The Science behind Dreams

Introduction

Have you ever wondered what’s happening in your brain when you dream? While we sleep, our minds are far from inactive. In fact, dreaming is a complex process that taps into various areas of the brain, triggering vivid images, emotions, and scenarios that often feel incredibly real. The science behind dreaming involves intricate brain activity—ranging from neural patterns that mimic waking consciousness to the brain's role in memory, emotion, and problem-solving. In this blog, we’ll take a deep dive into the fascinating science behind dreams, exploring what happens in the brain as we sleep and why our minds create these mysterious, often puzzling visions.

The Sleep

Sleep is an instinct (unlearned behaviour) that alternates with the waking.

 

Characteristics of sleep

        ·       The ability to respond to the external stimuli (e.g. noise, light, touch) is decreased.

·       Decrease in the transfer of electrical signals to the muscles and glands for their motor activities like muscle contractions, body movements and secretions.

·       Dream.

 

Polysomnography

It is the scientific study of sleep, which includes-

·       Electroencephalography (EEG) - The study of electrical activity of the brain.

Figure 1: EEG

·       Electrooculography (EOG) - The study of electrical activity of eye movements during sleep.

Figure 2: EOG

·       Electromyography (EMG) - The study of electrical activity of muscles.

          Figure 3: EMG

Stages of the sleep cycle

A full sleep cycle completes and repeats every 90 minutes. It is divided into the following stages- 

1.    Non-Rapid Eye Movement 1 (NREM 1)

It is the transition from wakefulness to sleep that lasts for about 5-10 minutes.

Here, the muscle tone, the heart rate and the blood pressure decrease.

2.    Non-Rapid Eye Movement 2 (NREM 2)

It is the light sleep stage that lasts for about 20-40 minutes.

Here the muscle tone, the heart rate and the blood pressure further decrease and the body temperature cools down.

3.    Non-Rapid Eye Movement 3 (NREM 3)

It is the deep sleep stage that lasts for about 20-40 minutes.

Here the muscles tone further decrease.

The heart rate and the blood pressure are at their lowest level.

4.    Rapid Eye Movement (REM)

It is the dreaming stage that lasts for about 10-15 minutes.

The eye movement becomes rapid.

The muscle tone and the blood pressure increase. 

Figure 4: A Hypnogram showing the sleep cycle.

Regulation of the sleep cycle by the Brain

The release of different neurotransmitters in different areas of the brain seems to determine which type of sleep should be activated.

At the onset of sleep, Serotonin is secreted in the Pons and Medulla Oblongata and seems to trigger NREM.

Figure 5: The structure of brain showing Pons and Medulla oblongata.

Figure 6: The structure of brain showing Thalamus and Cortex.

 

NREM switches to REM when the Acetylcholine is secreted in the Pons.

After that, signals from the Pons are sent to the Thalamus, which is sent to the Cortex and also shuts down the neurons in the spinal cord causing Muscle Atonia (Muscle contraction deactivation i.e. the switching of REM to NREM again).

 

Other hormones that regulate the sleep cycle

A.    Sleep-Promoting Hormones

1.      Melatonin

2.      Gamma Aminobutyric Acid (GABA)

3.      Adenosine

4.      Galanin

5.      Neuropeptide Y

6.      Neurotensin

7.      Prolactin

8.      Growth Hormone

 

B.     Wake-Promoting Hormones

1.      Cortisol

2.      Epinephrin

3.      Norepinephrin

4.      Dopamine

5.      Histamine

6.      Orexin

7.      Thyroid Stimulating Hormone (TSH)

 

The Dreams

Dreams are simply a form of sleep thinking or sleep cognition, where a very organized network of brain structures continues to function during sleep in very much same way they function in our wakefulness stage.

This is a subconscious experience of a sequence of images, ideas, emotions, and sensations that occur involuntarily in the mind during certain stage of sleep (mostly likely to occur in the REM stage).

 

Theories that explain why we dream

1.    Psychoanalytic dream theory/ Wish fulfillment theory

It was proposed by Sigmund Freud.

He believed that dreams:

1.         Represent repressed thoughts, desires and conflicts.

2.         Provide insights into the unconscious mind.

3.         Are ways for mind to process and resolve the unresolved issues.

    Figure 7: Dr. Sigmund Freud, the founder of Psychoanalysis.

2.    Biological dream theories

1.      Activation Synthesis Hypothesis by J. Allan Hobson and Robert McCarley

Dreams result from random brain activity, synthesized into coherent narratives.

Later, Hobson refined his theory to emphasize the cognitive processes like Attention, Perception, Memory consolidation, Problem-Solving, Emotional regulation, Decision making, Language processing, etc.

 

                                                 Figure 8: Dr. J. Allan Hobson,

 an American Psychiatrist and a dream researcher.

Figure 9: Dr. Robert McCarley, 

Former Chair and Professor of Psychiatry, Harvard Medical School.

2.      Reverse Learning Theory by Francis Crick and Mitchison

Dreams eliminate unnecessary neural connections, consolidating learning.

 

Figure 10: Dr. Francis Crick, 

an English Molecular Biologist, Biophysicist, and Neuroscientist.

Figure 11: Dr. Graeme Mitchison, 

an English Mathematician, Scientist, Musician, Author and Physicist.

3.      Neuropsychological Theory by Mark Solms

Dreams reflect emotional processing, memory consolidation and problem-solving.

Figure 12 : Dr. Mark Solms,

A South African psychoanalyst and neuropsychologist.

Brain Activity during REM Sleep

There is significant increase in the regional blood flow or glucose metabolism found in the Pontine Tegmentum, Thalamic Nuclei, Limbic and Paralimbic areas, Amygdaloidal complexes, Hippocampal Formation, and the Anterior Cingulate Cortex.

Figure 13 : Pontine Tegmentum.

Figure 14 : Thalamus of the brain.

Figure 15 : Anatomy of the brain showing the Thalamus.

Figure 16 : Thalamic nuclei, the different functional parts of the thalamus.

Figure 17 : The Limbic system, the Amygdala and, the Hippocampus.

Figure 18 : The anterior cingulate cortex.

        Posterior Cortices in Temporo-Occipital areas were also activated.

Figure 19 : The Temporal and Occipital lobes.

In contrast, Dorso-Lateral, Prefrontal and Parietal Cortices (the frontal parts of cortex) as well as Posterior Cingulate Cortex and Precuneus were least active.

Figure 20 : The Precuneus.

The main characteristic of the REM sleep is Limbic and Paralimbic activation, along with that the Frontal and Parietal Cortices go into quiescence.

The REM sleep is characterized by eye movements, and this is related to the occurrence of Phasic Neuronal Activity, named PGO (Ponto-Geniculo-Occipital) Waves.

Extensive researches also support the hypothesis that brain regions are comparatively more activated during REM sleep than wakefulness state.

A Cellular Hypothesis of Dream Generation

This hypothesis suggests that the neurons of Cerebral cortex involved in the perception of external input when awake. The same neurons are driven by internal input when dreaming. 

The Layer 1 of neurons is the most superficial layer of cerebral cortex, whereas the layer 5 is the most deeper layer of cortical neuron.

This internal input targets the apical integration zone (AIZ) of layer 5 pyramidal neurons (a group of cerebral cortex neuron, depicted in blue dotted ovals). 

External input mainly targets the somatic integration zone (red dotted ovals) in layer 1. When awake, the response to external input (continuous red arrow) can be amplified by apical input (dashed blue arrow), which increases the salience of external inputs that are relevant in the current context as signaled by the apical input. 

During  dreaming, internal input (continuous blue arrow) can activate an apical dendritic mechanism that enables it to drive the neuron’s output, consisting of action potentials in the axon (violet arrows), and that output is interpreted (by downstream circuits) as conveying information about the external world (external input) even though it does not.

Figure 21: Cellular hypothesis of dream generation.

Empirical Suppooort for Apical Drive 

It is the scientific experimentally evident that the dendrites of the Neocortex, a part of cerebral cortex drive the neural activity of dream generation.

  Figure 22: Neocortex.

The neocortex is a part of the brain that is involved in higher-order brain functions, such as sensory perception, cognition, spatial reasoning, and motor control. The neocortex is specifically involved in complex processes like thinking, planning, and language.

Figure 23: The role of neurotransmitters, acetylcholine (ACh) and noradrenalin (NA) during Wakefulness, Dream and Deep sleep. 

1. During wakefulness, the Noradrenalin (NA) regulates spatiotemporal summation (the information of time and space).

2. During dream state, the concentration of Acetylcholine (ACh) is greater than that of NA ; Due to which, the Apical Integration Zone (AIZ) is activated and helps in dream generation by contextual guiding into self fulfilling prophecies.

3. During deep sleep, due to low levels of both ACh and NA, the disconnection happens in between apical dendrites and soma.

Characteristics of Dream

·         The experience of sensory modalities like visual, auditory, taste, smell, movement and tactile (touch) sensations occur at the same time. Mostly visual sensations are seen as there is activation of the brain areas associated with the vision.

·         The predominance of negative emotion, like anxiety, and fear. Because the limbic system gets activated, particularly the Amygdala. The Amygdala mediates responses to threatening stimuli or stressful situations in humans and animals.

·         Lack of insights, Distortion of time perception, and Amnesia (Memory Loss) on waking up because of hypo-activation of Prefrontal Cortex.

 

Visual Distortions Experienced while Dreaming

The main reason is Heterogeneous Activation of Cerebral Regions in the Ventral Vision Stream during REM sleep.

Some of the common distortions are as follows:

 1)      Fregoli Syndrome

A rare neuropsychiatric disorder characterized by a person's delusional belief that multiple people are actually a single person, who changes appearance. 

The identification relies on large scale network involving occipital, temporal, limbic, and prefrontal areas. When there is a faulty triggering of those areas, a memory is triggered for a familiar individual.

Figure 24: Fregoli syndrome.

2)      Palinopsia

It is the multiplication of visual percept in time.

Here, the person visualizes the same image multiple times, even after the object is out of the vuisual field.

 

Figure 25: Palinopsia.

3)      Polyopia

       Multiplication of visual percept in space.

       Both Palinopsia and Polyopia are observed in patients having lesions in  visual associative areas.

4)      Macropsia and Micropsia

       These are the conditions, where the objects appear to be of different size  than actual size. 

      These occur when there is right occipital damage.

 

Conclusion and Take aways:

It all started in the ancient Egypt where thinkers described it as supernatural world. According to them, these were termed as the messages God sent as a warning.

 

Dreams are a universal human experience, fascinating and mysterious.

Understanding dreams can improve mental health and well-being.

Dreams can inspire creativity and innovation.

Dreams can provide insights into the subconscious mind.

Research has shed light on their nature, function, and significance.

Further research on dreams can advance neuroscience and psychology.

References:

1. Seligman, M.E.P. & Yellen, A. (1987). What is a dream? Behavioral Research and Therapy, 25(1), 1-24.

2. Aru, J., Siclari, F., Phillips, W. A. & Storm, J. F. (2020). Apical drive - A cellular mechanism of dreaming? Neuroscience and Biobehavioral Reviews, 119, 440-455.

3. Sleep cycle and it's stages from internet sources.