Background: Patients with autism show clinical features suggestive of abnormal processing of auditory and other sensory information. We hypothesized that low-functioning autistic subjects present abnormalities in discriminating simple auditory stimuli at sensory system preconscious stages of cortical processing.
Methods: To verify our hypothesis, we used magnetoencephalographic measurements of mismatch field (MMF), which reflects the detection of a change in the physical characteristics of a repetitive sound. Fourteen patients (aged 8-32 years) who met DSM-IV diagnostic criteria for autistic disorder participated in an auditory oddball experiment. Ten healthy participants matched for age and gender acted as control subjects.
Results: Significant differences in cerebral responses between patients and control subjects were recorded. Whereas control subjects showed a clearly identifiable MMF, with distinct generators in the M100 brain wave with regard to latency, position, and strength, no identifiable MMF was present in the autistic group.
Conclusions: Our findings suggest that low-functioning autistic subjects present a dysfunction at preconscious stages of cortical auditory discrimination, playing a role in the abnormal processing of auditory sensory afferences. The attention independence of the MMF allows for exclusion of an effect related to impaired attention or task-related responses.