Sleep, the other side of the mind
Sleep-Mind! These two phenomena are apparently contradictory. On the one hand, the resemblance of Sleep and Death illustrated by Hypnos and Thanatos, the twin brothers of Greek mythology, on the other hand, the Spirit, this witness of the higher nervous activity during awakening.
It is likely that this contradiction is at the origin of the concept of Spirit. Let’s imagine the first Hominins taking refuge in a cave in East Africa. They already have a rudimentary language and they think but they don’t think they think yet… A dreamer wakes up and tells that during the night, he had left the cave and had flown like a bird. His companions look at him, amazed and incredulous. The same thing happened again and again. How long did it take for the capital question to arise at the dawn of humanity: there must be something immaterial, the “Spirit or Soul”, which is fundamentally different from the material body. The indefatigable and invisible Spirit can indeed remain awake during Sleep. It travels wherever it wants, in space and time, past or future, and can deliver to the brain the fantastic images of its journey, or of its dialogue with gods and demons, while the body, immobile and tired, is crushed by Sleep.
Certainly, the human thought had to hesitate between two aspects of the individualization of the dream, the movement of the wandering soul leaving its body to give itself up to a nocturnal wandering, or the movement of the gods and the demons coming to visit the sleeping man and to grant him its revelations… But it seems likely that the dream was, according to Spencer and Malinovski, at the base of the belief in the soul, the spirit, the gods and the demons that we find under numerous avatars at the birth of all civilizations and all religions. It is thus of the prophetic dreams. The dreams of Jacob, Pharaoh and Nebuchadnezzar in the Old Testament, the dream of Joseph, the Magi and the flight into Egypt in the Gospels of Matthew. Thus, the dreams of Buddhism, of Maya the Mother of Buddha, of Cudhodana, his Father or of Gôpa, his wife. Thus the dreams of Islam, the most famous of which is the journey of Mohammed on his mare Elborak. Later, the founders of religious orders entered into a privileged relationship with God through dreams, such as Macarius, Francis of Assisi, Don Bosco and Saint Bruno.
This metaphysical trend of dreaming still persists today. The fellahs of the Nile Delta wrap their heads with a turban to prevent their souls from leaving their heads during sleep, and among the Masai tribes of Kenya, it is forbidden to wake up a sleeper suddenly for fear that the wandering spirit will have time to re-enter the body.
Of course, it is not the task of the neurobiologist to retrace the history of the dream, this first aspect of the unconscious discovered long before the concepts of consciousness and unconsciousness at the cognitive and affective levels. To the neurobiologist, the still impossible task of trying to explain with our current knowledge, the machinations of the night at the level of the Spirit.
We must first situate ourselves among the different “schools” that study consciousness, because this situation is responsible for our definition of the Mind.
Neither behaviorism (which evacuates the problem of the Mind or of consciousness), nor functionalism, which is only interested in performance and which can very well admit that a computer is conscious, nor panpsychism are appropriate to our study. In the absence of proofs allowing us to conceive of immaterial external influences that can act on the brain in violation of the laws of thermodynamics, we therefore situate ourselves, for the moment, within the school known as “psychoneural identity” and therefore in opposition to Cartesian dualism, in its original meaning or in its more recent developments.
By Spirit, we mean the functioning of the superior nervous activity: the perception or the apperception of the environment, the representation of absent beings (mental imagery) allowing the prediction of certain complex answers, the communication with the congeners. In short, in man, the reflective consciousness: “I think that I think”, the conscience: “I think”, the unconscious: “I made this complex act without thinking about it”. We admit that some aspects of consciousness can exist in all homeotherms, from birds (the Gabon grey parrot is able to retain 1,200 words, more than a 5 year old child) to mammals.
Self-awareness (recognition of one’s face in a mirror) appears with the chimpanzee, but does not exist in the gorilla. Reflexive consciousness is probably reserved for the waking human (I am conscious of being conscious) and for the dreamer. In the latter case, as we shall see below, reflexive consciousness can be subject to strange distortions.
The different synchronic operational modes of consciousness are extended by a diachronic wake related to memory. We can generally remember our conscious thoughts or acts easily, whereas associations of ideas allow us to find the origin of certain unconscious acts.
Neurobiology of the “Mind” during the Awakening
Before tackling the problem of the mind during sleep, we must summarize, a contrario, what we know about the correlates (or the set of conditions) that we observe when a man or a cat performs a conscious operation during wakefulness (attention, for example). We say correlates or conditions, because no one is yet able to assign a necessary and sufficient causality to consciousness.
Three major conditions seem to accompany conscious attention.
1) Awareness requires both the integrity of certain cortical areas (in particular the parietal cortex). Indeed, there is no evidence of perceptivity in subjects with diffuse cortical lesions.
2) The integrity of the cortex is not sufficient, however. A certain level of excitation of the numerous modules that constitute the basic element of cortical functioning is required. This level of excitation is expressed by a particular cerebral electrical activity (the arousal response), which can be recorded at the level of the scalp in humans or by electrodes placed directly on the cortex in animals. The cortical activation of attention, whether it is provoked by a signal from the external environment or whether it is the result of the reentry of signals generated by the cortex (mental images) is not a strictly cortical phenomenon but requires the active involvement of subcortical systems. These systems, staggered from the bulb to the hypothalamus, release neuromediators (catecholamines, indolamines, histamine, acetylcholine, neuropeptides) which “activate” the cortical modules according to complex hierarchies and modalities.
3) Conscious attention is finally accompanied by particular energetic phenomena highlighted by the positron camera. The cortical modules consume more glucose. However, there seems to be a decoupling between glucose and oxygen consumption, so that cortical areas can use the anaerobic pathway (production of lactate) during attention.
In summary, during wakefulness, conscious attention requires both a relative integrity of the cerebral cortex associated with the excitatory action of brainstem structures. This process requires an increase in energy in the form of glucose which can be metabolized anaerobically.