Pharmacological studies
As we have seen, the revelation of sensory correspondences in drug use was a subject of 19th century literature. Some writers took it seriously, but others treated it as entertainment or a snobbish trinket. However, two more serious thinkers developed two opposing views of drug-induced sensory correspondences.
In the 1950s and 1960s, there were many experiments with LSD (lysergic acid diethylamide). Some people reported side effects that resembled synesthesia when they described their color perceptions. For example, some people reported that LSD added color perceptions to non-visual stimuli such as pure tones. These reports were very similar to the descriptions of hyperesthesia and color hearing reported by Baudelaire and Gauthier.
In the 1960s, pharmacologist Leo Hollister found that after subjects were given LSD, adding a pure musical tone to the presentation of a visual flicker changed the color and patterns of the perceived flicker.
In the 1960s, pharmacologist Leo Hollister found that after subjects were given LSD, adding a pure musical tone to the presentation of a visual flicker changed the color and patterns of the perceived flicker. Later, in the 1980s, British neuroscientist Peter McKellar observed that a subject given mescaline responded to tactile stimulation with a sharp object by saying, «I have concentric circles, like around the top of a radio mast. If you touch me, jagged things jump up; little jagged things from the center».
In the 1960s, pharmacologist Leo Hollister found that after subjects were given LSD, adding a pure musical tone to the presentation of a visual flicker changed the color and patterns of the perceived flicker.
In the 1960s, pharmacologist Leo Hollister found that after subjects were given LSD, adding a pure musical tone to the presentation of a visual flicker changed the color and patterns of the perceived flicker. Later, in the 1980s, British neuroscientist Peter McKellar observed that a subject given mescaline responded to tactile stimulation with a sharp object by saying, «I have concentric circles, like around the top of a radio mast. If you touch me, jagged things jump up; little jagged things from the center».
At the same time, British perception researcher Richard Gregory subjected himself to an injection of ketamine, an anesthetic drug often used in plastic surgery, and reported his sensations to fellow researchers. When they stroked his palm with a hairbrush, Gregory had «the sensation of red wool woven in squares, like a tapestry» and when he ran his finger over the stubble, he perceived «purple, red images, clear, like hypnotic images that were very saturated, like Turkish tiles, orange, green and red». When he had a comb on his hand instead of a brush, he received «vivid green and red sensations when the comb was moved».
These studies have shown that hallucinogenic drugs lead to higher sensitivity to physical stimuli, resulting in co-perceptions such as moving colors and shapes. They support Gauthier's view that drugs can induce synesthetic perceptions that are hallucinatory. The participants in these studies were not synesthetes. What happens when a synesthete takes hallucinogenic drugs?
After decades of casual reports of synesthesia as a side effect of drug-induced hallucinations, drug-induced synesthesia began to be studied more systematically in the 1980s. One of the pioneers in this field is Washington, D.C.-based neurologist Richard Cytowicz. In his popular book «The Man Who Tasted Shapes» — he describes the case of his patient Michael Watson, in whom the taste of mint in his mouth evokes a tactile sensation that is as cool and fresh as the curve of a glass column in his hand. For Watson, flavors have form. While he tastes flavors in his mouth, he also feels shapes throughout his body, but mostly as sensations of objects rubbing against his face or in his hands.
For synesthete Michael Watson, tastes have shapes. While he feels tastes in his mouth, he also feels shapes all over his body, but mostly as sensations from objects rubbing against his face or in his hands.
According to Citovich, stimulants such as coffee stimulate higher cognitive functions in the neocortex (a relatively thin multilayered outer layer of the brain), whereas depressants such as alcohol suppress neocortical responses. Suppression of the rational cortical area allows the activity of the emotional limbic system (located more centrally in the brain) to emerge and brings it to the forefront of experience. Cytowic finds the source of synesthetic processes in this limbic system, and thus his predictions that coffee blocks and alcohol enhances synesthetic perception are confirmed.
In Cytowicz's research, unlike the experiments discussed earlier, synesthesia is not a temporary hallucination. Watson's synaesthesia is permanent and can be slightly altered by drug administration. More recent studies of drug-induced hallucinations in non-synesthetes confirm Gauthier's reports, but the only study of modification of synesthetic perception in synesthetes is consistent with Baudelaire's views. In fact, drug-induced hallucinations and drug-modified synesthesia are two different phenomena.
In Cytowicz's research, unlike the experiments discussed earlier, synesthesia is not a temporary hallucination. Watson's synaesthesia is permanent and can be slightly altered by drug administration. More recent studies of drug-induced hallucinations in non-synesthetes confirm Gauthier's reports, but the only study of modification of synesthetic perception in synesthetes is consistent with Baudelaire's views. In fact, drug-induced hallucinations and drug-modified synesthesia are two different phenomena.
Conclusion
So, the question remains: is there a direct link between synesthesia and drug-induced hallucinations? Although some overlap can be observed in both types of perception, I don't believe there is.
First, drug-induced hallucinations are temporary and last only as long as the drug lasts, whereas synesthetic perceptions are always present throughout life. Second, the perception of sensory correspondences changes in drug-induced hallucinations, whereas in synesthetic perceptions it is constant. Third, drug addicts can distinguish their drug-induced hallucinations from their normal state of mind, whereas synesthetes perceive their sensory correspondences while in their normal state of mind. In fact, no observations by others indicate that synesthetes exhibit hallucinatory behavior.
Fourth, whereas drug-induced hallucinations often disrupt normal human functioning, the «visions» that synesthetes see do not interfere with normal life, and in some cases they help synesthetes cope better, such as when synesthetes use colors to count verbally. Finally, many synesthetes report first discovering their synesthesia in childhood rather than during their first drug experience.
So, the question remains: is there a direct link between synesthesia and drug-induced hallucinations? Although some overlap can be observed in both types of perception, I don't believe there is.
First, drug-induced hallucinations are temporary and last only as long as the drug lasts, whereas synesthetic perceptions are always present throughout life. Second, the perception of sensory correspondences changes in drug-induced hallucinations, whereas in synesthetic perceptions it is constant. Third, drug addicts can distinguish their drug-induced hallucinations from their normal state of mind, whereas synesthetes perceive their sensory correspondences while in their normal state of mind. In fact, no observations by others indicate that synesthetes exhibit hallucinatory behavior.
Fourth, whereas drug-induced hallucinations often disrupt normal human functioning, the «visions» that synesthetes see do not interfere with normal life, and in some cases they help synesthetes cope better, such as when synesthetes use colors to count verbally. Finally, many synesthetes report first discovering their synesthesia in childhood rather than during their first drug experience.
Once dismissed as imagination or delusion, metaphor or drug-induced hallucination, the experience of synesthesia is now well documented by brain scans of synesthetes that show «crosstalk» between areas of the brain that don't normally communicate. What makes this phenomenon so exciting is that it raises questions that still puzzle scientists. Synesthesia is not an isolated phenomenon in human perception. It is not a fantasy, and it cannot be marginalized as an unimportant byproduct of a disturbed human brain process. Numerous synesthetes, consider synesthesia an integral part of their lives. While it may be impossible to replicate the true experience of synesthesia, reorganizing our view of the brain's sensory channels is a worthy goal. Ultimately, it may change our view of the human mind, and perhaps the physical world as well.