Psychedelic synaesthesia: Evidence for a serotonergic role in synaesthesia

Synaesthesia, a condition where stimulation of one sense triggers perception in another, is frequently induced by psychedelic substances that act on the serotonin system, such as LSD and psilocybin. A survey of recreational drug users found that these serotonergic agonists commonly cause synaesthetic experiences and can also intensify existing synaesthesia in those who have the congenital form. The findings suggest that the serotonergic system plays a key role in the neurobiology of synaesthesia, offering a pathway to understand broader questions about consciousness and how the brain binds sensory information.

Study at a glance

Abstract

The neurobiology of synaesthesia is receiving growing attention in the search for insights into consciousness, such as the binding problem. One way of decoding the neurocognitive mechanisms underlying this phenomenon is to investigate the induction of synaesthesia via neurochemical agents, as commonly occurs with psychedelic substances. How synaesthesia is affected by drugs can also help inform us of the neural mechanisms underlying this condition. To address these questions we surveyed a sample of recreational drug users regarding the prevalence, type and frequency of synaesthesia under the influence of psychedelics and other psychoactive substances. The results indicate that synaesthesia is frequently experienced following the consumption of serotonergic agonists such as LSD and psilocybin and that these same drugs appear to augment synaesthesia in congenital synaesthetes. These results implicate the serotonergic system in the experience of synaesthesia.