J. Lee Kavanau
My experimental studies of the last 15 years have related to avian behavior, evolution, and responses to unnatural light cycles, working primarily with small parrots. These studies led me into my most recent field of study, the evolution of mechanisms of memory (synaptic efficacy maintenance) and of sleep, and the function(s) of sleep. The nature of these studies and findings is conveyed by portions of the abstracts from four of my recent papers.
Abstract [Neuroscience 79:7-44 (1997)]
After the origin of activity-dependent synaptic plasticity, whereby single activations of synapses led to
short-term efficacy enhancement, lengthy maintenance of enhancements probably was achieved by
repetitive activations ("dynamic stabilization"). One source of selective pressure for the evolutionary
origin of neurons and neural circuits with oscillatory firing capacities may have been a need for
repetitive spontaneous activations to maintain synaptic efficacy in circuits that were in infrequent use during activity. This process is referred to as "non-utilitarian" dynamic stabilization.
Dynamic stabilization of synapses in "simple" invertebrates occurs primarily through frequent use. In complex, locomoting forms, it probably occurs through both frequent use and non-utilitarian activations during restful waking. With the evolution of increasing repertories and complexities of behavioral and sensory capabilities with vision usually being the vastly pre-eminent sense, brain complexity increased markedly. Accompanying the greater complexity, needs for storage and maintenance of hereditary and experiential information (memories) increased greatly.
It is suggested that these increases led to conflicts between sensory input processing during restful waking and concomitant non-utilitarian dynamic stabilization of infrequently used memory circuits. The selective pressure for the evolutionary origin of primitive sleep may have been a resulting need to achieve greater depression of central processing of sensory inputs, largely complex visual information, than occurs during restful waking.
The electrical activities of the brain during sleep (aside from those that subserve autonomic activities) may function largely to maintain sleep and to dynamically stabilize infrequently used circuitry encoding memories. Sleep may not have been the only evolutionary adaptation to conflicts between dynamic stabilization and sensory input processing. In some ectothermic vertebrates, sleep may have been postponed or rendered unnecessary by a more readily effected means of resolution of the conflicts, namely, extensive retinal processing of visual information during restful waking. By this means, processing of visual information in central regions of the brain may have been maintained at a sufficiently low level to allow adequate concomitant dynamic stabilization.
Many marine mammals that are active almost continuously engage only in unihemispheric non-rapid-eye-movement sleep. They apparently do not require rapid-eye-movement sleep and accompanying non-utilitarian dynamic stabilization of motor circuitry, because this circuitry is in virtually continuous use. Studies of hibernation by arctic ground squirrels suggest that each hour of sleep may stabilize brain synapses for as long as 4 h.
Phasic irregularities in heart and respiratory rates during rapid-eye-movement sleep may be a consequence of superposition of dynamic stabilization of motor circuitry on the rhythmic autonomic control mechanisms. Some information encoded in circuitry being dynamically stabilized during sleep achieves unconscious awareness in authentic and variously modified form as dreams and other sleep mentation.
Abstract [Brain Research Bulletin 42:245-264 (1997)]
The origin of both sleep and memory appears to be closely associated with the evolution of
mechanisms of enhancement and maintenance of synaptic efficacy. After the origin of
activity-dependent synaptic plasticity, whereby single activations of synapses led to short-term
efficacy enhancements, lengthy maintenance of the enhancements probably was achieved by
repetitive activations ("dynamic stabilization"). These are thought to have occurred either in the
course of frequent functional use, or to have been induced spontaneously within the brain to maintain
synaptic efficacies in circuits that were in infrequent use. The latter repetitive activations are referred
to as `non-utilitarian' dynamic stabilization.
With the evolution of increasing repertories and complexities of behavioral and sensory capabilities, with vision usually being the vastly preeminent sense, brain complexity increased markedly. Accompanying the greater complexity, needs for
storage and maintenance of hereditary and experiential information (memories) also increased greatly. It is suggested that these increases led to conflicts between sensory input processing during restful waking and concomitant `non-utilitarian' dynamic stabilization of infrequently used memory circuits.
The selective pressure for the origin of primitive sleep may have been a need to achieve greater depression of central processing of sensory inputs, largely complex visual information, than occurs during restful waking. The electrical activities of the brain during sleep (aside from those that subserve autonomic activities) may function largely to maintain sleep and to dynamically stabilize infrequently used circuitry encoding memories.
As endothermy evolved, the skeletal muscle hypotonia of primitive sleep may have become insufficient to prevent sleep-disrupting skeletal muscle contractions during `non-utilitarian' dynamic stabilization of motor circuitry at the accompanying higher body temperatures and metabolic rates. Selection against such disruption during dynamic stabilization of motor circuitry may have led to the inhibition of skeletal muscle tone during a portion of primitive sleep, the portion designated as "rapid-eye-movement sleep."
Abstract [Brain Research Bulletin 46:269-279 (1998)]
A major activity of the brain of most vertebrates during waking behavior is the processing of sensory information, preponderantly visual. This processing is not fully compatible with the brain's spontaneous oscillatory activity that maintains (refreshes) infrequently used circuits that store inherited and experiential information (memories). Great reduction in sensory input and processing during sleep permits the refreshment of memory circuits to occur unimpededly. Accordingly, sleep may have evolved as ever augmenting needs for processing visual information during waking
behavior by brains of great complexity conflicted increasingly with needs to refresh memory circuits.
The lack of a need for sleep by genetically blind fishes that live in caves, and sighted fishes that swim continuously, is consistent with this thesis, as their needs for processing of sensory information, predominantly visual, are either greatly reduced or nil.
Reduced requirements for processing sensory information by continuously swimming fishes owe to the following aspects of their behavior and ecology: (1) visual input is greatly reduced or absent during lengthy periods of nocturnal activity; (2)
schooling greatly reduces needs for sensory information, particularly visual; (3) being maintained through frequent use, circuitry for most inherited memories needs no refreshment; and (4) inasmuch as they lead a comparatively routine existence in essentially featureless, open waters, pelagic species acquire, and have need to refresh, relatively few experiential memories. Analogous circumstances could account for the ability of migrating birds to fly for days without rest or sleep.
Abstract (Neuroscience and Biobehavioral Reviews 23:635-648 (1999)]
Brain circuits for infrequently employed memories are reinforced largely during sleep by self-induced,
electrical slow-waves, a process referred to as "dynamic stabilization" (DS). The essence of waking
brain function in the absence of volitional activity is sensory input processing, an enormous amount of
which is visual. These two functions: circuit reinforcement by DS and sensory information processing
come into conflict when both occur at a high level, a conflict that may have been the selective
pressure for sleep's origin.
As brain waves are absent at the low temperatures of deep torpor, essential circuitry of hibernating small mammals would lose its competence if the animals did not warm up periodically to temperatures allowing sleep and circuit reinforcement. Blind, cave-dwelling vertebrates require no sleep because their sensory processing does not interfere with DS. Nor does
such interference arise in continuously-swimming fishes, whose need to process visual information is reduced greatly by life in visually relatively featureless, pelagic habitats, and by schooling.
Dreams are believed to have their origin in DS of memory circuits. They are thought to have illusory content
when the circuits are partially degraded (incompetent), with synaptic efficacies weakened through infrequent use. Partially degraded circuits arise normally in the course of synaptic efficacy decay, or pathologically through abnormal regimens of DS.
Organic delirium may result from breakdown of normal regimens of DS of circuitry during sleep, leaving many circuits incompetent. Activation of incompetent circuits during wakefulness apparently produces delirium and hallucinations. Some
epileptic seizures may be induced by abnormal regimens of DS of motor circuitry. Regimens of remedial DS during seizures induced by electroconvulsive therapy (ECT) apparently produce temporary remission of delirium by restoring functional or `dedicated' synaptic efficacies in incompetent circuitry. Sparing of sensory circuitry in fatal familial insomnia seemingly owes to supernormal circuit use in the virtual absence of sleep. ECT shocks and cardioverter defibrillation may have analogous remedial influences.
J. Lee Kavanau, "Biological time-keeping mechanisms:A need for broader perspectives", Medical Hypotheses, B.G. Charlton(Eds.), London Elsevier 67 : 1258-1262 (2006) .
J. Lee Kavanau, "Is sleep's 'supreme mystery' unraveling? An evolutionary anaysis of sleep encounters no mystery; nor does life's earliest sleep, recently discovered in jellyfish", Medical Hypotheses, B.G. Charlton(Eds.), London Elsevier 66 : 3-9 (2006) .
J. Lee Kavanau, "Evolutionary approaches to understanding sleep", Sleep Medicine Reviews, Michael V. Vitiello and Jean Krieger(Eds.), New York Elsevier 9 : 141-152 (2005) .
J. Lee Kavanau, "Evolutionary aspects of sleep and its REM and NREM states", Advances in Cell Aging and Gerontology, M.P. Mattson(Eds.), London Elsevier B.V 17 : 1-32 (2005) .
J. Lee Kavanau, "Dream contents and failing memories", Archives Italiennes de Biologie, M.P. Mattson(Eds.), 140 : 109-127 (2002) .
J. Lee Kavanau, "REM and NREM sleep as natural accompaniments of the evolution of warm-bloodedness", Neuriscience and Buibehavioral Reviews, M.P. Mattson(Eds.), 26 : 889-906 (2002) .
J. Lee Kavanau, "Memory Failures, Dream illusions and Mental Malfunction", Neuropsychobiology,, M.P. Mattson(Eds.), 26 : 199-211 (2001) .
J. Lee Kavanau, "Adaptations and pathologies linked to dynamic stabilization of neural circuitry", Neuroscience and Biobehavioral Reviews, M.P. Mattson(Eds.), 23 : 635-648 (1999) .
J. Lee Kavanau, "Origin and evolution of sleep: Roles of vision and endothermy", Brain Research Bulletin, M.P. Mattson(Eds.), 42 : 245-263 (1997) .
J. Lee Kavanau, "Memory, sleep and the evolution of mechanisms of synaptic efficacy maintenance", Neuroscience, M.P. Mattson(Eds.), 79 : 7-44 (1997) .