Dreams and Hallucinations

Dreams and Hallucinations

Dreams are hallucinations that we all experience – hallucinations that have been regarded by many as a “normal” form of psychosis. Freud was especially interested in dreams because he believed that, if he could understand their mechanism, he would be able to comprehend something fundamental about mental illness. Other forms of hallucination and delusion, primarily in schizophrenia, exist. The brain mechanism of dreaming (perhaps not surprisingly) overlap a great deal with those of consciousness, emotion, and memory.

Difficulties Investigating Dreaming

Dreams are notoriously difficult to investigate scientifically. All scientists are concerned with methodological questions regarding how brain mechanisms of dreaming have been investigated. Attention is drawn to the dangers of using inappropriate methods to investigate complex psychological states, and to the advantages of using more than one scientific method to study a difficult and elusive subject. In the past, one of the failing of psychoanalysis was its overreliance, despite the great complexity of its subject matter, on a single method for reaching its conclusions, but this has begun to change somewhat in recent years. Checking the findings of one method against those of another makes it possible to minimize the bias associated with a single method. Today's review of the dreaming brain draw mostly on findings from neurophysiological work on animals, sleep studies and function-imaging studies in neurologically intact humans, and clinical and experimental investigations of patients with focal brain lesions.

Dreams... Photo by Elena.

REM Sleep

Any discussion of the brain mechanisms of dreaming cannot begin before the phenomenon of Rapid-Eye-Movement (REM) sleep has been introduced, because REM sleep has become widely known as “dreaming sleep”. However, it is a mistake to equate the two phenomena. Indeed, the conflation of REM sleep with dreaming is one of the most substantial errors that has arisen from methodological impropriety in this field.

When the REM state was discovered in the 1950s, the scientists involved (Aserinsky & Kleitman, 1953; Dement & Kleitman, 1957) immediately suspected that it might be the physiological correlate of dreaming. This was because the REM state involves a period of physiological arousal in the context of otherwise quiescent sleep, just as the dream state involves conscious mental activity in the context of otherwise unconscious sleep. During REM, it is not only the eyes that are active. An electroencephalogram (EEG) – which provides a measure of the electrical activity in the brain – made during REM would suggest that although you are sleeping, your brain is in a state of heightened activation akin to full wakefulness. There is also activation of other bodily systems. You begin to breathe differently, your heart rate increases, and your genitals (in both males and females) become engorged. One is thus highly excited in several ways during REM sleep. By contrast, however, skeletal muscle tone drops dramatically (with the exception of the musculature controlling eye movements). This effectively paralyzes the sleeper, and it apparently prevents him or her from acting out dreams. This cycle appears more or less every 90 minutes in humans, sot that we spend some 25% of our sleeping hours in the REM state.

Taking into account the fallibility of human memory in general, let alone memory for dreams (which are particularly difficult to recall), it would have been unreasonable for early investigators to expect to obtain a 100% dream recall rate from REM sleep awakenings. 

A French neuroscientist, Michel Jouvet (1967), carried out the first key studies by performing a series of ablation experiments. Although REM sleep occurs in a remarkably wide variety of animals, cats were the main targets of this research – partly because their brains are so similar to ours, but no doubt also because they sleep for so much of the day. Jouvet made a series of slices through the neuraxis of the cat, starting at the highest level of the frontal lobes and moving progressively downward toward the brainstem. He then systematically investigated the effects on the sleep cycle. He wanted to ascertain the key lesion site that would obliterate REM sleep. To his amazement, he found the brainstem, and the REM state would still remain intact and would punctuate sleep with the same monotonous regularity.

The critical incision occurred only in the middle regions of the primitive brainstem, at the level of the pons. Subsequent investigators confirmed that REM sleep can only be obliterated entirely by creating fairly large lesions in the pons (Jons, 1979). In short, these studies demonstrated that, whatever REM sleep was, it was causally generated by structures in the pontine brainstem. The implications of this finding were enormous. Since the forebrain is the seat of all our higher mental functions (i.e., representational cognition), the early investigators concluded that REM sleep (read: dreaming) is an entirely “mindless” activity.  This raised serious questions for any psychological theory of the causation of dreams, not least among them being the Freudian theory that dreams are caused by wishful states of mind. The following quotation is from one of the most influential papers in the field

If we assume that the physiological substrate of consciousness is the forebrain, these facts completely eliminate any possible contribution of ideas (or their neural substrate) to the primary driving force of the dream process.

Hallucinations. Photo by Elena.