Delve into the fascinating world of the limbic system with this comprehensive guide! From its historical origins to its intricate neurophysiology, explore how this complex network of brain structures influences emotions, behaviors, and even decision-making.
Discover the role of key components li...
The Limbic System
The term “limbic” stems from the Latin word “limbus” which means “border” and was first used in
1664 by the physician Thomas Willis to denote the curved cortical border around the brainstem.
When Broca, another scientist, spoke of the “Great Limbic Lobe”, he thought of it as a primarily
olfactory structure. Then, during the mid 20th century, Papez and McLean associated the limbic system
with emotional functioning in humans. Also by looking at the drawings that these scientists made,
you can observe than going on with history, Papez succeeded into drawing connections and what
actually looks like a “system”.
Any pattern of neural activity in the brain, whether internally generated (feeling, recalling, imagining,
anticipating, prefiguring) or externally generated (sensory inputs) can be considered as a neural “cue”
(a cue is a signal to do something .
It is recognized:
® either by innate circuits
® or by comparing it with previously encountered cues and the resulting neural activity (as discussed
in the lecture on the ARAS) is bounced onto
• the amygdala that produces an assessment of vital relevance (quantitative: intensity)
• the VTA that assesses an emotional (hedonic) “value” (qualitative hedonic: good/bad)
• the SNpc that assesses the “operational” value (initiate, reconcile, harmonise, choose)
• the RAPHE that attributes an emotional “meaning” (qualitative): pain, failure, loss,
dismay, humiliation, rage, success, satisfaction, joy, wellbeing, enthusiasm...
– it also helps the exam of reality by assessing the likelihood and consistency of the brain
activity with sensory input.
The combination of the activities of amygdala, VTA, and raphe, brings about an emotional
colouring of the experience (pleasure, nuisance, joy, sorrow, disgust, rage, joy, desire, despair, satisfaction,
expectation, hope ...) and its reality value (i.e., we obviously discern whether the source of an emotion is
something real out there or some mental or imaginative activity)
Such emotional colouring and evaluation is linked to a corresponding motivational value, which is
represented by dopamine activity at the dorsal striatum and at the prefrontal cortex and influences both
“autopilot” and rational, strategic behaviour.
The emotional colouring participates to the elaboration by many cortical circuits, and provides a
bottom-up contribution to the mechanisms of selective attention (based on emotional relevance) that
competes with the top-down control of attention, by the central executive of the working memory, based
on pertinence with the current line of thought.
The information about the emotional colouring also converge on the hypothalamus as well; here, it
contributes to
• → elicit consummatory behaviours (smell, sight or mention of food, water; sexual cues)
• → elicit the fight-or-flight response (fearful cues, pain)
• → elicit the aggressiveness / rage response
• → elicit preparatory visceral-vegetative responses
• → suppress inappropriate visceral-vegetative responses
• → elicit appropriate skeleto-motor stereotyped responses
Notice that the hypothalamus in in charge of responses to re-establish homoeostasis through hormonal
as well as nervous responses (mostly through the autonomic nervous system), but often this is not enough,
even for mere homoeostasis: behavioural responses are required, such as fetching food, drinking, finding
a shelter, putting on clothes...
Thus, in addition to controlling the autonomic nervous system and producing hormones that directly or
indirectly regulate a number of physiological functions, the hypothalamus must be able to generate
motivational drives to elicit the appropriate behaviours to face the physiological and homoeostatic needs.
In synthesis, a clear connection exist between vital, hedonic relevance, emotions and motivational drives
guiding behaviour
Relevant cues, emotions and responses
All living organisms possess mechanisms capable of detecting cues that have vital relevance and
produce appropriate reactions. In very general terms, such phenomenon can be defined as an
190 Body At Work II
, Enrico Tiepolo
“emotion”. Vitally relevant cues can be stimuli, events, internal states; they may elicit defence,
avoidance, consummatory, reactive or anticipatory responses, and possibly visceral and somatic
adaptations with preparatory or communicational function.
Such a definition of “emotion”, though quite different from what we generally mean by the term, is quite
precise, unambiguous, self-explanatory and applicable to any organism, whether it does or does not
possess a brain. This terminology is in line with the framework proposed by A. Damasio, that the
emotion is a biological phenomenon, characterized by vegetative, visceral and somatic reactions (the
body marker), and its cognitive elaboration is another story, which he proposed to refer to as feeling.
This has constituted a revolutionary, efficient way to study the neurobiology of emotions.
Emotions are body markers: they comprise visceral and somatic responses, which have the function
to favor appropriate behaviors and communication. On the other hand, emotions may be coupled to
cortical elaboration to give rise to feelings. Ekman proposed criteria to classify basic
emotions:
• they must be present in all species;
• they must have universal sings;
• they must present a distinctive physiology (thus, they must be associated to specific viscero-
somatic responses);
• they must occur in response to well-defined events for all species;
• they must ensue rapidly;
• they must last shortly;
• they must be learnt automatically (they are not taught);
• they must come about without us asking for them (unbidden occurrence).
About 5 basic emotions can be classified according to these criteria.
Some distinction between the physiological reaction and the cognitive experience of emotions had been
proposed by several researchers, in the course of the XX century: for example, James and Lange
proposed the provocative idea that we do not weep because we are sad but, we are sad because we weep,
and similarly one does not quiver because they are afraid, but they are afraid because their heart
accelerates and they quiver. Cannon and Bard proposed that, following an event, the cortex produces
feelings, whereas the subcortical systems elicit a quick physiological and behavioral response.
191 Body At Work II
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