The Nature of Dreams: an interview with Eric Nofzinger
Eric Nofzinger was Professor of Psychiatry and Director of the Sleep Neuroimaging Research Program at the University of Pittsburgh, School of Medicine, before founding the company Cereve in 2008. He has also been a President of the United States Sleep Research Society and a President of the Sleep Research Society Foundation. His research focuses on the brain mechanisms involved in sleep and sleep disorders, using data from Positron Emission Tomography (PET) and functional Magnetic Resonance Imaging (fMRI). He published widely in this field and pioneered the use of these neuroimaging methods to develop a neurobiological model of insomnia. He recently co-edited the book Neuroimaging of Sleep and Sleep Disorders with Pierre Maquet and Michael J. Thorpy (Cambridge: Cambridge University Press, 2013).
Stéphane Verlet-Bottéro — In a 2004 study you discovered an anterior paralimbic REM activation area containing key cortical & subcortical components of the emotional and social brain. What do these neural structures contribute to the experience of dreaming?
Eric Nofzinger — Correct. The “content” of dreams, including the images, the stories, the feeling states would be expected to be derived from the relative activation of these structures. So, the dream experience is a by-product of the cognitions and emotional states that reside in these structures. For example, our strong, primitive emotions such as fear, anxiety, anger and sexual drives are thought to reside in or are regulated by these structures and activation of these structures could be thought to be responsible for the typical dream-like experiences we typically associate with dreaming.
SVB — PET/fMRI neuroimaging techniques have also revealed that contrary to limbic and paralimbic functions, areas of the prefrontal cortex sustaining cognitive control and metacognition are largely deactivated. That could explain that something we would recognize as absurd in awake state may feel normal in dream-state. Could we argue that recent research validates the Freudian theory of the unconscious in the case of dreams?
EN — I would agree. The ‘executive’ brain, including the prefrontal cortex is thought to be responsible for our waking, conscious cognitive sense of control, planning and willed thought. These typically modulate our more primitive impulses, emotions and basic emotional drives. The apparent lack of activation of these structures in REM sleep implies that these processes are not active in dreaming, allowing for the expression and more unfiltered experience of more primitive emotional states and feelings in dreaming.
In terms of Freudian structural models of mental processes or the psyche, the id, ego and super-ego are the three parts of the psychic appartus; they are the three theoretical constructs in terms of whose activity and interaction mental life is described. According to this model of the psyche, the id is the set of uncoordinated instinctual trends; the super-ego plays the critical and moralizing role; and the ego is the organized, realistic part that mediates between the desires of the id and the super-ego. The id processes closely resemble what we currently ascribe to be the functions of anterior paralimbic cortex and would be active in dreaming. The ego and super-ego processes closely resemble what we currently ascribe to be the functions of the executive cortex and would tend to be less active or play less of a role in dreaming. The functional neuroanatomy of REM sleep then would be supportive of this basic notion of Freudian models of the psyche in which dreams represent the expression of the id in the absence of oversight, or control by the super-ego and ego.
SVB — Some of your more recent research focuses on the relationship between depression and REM sleep, demonstrating that the anterior paralimbic function is altered while tectal and left hemispheric areas are more active than in healthy REM sleep. How does this affect the sleep and dreaming process of people suffering from depression?
EN — The experience of depression, which includes feelings of lack of control, loss of will, impaired cognition and a general loss of regulation of strong emotions could be explained by the general impairment of frontal and pre-frontal cortex function and unregulated limbic and paralimbic activity. The imaging studies of depressed patients show impaired frontal cortex function and an upregulation of limbic and paralimbic structures in REM sleep. In this manner, the alterations in brain function during REM sleep may be a reflection of a loss of balance between executive and limbic and paralimbic cortex in depressed individuals in which they are driven more by strong, mostly negative emotional states that tend to be unregulated by more rationale thought.
SVB — Neuroimaging has also contributed to the discovery of fundamental alterations of the function of limbic and paralimbic neural systems in human sleep pathologies. Has this helped understanding sleep disorders and finding ways to cure them?
EN — The depression findings, and the characteristic sleep pathologies noted in depressed patients such as difficulty falling asleep, staying asleep and early morning awakenings, are perhaps the best and most studied example of fundamental alterations of limbic and paralimbic neural systems among all sleep disorders. Similar findings have been shown in the sleep disturbances of patients with post-traumatic stress disorder, a disorder characterized by sleep disruption and by the repetitive unwanted traumatic dreams they can experience, often reliving their original traumatic event. Examples include trauma related to combat and trauma related to rape.
Patients who suffer from insomnia alone, which is difficulty falling asleep or staying asleep, even in the absence of depressed or anxious symptoms, have also been shown to have abnormal degrees of activity in brain structures that mediate arousal and that overlap extensively with limbic and paralimbic brain structures. Indeed, some studies showing successful treatment of insomnia with cognitive behavior therapy have shown reductions in limbic activity during sleep following treatment.
SVB — In that perspective, how much does REM brain activity contribute to functional restoration and feeling well during the day?
EN — While the evidence here is a little more indirect, there are several research findings that would suggest that REM brain activity plays an important role in functional restoration and feeling well during the day. As noted above, depressed patients have abnormal REM brain activity and do not feel refreshed on awakening and do not feel well during the day. Many medications that treat depression are known to inhibit REM sleep likely by dampening activity in limbic and paralimbic structures. Individuals going through stressful life events who show some degree of working through their stressors in their dreams tend to do better over time, i.e. feel better during the day, than individuals who do not show evidence of working through their stressors in their dreams. There are many lines of evidence, therefore that what the brain is doing in REM sleep has a significant influence on how we feel when we awaken and how we feel and function during the day.
SVB — There has been cases of people with cortical lesions depriving the brain from REM sleep, who have a totally normal existence otherwise. Ultimately, can neurobiology say if dreaming is essential to brain function or more an epiphenomenon of REM sleep?
EN — One can find exceptions where REM sleep does not occur, either resulting from some brain lesion or from certain medications, and otherwise normal function is present. In these instances, presumably, the brain is able to find alternate ways of adapting to life than through the normal occurrence of REM sleep dreaming. This is probably more an example of how the nervous system can adapt to somewhat unnatural conditions rather than providing evidence that REM sleep is not essential for normal functioning. The more parsimonious view would be that REM sleep is a naturally occurring phenomena in the vast majority of individuals, is known to activate structures known to play a fundamental role in the regulation of instinctual behavior and probably plays some essential role in the overall regulation of emotional behavior and subsequently how we feel and act when we are awake.