I recently engaged a discussion on Facebook that piqued my interest in the area of sleep and dream research. The conversation started on other topics and soon moved toward sleep and dreams and the possible reasons for their existence, both from an evolutionary perspective and from an individual physiological perspective. I think a proper theory of sleep and dreams must include what we know concerning the development of our species in the ancient past and how the increased cortical development that our ancestors experienced might have led to the selection of the ability to dream as a key survival advantage. First let's talk a bit about what we know about human cortical development.
Development of the human cortical mind
There are many related theories as to why our brains evolved into the large masses that they occupy today , relative to our cranium size. Compared to other primates humans have the largest brain size to cranium ratio, in fact it is believed that the gyri and sulci that make up the convolutions on the brain allow the extensive surface area of the higher cortex to fit into our relatively small brain cases. From a developmental perspective this is amazing as it hints at a runaway process of evolution of the brain that far outstripped the rate at which other structures (the skull itself) could evolve to match. So it is plausible to conclude that the changes that occurred in cortical development are relatively recent ones on this evidence alone. Fortunately, we don't have to rely on this modern interpretation of human physiology as it compares to other primates alone. We can also look at fossil finds from primate relatives going back millions of years, many of these finds presenting perfect cranial domes for us to determine the changes that occurred to their brains as they developed. More important than cross lineage comparative analysis though, is the ability to compare within our lineage of hominin ancestors. When this is done we see that the human brain went from the very chimpanzee like capacity of individuals of Austraipithicus Aferensis ("Lucy" made this ancestor famous) to the progressively larger cranial capacities of subsequent iterations of the hominin line that led directly to us according to the paleoanthropological evidence of morphological continuity. From A. Aferensis , H. Habilis, H. Ergaster, H. Erectus, archiac H. Sapien and modern H. Sapiens Sapiens. Observations of the various fossils show a marked acceleration in brain size between H. Habilis and H. Erectus.
The theories suppose that the shift of those ancestors from a predominantly herbivorous diet to ones including more protein and meat as the Rift Valley ecosystem continued to be denuded of the former dense canopy that had afforded previous ancestors protection, ushered in a growth of the brain , which itself is a large mass of proteins. The selection pressures during such a time of transition included the need to develop ways to maintain alertness to nearby dangers as absent a canopy, attack could could from many areas. An interesting correlation of the acceleration in brain growth is that it coincides with the emergence of up right walking ancestors. It is theorized that upright walking was more efficient to survival in an environment consisting of Savanna rather than forest as it allowed individuals to attain a higher position on the horizon and thus be better able to see or hear threats as they approach and it allowed escape to cover should a threat approach in a manner that our previous hominid ancestors could not match. That said, the shift in diet and the upright walking gait in a changing environment favored individuals that used those advantages to survive. As tool use coupled with mental development synergized a run away process of development occurred, particularly as it was now possible for individuals to use their hands to do things other than for the purpose of locomotion. It is likely that this aided in the transmission of knowledge through instruction performed using the hands. Individuals that mastered tools were able to train their progeny and relations and that fostered development of the brain areas necessary to retain such training a cycle of growth enabled by the serendipitous formation of the rift valley, beginning about 5 million years ago that led to the modern human mind. Homo. Erectus is the first homo species to make it out of Africa as result and in continued development in other parts of the world went on to develop actual culture and drawing ability as learned from finds in the Neander Valley in Germany.
Meanwhile, back in Africa the development continued as ancestral H. Erectus continued to evolve with the changing ecology, continued to develop their brains. In such a time, where the ability to think symbolically would have surely been an advantage in determining uses for the new elements of the changing environments, the brain may have found it useful to conserve energy after long periods of use and thus necessitated sleep periods to perform this conservation. We know that humans have a requirement for sleep that becomes progressively mandatory the longer we are deprived of it. Any theory of dreams must take into account this interesting correlation between sleep deprivation and the reduced function of the mind.
Sleeping versus dreaming
Given the correlation that exists between sleep deprivation and reduced mental and physical performance, a theory of dreams must in some way explain why sleep is necessary to restore the mental and physical function of a normal waking state. To this end I put forward yet another hypothesis on the purpose of sleep and dreams, as described by the REM state episodes that characterize their occurrence. The idea is that sleep serves to repair damage done to the cortical mind during continuous use, be it in the day time or at night (since our biorhythms vary across the globe these points are specific to the day/night cycles of the individual in a subjective sense)
This cortical damage requires the sleep phase to perform repair at which time incoming signals are unavailable to confound the repair process this leads to a first assertion of the theory.
a) The majority of repairs performed during sleep are performed on those regions that are active exclusively when the individual is awake. Thus the regions of the brain that shuttle real time sensation from the body into the processing regions of the brain for those sensations undergo some repair.
There are many other theories of dreams but many of them lack an explanation for why sleep deprived individuals experience gradual inability to perform, and posit only internal processes of the brain ,such as shuttling memories from short to long term (Continual Activation theory) or pruning abberant data from the mind (Junk removal theory ) as the cause for dreams. However, without addressing the facilitator of dreams (sleep) and the reasons for its occurrance we are only able to synthesize part of a solution to the puzzle. When we add sleep and recognize sleep deprivation as being a key cause of deficits, we must modify the dream theory to address this occurrance. This leads to the second assertion of this theory:
b) Sleep is required to reverse the damage of continual use of the cortical mind, it shuts down and repairs regious formerly in continuous use while organizing data in the form of memories stored for each of these sensory regions. An analogy from electronics expresses this assertion best. In a computer the ability to read and write data has an inverse correlation with speed, if we wish to read data quickly the data design required necessitates that writing will be slow, if we want to write data quickly then data design necessitates that reading data will be slow. A waking individuals storage mechanism is more like a system that needs to write quickly and read slowly, if the brain is acquiring billions of bits of new data every waking moment it must store that data away immediately in order to continue to acquire new data, in the background low level processes organize the incoming data but the flood of new data retards this ability. As time goes on the ability to organize incoming data becomes swamped by the incoming data and the system must shut down to continue the organization process. In computer hard disk drives new data is written to sectors of the disk such that the data is written to the nearest free memory cells, as old data is expunged this leads to gaps of free data that are then overwritten with new data, because this data is not written contiguously, subsequent reading of the written data requires more time. However, reading of the data can be accelerated, if a consolidation process called defragmentation is performed on the drive. Defragmenation requires that the portions of the drive undergoing the optimization is temporarily unavailable , much like how the sensory processing regions of the brain are unavailable when we sleep. Sleeping could be the defragmentation analog for our brains.
If sleeping is a repair process that reorganizes acquired sensory data for more efficient retrieval in the next waking state then dreaming characterized by REM states is the process of testing the reals. Playback of previously acquired data in order to calibrate the memory repair process previously performed. However, this testing phase may have had a beneficial side effect. The data acquired is played in way that is not random and may aid in determining solutions to events and situations experienced during the wake state. The REM state could serve to enhance creativity and that would easily be a selected attribute for survival for those individuals that could dream while undergoing the brain repair during sleep. Thus over time individuals that engaged in REM sleep and derived benefit could get the best of both worlds, using their brains during the wake state to survive and using it for a portion of the sleep state to engineer solutions to problems faced in the wake state. This hypothesis would be difficult if not impossible to test.
Testable hypothesis
Hypothesis, sleep deprivation experiments geared to induce sleep but prevent REM states will prevent the calibration from taking place and thus prevent individuals from restoring optimal performance during the wake state. Experiments to REM deprive individuals during sleep can explore this assertion.
Hypothesis, if sleep is a repair process, then neurotransmitters unique to the process must become active during sleep in the regions that are formerly active during the wake state. Analysis of brain scans should find such correlations between brain region and neurotransmitters.
Hypothesis, isolation and extraction of the repair neurotransmitters may allow the development of sleep deprivation aids that are more efficient than the use of stimulants, which don't really address the problem (required repair of continual use of sensory areas)
I welcome alternative ideas or corrections to this theory, feel free to weigh in the comment section below.
Links:
http://en.wikipedia.org/wiki/Homo_habilis
http://en.wikipedia.org/wiki/Homo_erectus
http://en.wikipedia.org/wiki/Dream#Dream_theories
http://en.wikipedia.org/wiki/Defragmentation
Development of the human cortical mind
There are many related theories as to why our brains evolved into the large masses that they occupy today , relative to our cranium size. Compared to other primates humans have the largest brain size to cranium ratio, in fact it is believed that the gyri and sulci that make up the convolutions on the brain allow the extensive surface area of the higher cortex to fit into our relatively small brain cases. From a developmental perspective this is amazing as it hints at a runaway process of evolution of the brain that far outstripped the rate at which other structures (the skull itself) could evolve to match. So it is plausible to conclude that the changes that occurred in cortical development are relatively recent ones on this evidence alone. Fortunately, we don't have to rely on this modern interpretation of human physiology as it compares to other primates alone. We can also look at fossil finds from primate relatives going back millions of years, many of these finds presenting perfect cranial domes for us to determine the changes that occurred to their brains as they developed. More important than cross lineage comparative analysis though, is the ability to compare within our lineage of hominin ancestors. When this is done we see that the human brain went from the very chimpanzee like capacity of individuals of Austraipithicus Aferensis ("Lucy" made this ancestor famous) to the progressively larger cranial capacities of subsequent iterations of the hominin line that led directly to us according to the paleoanthropological evidence of morphological continuity. From A. Aferensis , H. Habilis, H. Ergaster, H. Erectus, archiac H. Sapien and modern H. Sapiens Sapiens. Observations of the various fossils show a marked acceleration in brain size between H. Habilis and H. Erectus.
The theories suppose that the shift of those ancestors from a predominantly herbivorous diet to ones including more protein and meat as the Rift Valley ecosystem continued to be denuded of the former dense canopy that had afforded previous ancestors protection, ushered in a growth of the brain , which itself is a large mass of proteins. The selection pressures during such a time of transition included the need to develop ways to maintain alertness to nearby dangers as absent a canopy, attack could could from many areas. An interesting correlation of the acceleration in brain growth is that it coincides with the emergence of up right walking ancestors. It is theorized that upright walking was more efficient to survival in an environment consisting of Savanna rather than forest as it allowed individuals to attain a higher position on the horizon and thus be better able to see or hear threats as they approach and it allowed escape to cover should a threat approach in a manner that our previous hominid ancestors could not match. That said, the shift in diet and the upright walking gait in a changing environment favored individuals that used those advantages to survive. As tool use coupled with mental development synergized a run away process of development occurred, particularly as it was now possible for individuals to use their hands to do things other than for the purpose of locomotion. It is likely that this aided in the transmission of knowledge through instruction performed using the hands. Individuals that mastered tools were able to train their progeny and relations and that fostered development of the brain areas necessary to retain such training a cycle of growth enabled by the serendipitous formation of the rift valley, beginning about 5 million years ago that led to the modern human mind. Homo. Erectus is the first homo species to make it out of Africa as result and in continued development in other parts of the world went on to develop actual culture and drawing ability as learned from finds in the Neander Valley in Germany.
Meanwhile, back in Africa the development continued as ancestral H. Erectus continued to evolve with the changing ecology, continued to develop their brains. In such a time, where the ability to think symbolically would have surely been an advantage in determining uses for the new elements of the changing environments, the brain may have found it useful to conserve energy after long periods of use and thus necessitated sleep periods to perform this conservation. We know that humans have a requirement for sleep that becomes progressively mandatory the longer we are deprived of it. Any theory of dreams must take into account this interesting correlation between sleep deprivation and the reduced function of the mind.
Sleeping versus dreaming
Given the correlation that exists between sleep deprivation and reduced mental and physical performance, a theory of dreams must in some way explain why sleep is necessary to restore the mental and physical function of a normal waking state. To this end I put forward yet another hypothesis on the purpose of sleep and dreams, as described by the REM state episodes that characterize their occurrence. The idea is that sleep serves to repair damage done to the cortical mind during continuous use, be it in the day time or at night (since our biorhythms vary across the globe these points are specific to the day/night cycles of the individual in a subjective sense)
This cortical damage requires the sleep phase to perform repair at which time incoming signals are unavailable to confound the repair process this leads to a first assertion of the theory.
a) The majority of repairs performed during sleep are performed on those regions that are active exclusively when the individual is awake. Thus the regions of the brain that shuttle real time sensation from the body into the processing regions of the brain for those sensations undergo some repair.
There are many other theories of dreams but many of them lack an explanation for why sleep deprived individuals experience gradual inability to perform, and posit only internal processes of the brain ,such as shuttling memories from short to long term (Continual Activation theory) or pruning abberant data from the mind (Junk removal theory ) as the cause for dreams. However, without addressing the facilitator of dreams (sleep) and the reasons for its occurrance we are only able to synthesize part of a solution to the puzzle. When we add sleep and recognize sleep deprivation as being a key cause of deficits, we must modify the dream theory to address this occurrance. This leads to the second assertion of this theory:
b) Sleep is required to reverse the damage of continual use of the cortical mind, it shuts down and repairs regious formerly in continuous use while organizing data in the form of memories stored for each of these sensory regions. An analogy from electronics expresses this assertion best. In a computer the ability to read and write data has an inverse correlation with speed, if we wish to read data quickly the data design required necessitates that writing will be slow, if we want to write data quickly then data design necessitates that reading data will be slow. A waking individuals storage mechanism is more like a system that needs to write quickly and read slowly, if the brain is acquiring billions of bits of new data every waking moment it must store that data away immediately in order to continue to acquire new data, in the background low level processes organize the incoming data but the flood of new data retards this ability. As time goes on the ability to organize incoming data becomes swamped by the incoming data and the system must shut down to continue the organization process. In computer hard disk drives new data is written to sectors of the disk such that the data is written to the nearest free memory cells, as old data is expunged this leads to gaps of free data that are then overwritten with new data, because this data is not written contiguously, subsequent reading of the written data requires more time. However, reading of the data can be accelerated, if a consolidation process called defragmentation is performed on the drive. Defragmenation requires that the portions of the drive undergoing the optimization is temporarily unavailable , much like how the sensory processing regions of the brain are unavailable when we sleep. Sleeping could be the defragmentation analog for our brains.
If sleeping is a repair process that reorganizes acquired sensory data for more efficient retrieval in the next waking state then dreaming characterized by REM states is the process of testing the reals. Playback of previously acquired data in order to calibrate the memory repair process previously performed. However, this testing phase may have had a beneficial side effect. The data acquired is played in way that is not random and may aid in determining solutions to events and situations experienced during the wake state. The REM state could serve to enhance creativity and that would easily be a selected attribute for survival for those individuals that could dream while undergoing the brain repair during sleep. Thus over time individuals that engaged in REM sleep and derived benefit could get the best of both worlds, using their brains during the wake state to survive and using it for a portion of the sleep state to engineer solutions to problems faced in the wake state. This hypothesis would be difficult if not impossible to test.
Testable hypothesis
Hypothesis, sleep deprivation experiments geared to induce sleep but prevent REM states will prevent the calibration from taking place and thus prevent individuals from restoring optimal performance during the wake state. Experiments to REM deprive individuals during sleep can explore this assertion.
Hypothesis, if sleep is a repair process, then neurotransmitters unique to the process must become active during sleep in the regions that are formerly active during the wake state. Analysis of brain scans should find such correlations between brain region and neurotransmitters.
Hypothesis, isolation and extraction of the repair neurotransmitters may allow the development of sleep deprivation aids that are more efficient than the use of stimulants, which don't really address the problem (required repair of continual use of sensory areas)
I welcome alternative ideas or corrections to this theory, feel free to weigh in the comment section below.
Links:
http://en.wikipedia.org/wiki/Homo_habilis
http://en.wikipedia.org/wiki/Homo_erectus
http://en.wikipedia.org/wiki/Dream#Dream_theories
http://en.wikipedia.org/wiki/Defragmentation
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