Are the non-classical auditory pathways involved in autism and PDD?

OBJECTIVE To test the hypothesis that some of the abnormal sensory perceptions that characterize autism may be explained by an abnormal activation of non-classical (extra-lemniscal) sensory pathways. METHODS Twenty-one individuals, 18--45 years of age who were diagnosed with autism participated in the study. Sounds (clicks presented at a rate of 40 per second and 65 dB above the normal threshold) were applied through earphones. Electrical stimulation (100 microS rectangular impulses at a rate of 4 per second) was applied through electrodes placed on the skin over the median nerve at the wrist. The participants were asked to match the loudness of the sound with and without the electrical stimulation applied to the median nerve. RESULTS Electrical stimulation of the median nerve at the wrist in individuals with autism could change the perception of loudness of sounds presented to one ear through an earphone showing a statistically significant abnormal sensory cross-modal interaction. DISCUSSION We interpreted our results to support the hypothesis that some individuals with autism have an abnormal cross-modal interaction between the auditory and the somatosensory systems. Cross-modal interaction between senses such as hearing and the somatosensory system does not occur normally in adults. As only the non-classical (extralemniscal) ascending auditory pathways receive somatosensory input, the presence of cross-modal interaction in autistic individuals is a sign that autism is associated with abnormal involvement of the non-classical auditory pathways, implying that sensory information is processed by different populations of neurons than in non-autistic individuals.