Abnormal sensory experiences, synaesthesia, and neurodevelopmental disorders.

Preliminary evidence suggests that sensory processing may be affected in autism spectrum disorders (ASD). The purpose of this letter is to highlight a few recent studies on the topic and tie the findings to a recently identified epidemiological risk factor for ASD, principally environmental exposure to the air pollutant, nitrous oxide (N2O). Animal studies have shown that trace levels of chronic N2O exposure are thought to involve dynorphin opioid peptide release and altered serotonergic neurotransmission, both of which may elicit profound changes in consciousness and induce synaesthesia experiences. Future research investigating abnormal sensory sensitivity in ASD should consider environmental exposure to N2O, which may induce the requisite neurochemical changes thought to underpin sensory dysregulation even at trace levels of exposure.