ERP Responses to Probe Words Following a Sentence Context during Reading in Individuals with Autism Spectrum Disorders: An MEG Study

Background: Numerous studies have shown that individuals with ASD have difficulties in spontaneous use of sentence context during reading.

Objectives: To use magnetoencephalography (MEG) to study the neural basis of abnormalities in sentence context effects in individuals with ASD.

Methods: 22 individuals with ASD and 22 typically developing (TD) adults participated in the study. Participants were matched on age, gender, and IQ. All measurements were taken at the Oxford Neurodevelopmental Magnetoencephalography Centre using a Neuromag-306 VectorView^TM system, providing a helmet-shaped array of 102 pairs of gradiometers. Participants read sentences ending either with a homonym (dominant vs. subordinate meanings) or an unambiguous word. The sentences were followed by a probe word that was semantically related or unrelated to the meaning of the sentence. Participants were asked to indicate whether the probe word was related or unrelated to the meaning of the sentence that it followed and to give their responses with a key press. This study has been approved by the local NHS (UK) Ethics Committee. All participants gave written informed consent before the experiment.

Results: At 100ms both TD and ASD groups show similar activity for all the probe word conditions except for the DHR (related probe word that follows a dominant homonym final word) condition in the ASD group which shows a stronger response over the occipital and posterior-parietal areas. The word response at 150ms is stronger over the left temporal areas in the TD group than in the ASD group, in all probe word conditions. Between 200-300ms both groups show bilateral activity over the temporal and occipital areas. At N4-like latencies, both TD and ASD groups show stronger responses to the unrelated probe words, with stronger activity observed over right temporo-parietal areas for the unrelated conditions in the ASD group.

Conclusions: These results suggest that the ASD group exhibit close to typical patterns for the evaluation of semantic relatedness at the 450ms latency. The initial stages of the probe word activity in ASD shows dissimilarities from the TD group, which may indicate the existence of different processing strategies.