The limbic system
" Is emotion a magical product, or is it a physiological process that depends on an anatomical mechanism? " James Papez.
History :
The term limbic (Limbus, meaning "border" or "edge" in Latin [39]) was first introduced by the French physician and anatomist Paul Pierre Broca in 1878 [74]. He used the term "great limbic lobe" to designate a supplemental lobe particularly involved in emotion, consisting of the olfactory bulb and tract, the hippocampus, and the cingulate gyrus (cingulum, meaning "belt" in Latin) [75]. Of course, the limbic system [32, 41] is not currently recognized as a true lobe [38].
In 1937, the American neuroanatomist James Papez published his research [80] on an emotional circuit now known as the Papez circuit [38, 50]. This circuit includes the hippocampus, the cingulate gyrus [41], the thalamus, the hypothalamus, and some of their interconnections.
A few years later, in 1949, Paul MacLean [39] expanded on Papez's ideas and integrated them with the concept of the "great limbic lobe" proposed by Paul Broca, leading to the notion of a limbic system [80]. Since then, other anatomical structures have gradually been added to this system, such as the prefrontal cortex and the orbitofrontal region [71].
Functions of the limbic system:
The limbic system is a group of brain structures that play a very important role [39] in behavior, particularly in emotions, memory, learning, and some of the executive functions [161, 162].
In the field of neurophysiology, "emotion" does not mean "feeling," which is the internal and purely subjective experience a person has in response to a particular situation. Emotions are instead the physiological reactions that accompany these feelings - changes in behavior or the functioning of organs [176].
The limbic system is often called the "visceral brain" or "emotional brain" [119] because it plays a significant role in a series of emotions, including pain, pleasure, docility, affection, anger, aggression, fear, and pleasure...
Executive functions include skills related to planning, working memory, anticipation, initiative, organization, problem-solving, logical reasoning, cognitive control, abstract thinking, rule learning, selective attention, the selection of motor responses, and motivation. Executive functions are primarily linked to the functioning of the prefrontal cortex and the orbitofrontal region [177]. The limbic system also influences the endocrine system and the autonomic nervous system [166].
Anatomy of the limbic system:
The limbic system comprises several cortical and subcortical structures located around the thalamus [80]. All these structures form an integrated system that ensures the survival of the individual through the implementation of visceral responses and adaptive behaviors.
Since the 1950s, the list of brain structures defining the limbic system has continuously expanded; among these essential structures are: the cingulate gyrus [32], the hypothalamus, the anterior nuclei of the thalamus, the olfactory apparatus, the hippocampus, and the amygdaloid nuclei...
At the heart of this system is the Papez circuit, which is very important for memory. In this circuit, information circulates in a loop from the hippocampus to the mammillary bodies of the hypothalamus (via the fornix), then passes to the anterior nuclei of the thalamus, then to the anterior cingulate cortex, before returning to the hippocampus.
The amygdaloid complex [38] plays several roles: it is involved in olfaction, emotions, and especially in the development of appropriate responses to danger [96]. The classic experiment of a mouse with both amygdalae destroyed shows that it no longer tends to flee from a potential predator.