The chemical induction of synaesthesia

Abstract

Objective Preliminary research suggests that experiences resembling synaesthesia are frequently reported under the influence of a diverse range of chemical substances although the incidence, chemical specificity, and characteristics of these effects are poorly understood. Methods Here we surveyed recreational drug users and self-reported developmental synaesthetes regarding their use of 28 psychoactive drugs comprising 12 different drug classes and whether they had experienced synaesthesia under the influence of these substances. Results The drug class tryptamines exhibited the highest incidence rates of drug-induced synaesthesia in controls and induction rates of novel forms of synaesthesia in developmental synaesthetes. Induction incidence rates in controls were strongly correlated with the corresponding induction and enhancement rates in developmental synaesthetes. In addition, the use of LSD was the strongest predictor of drug-induced synaesthesia in both controls and developmental synaesthetes. Clear evidence was observed for a clustering of synaesthesia-induction rates as a function of drug class in both groups, denoting non-random incidence rates within drug classes. Sound-colour synaesthesia was the most commonly observed type of induced synaesthesia. Further analyses suggest the presence of synaesthesia-prone individuals, who were more likely to experience drug-induced synaesthesia with multiple drugs. Conclusions These data corroborate the hypothesized link between drug-induced synaesthesia and serotoninergic activity, but also suggest the possibility of alternative neurochemical pathways involved in the induction of synaesthesia. They further suggest that the induction and modulation of synaesthesia in controls and developmental synaesthetes share overlapping mechanisms and that certain individuals may be more susceptible to experiencing induced synaesthesia with different drugs.

Dose-response relationships of LSD-induced subjective experiences in humans

“…Interestingly, our findings seem to indicate that LSD is more prone to evoke Audio-Visual Synesthesia compared to psilocybin, supporting previous reports that LSD is highly effective in inducing synesthesia [73,74]. In a survey among recreational psychedelic users, the highest incidence rate of drug-induced synesthesia was reported for LSD [75] and a study comparing the effects of LSD (1 μg/kg) and psilocybin (150 μg/kg) also found significantly more synesthesia in the LSD group [4]. Considering that LSD not only interacts with serotonin receptors, but also with dopaminergic and adrenergic receptors [76,77], our results could be interpreted in line with evidence that drug-induced synesthesia is not exclusively a result of serotonergic activation [75].…”

“…Considering that LSD not only interacts with serotonin receptors, but also with dopaminergic and adrenergic receptors [76,77], our results could be interpreted in line with evidence that drug-induced synesthesia is not exclusively a result of serotonergic activation [75]. LSD's pronounced modulation of Audio-Visual Synesthesia via non-5-HT2A mechanism of action may be associated with the etiology of the rarely occurring hallucinogen-persistent perception disorder (HPPD).…”

“…Audio-Visual Synesthesia compared to psilocybin, supporting previous reports that LSD is highly effective in inducing synesthesia [73,74]. In a survey among recreational psychedelic users, the highest incidence rate of drug-induced synesthesia was reported for LSD [75] and a study comparing the effects of LSD (1 μg/kg) and psilocybin (150 μg/kg) also found significantly more synesthesia in the LSD group [4].…”

“…In a survey among recreational psychedelic users, the highest incidence rate of drug-induced synesthesia was reported for LSD [75] and a study comparing the effects of LSD (1 μg/kg) and psilocybin (150 μg/kg) also found significantly more synesthesia in the LSD group [4]. Considering that LSD not only interacts with serotonin receptors, but also with dopaminergic and adrenergic receptors [76,77], our results could be interpreted in line with evidence that drug-induced synesthesia is not exclusively a result of serotonergic activation [75]. LSD’s pronounced modulation of Audio-Visual Synesthesia via non-5-HT 2A mechanism of action may be associated with the etiology of the rarely occurring hallucinogen-persistent perception disorder (HPPD).…”

An encounter with the self: A thematic and content analysis of the DMT experience from a naturalistic field study

“…While synaesthesia of some description was shared by many subjects (common to tryptamine psychedelics, especially LSD, and typically sound color, Luke et al, 2022 ), one individual, ST , depicted an elaborate multisensory-cognitive manifestation. Psychedelic synaesthesia may be prompted by the global hyperconnectivity of non-local networks, which is concomitant with the disintegration of the DMN, which facilitates ego consciousness.…”