What Your Brain Is Really Doing When You Dream

Every one of us has, at some point, dreamed. Whether it was a good dream or a nightmare, you have probably wondered about questions like these: why do we dream? And what are those dreams actually about?

Among the early scholars who studied dreams, the psychologists Freud (Sigmund Freud) and Jung (Carl Jung) are probably the most famous. Yet the theories of both men lean towards abstract concepts such as psychoanalysis and the unconscious. So this time we take a biological and neuroscientific angle to introduce some other scholars — in particular John Hobson — and how they explain why we dream.

Understanding Sleep and Dreaming

In the 1970s, two American psychiatrists, John Hobson and Robert McCarley, set out to explain why we dream from a biological and neuroscientific perspective. Their hypothesis was called the activation-synthesis model of dreaming (Hobson & McCarley, 1977). Most people will have heard that our sleep can be divided into different stages, principally the non-rapid eye movement (N-REM) sleep stage and the rapid eye movement (REM) stage (Altevogt & Colten, 2006). As we move from wakefulness into the N-REM stage, body temperature and heart rate fall, and the EEG shows the brain's alpha waves gradually being replaced by low-amplitude mixed-frequency (LAMF) activity (Patel et al., 2021). As sleep deepens, the brain waves shift again into theta waves, sleep spindles, and K-complexes (Patel et al., 2021). After that, we enter the REM stage. At that point, not only do the eye muscles and the diaphragm become active and the breathing rate turn irregular, but our brain becomes active once more, and delta waves can be detected (Altevogt & Colten, 2006). Because alpha waves are associated with the relaxed state of wakefulness, while sleep spindles and K-complexes are linked to memory consolidation; delta waves, by contrast, are very similar in frequency to the beta waves of wakefulness, and it is at this stage that most people dream (Altevogt & Colten, 2006; Patel et al., 2021). Scholars therefore generally conclude that our brain activity recedes during N-REM but becomes active again during REM, much as it is when we are awake.

The Brain and Dreaming — Neuroscience

You might find yourself puzzled: if the brain waves during the REM stage are the same as those when we are awake, why do we only dream? Hobson and McCarley (1977) likewise argued that it is precisely because our brain is so active during the REM sleep stage that it synthesises and creates dreams — that is, dreaming. Within this, the pons plays a crucial role. During REM sleep, the pons is responsible for relaxing our muscles, so that we do not physically "act out" our dreams (National Institute of Neurological Disorders and Stroke, 2022). Beyond this, the activity of the aminergic and cholinergic neuron populations in our pons is inversely related: that is, the activity of aminergic cells decreases, while the activity of cholinergic cells increases (Hobson & McCarley, 1977). This pattern is reversed when we are awake, so although our brain activity is very similar during wakefulness and dreaming, at the neurochemical level it is in fact very different.

The Brain and Dreaming — The Unconscious

Another key lies in our unconscious. Hobson (2009) proposed that we have, respectively, primary consciousness (Edelman, 2003) and secondary consciousness. Primary consciousness refers to the simple awareness we share with animals, derived from perception and emotion. Secondary consciousness is of a higher order than primary consciousness; it not only includes primary consciousness but also involves metacognition, self-reflective awareness, abstract thinking, and volition. Put simply, secondary consciousness represents the capacity to discern whether or not you have awareness (Hobson, 2009).

They pointed out that primary consciousness is still present when we dream, because we still have perception and emotion, which means we are still aware in a conscious way. Yet everyone surely knows that within a dream we have no capacity to discern whether or not we have awareness. Hobson therefore later termed this dream consciousness, to convey that when we dream we possess only a single state of consciousness, rather than the multiple states of consciousness we have when awake.

Hobson subsequently extended this theory to propose the "AIM" theory, which uses activation level (Activation level), input–output gating (Input–output gating), and mode of processing (Mode) to distinguish and detect different states of consciousness, as well as the condition of the brain (APA Dictionary of Psychology, 2022). Hobson (1992) explained that the brain's activation level, and the regions that are active, differ across wakefulness, N-REM, and REM sleep, so we can judge from the brain's level of activity and the quality of consciousness whether the brain is active and able to process information (Hobson et al., 2000). Input–output gating refers to whether external sensory information input and internal motor-neuron output commands are blocked; among these, pontogeniculooccipital (PGO) waves are responsible for organising perception and controlling the action neurons as we fall asleep (Hobson et al., 2000). And the mode of processing refers to how the changes in aminergic and cholinergic cell activity just mentioned can also be linked to the reduced self-reflective awareness, directional instability, and poor memory of REM sleep and dreaming (Hobson, 1992). Thus, when we are awake, all three aspects of AIM are very high; whereas during REM sleep only the A component remains at a high level.

Does the Dreaming Brain Run on "Autopilot"?

At the end of the 20th century, Hobson and another scholar, David Kahn, proposed the self-organisation theory of dreaming (Kahn & Hobson, 1993). Sleep not only helps the body repair fatigue and tears, but also helps consolidate memory and encode knowledge into long-term memory (Assefa et al., 2015). Kahn and Hobson (1993) held that during sleep the brain is like a system that self-organises neuronal signals; and within this complex system different elements interact with one another, with some discontinuous and uncoordinated elements emerging in the process. However, because the brain has the capacity to self-organise, these discontinuous and uncoordinated memories are automatically organised into a complete picture — that is, dreaming (Kahn, 2013). Some people therefore describe dreams as actually being a "by-product" of consolidating our memories.

In sum, from a biological and neuroscientific point of view, scholars suggest that dreaming arises either because brain activity becomes active again during REM sleep, or because a picture is formed from neurons that are "out of step" while the brain is being "cleaned". This school of thought differs from what Freud and Jung proposed: Hobson and his colleagues believe that dreams hold no complex psychological meaning, since dreams are formed through the brain's process of self-communication, preparing itself for a new day.

As a dreamer yourself, which school of thought do you find more convincing? Tonight, why not try having a little conversation with your brain in your dreams!

References:

Altevogt, B. M., & Colten, H. R. (Eds.). (2006). Sleep disorders and sleep deprivation: an unmet public health problem.

AIM model. (2022). APA Dictionary of Psychology. https://dictionary.apa.org/aim-model

Assefa, S. Z., Diaz-Abad, M., Wickwire, E. M., & Scharf, S. M. (2015). The functions of sleep. AIMS Neuroscience, 2(3), 155-171.

Brain Basics: Understanding Sleep. (2022). National Institute of Neurological Disorders and Stroke. https://www.ninds.nih.gov/health-information/patient-caregiver-education/brain-basics-understanding-sleep

Edelman, G. M. (2003). Naturalizing consciousness: a theoretical framework. Proceedings of the National Academy of Sciences, 100(9), 5520-5524.

Hobson, J. A. (1992). A new model of brain–mind state: Activation level, input source, and mode of processing (AIM). The neuropsychology of sleep and dreaming, 12, 227-245.

Hobson, J. A. (2009). REM sleep and dreaming: towards a theory of protoconsciousness. Nature Reviews Neuroscience, 10(11), 803-813.

Hobson, J. A., & McCarley, R. W. (1977). The brain as a dream state generator: an activation-synthesis hypothesis of the dream process. The American journal of psychiatry.

Hobson, J. A., Pace-Schott, E. F., & Stickgold, R. (2000). Dreaming and the brain: toward a cognitive neuroscience of conscious states. Behavioral and brain sciences, 23(6), 793-842.

Kahn, D. (2013). Brain basis of self: self-organization and lessons from dreaming. Frontiers in Psychology, 4. https://doi.org/10.3389/fpsyg.2013.00408

Kahn, D., & Hobson, J. A. (1993). Self-organization theory of dreaming. Dreaming, 3(3), 151–178. https://doi.org/10.1037/h0094378

Patel, A. K., Reddy, V., & Araujo, J. F. (2021). Physiology, sleep stages. In StatPearls [Internet]. StatPearls Publishing.