To Sleep, Perchance To...

Hello everyone! Dreams are very mysterious phenomena, yet something that occurs regularly for many of us. In Hindu mythology, Lord Brahma (left), created the universe in a cosmic dream. In aboriginal culture (bottom) ”Dreamtime” refers to the time when ancestral spirits created the land, its features, and all living creatures. In Greek mythology, Morpheus (right) the god of dreams (#matrix) is a messenger of the gods for resting souls. For super-beings, dreams are classically modes of synthesis or a conduit of information. But why do we dream, and what are dreams? Let's explore!

Yes, I have dreamt about dreaming before (top)!

It seems that dreams come in different categories (including the ones below):

But where have dreams come from, in terms of human evolution?

Evolutionary origins of dreams

There are many theories for the origins of dreams. Here are two:

1. The threat simulation theory of dreaming (TST) holds that dream consciousness is essentially an ancient biological defence mechanism. It is theorised that the dream sequence allows a rehearsal of the cognitive mechanisms required for efficient threat perception and threat avoidance, leading to increased probability of survival during evolution. Therefore, threatening events experienced while awake would lead to an increased frequency and severity of threatening events in dreams. Lending credence to this theory, severely traumatised children reported a significantly greater number of dreams with a higher number of severely threatening dream events, compared to non-traumatised children (Valli, K. et al. (2005)).

2. During rapid eye movement (REM) sleep, the brain undergoes desynchronized electrophysiological activity. This is usually accompanied by dreams. REM dreams are often emotional, bizarre and incohesive. In light of the proposal by Hebb (a pioneer of the concept of neuroplasticity), that an increase in synaptic efficacy arises from a presynaptic cell's repeated and persistent stimulation of a postsynaptic cell (Hebb, D. O. (1949)), the nature of seemingly disjointed sequences of REM dream has led to the theory that REM dream bizarreness possibly enables either a restructuring and integrative consolidation or deletion of learning experiences acquired in waking (Voss, U., Klimke, A. (2018)). The occurrence of recurrent dreams, particularly of pleasant experiences, supports this hypothesis. This fine-tuning of the mind would, in terms of evolution, lead to brains more efficient in terms of energy and processing time, - an advantage.

I personally think that dreaming is geared towards a mix of both of these functions.

Well, that's all well and good, but how are dreams actually created in the mind?

How dreams are made.

Disclaimer: Most of what I will relate is a viewpoint into this mysterious region of neurology. It is not the complete picture by a long shot!

Within the temporal lobe of the brain is the hippocampus, very closely apposed to the amygdala and limbic system. The hippocampus plays a central role in memory, imagination and dreams. Input from the limbic system might also be reflected in dreams. For example, the anterior cingulate cortex is involved in suppressing painful autobiographical memory (like in healing dreams) and the posterior cingulate gyrus is active when the mind wanders (potentially daydreaming).

Individuals that have a damaged hippocampus have a significantly lower number of dreams and the complexity of these dreams appear to be greatly reduced. (Spanò, G. et al. (2020)) The roles of consciousness, memory and perhaps also imagination are thus highlighted. This also suggests that dreaming is a part of a continuum of spontaneous, constructive thought and imagery continuously generated across the sleep and waking states.

One study found anterior temporal lobectomy patients to experience dreams with less physical aggression, thus highlighting roles of limbic input in dream content. (Joswig, H. et al. (2021))

When dream content, at specific times throughout the night, was catalogued from sleep study volunteers it was found that recent memory sources were incorporated more than distant memories. It was also found that late-night dreams in all stages have relatively less recent and more remote memory sources than dreams earlier in the night. This suggests that dream content might reflect the mechanisms of sleep-dependent memory consolidation. (Picard-Deland, C. et al. (2023) Sleep.)

Lucid Dreams: Lucid Dreamers are aware that they are dreaming. Comparing high-frequency lucid dreamers with a matched control group shows that a key factor associated with lucid dreaming is functional connectivity between the anterior prefrontal cortex (higher cognitive behaviour) and temporoparietal (recognition and association; spatial awareness, etc.) areas. (Baird B et al. (2018)) This could explain the linking of consciousness and memory recollection during lucid dreams.

Rats, Cats and Automatons!

Yes, animals dream too, thankfully. That’s why we can study dreams in several animal models.

Neuronal activities in rat brains were recorded when the animal was awake and running in a maze, and when asleep. Simultaneous measurement of neuronal activity in the hippocampus and the visual cortex showed that rats replayed memories containing the visual images that were present during a maze-run (Ji, D. (2007)), - dreaming of visual cues to food!

The pons is a structure in the brainstem that causes atonia (lack of movement) during sleep, among many other things. Cats with lesions in the pons showed stereotypic behaviour of an alert cat while experiencing REM sleep. These included turning of its head to search or hunt, grooming, jumping and aggressively defending themselves against invisible threats (Jouvet, M (1979)),- obviously dreaming of a typical cat day.

Dreaming can improve AI as well. A standard on-line (awake) learning mechanism and an off-line (asleep) unlearning and consolidating mechanism was applied to associative AI neural networks. This allowed removal of spurious patterns and reinforced pure patterns, thus improving efficiency to a theoretical maximum. (Fachechi, A. et al (2019)) So, machine learning too is improved by dreams!

Closing eyes..., no I mean "remarks"!

I think that dreams are complex products of waking experience and imagination and contribute to conscious behaviour. And if you're asking me what they could mean, I have a long answer and short answer:

Long: Dreaming and dreams are definitely important. They may mean something, or they may not. It is however more important what you see and do when you are awake! The more you do and see, the more interesting your dreams will be (vis. Technicolour Dreaming by Joseph!).

Short: Dude, I ain't no astrologer!

Please share your thoughts and any wacky dream stories (I promise I won't interpret!) in the comments below and C U soon!