trials. Our study differs from the early existing IHTT-like study by Nyden et al. (2004), which did not use ERP, especially in the simplicity of our task vs. their complex auditory and visual tasks. Kana (in press; see also Gaigg and Bowler, 2007; South et al., in press) notes that impaired neural connectivity is most notable in tasks with higher levels of complexity and that simpler tasks may be processed in normal fashion. This may in part explain the particular trouble in ASD with social interactions, which are by nature high in complexity and required speed of processing. Further research regarding task complexity in autism, including tasks measuring speed of neural transmission, will help to refine this hypothesis.
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