mystery of yawning
Le bâillement, du réflexe à la pathologie
Le bâillement : de l'éthologie à la médecine clinique
Le bâillement : phylogenèse, éthologie, nosogénie
 Le bâillement : un comportement universel
La parakinésie brachiale oscitante
Yawning: its cycle, its role
Warum gähnen wir ?
 
Fetal yawning assessed by 3D and 4D sonography
Le bâillement foetal
Le bâillement, du réflexe à la pathologie
Le bâillement : de l'éthologie à la médecine clinique
Le bâillement : phylogenèse, éthologie, nosogénie
 Le bâillement : un comportement universel
La parakinésie brachiale oscitante
Yawning: its cycle, its role
Warum gähnen wir ?
 
Fetal yawning assessed by 3D and 4D sonography
Le bâillement foetal
http://www.baillement.com

mclean

Paul Mc Lean

01/05/1913

26/12/2007

mise à jour du
17 juillet 2003
 
lexique
Le schéma du cerveau tri-unitaire
de Paul Mac Lean
 
 
MacLean, Paul D. (1990).
The triune brain in evolution: role in paleocerebral functions
New York: Plenum Press

Chat-logomini

Chez les différents types de vertébrés, le système nerveux central répond à un plan général commun d'organisation, et montre, des plus anciens aux plus récents d'entre eux, une complication graduelle en rapport avec des niveaux de vie de plus en plus indépendants et fonctionnellement de plus en plus élevés.
 
Certaines formations correspondraient à des activités nerveuses rudimentaires propres aux vertébrés inférieurs: chordencéphale, centre de réflexes locaux et régionaux (tronc cérébral). Le mésencéphale des reptiles véritable cerveau primitif (voies senitives centripètes, et motrices centrifuges) devient le lieu de centres secondaires chez les mammifères à écorce ou pallidum développé.
 
La théorie de Paul Mac Lean ( Les 3 cerveaux : 1971) explicite cela de façon plus précise et construite. Selon lui, le cerveau s'est développé par "couches successives", répondant ainsi progressivement aux besoins de l'évolution :
 
d'abord de purs instincts (cerveau reptilien) qui ne possède pas de mémoire, lieu d'origine du bâillement ;
puis acquisition de réponses émotionnelles contrôlées (système limbique) ou cerveau «paléomammalien» interface synaptique et humorale commune à tous les mammifères, siège du bâillement d'émotivité des singes (et des bâillements sexuellement induits); il possède une mémoire;
 
enfin cerveau «néomammalien» caractérisé par le développement cortical chez l'homme, en particulier des lobes frontaux siège de la réplication du bâillement.
 
Ces trois cerveaux cohabitent toujours en nous. Un fonctionnement harmonieux des différents cerveaux est nécessaire en incluant des émotions ou certaines formes de comportement archaïques pour le profit / contôle du néo-cortex siège de la raison / pensée consciente.
maclean 
- Cerebral evolution and emotional process: new findings on the striatal complex PD MacLean Ann NY Acd Sci 1972; 193; 137-149
- The triune brain in conflict PD MacLean Psychother Psychosom 1997; 28; 207-220
- Evolutionay psychiatry and the triune brain MacLean Psychological Medecine 1985; 15; 219-221

The American neurologist Paul MacLean is a proponent of "microgenesis", the view that the structure of our brain mirrors its evolution over the ages.
 
Mac Lean believes that our head contains not one but three brains: a "triune" brain. Like the layers of an archeological site, each brain corresponds to a different stage of evolution. Each brain is connected to the other two, but each operates indivually with a distinct "personality".
 
The neocortex does not control the rest of the brain: all three parts interact, although it is true that the neocortex interacts in a more "cognitive" manner. But the "brain" that interacts in a more "instinctive" manner can be as dominant and even more. And ditto for the "emotional" one. The oldest of the three brains, the "reptilian" brain, is a midbrain reticular formation that has changed little from reptiles to mammals and to humans. This "brain" comprises the brainstem and the cerebellum. It is responsible for species-specific behavior: instinctive behavior such as self-preservation and aggression.
 
The cerebellum and the brainstem constitute virtually the entire brain in reptiles. The most basic life-sustaining processes of the body, such as respiration, heart beat and sleep, are controlled by the brainstem. More precisely, the brainstem is the brain's connection with the autonomic nervous system, the part of the nervous system that regulates functions such as heartbeat, breathing, etc. that do not require conscious control. It has always active, even when we sleep. It endlessly repeats the same patterns over and over, mechanically. It does not change, it does not learn. In the beginnings, this system was basically most of the brain, and limbs and organs were controlled locally.
 
Most mammals share with us the limbic system, which MacLean believes was born after the reptilian system and was simply added to it. The earliest mammals had a brain that was basically the reptilian brain plus the limbic system. MacLean therefore believes this to be the old mammalian (or "paleomammalian") brain. The limbic system contains the hippocampus, the thalamus and the amygdala, which are considered responsible for emotions and emotional insticts (behaviors related to food, sex and competition). These emotions are functional to the survival of the individual and of the species. This system is capable of learning, because it contains "affective" memories, which is emotion-laden memories. Ultimately, the limbicsystem is about "pain" and "pleasure": avoiding pain and repeating pleasure.
 
The neocortex is the main brain of the primates, which are among the latest mammals to appear. All animals have a neocortex but only in primates it is so relevant: most animals without a neocortex would behave normally. This "neomammalian" brain is responsible for higher cognitive functions such as language and reasoning.
The oldest brain is located at the bottom and to the back. The newest sits on top and to the front. They all complement each other to produce what we consider human behavior. Each is an autonomous unit that could exist without the others The elegance of MacLean's model is that it neatly separates mechanical behavior, emotional behavior and rational behavior. It shows how they arose chronologically and for what purpose. And it shows how they coexist and complement each other. They constitute three steps towards modern "intelligence".
 
brain evolution
 

Brain evolution relating to family, play, and the separation call.
MacLean PD.
Arch Gen Psychiatry 1985; 42; 4; 405-17
Mammals stem from the mammal-like reptiles (therapsids) that were widely prevalent in Pangaea 250 million years ago. In the evolutionary transition from reptiles to mammals, three key developments were (1) nursing, in conjunction with maternal care; (2) audiovocal communication for maintaining maternal-offspring contact; and (3) play. The separation call perhaps ranks as the earliest and most basic mammalian vocalization, while play may have functioned originally to promote harmony in the nest. How did such family related behavior develop? In its evolution, the forebrain of advanced mammals has expanded as a triune structure that anatomically and chemically reflects ancestral commonalities with reptiles, early mammals, and late mammals. Recent findings suggest that the development of the behavioral triad in question may have depended on the evolution of the thalamocingulate division of the limbic system, a derivative from early mammals. The thalamocingulate division (which has no distinctive counterpart in the reptilian brain) is, in turn, geared in with the prefrontal neocortex that, in human beings, may be inferred to play a key role in familial acculturation.

The Portuguese neurologist Damasio thinks that consciousness is an internal narrative. The "I" is not telling the story: the "I" is created by stories told in the mind ("You are the music while the music lasts").
 
Damasio breaks the problem of consciousness into two parts: the "movie in the brain" kind of experience (how a number of sensory inputs are trasnformed into the continuous flow of sensations of the mind) and the self (how the sense of "owning" that movie comes to be). The former is a purely non-verbal process: language is not a prerequisite for consciousness. Nonetheless, language is the source of the "I", a second order narrative capacity.
Neurological research has proven that distinct parts of the brain work in concert to represent reality. Brain cells represent events occurring somewhere else in the body Brain cells are "intentional", if you will. They are not only "maps" of the body: besides the topography, they also represent what is taking place in that topography.
 
Indirectly, the brain also represents whatever the organism is interacting with, since that interaction is affecting one or more organs (e.g., retina, tips of the fingers, ears), whose events are represented in brain cells. The brain stem and hypothalamus are the organs that regulate "life", that control the balance of chemical activity required for living. Consequently, they also represent the continuity of the same organism. Damasio believes that the self originates from these biological processes: the brain has a representation of the body and has a representation of the objects the body is interacting with, and therefore can discriminate self and non-self and then generate a "second order narrative" in which the self is interacting with the non-self (the external world). This second-order representation occurs mainly in the thalamus.
 
From an evolutionary perspective, we can presume that the sense of the self is useful to induce purposeful action based from the "movie in the mind". The self provides a survival advantage because the "movie in the mind" acquires a first-person character, i.e. it acquires a meaning for that first person, i.e. it highlights what is good and bad for that first person, a first person which happens to be the body of the organism, disguised as a self. This second-order narrative derives from the first-order narrative constructed from the sensory mappings. In other words, all of this is happening while the "movie" is playing. The sense of the self is created while the movie is playing by the movie itself. The thinker is created by the thought. The spectator of the movie is part of the movie.
 
mclean