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Modern scientific studies of the brain have led to some contradictory theories of dreaming that initially seemed to contradict the ideas Sigmund Freud propounded in the Interpretation of Dreams. Recent studies have indicated that many of Freud’s ideas were correct.

Freud began studying dreams after years of neurological research, but gave up because at the time there was no way to map the functions of the brain. (At that time learning what part of the brain did what required finding subjects who had suffered trauma to a part of their brain and then finding what brain function they had lost.)

Today, using a variety of electronic scans, scientists are able to determine what part of the brain is doing what, which allows for the exploration of the neurological foundations of Freud's theories.

This conversational essay examines the current state of the science of dreaming and its relationship to the theories in Freud's The Interpretation of Dreams. It is based on the work of Mark Solms, a British scientist and one of today's foremost neurological researchers.

What is REM sleep?
In 1953 neuroscientists discovered a physiological state which occurs periodically during sleep (every 90 minutes). There is a heightened brain activation during this time including a burst of rapid eye movement (REM), increased breathing and heart rate, genital engorgement, and paralysis of bodily movement (the person is highly aroused yet fast asleep).

Are dreams and REM sleep synonymous?
Of people awakened during REM sleep, as many as 70-95% of them report dreams in contrast to 5-10% of awakenings during non-REM sleep. This led neuroscientists (particularly Hobson and McCarley) to assume that REM and dreaming are synonymous and that dreams are meaningless conscious images triggered by signals sent by the brain stem.

What part of the brain is responsible for REM sleep?
REM sleep is produced by the excretion of the chemical acetylcholine in the pons which is part of the brainstem. Other neurotransmitters (noradrenaline and serotonin) produced by other cells in the pons switch off the REM sleep. (This is known as the reciprocal interaction/activation-synthesis model).

Why did the reciprocal interaction/activation-synthesis model contradict the psychoanalytic hypothesis proposed by Freud that dreams have meaning?
This model proposed that reciprocally interacting chemicals secreted in an elementary part of the brain that has nothing to do with complex mental functioning were responsible for the creation of dream images. (The images were simply turned on and off and were not generated by any kind of motivation in the person.) In this model, dreaming is simply an epiphenomenon of REM sleep.

What is the evidence that REM sleep and dreaming are NOT physiologically equivalent?

• As many as 50-70% of awakenings during sleep onset lead to dream reports i.e., non-REM dream reports before any REM sleep during the nightalmost as many as during REM sleep.
• Except for the length of the dream report, sleep-onset non-REM dream reports and REM dream reports are identical.
• Twenty-six cases have been reported in the neurological literature of damage to the pons resulting in total or near-total loss REM sleep. Loss of dreaming was reported in only 1 of those cases. In the other 25, loss of dreaming could not be established or was not considered.
• 110 cases published in the neuroscientific literature included reports of loss of dreaming. In all these cases, the damage to the brain spared the pons (the center for REM sleep). REM sleep was spared in those cases despite their loss of dreaming.

What part of the brain is responsible for dreaming?
Two areas in the cerebral hemispheres (very far away from the pons, which is responsible for REM sleep) and the areas of the brain responsible for higher mental functions:

1. Deep white matter of the frontal lobes which contains large fiber pathway which transmit the neurotransmitter dopamine from the middle part of the brain to the higher parts of the brain.
2. Gray cortex at the back of the brain (occipito-temporo-parietal junction) which is where the brain performs the highest level of processing of perceptual information.

What is the evidence that the frontal lobe of the brain is responsible for dreaming?

• Damage to the frontal areas renders dreaming impossible but leaves the REM cycle unaffected.
• L-dopa (a drug, used against Parkinson’s disease, which increases the amount of dopamine) leads to a massive increase in the frequency and intensity of dreaming without any effect on the frequency or intensity of REM sleep.
• The intensity of dreaming caused by dopamine stimulants (like L-dopa) can be stopped by drugs which block the transmission of dopamine (like anti-psychotics).

What is the function of the forebrain in dreaming and how do these functions relate to Freud’s ideas?
To cause the subject to seek out and engage with the external world to satisfy inner biological needs. (This is the function Freud attributed to the libidinal drivethe primary instigator of dreamsa person's wishes.)

What is the evidence that the forebrain is responsible for motivation and that this is an important trigger for dreaming?

• Damage to this pathway causes both cessation of dreaming and a massive reduction in motivated behavior
• Prefrontal leucotomies (in the 1950’s and 60’s) as a treatment for schizophrenia targeted damage to this area. There was both a cessation of dreaming and a decrease in psychotic symptoms as well as a reduction in motivation (these patients became amotivational).

What then is the role of REM in dreaming?
The REM state is one of the triggers for dreaming. The REM state is a cholinergic mechanism that is motivationally neutral. But the dream state (a dopaminergic mechanism) is driven by our wishes.

Are there other triggers to dreams (other than REM sleep)?
Sleep-onset dreams; late-morning dreams; drug-induced (like L-dopa and other stimulant drugs); and some seizures which occur during sleep (those in the temporal limbic systemresponsible for emotions and memory). These seizures usually occur during non-REM sleep.

What do these triggers have in common? Is there any connection to Freud's theories?
All of these triggers to dreams create a state of arousal in dreams. (Another connection to one of Freud’s hypothesis that dreams are a response to a disturbance of the sleep.)

We have reviewed the function of dreaming and the causes for dreaming. What about the mechanism of dreaming? Is there a connection between Freud's ideas and neuroscientific evidence?
Yes, in regression where dreaming reverses the normal sequence of perceptual events. When awake we perceive something from the outside and then process the information in the cortex. In dreams, there are internally generated images, which are fed backwards as if coming from the outside and abstract thoughts are converted into concrete perceptions. That is why there is a cessation of dreaming when there is damage to the gray cortex at the back of the brain (occipito-temporo-parietal junction) which is where the brain performs the highest level of processing of perceptual information.

(These neuroscientific ideas are consistent with Freud's idea of regression in the process of dreaming.)

What do brain imaging studies show?
The frontal and limbic areas of the brain are concerned with arousal, emotion, memory, and motivation. The back parts of the brain are concerned with abstract thinking and perception. However, the in-between areas (the dorsolateral frontal convexity - the upper end of the motor system) is inactive during sleep. This area is most active during awake activities.

What does this imply?
In waking life the normal course of events leads to action while in dreams the scene shifts to perceptions (the dream images). In dreams the motor output channel is blocked and the dream process assumes a regressive path to the perceptual system. This is what Freud hypothesized. There is also an inactivation of the reflective system (in the frontal parts of the limbic brain). This allows the dreamer to accept the dream scene without critical judgement.

References:
Mark Solms (in press): Introductory Essay for a Centenary Reprint of the 1st Edition of Freud's "Traumdeutung" (Fischer Verlag, Frankfurt am Main).

Mark Solms (in press): Dreaming and REM Sleep Are Controlled by Different Brain Mechanisms. In Behavioral and Brain Science.

Other references:
Ernest Hartmann (In press): The Psychology and Biology of Dreaming. In Dreams 1900-2000: Art, Science and the Unconscious Mind, edited by Lynn Gamwell, published by Cornell University Press in their History of Psychiatry Series.

Drew Westen (In press): The Scientific Status Unconscious Processes: Is Freud Really Dead? Journal of the American Psychoanalytic Association.

Malcolm McLeod (1992): The Evolution of Freud’s Theory About Dreaming. Psychoanalytic Quarterly : 61:37-64

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