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Why Do We Forget Dreams? Part II
This is Part II of Krishnagopal Dharani’s two-part blog series on dreams. You may find Part I here.
We have discussed dreams in the previous blog post, and concluded by asking the following two questions “Why are the dreams random, and why do we forget dreams?” We will now employ the molecular-grid model to explain the mechanism of dreams. The following five question-and-answers offer a new dimension to the problem of sleep and dreams!
Question 1: How are Primary Thoughts Generated?
The molecular-grid model, as proposed in my book, suggests that primary thoughts (i.e. the most fundamental units of thought) are generated by the molecular-grids situated in the dendritic membranes of special sensory neurons called perceptual neurons. An elaborate description is undertaken in Chapters 4-7.
Question 2: How are these primary thoughts arranged in sequence?
In order to produce a meaningful idea of the external world the primary thoughts would have to be arranged in a sequential order, as we have seen in the above example. Chapter 8 proposes a mechanism by which dendrites containing the molecular-grids are arranged in orderly bundles which when serially fired result in generation of primary thoughts in sequence. Current research, in fact, has shown that dendrites in the human cortex are arranged in spatially oriented bundles (Barrett et al, 2012, p. 272). It is proposed that these dendritic bundles, named dendritic pleats, are arranged in a particular fashion as the input of sensory signals direct, and thus when these dendrites are excited it results in orderly thoughts. These dendritic pleats would thus form the physiological basis of memory traces in the human brain. This whole process of memory storage is called memory consolidation.
Dendritic pleats represent the hardware; memory constitutes the software!
Question 3: How are the dendrites held together?
Current research has proved two outstanding features related to protein synthesis in brain:
- It has been experimentally shown that for memory consolidation to occur protein synthesis is essential – if protein synthesis is blocked the formation of long-term memories is abolished. Experimental research has shown that memory consolidation starts after 5-10 minutes and is completed after about 1 hour or so – and if protein synthesis is blocked in animals during the acquisition of long-term memory then the formation of LTM is prevented (Guyton & Hall, 2008, p. 726). Furthermore, it is documented that if protein synthesis is blocked after about 4 hours it shows no effect on learning (Barrett et al, 2012, p. 285) – obviously because consolidation is completed by then.
- It has long been known that protein synthesis in the brain is increased during sleep. Now it is shown that protein synthesis is increased exclusively in deep sleep, not in light sleep (Nakanishil et al., 1997). Another study shows that protein synthesis is not affected in wakefulness and REM sleep, but is significantly enhanced in slow sleep (non-REM sleep) (Ramm and Smith, 1990).
The implications of the above two findings in our present discussion becomes obvious in Question 5.
It has been suggested in Chapter 8 (along with further evidence) that proteins are responsible for binding the dendrites together to form dendritic pleats – these protein bonds and their effect on memory storage are discussed in some detail in the book (p 156).
Question 4: What directs the rational sequence?
Finally the question of what allows us to arrange these thoughts in a rational order. Chapter 9 of The Biology of Thought undertakes a scientific study of mind and consciousness, and as a part of the study, also discusses how the human mind has progressed to achieve intelligence. The outstanding feature of human brain is its ability to execute working memory which has a central executive, as proposed by Baddeley and Hitch (p 58). The central executive controls the subordinate sensory systems and is responsible for arranging the human thoughts in a coherent manner. Central executive is discussed in some detail in the book (Chapter 9, pp 171-174).
Question 5: What happens in dreams?
Now the crux of the problem: Why are dreams disorderly and ephemeral? The central executive appears to play a central role in orchestrating dreams. Whereas in the waking periods the central executive takes charge of our memory formation, in sleep it is not in full action, and hence in dreams the dendritic pleats fire indiscriminately resulting in haphazard activation of memory traces and thus forming distorted ideas. Research has shown that in deep sleep (or non-REM sleep) protein synthesis is activated thus helping in our memory consolidation – forming protein bonds in the dendritic pleats – and in REM sleep protein synthesis is slackened resulting in breaking down of dendritic pleats too soon which makes these memories transient! This is the reason why dreams usually fade into oblivion soon after waking up.
If a person wakes up during REM sleep there is a likelihood of CE being revived instantly which can press protein bonds into action resulting in ‘tight’ dendritic pleats, thus leading to memory consolidation – hence we tend to remember these for a long-time.
But there are many loose ends and open questions that remain to be answered – for example what exactly is this central executive which bosses around our thoughts? What about our free will? These abstract problems are discussed in Chapter 10!
About the Book
The question of “what is thought” has intrigued society for ages, yet it is still a puzzle how the human brain can produce a myriad of thoughts and can store seemingly endless memories. All we know is that sensations received from the outside world imprint some sort of molecular signatures in neurons – or perhaps synapses – for future retrieval. What are these molecular signatures, and how are they made? How are thoughts generated and stored in neurons? The Biology of Thought explores these issues and proposes a new molecular model that sheds light on the basis of human thought. Step-by-step it describes a new hypothesis for how thought is produced at the micro-level in the brain – right at the neuron.
About the Author
Krishnagopal Dharani is a medical doctor practicing at Adoni, a large town in South India. He has graduated in medicine from Kurnool Medical College in Andhra Pradesh, and did his general surgery from Kasturba Medical College, Manipal, South Canara. He took his post-doctoral specialization in vascular surgery at the Nizam’s Institute of Medical Sciences, Hyderabad. He is presently holding the post of Specialist Civil Surgeon in AP Medical Services, and despite having a large surgical practice, he manages to split his time between his profession and his academic pursuits in science. The author can be contacted at firstname.lastname@example.org
1. Barrett KE, Barman SM, Boitano S, Brooks HL (eds.) (2012) Ganong’s Review of Medical Physiology, 24th Edition, New Delhi: Tata McGraw Hill
2. Guyton AC, Hall JE (eds.) (2008) Textbook of Medical Physiology, 11th Edition, Noida: Elsevier-Saunders
3. Nakanishil H, Sun Y, Nakamura RK, Moril K, Ito M, Suda S, Nambal H, Storch F, Dangl T, Mendelson W, Mishkin, Kennedyi C. Positive correlations between cerebral protein synthesis rates and deep sleep in Macaca mulaffa. European Journal of Neuroscience 1997;(9)271-279
4. Ramm P and Smith CT. Rates of cerebral protein synthesis are linked to slow wave sleep in the rat. Physiology and Behavior 1990;(48)749-753
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