Dream Facts

Dreams are the images, thoughts and feelings experienced while sleeping, particularly strongly associated with rapid eye movement sleep. The contents and biological purposes of dreams are not fully understood, though they have been a topic of speculation and interest throughout recorded history. The scientific study of dreams is known as oneirology.

All mammals and birds dream.^{[citation needed]} According to scientists^[who?], it is also possible that cephalopods dream as well.

There is no universally agreed biological definition of dreaming. General observation shows that dreams are strongly associated with rapid eye movement (REM) sleep, during which an electroencephalogram shows brain activity to be most like wakefulness. Participant-nonremembered dreams during non-REM sleep are normally more mundane in comparison.^[1] During a typical lifespan, a human spends a total of about six years dreaming^[2] (which is about 2 hours each night^[3]). It is unknown where in the brain dreams originate, if there is a single origin for dreams or if multiple portions of the brain are involved, or what the purpose of dreaming is for the body or mind.

During REM sleep, the release of certain neurotransmitters is completely suppressed. As a result, motor neurons are not stimulated, a condition known as REM atonia. This prevents dreams from resulting in dangerous movements of the body.

Discovery of REM

In 1953 Eugene Aserinsky discovered REM sleep while working in the surgery of his PhD advisor. Aserinsky noticed that the sleepers' eyes fluttered beneath their closed eyelids, later using a polygraph machine to record their brain waves during these periods. In one session he awakened a subject who was wailing and crying out during REM and confirmed his suspicion that dreaming was occurring.^[4] In 1953 Aserinsky and his advisor published the ground-breaking study in Science.^[5]

Dream theories

Activation-synthesis

In 1976, J. Allan Hobson and Robert McCarley proposed a new theory that changed dream research, challenging the previously held Freudian view of dreams as unconscious wishes to be interpreted. The activation synthesis theory asserts that the sensory experiences are fabricated by the cortex as a means of interpreting chaotic signals from the pons. They propose that in REM sleep, the ascending cholinergic PGO (ponto-geniculo-occipital) waves stimulate higher midbrain and forebrain cortical structures, producing rapid eye movements. The activated forebrain then synthesizes the dream out of this internally generated information. They assume that the same structures that induce REM sleep also generate sensory information.

Hobson and McCarly's 1976 research suggested that the signals interpreted as dreams originated in the brain stem during REM sleep. However, research by Mark Solms suggests that dreams are generated in the forebrain, and that REM sleep and dreaming are not directly related.^[6] While working in the neurosurgery department at hospitals in Johannesburg and London, Solms had access to patients with various brain injuries. He began to question patients about their dreams and confirmed that patients with damage to the parietal lobe stopped dreaming; this finding was in line with Hobson's 1977 theory. However, Solms did not encounter cases of loss of dreaming with patients having brain stem damage. This observation forced him to question Hobson's prevailing theory which marked the brain stem as the source of the signals interpreted as dreams. Solms viewed the idea of dreaming as a function of many complex brain structures as validating Freudian dream theory, an idea that drew criticism from Hobson.^[7] Unhappy about Holmes' attempts at discrediting him, Solms, along with partner Edward Nadar, undertook a series of traumatic-injury impact studies using several different species of primates, particularly howler monkeys, in order to more fully understand the role brain damage plays in dream pathology. Solms' experiments proved inconclusive, however, as the high mortality rate associated with using an hydraulic impact pin to artificially produce brain damage in test subjects meant that his final candidate pool was too small to satisfy the requirements of the scientific method.

Continual-activation

Combining Hobson's activation synthesis hypothesis with Solms's findings, the continual-activation theory of dreaming presented by Jie Zhang proposes that dreaming is a result of brain activation and synthesis; at the same time, dreaming and REM sleep are controlled by different brain mechanisms. Zhang hypothesizes that the function of sleep is to process, encode, and transfer the data from the temporary memory to the long-term memory, though there is not much evidence backing up this so-called "consolidation." Non-REM sleep processes the conscious-related memory (declarative memory), and REM sleep processes the unconscious related memory (procedural memory).

Zhang assumes that during REM sleep, the unconscious part of a brain is busy processing the procedural memory; meanwhile, the level of activation in the conscious part of the brain will descend to a very low level as the inputs from the sensory are basically disconnected. This will trigger the "continual-activation" mechanism to generate a data stream from the memory stores to flow through the conscious part of the brain. Zhang suggests that this pulse-like brain activation is the inducer of each dream. He proposes that, with the involvement of the brain associative thinking system, dreaming is, thereafter, self-maintained with the dreamer's own thinking until the next pulse of memory insertion. This explains why dreams have both characteristics of continuity (within a dream) and sudden changes (between two or more dreams).^[8][9]

Dreams and memory

Eugen Tarnow suggests that dreams are ever-present excitations of long-term memory, even during waking life. The strangeness of dreams is due to the format of long-term memory, reminiscent of Penfield & Rasmussen’s findings that electrical excitations of the cortex give rise to experiences similar to dreams. During waking life an executive function interprets long term memory consistent with reality checking. Tarnow's theory is a reworking of Freud's theory of dreams in which Freud's unconscious is replaced with the long-term memory system and Freud's “Dream Work” describes the structure of long-term memory.^[10]

Location of hippocampus

Hippocampus and memory

A 2001 study showed evidence that illogical locations, characters, and dream flow may help the brain strengthen the linking and consolidation of semantic memories. These conditions may occur because, during REM sleep, the flow of information between the hippocampus and neocortex is reduced.^[11] Increasing levels of the stress hormone cortisol late in sleep (often during REM sleep) cause this decreased communication. One stage of memory consolidation is the linking of distant but related memories. Payne and Nadel hypothesize that these memories are then consolidated into a smooth narrative, similar to a process that happens when memories are created under stress.^[12]

Functional hypotheses

There are many hypotheses about the function of dreams, including:^[13]

• During the night there may be many external stimuli bombarding the senses, but the mind interprets the stimulus and makes it a part of a dream in order to ensure continued sleep.^[14] The mind will, however, awaken an individual if they are in danger or if trained to respond to certain sounds, such as a baby crying.
• Dreams allow the repressed parts of the mind to be satisfied through fantasy while keeping the conscious mind from thoughts that would suddenly cause one to awaken from shock.^[15]

• Freud suggested that bad dreams let the brain learn to gain control over emotions resulting from distressing experiences.^[13]
• Jung suggested that dreams may compensate for one-sided attitudes held in waking consciousness.^[16]
• Ferenczi^[17] proposed that the dream, when told, may communicate something that is not being said outright.
• Dreams are like the cleaning-up operations of computers when they are off-line, removing parasitic nodes and other "junk" from the mind during sleep.^[18][19]
• Dreams create new ideas through the generation of random thought mutations. Some of these may be rejected by the mind as useless, while others may be seen as valuable and retained. Blechner^[20] calls this the theory of "Oneiric Darwinism."
• Dreams regulate mood.^[21]
• Hartmann^[22] says dreams may function like psychotherapy, by "making connections in a safe place" and allowing the dreamer to integrate thoughts that may be dissociated during waking life.
• More recent research by Griffin has led to the formulation of the 'expectation fulfillment theory of dreaming', which suggests that dreaming metaphorically completes patterns of emotional expectation and lowers stress levels.^[23][24]
• Coutts^[25] hypothesizes that dreams modify and test mental schemas during sleep during a process he calls emotional selection, and that only schema modifications that appear emotionally adaptive during dream tests are selected for retention, while those that appear maladaptive are abandoned or further modified and tested.
• Dream is a product of "dissociated imagination", which is dissociated from conscious self and draws material from sensory memory for simulation, with sensory feedback resulting in hallucination. By simulating the sensory signals to drive the autonomous nerves, dream can effect mind-body interaction. In the brain and spine, the autonomous "repair nerves", which can expand the blood vessels, connect with pain and compression nerves, and are grouped into many chains called meridians by the Chinese. Dream also exploits the chain-reacting meridians to repair body by sending out very intensive movement-compression signals when the level of growth enzyme goes high. ^[26]

Dreams and psychosis

A number of thinkers have commented on the similarities between the phenomenology of dreams and that of psychosis. Features common to the two states include thought disorder, flattened or inappropriate affect (emotion), and hallucination. Among philosophers, Kant, for example, wrote that ‘the lunatic is a wakeful dreamer’.^[27] Schopenhauer said: ‘A dream is a short-lasting psychosis, and a psychosis is a long-lasting dream.’^[28]In the field of psychoanalysis, Freud wrote: ‘A dream then, is a psychosis’,^[29]and Jung: ‘Let the dreamer walk about and act like one awakened and we have the clinical picture of dementia praecox.’^[30]

McCreery^[31][32] has sought to explain these similarities by reference to the fact, documented by Oswald,^[33] that sleep can supervene as a reaction to extreme stress and hyper-arousal. McCreery adduces evidence that psychotics are people with a tendency to hyper-arousal, and suggests that this renders them prone to what Oswald calls ‘microsleeps’ during waking life. He points in particular to the paradoxical finding of Stevens and Darbyshire^[34] that patients suffering from catatonia can be roused from their seeming stupor by the administration of sedatives rather than stimulants.