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Recurrent sensory experiences


Flashbacks are recurring sensory or emotional experiences that happen independently of the initial experience or event. Almost everybody experiences flashbacks of some kind, triggered by a familiar smell or sound that takes them back to a special or poignant moment. An example is re-experiencing the feeling of being back at school after smelling a familiar school smell, such as the lead of a pencil or a disinfected hallway.

In the case of drug-related flashbacks, the person usually re-experiences a visual or emotional hallucination previously seen or felt during a strong trip. This is defined by Grinspoon and Bakalaar as 'a transitory recurrence of emotions and perceptions originally experienced while under the influence of a psychedelic drug'.1 Flashbacks are usually associated with LSD, DOM and cannabis use. Studies generally show that roughly a quarter of LSD and cannabis users experience some kind of flashback.

Such flashbacks may or may not be triggered by a sight or sound. In the most extreme cases, strong visual hallucinations occur without warning, often causing alarm. Most flashbacks are episodes of visual distortion, time distortion, physical symptoms or relived intense emotion lasting a few seconds to a few minutes.

There appear to be different types of flashbacks:

Spontaneous return of perceptual distortions

During a flashback an individual suddenly sees a familiar object in a way he or she remembers seeing while hallucinating. This may be the glowing stripes on a road or auras around people's head.

Increased susceptibility to spontaneous imagery

This is similar to spontaneous return of perceptual distortions but involves seeing or thinking about visual imagery regularly. People who have them also say their imagery takes on a different quality - it is more vivid, seems to just spring from an unknown source and is less readily suppressed than formerly. Such flashbacks can be very vivid, involving disturbing images of animals or people. Though the distortions can live with a person for along time, the stronger animate images tend to lessen with time.

Recurrent unbidden images

Unbidden images are those that repeatedly force themselves into a person's awareness, demanding attention and resisting efforts to dispel them. Unlike spontaneous images, these tend to be more life-like and personally threatening. They have been described by those who experience them as having 'a will of their own'. Some people are frightened by not being able to dispel the images. Anxiety reactions, even psychotic reactions, may result.

What causes flashbacks?

Several explanations for flashbacks have been proposed. One implies deconditioning (or conditioning theory, depending on whether you regard the initial hallucination as adding or distorting the environment). Many experiences add to or change how a person sees or experiences a particular object or situation. Our brains help us see and understand all things. It follows that once we see something in a certain way, that perception will stick or re-occur every time we encounter it.

Which heads can you see? Sax player or lady?
How many heads do you see? Do you see a woman's head or a saxaphone player?

Good examples are in the pictures above. Each shows more than one image. Once an image is seen, the image sticks. For example Figure 1 shows three heads, one male. Most people see just one first, usually the man. After closer examination, however, the viewer starts to see the other heads. Once these are seen, the previous images are no longer invisible.

With flashbacks, the same is thought to happen, with hidden images and colours getting uncovered, or new ones imprinted while high. Once conditioned to seeing this we tend to see it every time we encounter the same or similar objects.

Another theory regards the drug as opening the individual's consciousness to imagery and fantasy that make them less subject to voluntary control. In another version of this explanation, flashbacks are caused by a heightened attention to certain aspects of an object or situation, suggested by a drug trip which are then reinforced by other drug using friends. In doing so, the quality and feeling of a trip are perpetuated by the users and the context around them.

Something more seems to be needed to account for repeated fearful unbidden images or sequences from past drug trips however. These have been explained as similar to traumatic neuroses caused by fright. Here, disturbing unconscious thoughts rise to consciousness during the drug trip and can be neither accepted nor repressed. To re-live them, as psychodynamic theory goes, is to re-address them. Bringing them back into consciousness therefore is a way of trying to control them or at least come to terms with the fear.

Another theory assumes that by the drug is still present in the body, and on release, triggers another short but intense hallucinations. This is unlikely. Any residue is unlikely to be present in sufficient amounts to bring on strong hallucinations such as flashbacks. Furthermore, if such flashbacks were caused by a chemical release, the duration would not be so short, but would instead last as long as the initial trip itself - usually 2 to 12 hours.

A more plausible theory is a permanent change to the neurophysiologic processes that help us see and remember images. It is believed some drugs, such as chlordiazepoxide, can changed how we retain images such that images can spring into consciousness in a similar way those experiencing epileptic seizures or electric stimulation see images flash before them. The types of flashbacks lend some support to this theory, such as spiral shapes of a whirlpool, radiating lines of an animal or person, and broken glass or surfaces - all of which occur during migraines, epileptic fits and electric stimulation.


1. Lester Grinspoon and James B. Bakalar, "Psychedelic Drugs Reconsidered," Basic Books, Inc. New York, 1979. pp. 159-163