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REM SLEEP, PERCEPTION AND THE HUMAN BRAIN
Neuroscience of Dreaming: Text
"In order for a given species to preserve itself... it must capture in its conception of reality enough of what is uniform and predictable [so] that a scheme of its behavior can be constructed on that basis. The utility of preservation, and not some abstract theoretical need to be undeceived, stands as the reason for the development of of the sensory organs..."
Friedrich Nietzsche
Neuroscience of Dreaming: Quote
Brain Waves
The nervous system uses electrical impulses or "action potentials" transmits information throughout itself. I will use the term “neural activity” to describe action potentials taking place over many neurons, particularly in specific brain structures.
Neuroscience of Dreaming: Welcome
Neural activity is incredibly physically demanding on an organism. It requires constant blood flow, as well as a multitude of chemical and metabolic processes. More neurons means more energy is required to keep the nervous system heathy and functioning. Consequently, neural activity becomes increasingly more demanding as the nervous system of an organism becomes larger and more complex.
Neural activation occurs across the brain in oscillating wavelike patterns that can be measured with a device called an electroencephalograph (EEG) which records electrical activity in the brain and outputs lines.Tall lines indicate large spikes in electrical activity across the brain while more flat lines indicate less neural activity. Activation patterns in an organism's nervous system constantly change throughout the day depending on what the organism is doing.
When an organism is awake and alert, brain waves typically oscillate at low voltages and in rapid and random patterns. Quick and spontaneous activation is indicative of an alert organism that is navigating its environment as it reacts to spontaneously occurring stimuli. But would be far too physiologically taxing for an organism to invariably maintain an alert pattern of neural activity activation. It must eventually sleep.
Neuroscience of Dreaming: Text
Alert EEG Recording
Neuroscience of Dreaming: Image
At the onset of sleep, an organism loses touch with its physical world; it does not perceive external stimuli and thus, physical stimuli do not elicit a neural response. The voltage of the waves increases and the rate at which they oscillate begins to slow down, activation patterns also become increasingly more synchronized and predictable.This stage of sleep technically involves many states (the deepest of which being delta wave sleep). For practical purposes we will group all these stages together and refer to them as non-REM sleep. Since these stages are less physiologically demanding, non-REM sleep gives the body and nervous system time to rest and heal.
Neuroscience of Dreaming: Text
Non-REM Deep Sleep EEG Recording
Neuroscience of Dreaming: Image
Eventually, after a certain point of the organism being asleep, its pattern of neural activation changes and again starts to resemble that of wakefulness. Spikes occur at lower voltages and begin to oscillate faster in less predictable patterns. Intuitively, this would suggest that the organism has woken up and regained contact with its physical perceptual world. But interestingly, these EEG observations occur while the organism is still asleep and oblivious to its external environment. It’s quite possible depending on the organism, that its neurons are reacting to internally generated perceptions, perceptions that trick the nervous system into behaving as though it were more or less awake which would account REM sleep EEG readings being so similar to awake EEG readings. This stage of sleep is REM sleep.
Neuroscience of Dreaming: Text
REM Sleep EEG Recording
Neuroscience of Dreaming: Image
Prehistoric Fish Dreams
A recent study looked at zebrafish and observed patterns of neural activation that resemble REM sleep. This finding challenged what we thought we knew about REM sleep and its evolutionary origins.
Neuroscience of Dreaming: About Me
Sometime around 450 million years ago, a small fish with only a few thousand neurons learned how to dream. I'll refer to this ancient fish as "the originator". Now, technically, that first statement probably isn’t very accurate. Because what we call a ‘dream’ is a subjective experience. An internally generated subjective perceptual experience (IGPSE). And as of now, science is unable to verify whether or not a fish has a subjective experience that is comparable to our own. A more scientifically accurate statement would be: sometime around 450 million years ago, a small fish with only a few thousand neurons began to develop patterns of neural activity that resembled REM sleep, the stage of sleep that often accompanies dreaming in humans.
REM sleep stands for rapid eye movement sleep because while we are in REM sleep, our eyes dart back and forth underneath our eyelids as if we’re scanning some sort of internally generated environment. Because that is precisely what we are doing, looking around our dream world. Waking a person out of REM sleep reliably yields a subjective report of a dream from that person. Such reports are what established the link we made between REM sleep and dreaming. They're also reason we're unable to determine whether or not this 450 million year old fish had the first dream; there is no way to solicit a subjective report out of any non-human animal, much less a long extinct fish with a comparatively primitive nervous system.
For this reason, I think it would be better suited to remove the subjective quality of the an IGSPE and call a fish "dream" an internally generated perceptual experience (IGPE). Similarly, the detection of any stimuli from its environment while awake would constitute an externally generated perceptual experience (EGPE).
Before researchers found REM-like activations in a zebrafish, science initially believed that REM sleep occurred exclusively in mammals, reptiles and birds. Taking this discovery into consideration, it seems that all mammals, birds and reptiles share a common ancestor with the zebrafish. This ancestor is our hypothesized 450 million year old "originator". The neural mechanisms that allow us to dream extend back and originate with this creature. Assuming this is true, these original REM sleep mechanisms would also be present in all spider monkeys, yellow bellied turtles, antipolice kangaroos, sumatran elephants, white tailed eagles, bottlenose dolphins, rhinoceros vipers, dogs, and millions and millions of more species since the originator.
Neuroscience of Dreaming: Text
Neuroscience of Dreaming: Image
Evolution is a gradual process, the nervous system of the originator slowly changed and evolved into the millions of mammal, reptile and bird nervous systems that exist today. The brains of all the originators descendants fall along a spectrum of complexity, with human beings being the most complex. It stands to reason that all perceptual experiences, whether internally or eternally generated also fall along a spectrum with ours being the most complex. The essential yet unanswerable question is at what point in time and physiology does an organisms experience become subjective? When did the first 'dream' occur and how complex does the brain have to be to necessarily give rise to one?
Although dreams are internally constructed, the perceptions that create them them are generated by sensory information that the brain has stored from the physical world. Our internal world reflects the ways in which we absorb the external world. During REM sleep, the brain reconstructs a world based on the perceptual information it has in its arsenal. Dreams are essentially IGPEs, but EGPEs are essentially necessary for establishing the perceptual neural pathways that create the experience. Different species view the external world through a unique perceptual lenses. These lenses can be referred to as the perceptual "umwelt" of a species. And an organism's umwelt depends entirely on the structure of its brain and the configuration of neural pathways between them.
I have a boxer named Duke. I know he dreams. I’ve seen him on the floor; barking and growling from behind his closed jowls, twitching back and forth as if he were trying to chase after something. Typically, I imagine that he's chasing a rabbit across a grassy landscape (the type of situation he experiences on a daily basis). However I am utterly unable to imagine this experience in the way he does because I do not have the brain of a dog. Tragically, Duke's umwelt is inconceivable to me. Is he smelling the rabbit in the dream or seeing it? Even if I knew the answer it would make no difference because I can't see or smell a rabbit the way he does. It's possible that other species have dreams or primitive IGPEs of sensory experiences that are inaccessible to us.
Neuroscience of Dreaming: Text
The IGPE of a bat in REM sleep might perhaps involve whatever sensation is associated with echolocating an insect to eat.
Pit vipers can detect infrared light waves, perhaps they have some rudimentary form of a dream involving such a perception of a mouse.
The zebrafish, shown to have REM-like neural behavior might experience IGPEs that involve sensing magnetic fields.
Neuroscience of Dreaming: Work
It seems reasonable that every species that experiences REM sleep has a unique type of internally generated perceptual experience that depends on what brain structures are present and active during the REM stage. The essential yet unanswerable question is at what point in time and physiology does an organisms experience become subjective? When did the first 'dream' occur and how complex does the brain have to be to necessarily give rise to one? What brain structures are required to turn a REM perception into a dream? What role do these structures play during a waking EGSPE? And how does this effect the perceptual umwelt of such an organism?
Neuroscience of Dreaming: Text
100,000,000 Times More Neurons
Countless changes have taken place over the course of evolution from our fish ancestors to us, changes that influenced the ways we sleep, perceive and dream. We are the only species that we can verify to have subjective experiences. But what makes these experiences possible?
Neuroscience of Dreaming: Welcome
You and I around a hundred billion neurons, over a hundred million times more; and we have a lot to show for it. We have complex conscious experiences, and the ability to talk about our complex conscious experiences, this is an incredible feat of biology that we rarely stop to think twice about. But how is it possible? It would make sense to assume that more neurons and more neural activity equates to more elaborate conscious experiences. However it’s not just the number of neurons that matters when it comes to complex conscious experiences, but the ways in which those neurons are organized.
The cerebral cortex is the outer layer of the brain, it is made up of different regions that serve different functions, these layers are referred to as cortical regions. Cortical regions are particularly well developed in humans. An advanced cerebral cortex is associated with the ‘higher cognitive processes’ that make us unique as humans. The complexity of the cerebral cortex is also thought to contribute to our ability to have powerful conscious experiences. This means not only do we have perceptions, but we also have the capacity to be highly conscious of our perceptions. Research has shown that the size and number of folds in an organism’s cerebral cortex positively correlates with its ability to form more complex thoughts.
Neuroscience of Dreaming: Text
Neuroscience of Dreaming: Image
So how exactly do these hundred billion neurons and a well developed cerebral cortex work to produce complex experiences? Let me give a somewhat simplified scenario of how our brains and neurons construct an EGSPE from physical stimuli.
Imagine you’re looking at a photograph, taken years ago, of you and and old friend. Particles of light reflect off the photograph and enter your retina where they react with ganglion cells (specialized neurons that detect light). The millions of ganglion cells then transmit a summated electrical signal through the optic nerve to a brain region called the thalamus (composed of thalamic neurons). The thalamus is a hub that refines and organizes the signals and then relay them to the very back of the brain to the visual cortex, which creates conscious visual experiences. This conscious experience was initiated by external stimuli (particles of light) which initiated a cascade of electrical signals which ended up in a cortical region where they became an EGSPE.
Neuroscience of Dreaming: Text
Neuroscience of Dreaming: Image
After you are consciously aware that you’re looking at a photograph of you and a childhood friend, further neural signals are sent out that cause other brain regions to light up. Due to the nature of the photo (a nostalgic image of you with an old friend) it’s possible that there would be a fair degree of activation in your hippocampus, which is associated with memory storing and processing. Another region that may show activation is the amygdala, which is vital for emotional regulation.
But let’s say that while you’re looking at the photo this time, you notice something new. Your friend is giving you an odd, slightly disapproving, look as you grin at the camera totally unaware. This realization of this might trigger activation in your prefrontal cortex, which helps us navigate social situations, engage in self reflection and plan out logical future actions. Maybe now the next time you see that friend, you’ll ask them if you did anything to bother them on the particular day that photo was taken. These thoughts about what might have happened resulted from additional neural activity caused by the visual perception of the photograph. But these abstract conscious thoughts, even if they do involve imagery are not IGSPEs because they still depend on external stimuli to trigger them.
Neuroscience of Dreaming: Text
Neuroscience of Dreaming: Image
So what does constitute an IGSPE? What makes a dream a dream? To answer that question, we need to look at the ways in which the dreaming brain functions differently from the waking brain.
EEG recordings have already shown that there are many similarities between EGSPEs (awake EEGs) and IGSPE (REM sleep) in terms of neural activation. But there are many ways that the dreaming brain behaves differently from the awake brain. Waking experience involves a fair degree of neural activity across the entire brain. However, this is not the case for the dreaming brain. Most of the brain is notable inactive during REM sleep with a few notable exceptions. Spontaneous activation of these “exceptions” during sleep not caused (even indirectly by external stimuli) are what give rise to the IGSPE of dreaming. These notable exceptions are the regions of: the visual cortex, the hippocampus, and the amygdala. Even though most of the brain is relatively inactive during REM sleep, there is one region who’s inactivity if of particular importance in distinguishing dreaming consciousness from waking consciousness, the prefrontal cortex.
These findings should not be much of a surprise considering a normal dream experience. Dreams are internally generated visual worlds (hence activation in the visual cortex) that are constructed out of memories of the real world (hence activation in the hippocampus). The environment and context of dreams change and involve nonsensical or dramatic subject matter that often produces intense emotions (hence activation in the amygdala). We do not however, process this subject matter from a logical standpoint or pause to self-reflect (hence the lack of activation in the prefrontal cortex). Even if the content of a dream is inconsistent with reality, we fail to notice any irregularities until we reflect back on it during waking consciousness; once the prefrontal cortex become active again we weave the contents of our dreams into a coherent storyline and retroactively interpret intentions that we not there.
Every change in our consciousness, in our mind, has some change in neurological activity to account for it. These conscious experiences, whether externally or internally generated, would not be possible without the unique size and shape of the human brain. Although we cannot know for sure, it seems safe to assume that activation in cortical regions accounts for the subjectivity of an experience, and that activation in different cortical regions correspond to different types of subjective awareness.
The dreaming brain shows us what activation in certain brain regions means in terms of a subjective experience. The dichotomy between dreaming and waking reality is an incredible interesting topic to analyze. However things become a whole lot more interesting and pertinent to the topic of human uniqueness is when the brain behaves in ways that combine aspects of internal and external perceptions. In other words: when REM sleep goes awry.
Neuroscience of Dreaming: Text
Neuroscience of Dreaming: Text
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