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Why Do We Forget Dreams? Part I

By: , Posted on: October 8, 2014

The Biology of ThoughtOne of the most intriguing features of the brain is the phenomenon of sleep and dreams. What are dreams? What purpose do they serve? Why do we forget most of the dreams, but remember some? We do not know. Whatever is the mechanism of dreams, one thing is certain – dreams are the surreal manifestations of memory stored in the brain – which simply means that stored memory is the basic prerequisite for the formation of dreams. Putting it in another way: Sensory thoughts collected during the awaken state are obviously essential for the recollection of memory – either from the conscious mind as in day-to-day activities; or from the unconscious mind as in dreams.

Now, we can say that to study dreams in any meaningful way, we must know the fundamental mechanism by which the brain stores vast amounts of information in it as memory – i.e. an understanding of the mechanism of forgetfulness/remembrance would definitely lead us into a better analysis of dreams!

The molecular-grid model (as proposed in The Biology of Thought) unfolds a new molecular mechanism by which thoughts may be generated by the neurons by converting external stimuli into internal thoughts (Chapters 4 through 7). This model also proposes a mechanism by which memory is stored in the brain for variable periods as short-term memories and long-term memories (Chapter 8, and see below). We will now employ this model to see how it answers these questions: “Why are dreams random, and why do we forget dreams?”

A Brief Note on Dreams

Dreams are successions of bizarre and meaningless ideas and emotions that occur during certain stages of sleep, which are produced involuntarily without obvious external sensory inputs. While sleep itself is a puzzling phenomenon of the brain, dreaming is no less enigmatic!  There are various theories about their origin – Sigmund Freud famously postulated that they are the manifestations of our repressed desires and anxieties, while Carl Jung, his student, said they represent not only pent-up anxieties but dreams are meant to offer some solutions to problems. Some researchers took a more physiological explanation (in contrast to the above psychological explanations) and said that dreams are merely the manifestations of random stimulation of memory traces (see below) in the brain resulting in disorderly thoughts! Yet another theory, called the activation-synthesis hypothesis (by Hobson and McCarley – perhaps a theory much in vogue today), clubs both of these theories and says that the brain is randomly activated during dream state but the resultant irrational ideas are interpreted by the analytical human brain as some rational sequences and hence understood as purposeful “visitations”. However the disagreement continues!

Human sleep occurs in several cycles during the night, each cycle consisting of 5 stages of sleep. The first 4 stages of sleep are of varying depths ranging from light sleep to very deep sleep, and these stages correspond well with a gradual decrease in the brain activity (as demonstrated by the slowing of electrical wave rhythms in EEG). All these stages put together are referred to as non-REM sleep (or slow-wave sleep). The last stage of sleep is paradoxical in the sense that there is an increased activity of the brain (almost akin to the awaken state), and is associated with roving eye movements – hence called REM (rapid eye movement) sleep. Dreams typically occur during REM sleep.

Characteristically, the dreams experienced during sleep are not remembered after waking up and frequently they are unpleasant and ominous – though some are pleasant and welcome! Dreams are usually claimed to be associated with consolidation of memory and learning (see below) – even they are said to induce creative ideas and spur some people on new innovations. It is believed that some Renaissance painters have employed a technique of waking up while they were dreaming and depicting their dreams in their art!

A Brief Note on Neural Circuits in Sleep and Dreams

Slow, rhythmic and synchronized activity of neuronal circuits between thalamus and cortex generate oscillatory waves (the thalamo-cortical loop) and this is thought to be crucial for the development of sleep in humans. During waking periods this neural loop generates high-frequency oscillations (30-80 Hz gamma rhythm), which is suggested to be responsible for the binding of individual sensations into complex thoughts. However, in sleep primary cortical areas are shown to be shut off thus forming a “closed neural system”. Especially in REM/dream state the cholinergic neurons of the pons are activated, which then pass signals to the lateral geniculate body (in thalamus) thence to the visual cortex (ponto-geniculo-occipital spikes) (Barrett et al, 2012, pp. 272-273). It is also noted that pons sends signals to the frontal lobes which are especially activated in dreaming. Thus the integrity of brainstem is supposed to be essential for REM/dream state. Dreaming is a dopaminergic process that occurs in the limbic areas involving cortex through the Papez circuit (adding a significant emotional content to dreams).

It is thought that the characteristic inability to remember many dreams is a consequence of the dynamics of neural circuits and their neuromodulatory systems – but the following discussion reveals a different dimension to this problem!

Original Artwork by KG Dharani
Original Artwork by KG Dharani

Biological Explanation of Dreams

By the above discussion it becomes clear that there are two problems that needs explanation – one, dreams are random and disorderly, and two, we tend to forget dreams upon waking. These two outstanding features of the dreams can be accounted for by using the molecular-grid model, as shown below.

The Orderly Human Memory

Human thought is exceedingly complex, but at the same time is highly orderly. The multitude of sensory inputs we receive each moment are arranged in a sequential order to enable a meaningful idea of the external world we perceive. For example, when an image of a rose flower impinges on the retina, several signals of color are sent to the neurons in the brain where they are converted into several primary thoughts of color (details in the book!). Only when the perceptions of these colors and shades are arranged in a sequential order, we can get a meaningful idea of the rose we see – if they were to be disorderly the image we appreciate would no longer be that of a rose! Consider a more complex situation – when we pick up a rose and smell it, we are utilizing at least three modalities of sensation all at once. We look at the flower, we feel the texture of it while picking and we smell the odor of it – only when all these sensory inputs are arranged in a sequential and organized manner, it gives us the knowledge of a real rose (i.e. not a paper-rose!). When our thoughts are disorderly (as for example in an inebriated state or in insanity) the information becomes disorderly and hence the inference routs into irrational ideas (perhaps the rose is perceived as a paper rose or a blob of red waste-tissue).

What causes our conscious thoughts to be arranged in an orderly fashion, what are the mechanisms involved? And why are dreams disorderly and ephemeral?

We will answer these questions in my next blog post by looking at five questions in my next blog post. See them now!

About the Author

KG DharaniKrishnagopal 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




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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  • Laurin Machado

    awesome report. can’t wait for part two.namaste

  • Yo1041994

    Its a beautiful article, sir. I liked the language too.
    I’m an engineering student and I have a fascination for dreams, working of brains, molecular biology. As a non-academic in Biological sciences, which book do you recommend for a casual reading, that which may further my interest in this topic?
    Thank you,
    Asesh Basu.

    • Shikha Prasad

      Sir its one of the best article i have read after ages on brain’s thought process and working. Though i am a PhD student doing research in botany but i love reading articles on dreams and brain, so sir i would like to know some more articles and research papers from any author on this particular topic.
      Thank You,
      Shikha Prasad
      PhD Scholar
      Department of Botany
      University of Delhi.

  • Mike Hackett

    A very nice article overall and thank you for your work on understanding brain processes in sleep and dreaming.

    One point however I would like to make please? I’m afraid I cannot agree with your definition of a dream as “…successions of bizarre and meaningless ideas and emotions…”. How can anyone but the person having the dream say that a dream is meaningless? If I read something bizarre or seemingly bizarre, this does not make it meaningless. It makes it meaningless to me. Your definition then creates a generalisation that discounts the dreamers experience of the dream from an expert position. It is my humble opinion that the dreamer is the expert on what is meaningful in their lives, not an external expert.

    As a counselling psychotherapist, I have had clients bring dreams or fragments of dreams to therapy which have been profoundly meaningful and created touchstone opportunities to understand something deeply affective in their lives. Though we may not know why we sleep/dream, I see no valid reason why we should not use all of the client’s experience to assist their our cognitive, emotional and existential wellbeing by integrating all aspects of their experience (those during wakefulness and those during sleep) to explore their relevance to our current life situation and assess if these experiences are meaningful to them or not.

    Thanks for offering us the opportunity to comment and contribute. I look forward to your next blog post on the topic of sleep and dreaming.

    • Summer Victor

      I am so glad that I happened upon this article tonight. I appreciate and tend to side with your viewpoint Dr. Hackett. Throughout my life, especially during times of great stress and/or change, I have often kept a dream journal. I have found that analyzing my subconscious brain activity, both independently and also during therapy, is extremely beneficial to my emotional, mental, and spiritual health. It is and was, however, always up to me to determine what was pertinent and what was simply bizarre and meaningless” residual shedding of my short and long term memory.

      I would also like to make mention of your statement Dr. Dharani that dreams are “characteristically” and “frequently” both “unpleasant and ominous- though some are pleasant and welcome!” to be untrue for me and it would seem rather subjective to your own personal experience. I wonder what the statistics are pertaining to your particular point of view versus my rather positive experience with dreams? Am I within the minority, rather than what I have always believed as the majority, of the population’s perspective?
      I would like to thank you both for such an interesting, well written, and quite thought provoking discourse!. Dreams are one of my favorite topics to discuss and research. What fantastic food for thought! I am not a doctor or scholar but I have such a fascination and curiosity when it comes to psychology. I look forward to future posts! I appreciate the opportunity to comment as well.

  • J.Garcia

    Would mirror neurons be active during sleep stages, in people that sleep walk?

  • Catherine Verney

    I found your blog post fascinating and I really enjoyed reading it. But was put off a little by your use of the Americanism, ‘chapters 4 through 8.’ Is this really necessary?

  • Behnaz

    This is a wonderful topic and i am really interested.

  • Krishnagopal Dharani

    Thanks for the comment and your kind appreciation. I would
    rather explain my point in calling dreams “meaningless”. If we could slice our
    dreams into small bits they all carry meaning – just because they are all
    invariably parts of the sensory inputs we receive from the external world in
    the wakeful state, and each of the sensory input we receive are valid and “real”
    happenings of the world! But the sequence in which the bits assemble and
    present themselves in the dreaming state is most often random and this makes
    the dreams bizarre and somewhat meaningless. Sometimes (or most of the times?) we
    all could rearrange the bits into their proper sequence and understand dreams in
    their right perspective – this is our common experience. But an outstanding
    number of dreams (here I presume the number is outstanding!) remain elusive and
    the dreamer himself/herself may not be able to reset the segments of dream into
    some intelligible sequence – and here, I think, would come the help of a specialist
    who could, to some greater or lesser extent, rearrange the sequence to help bring
    bizarre dreams into some sensible thoughts. In this context, I fully realize
    that dream is a portal for the study of a person’s cognitive and emotional state
    which underscores the importance of various specialists in the field.

    However, I should stress here that I am no specialist in analyzing
    dreams. I am a biologist, at best, and I would strive to find out the
    physiological (or molecular) basis of dreams (as a part my work in delineating
    the molecular basis of thought in general). And consequently, my purpose of
    study of dreams as such is limited. Anyway, I wish you could have commented on
    the Part II of the article as well.


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