The activation-synthesis hypothesis, proposed by Harvard University psychiatrists John Allan Hobson and Robert McCarley, is a neurobiological theory of dreams first published in the American Journal of Psychiatry in December 1977.
It has been shown through experimentation that animals subjected to inability to enter REM sleep show an immediate attempt to quickly enter REM stages and long-term effects on motor coordination and habitual motor habits, eventually leading to the death of the animal.
Sleeping can be described as the lack of conscious awareness of the outside world, meaning large portions of the brain that receive and interpret signals are deactivated during this time, while dreaming is a specific state of sleep in which enhanced brain activity has been shown to occur,[1] theorizing the primary consciousness could be active during dreaming.
Unlike the waking state, the brain cannot recognize its own condition; that it is in the midst of the dream and is not the same as the real world.
The brain shows dulled or limited senses of perception, though the thought process has been shown to be logical and perseverative.
The thought process is sometimes non-logical or even bizarre, sensation and perception is vivid but created internally by the brain, and the body's movements are inhibited.
The scientific tracking of REM sleep stages can be measured by neuronal signals within the pontine brainstem.
[4] These are phasic waves that occur in cycles, and originate from the pontine brainstem (P), lateral geniculate of thalamus (G), and occipital cortex (O).
Aminergic monoamines serotonin, noradrenaline, histamine, and dopamine are balanced between acetylcholine cholinergic signals, and play a part in the regulation of cognition.
Aminergic cell signal strength is lowest during REM sleep, increases during NREM, and is highest at waking.
The development of consciousness is a gradual, time-consuming and lifelong process that builds upon and uses a more primitive virtual reality generator that is more definable in our dreams.
[5] This was perceived as the activation-synthesis model, stating that brain activation during REM sleep results in synthesis of dream creation.
[1] Hobson's five cardinal characteristics include: intense emotions, illogical content, apparent sensory impressions, uncritical acceptance of dream events, and difficulty in being remembered.
The model is limited however, in that it cannot yet explain the regional differences in brain activity that distinguish REM sleep from waking.
This was observed by two experiments: development of sleepiness after dopamine neuron destruction in substantia nigra in the midbrain, and discovery of the reticular activating system, which are visual cues received through our eyes and to our brain that begin the waking process, that waking consciousness depends sleep.
[9] PGO waves play a part in the ability of the brain to remain asleep while constituting the building blocks for perception and fine motor control via their phasic coordination.
It suggests the possibility that the state of waking consciousness is only present in humans due to the evolution of extensive cortical structures within the brain.
[1] Dreaming is a state of the brain that is similar to yet different from the waking consciousness, and interaction and correlation between the two is necessary for optimal performance from both.