Psilocybin, Lysergic Acid Diethylamide, Mescaline, and Drug-Induced Synesthesia, Berit Brogaard & Dimitria Electra Gatz, 2016

Psilocybin, Lysergic Acid Diethylamide, Mescaline, and Drug-Induced Synesthesia

Berit Brogaard, Dimitria Electra Gatzia

Neuropathology of Drug Addictions and Substance Misuse, 2016, Volume 2, chapter 83, 890-905.
Copyright © 2016 Elsevier Inc. All rights reserved



Synesthesia typically involves either the stimulation of one sensory modality giving rise to an experience in a different sensory modality (such as when a smell or taste gives rise to a color experience) or the stimulation of a single sensory modality giving rise to an unusual qualitative experience (such as when an achromatic grapheme appears colored) (Baron-Cohen, Wyke, & Binnie, 1987; Brogaard, 2012; Cytowic, 1989; Day, 2005; Rich & Mattingley, 2002; Sagiv, 2005; Sagiv & Ward, 2006). More generally, synesthesia involves an aberrant binding of features from different sensory or cognitive streams that are associated with atypical conscious experiences or thoughts.

The trigger of a synesthetic experience, say, a grapheme or a sound, is known as the inducer, whereas the experience to which the inducer gives rise, say, the synesthetic color associated with a grapheme or a sound, is known as the concurrent (Grossenbacher & Lovelace, 2001). There is extensive variability in the inducer– concurrent pairs among synesthetes. Some synesthetes experience interactions between taste or smell and vision, reporting, for example, that the taste of beef is dark blue or that the smell of
almonds is pale orange (Day, 2005; Dixon, Smilek, & Merikle, 2004). Others experience interactions between music and smell or color, reporting, for example, that they are smelling music or experiencing a French tenor’s voice as being simultaneously red and green (Ramachandran & Hubbard, 2005). Sometimes context affects the nature of the inducer–concurrent pair. For example, Blake, Palmeri, Marois, and Kim (2005) found that subjects described the same grapheme as having different synesthetic colors when viewed amid letters and when viewed amid numbers (see Figure 1).

Three main types of synesthesia have been identified (Grossenbacher & Lovelace, 2001). The most common of them is developmental or genuine synesthesia. It reportedly develops at birth or in early childhood (Hubbard, 2007); it tends to be hereditary (Baron-Cohen, Burt, Smith-Laittan, Harrison, & Bolton, 1996) and remains relatively consistent (or enduring) and systematic (or nonrandom), as each inducer has a highly specific concurrent (Baron-Cohen et al., 1987; Cohen Kadosh, Henik, & Walsh, 2007; Mattingley, Rich, Yelland, & Bradshaw, 2001; Simner et al., 2005, 2006; Ward, Huckstep, & Tsakanikos, 2006; Ward & Simner, 2003).1 For example, a 5-year-old synesthete who experiences the number 3 as a particular shade of green will most likely continue to experience the number 3 as that particular shade of green for a considerable length of time (see Figure 2).

In visual synesthesia, the concurrent can be either projected out into space (when, for example, the number 3, printed in black, looks green) or merely be associated with the inducer (when, for example, the number 3 is seen in the “mind’s eye” as being dark blue or as having a detailed personality, as if it were a person) (Dixon et al., 2004; Smilek et al., 2007). The former condition is also known as projector synesthesia, whereas the latter is known as associator synesthesia.

Subjects with projector grapheme–color synesthesia tend to describe seeing the concurrent as positioned spatially in the same location as the inducing achromatic grapheme (and not simply as existing in their mind’s eye). As a result, at least some grapheme– color synesthetes are subject to pop-out and grouping effects grounded in their concurrent synesthetic experiences (see Figure 3). Pop-out effects allow synesthetes to identify graphemes in visual-search paradigms with far greater speed and accuracy than non-synesthetes (Blake et al., 2005; Edquist, Rich, Brinkman, & Mattingley, 2006; Ramachandran & Hubbard, 2001a, 2001b). For example, when an array of 2’s that form a triangle is hidden within a field of distractor graphemes with incongruent synesthetic colors, the shape formed by the 2’s may appear immediately and conspicuously, as if it were popping out of the array (see Figure 3, box on the right) (Ramachandran & Hubbard, 2001b). For non-synesthetes, by contrast, the 2’s and the distractor graphemes appear too homogeneous for the triangle formed by the 2’s to be immediately noticed (see Figure 3, box on the left).

The second type of the condition is acquired synesthesia. This type has been reported to emerge after traumatic brain injury (Brogaard & Marlow, 2013; Brogaard, Vanni, & Silvanto, 2012), stroke (Beauchamp & Ro, 2008; Ro et al., 2007; Schott, 2012; Thomas-Anterion et al., 2010), seizures (Jacome & Gumnit, 1979), migraine (Alstadhaug & Benjaminsen, 2010), posthypnotic suggestion (Cohen Kadosh, Henik, Catena, Walsh, & Fuentes, 2009), sensory substitution (Ward & Wright, 2014), and neuro-pathology involving the optic nerve and/or chiasm (Afra, Funke, & Matuso, 2009; Armel & Ramachandran, 1999; Jacobs, Karpik, & Bozian, 1981). Like its developmental counterpart, the acquired form tends to be enduring and involuntary in the sense that synesthetes are unable to suppress the association between an inducer and its concurrent, although there are reports that the condition does not always persist (Afra et al., 2009; Jacome & Gumnit, 1979; Lessell & Cohen, 1979). Although acquired synesthesia can be experientially indistinguishable from developmental synesthesia, it is often simpler than its developmental counterpart, say, resembling light flashes (phosphenes) or pure color experiences (Afra et al., 2009). In some cases acquired synesthesia appears to be less inducer-specific than its developmental counterpart, meaning that the same concurrent may have several different inducers (Brogaard et al., 2012).

The third type, which is the main focus of this paper, is drug-induced synesthesia.2 This condition tends to be experienced during exposure to hallucinogenic substances, such as psilocybin (which occurs naturally in some mushrooms, the most common of which are Psilocybe cubensis), lysergic acid diethylamide or LSD (which is a semisynthetic hallucinogen derived from rye fungus), and mescaline (which occurs naturally in peyote cacti) (Friedrichs, 2009; Shanon, 2002; Sinke et al., 2012).3 Hallucinogens (also known as psychedelics, psychotomimetics, or entheogens; see Ray, 2010, for a survey of 35 different hallucinogens) are psychoactive substances known to (dose-dependently) induce profound changes in perception, including changes in the experience of time or space as well as alterations in moods, thoughts, and other mental states. LSD, the most potent of the three hallucinogens mentioned above, was found to have the highest correlation with visual disturbances compared to consciousness-altering substances such as amphetamines, cocaine, hypnosedatives, opiates, marijuana, and alcohol (Abrahams, 1983).

Whereas some hallucinogens are artificially produced, others (for example, psilocybin and mescaline) occur naturally in plants. Plant-based hallucinogens were used by early cultures, for example, various groups of indigenous peoples native to the central or southern regions of Mexico, in a variety of sociocultural, medical, or ritual contexts (Guzmán, Allen, & Gartz, 2000; Stamets, 1996). Some hallucinogens have been found to produce mysticaltype experiences marked by substantial and persisting personal meaning and spiritual significance, to which subjects attributed sustained positive changes in attitudes, moods, and behavior (Griffiths, Richards, Johnson, McCann, & Jesse, 2008; Griffiths, Richards, McCann, & Jesse, 2006).