Scientific Understanding of Consciousness
Consciousness as an Emergent Property of Thalamocortical Activity

Sleep -- Dreaming -- Memory Consolidation -- Creativity

Dreaming is an important aspect of consciousness. Experts hypothesize that memories are consolidated during sleep and dreaming. I think most of us have had experiences in which we go to bed with a problem and then in the morning awake with fresh insight after a good night’s sleep. Moreover, it is hypothesized that wake-time thoughts are fragmented into smaller cell assemblies during sleep and dreaming, followed by a process of self-organization, allowing creative concepts and ideas to emerge.

Allan Hobson’s AIM Sleep Model

Forebrain Processes in Normal Dreaming — Allan Hobson diagrams the processes in dreaming.

Link to — Anatomy of Sleep diagram

Researach Study — Sleep Visual Imagery and Wakefulness Perception

Researach Study — Sleep promotes formation of Dendritic Spines

Researach Study — Circuit-based Interrogation of Sleep Control

Why is sleep necessary?

Research study — Sleep Drives Metabolite Clearance from the Adult Brain — Convective fluxes of interstitial fluid increased the rate of β-amyloid clearance during sleep. Thus, the restorative function of sleep may be a consequence of the enhanced removal of potentially neurotoxic waste products that accumulate in the awake central nervous system.

Research study — Sleep Necessity

The results of a research study support the hypothesis that plasticity changes in synapses during waketime lead to a net increase in synaptic strength in many brain circuits and that sleep is required for synaptic renormalization.

Research study — Sleep and Synaptic Homeostasis

Diagram — Sleep Stages Diagram

Diagram — Anatomy of Sleep

During REM sleep, the presence of dreams, which can sometimes be subsequently recalled, implies some form of consciousness, a state that is also reflected in the electrical activities of the brain. (Baddeley; Working Memory, 303)

Sleep-dream-wake cycle is triggered and tuned by neuronal circuits in the pons. (Hobson; Consciousness, 59)

Hypothalamus contains the biological clock that times cycles of rest and activity and gates the sleep-wake cycle in the pons. (Hobson; Consciousness, 60)

Dreaming may be our most creative conscious state, one in which the chaotic, spontaneous recombination of cognitive elements produces novel configurations of information -- new ideas. (Hobson; Consciousness, 45)

When the activation level of the brainstem falls, even a little, the thalamocortical circuits begin to oscillate. This kind of synchrony contributes to the global loss of consciousness that occurs in NREM sleep. (Hobson; Consciousness, 70)

Oscillations of the thalamocortical circuits that occur at sleep onset are robust and so highly synchronous that they cause the characteristic EEG pattern of slow wave sleep. (Hobson; Consciousness, 71)

In waking, the whole brain is primed to capture data. In sleep, the data may processed. (Hobson; Consciousness, 74)

Stages of Sleep

In humans, at least five stages of sleep with progressively higher wakening thresholds can be distinguished, with the deepest stage being a rapid eye movement (REM) phase. (Buzsáki; Rhythms of the Brain, 187)

Stages 3 and 4 are often referred to as slow wave or delta sleep. (Buzsáki; Rhythms of the Brain, 187)

Stage 5, REM sleep, is characterized by a waking-type EEG, rapid eye movements, loss of muscle tone, and dreaming. (Buzsáki; Rhythms of the Brain, 187)

REM sleep composes usually 20 -- 25% of total sleep time in humans adults, and is an indication of the end of a non-REM/REM sleep cycle. (Buzsáki; Rhythms of the Brain, 187)

Typically, four or five non-REM/REM cycles with a period of 70 -- 90 minutes each, occur within a night. (Buzsáki; Rhythms of the Brain, 187)

Sleep spindles are the hallmark of natural non-REM sleep. (Buzsáki; Rhythms of the Brain, 188)

Spindle oscillations consists of 7-14 Hz waxing and waning field potentials, grouped in sequences that last for 1-3 seconds and recur every 3-10 seconds. (Sejnowski; Thalamocortical Oscillations, 978)

Waking and dreaming -- two states of consciousness

Waking and dreaming are two states of consciousness, with differences that depend on chemistry. (Hobson; Dreaming, 64)

In REM sleep, brain waves are similar to awake brain, hence the name paradoxical sleep, since the person is asleep but the brain appears to be awake. (Crick; Astonishing Hypothesis, 111)

Activation-synthesis model of dream neuropsychology -- dreams are actively generated by the brainstem and passively synthesized in the forebrain. (Solms; Dreaming and REM Sleep, 52)

Difference between dreaming and wakefulness: the external world is not perceived during REM sleep because the intrinsic activity of the nervous system does not place sensory input within the context of the functional state being generated by the brain. (Llinás; I of the Vortex, 130)

Functional states such as wakefulness (or REM sleep and other sleep stages) appear to be particular examples of the multiple variations provided by the self-generated brain activity. (Llinás; Perception as Oneiric-like, 114)

Front-to-back phase shift of the 40-Hz activity over the head during REM sleep; well-organized 12-msec phase shift for the 40-Hz oscillation. (Llinás; Perception as Oneiric-like, 120)

Architecture of sleep. EEG recordings, waking, sleeping; cyclical patterning of sleep. - (illustration) (Zeman; Consciousness, 88)

Adults spend about one-fifth of their seven hours of sleep in REM. (Zeman; Consciousness, 90)

A self-activating system is capable of emulating reality, even in the absence of input from reality, as occurs in dream states and daydreaming. (Llinás; I of the Vortex, 57)

Encode memories during sleep (Hobson; Dreaming as Delirium, 115)

An event at the nonconscious level -- the firing of cholinergic neurons, could be said to cause the vision of our dreams. (Hobson; Dreaming as Delirium, 211)

During REM sleep, the source of brain waves is in the base of the brain stem. (Hobson; Dreaming as Delirium, 135)

Normal sleep cycle in AIM state space - (illustration) (Hobson; Dream Drug Store, 47)

Human sleep stages, EEGs - (illustration) (Hobson; Dream Drug Store, 51)

In the deep sleep state, sensory input of all types (modalities) is for the most part rejected by the thalamocortical system. (Llinás; I of the Vortex, 207)

40-Hz oscillations and thalamocortical resonance

The waking and REM sleep states are very similar with respect to the presence of 40-Hz oscillations. (Llinás; I of the Vortex, 130)

What distinction is there between dreaming and wakefulness? If cognition is a function of the 40-Hz thalamocortical resonance, what happens to this oscillatory rhythm during sleep, particularly dream or REM sleep? (Llinás; I of the Vortex, 129)

The 40-Hz coherent activity was present in the awake and REM sleep states, but greatly reduced in delta (slow-wave, deep sleep). (Llinás; I of the Vortex, 129)

An auditory stimulus produced 40-Hz oscillations in the wakefulness state. (Llinás; I of the Vortex, 130)

40-Hz oscillations are not reset by sensory input during REM sleep, even though studies have clearly shown that the thalamocortical system is accessible to sensory input during sleep. (Llinás; I of the Vortex, 130)

Tones played to waking subjects 'reset' their gamma rhythm, but had no effect on the fast oscillation in the brains of subjects in REM. (Zeman; Consciousness, 90)

40 Hz oscillations in sleep and wakefulness. - (illustration) (Zeman; Consciousness, 91)

In drowsiness or non-REM sleep, the thalamic relay cells go into an oscillatory mode in which they alternate between short, high-frequency bursts and extended periods of hyperpolarization, repeating at a frequency of 7-14 Hz. (Mumford; Thalamus, 981)

Dreaming <--> Delirium during wakefulness

The mechanisms active during dreaming are some of the same as those in delirium states during wakefulness.

Much of the brain is active in sleep and dreaming. (Hobson; Dreaming as Delirium, 117)

Dreaming is an altered state of consciousness, akin to those induced by psychedelic drugs in waking. Brain stores its own drugs and releases them depending on the brain's state. Why are dreams so bizarre? Without norepinephrine and serotonin, the cerebral and hippocampus create odd and remote associations. Dreams are therefore inherently and primarily bizarre. Dreams are dripping with emotional salience, even when they are cognitively delirious. (Hobson; Dream Drug Store, 71)

Memory Consolidation in Dreming

One of the reasons we need sleep is to permanently encode memories. (Hobson; Dreaming as Delirium, 115)

Allan Hobson suggests that the function of dreaming is memory consolidation and the linking of memory representations with motor programs. (Revonsuo; Evolutionary Function of Dreaming, 106)

Among the neuromodulators crucial to memory: (1) norepinephrine (2) serotonin; both are conspicuously diminished during dream consciousness. (Hobson; Consciousness, 137)

Neural assemblies Fragment -- Self-Organize -- Creative Thought

All complex systems with chaotic properties can self-organize. (Hobson; Consciousness, 45)

Self-organization is more likely to be achieved in undirected states, such as meditation, fantasy or reverie that border on waking. (Hobson; Consciousness, 45)

Reticular Formation

Brain stem functions have some control over consciousness state.

Allan Hobson’s AIM diagram

AIM diagram (Hobson), sleep-wake states - (diagram) (Purves; Neuroscience, 681)

Neuromodulatory neurons of the brainstem distribute their axons diffusely throughout the brain. The aminergic group, which is most active during waking, consists of norepinephrine- and serotonin-releasing cells that project directly to the cortex. The cholinergic, which is most active during REM sleep, projects to the cortex via an intermediary in the basal forebrain. Neuromodulatory neurons of both types exert their effects upon reflex circuits composed of sensory and motor neurons of the cortex and other parts of the brain. In this way brain circuits, and hence consciousness, are biased toward either external (waking) or internal (dreaming) modes of operation. (Hobson; Consciousness, 47)

Sleep-dream-wake cycle is triggered and tuned by neuronal circuits in the pons. (Hobson; Consciousness, 59)

The hypothalamus contains the biological clock that times cycles of rest and activity and gates the sleep-wake cycle in the pons. (Hobson; Consciousness, 60)

Dreaming; integration of vision with other sensory modalities, hyperactivity of the parietal operculum, where vision, space, and movement meld. (Hobson; Dream Drug Store, 59-64)

Chemicals shift the balance of the brain to be awake or dreaming.

Scientists think that all dreams are chemically mediated. REM sleep dreaming is mediated by acetylcholine when noradrenaline and serotonin are at very low levels. (Hobson; Dreaming as Delirium, 67-68)

Dramatic change in neuromodulation distinguishes REM sleep from waking. (Hobson; Dreaming, 63)

Brain stem cells containing the neuromodulators norepineprine and serotonin change their outputs when animals go to sleep. (Hobson; Dreaming, 63)

Serotonin and noradrenaline cells that modulate the brain during waking reduce their output by half during non-REM sleep and shut off completely during REM sleep. (Hobson; Dreaming, 63)

Serotonin and noradrenaline implicated in awake state functions (attention, memory, reflective thought) that are lost in dreaming. (Hobson; Dreaming, 63)

Neuromodulatory cells of the brain stem (pons) project up to the thalamus and cortex and down to the spinal cord. (Hobson; Dreaming, 64)

Brain self-activates in sleep; it changes its chemical self-instructions. (Hobson; Dreaming, 64)

All the drugs that are used to treat psychoses have a role on the neuromodulators. (Hobson; Dreaming, 67)

Jet lag

Dream sleep, cortex is in a state of arousal, very similar to the alert waking state; no access to external stimuli and only processes internal events. (LeDoux; Emotional Brain, 286)

Research study — Sleep in Individual Neurons

Research study — Sleep and Dreaming — Recent Research

Link to — Consciousness Subject Outline