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Help Psychobiologie humaine Modèle psychobiologique du comportement humain Rôle et importance des processus de renforcement dans l'apprentissage du comportement de reproduction chez l'Homme
Social Interactions Can Alter Gene Expression In Brain, And Vice Versa

Some of our behaviours are very primitive and incapable of adaptation. They make us react to external or internal stimuli automatically. They meet our most fundamental needs: eating, drinking, and copulating. Neurophysiologically speaking, these behaviours represent the activation of the “reptilian” structures of the brain, bringing the hypothalamus and the brainstem into play.

Other, more sophisticated behaviours involve remembering pleasant or unpleasant sensations that we experienced in the past and the actions that caused us to experience them at the time. These behaviours represent most of the social and cultural knowledge that we acquire. In connection with these behaviours emotions arise–the awareness of the cardiovascular adjustments necessary for action. Neurophysiologically speaking, these behaviours represent the activation of the “mammalian” structures of the brain, bringing the limbic system into play.

Yet other behaviours involve more elaborate planning. They call on the imagination, and hence on the associative cortex, to develop strategies for ensuring that our actions will be gratifying rather than painful. They represent the creative and innovative abilities of the human mind. Neurophysiologically speaking, these behaviours represent the activation of the “neocortical” structures of the brain, bringing the associative areas of the cerebral cortex into play.


To understand the ultimate origin of familiar behaviours such as walking, aggression, and making love, we must go back to the fundamental laws of physics, and specifically the second law of thermodynamics. This law states that entropy always increases: a cathedral will end up as a pile of stones, but a pile of stones will never become a cathedral. Consequently, for an organism to stay alive in an environment that is less organized than the organism itself, that organism must constantly seek the energy to combat entropy. It follows that, to paraphrase Henri Laborit, the only reason for being is to be–in other words, to maintain the body’s highly organized structure in an environment where everything tends toward disorder.

Living organisms have developed two major ways of obtaining this energy:

  1. drawing it directly from the sun’s rays; this is what plants do when they use photosynthesis to produce energy from solar entropy;

  2. evolving behaviours to secure solar energy that plants have already converted into edible form; this is what animals do, including human beings.

To guide these behaviours, animals have developed a nervous system that:

  1. informs them of the needs of their internal environment;

  2. lets them know what is happening in their external environment.

An animal perceives this external world through its senses. The animal’s brain then processes this sensory information to construct a certain representation of this world, drawing on memory to attribute pleasant or not-so-pleasant affective values to it. After that comes the behaviour as such. It involves a movement whereby the animal acts on its environment so as to maintain its integrity as an organism.

The following diagram shows how the expression of a specific behaviour fits into the larger evolutionary scheme.

Credit: Jacob L. Driesen

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