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.2018 Jan 22:12:7.
doi: 10.3389/fnins.2018.00007. eCollection 2018.

The Experience Elicited by Hallucinogens Presents the Highest Similarity to Dreaming within a Large Database of Psychoactive Substance Reports

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The Experience Elicited by Hallucinogens Presents the Highest Similarity to Dreaming within a Large Database of Psychoactive Substance Reports

Camila Sanz et al. Front Neurosci..

Erratum in

Abstract

Ever since the modern rediscovery of psychedelic substances by Western society, several authors have independently proposed that their effects bear a high resemblance to the dreams and dreamlike experiences occurring naturally during the sleep-wake cycle. Recent studies in humans have provided neurophysiological evidence supporting this hypothesis. However, a rigorous comparative analysis of the phenomenology ("what it feels like" to experience these states) is currently lacking. We investigated the semantic similarity between a large number of subjective reports of psychoactive substances and reports of high/low lucidity dreams, and found that the highest-ranking substance in terms of the similarity to high lucidity dreams was the serotonergic psychedelic lysergic acid diethylamide (LSD), whereas the highest-ranking in terms of the similarity to dreams of low lucidity were plants of theDatura genus, rich in deliriant tropane alkaloids. Conversely, sedatives, stimulants, antipsychotics, and antidepressants comprised most of the lowest-ranking substances. An analysis of the most frequent words in the subjective reports of dreams and hallucinogens revealed that terms associated with perception ("see," "visual," "face," "reality," "color"), emotion ("fear"), setting ("outside," "inside," "street," "front," "behind") and relatives ("mom," "dad," "brother," "parent," "family") were the most prevalent across both experiences. In summary, we applied novel quantitative analyses to a large volume of empirical data to confirm the hypothesis that, among all psychoactive substances, hallucinogen drugs elicit experiences with the highest semantic similarity to those of dreams. Our results and the associated methodological developments open the way to study the comparative phenomenology of different altered states of consciousness and its relationship with non-invasive measurements of brain physiology.

Keywords: consciousness; deliriants; dissociatives; dreams; hallucinogens; phenomenology; psychedelics.

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Figures

Figure 1
Figure 1
Ranking of psychoactive substances in the Erowid corpus in terms of the similarity of their subjective reports to those of high lucidity dreams (Dreamjournal corpus). The rectangles on the left/right zoom into the top 20 lowest/highest ranking substances and the pie charts indicate the proportion of each primary category. Substances are represented with circles that are color-coded based on their category (the color of the center/border corresponds to the primary/secondary category).
Figure 2
Figure 2
Ranking of psychoactive substances in the Erowid corpus in terms of the similarity of their subjective reports to those of low lucidity dreams (Dreamjournal corpus). The rectangles on the left/right zoom into the top 20 lowest/highest ranking substances and the pie charts indicate the proportion of each primary category. Substances are represented with circles that are color-coded based as in Figure 1.
Figure 3
Figure 3
(A) Average substance rank (per category) in terms of the similarity of the reported effects to high/low lucidity dream reports (median ± 25th and 75th percentiles, “+” represents outliers). Higher numbers correspond to higher similarity (the highest possible rank is 165). The categories “oneirogen,” “MAOI,” and “other” were excluded from this figure due to their small sample size (n ≤ 6). The drug category presented a significant effect on the similarity with dream reports (F = 31.34,p < 0.0001, multi-factor ANOVA), while the interaction between dream lucidity and similarity with dream reports was non-significant (F = 0.02,p = 0.88).(B)Post-hoc Wilcoxon signed-rank tests for the difference in the similarity to dreams for each pair of drug categories. Black squares represent significant differences (p < 0.05) for the pair of drug categories in the corresponding rows and columns.
Figure 4
Figure 4
Prediction of the similarity between the subjective report of substances and dreaming experiences of high lucidity, based on the similarity to LSD, plants of theDatura genus, PCP and MDMA(A) and to reports of barbiturates, cocaine, venlafaxine andCalea zacatechichi(B). Substances are represented with circles that are color-coded as in Figure 1. The inset shows the value of the Spearman's rank correlation coefficient (ρ).
Figure 5
Figure 5
Prediction of the similarity between the subjective report of substances and dreaming experiences of low lucidity, based on the similarity to LSD, plants of theDatura genus, PCP and MDMA(A) and to reports of barbiturates, cocaine, venlafaxine andCalea zacatechichi(B). Substances are represented with circles that are color-coded as in Figure 1. The inset shows the value of the Spearman's rank correlation coefficient (ρ).
Figure 6
Figure 6
Word clouds for the top 40 most frequent terms in dream reports of high(left) and low(right) lucidity.
Figure 7
Figure 7
Word clouds for the top 40 most frequent terms in the reports of four substances with high similarity to dream reports (LSD, plants of the Datura genus, PCP and MDMA) and in the reports of four substances with lower similarity to dream reports (barbiturates, venlafaxine, cocaine, andCalea zacatechichi)(A).(B) shows word clouds based on the average ranking of each term in the reports of the four psychoactive substances of(A) and in the reports of high/low lucidity dreams.
Figure 8
Figure 8
Pairwise correlation matrices between the rank of the substances in terms of their similarity to dreams of low (left) and high (lucidity), computed after retaining different numbers of singular values.
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