Scientific Understanding of Consciousness
Consciousness as an Emergent Property of Thalamocortical Activity

Limbic System – the Emotional Brain

The emotional brain is centered in the limbic system (diagram) and its connections to the cortex and other subcortical structures.  The limbic system comprises a group of structures surrounding the top of the brain stem, which serve to quickly evaluate sensory data and trigger an animal’s motor responses.

Papez circuit theory, takeoff point for limbic system theory. (LeDoux; Emotional Brain, 90)

Papez suggested that emotional experiences could be generated in two ways: (1) stream of feeling by sensory objects, (2) stream of thought to cerebral cortex, then to cingulate cortex. (LeDoux; Emotional Brain, 90)

The term "limbic" system derives from the ringlike arrangement of allocortical structures, including the amygdala, hippocampus, entorhinal cortex, and hypothalamus, that provide a relative distinct border separating the brain stem from the new cortex. (Buzsáki; Rhythms of the Brain, 281)

Limbic System and Neocortex

In 1952, MacLean introduced the term 'limbic system'. (LeDoux; Emotional Brain, 97)

Paleomammalian brain, present in all mammals, is essentially the limbic system. (LeDoux; Emotional Brain, 98)

Emotions involve relatively primitive circuits that are conserved throughout mammalian evolution. (LeDoux; Synaptic Self, 212)

Neocortex is a mammalian specialization. (LeDoux; Synaptic Self, 210)

As a central player in your emotional life, your insula  sends signals to and receives signals from  other emotional centers in your brain including the amygdala, the autonomic nervous system (powered by the hypothalamus), and the orbitofrontal cortex, which is involved in nuanced emotional judgments. (Ramachandran; Tell-Tale Brain, 98)

Limbic system, a catchall term for a number of evolutionarily old structures, many neuroscientists resist using the term. (Damasio; Descartes' Error, 28)

No generally accepted criteria for stipulating which areas of the brain belong to the limbic system. (LeDoux; Synaptic Self, 211)

 

Research study — Amygdala engaged by Serotonin anxiety and fear-promoting circuit

Research study — Thalamic Input to the Nucleus Accumbens mediates Opiate Dependence

Research study — Prefrontal cortical regulation of reward-related behavior

 

    Link to — Nuclei of the Hypothalamus — diagram

 

Brodmann area 24 in the cingulate cortex is at the crossroads of pathways linking the limbic system with the frontal lobe. (Fuster; Prefrontal Cortex, 199)

Emotions are among the very oldest of our brain properties. (Llinás; I of the Vortex, 156)

Limbic system accomplishes both novelty detection and reward. (Ratey; User's Guide to Brain, 115)

Hypothalamus, brain stem and the limbic system intervene in body regulation and in all neural processes on which mind phenomena are based (perception, learning, recall, emotion, feeling, reasoning, creativity). (Damasio; Descartes' Error, 123)

Hypothalamus communicates reciprocally with areas of the cerebral cortex; information about the conscious and peripheral aspects of emotion affect each other. (Kandel; Principles of Neural Science, 987)

Hypothalamus provides information to the cingulate gyrus by a pathway from the mammillary bodies to the anterior thalamic nuclei and from there to the cingulate gyrus. (Kandel; Principles of Neural Science, 987)

Motor FAPs of relatively primitive animals are accompanied by a well-defined emotional component. (Llinás; I of the Vortex, 157)

Emotions are linked to the motor aspects of FAPs by access through the amygdala and the hypothalamus and their connectivity with the brain stem. (Llinás; I of the Vortex, 161)

Two major foci of emotional representations within the prefrontal cortex -- (1) orbital cortex, and (2) anterior cingulate cortex. (Fuster; Prefrontal Cortex, 345)

No generally accepted criteria for stipulating which areas of the brain belong to the limbic system. (LeDoux; Emotional Brain, 211)

Some researches include the orbitofrontal cortex as a part of the limbic system.

 

 Cognition and Emotion, Tightly Entwined

The cognitive brain of the cortex and the emotional brain are tightly entwined, providing control for movement and behavior. Emotion is the more ancient function, existing in well developed form in primitive mammals whose cortex is much less well developed than humans. Emotion and thinking contribute to the ‘value system’ enunciated by Edelman as a basis for decision making in humans. Both the emotional brain and the cognitive brain have aspects of unconscious as well as conscious functionality. Humor and music are two functions for which cognition and emotion are tightly entwined.

Humor is what happens when an assumption is epistemically committed to in a mental space and then discovered to have been a mistake. (Hurley, Dennett, Adams; Inside Jokes, 121)

 

Discussion of Humor and Laughterleft hemisphere constructs a story or model and then a sudden unexpected twist is introduced to generate a paradigm shift, i.e. a completely new model is invoked to explain the same data.

 

As music unfolds, the brain constantly updates the estimates of when new beats will occur, and take satisfaction in matching a mental beat with a real-world one, and takes delight when a skillful musician violates that expectation in an interesting way. (Levitin; Your Brain on Music, 187)

 

Research study — Music Processing Modular Modelblock diagram of music processing in the brain.

 

Orbitofrontal cortex (OFC) and the insular; two major components of the paralimbic belt. (Miller; Human Frontal Lobes, 59)

Temporal-insular-orbitofrontal region is largely devoted to olfaction. (Miller; Human Frontal Lobes, 59)

 

Hypothalamus as a focus of emotional activity

The hypothalamus is the focus of much of the emotional action in the limbic system and the cortical areas. The hypothalamus tightly regulates bodily responses and influences modulator neurotransmitters that widely spray the frontal cortex neurons to influence attention and decision making. The hypothalamus is tightly entwined with the sense of self.

Importance of the hypothalamus in emotional expression; importance of the cerebral cortex in emotional experience. Neocortex lacks significant connections with the hypothalamus; evolutionarily older areas of the medial cortex (rhinencephalon) are intimately connected with the hypothalamus. (LeDoux; Emotional Brain, 92)

Unconscious bodily responses of emotion include the facial expressions of emotion, some of which, such as a snarl of teeth, may exist in non-human mammals. These unconscious bodily responses of emotion are produced by innate FAPs.

Some emotional systems in the brain are essentially the same in many vertebrates, including mammals, reptiles, birds and possibly amphibians and fishes. Evolution stubbornly maintains emotional functions across species. (LeDoux; Emotional Brain, 107)

Limbic System

In 1952, MacLean introduced the term 'limbic system'. (LeDoux; Emotional Brain, 97)

Forebrain, according to MacLean (1970), had gone through three stages of evolution: (1) reptilian, (2) paleomammalian, (3) neomammalian. (LeDoux; Emotional Brain, 98)

Emotional Brain, MacLean's "Limbic System" - (illustration) (Johnston; Why We Feel, 111)

Emotions involve neurons in the hypothalamus and the limbic system. (Changeux; Neuronal Man, 158)

Limbic system, inherited from primitive mammals. (Changeux; Neuronal Man, 111)

Limbic system, located in the subcortical area, forms a circle around the brainstem. (Edelman; Universe of Consciousness, 105)

Forebrain and the limbic system are richly connected. Thoughts can excite emotion. Value system.

Two systems, limbic-brain stem and thalamocortical, were linked during evolution.  The later-evolving cortical system served learning behavior that was adapted to increasingly complex environments. (Edelman; Bright Air, 118)

Limbic-brain stem system are often arranged in loops; they respond relatively slowly (seconds to months), and do not consist of detailed maps. (Edelman; Bright Air, 117)

A pronounced rhythm dominates the EEG throughout the nonprimate mammalian limbic system during exploratory activity and learning. Theta rhythm range 5-12 Hz. (Eichenbaum; Olfactory Perception and Memory, 181)

 

Evolving understanding of limbic system.

Limbic system is not precisely defined; it remains a catchall for a number of evolutionarily old structures; many neuroscientists resist using it. (Damasio; Descartes’ Error, 28)

Extended notions about the limbic system include a host of prefrontal, paralimbic, telencephalic basal forebrain and subcortical gray matter systems (including the ventral basal ganglia, septal regions, and amygdala) many diencephalic regions, particularly anterior thalamus and hypothalamus, midbrain areas, and monoaminergic portions of the brainstem core. (Watt; Emotion and Consciousness, 218)

Limbic system contains both innate circuitry and circuitry modifiable by experience. (Damasio; Descartes’ Error, 118)

Specific portions of the limbic system project to different areas of the cingulate gyrus, allowing different patterns of limbic activity to generate qualitatively different emotional feelings and bias cognitive processes. (Johnston; Why We Feel, 119)

[Robert Ornstein - "One way to remember limbic functions is that they are the four 'F's of survival: Feeding, Fighting, Fleeing and sexual reproduction."]

Limbic System concept builds upon the earlier Papez Circuit concept

Papez circuit is composed of the hippocampus, mammillary bodies, anterior nuclei of the thalamus, and cingulate gyrus. All of these nuclei are interconnected into a feedback circuit allowing for the integration of emotion and memory. (Norden, Understanding the Brain, 90)

· Hippocampus

· Mammillary bodies

· Anterior nuclei of the thalamus

· Cingulate gyrus

Papez Circuit -- (diagram) (LeDoux; Emotional Brain, 89)

Papez suggested that emotional experiences could be generated in two ways: (1) stream of feeling by sensory objects, (2) stream of thought to cerebral cortex, then to cingulate cortex. (LeDoux; Emotional Brain, 90)

Papez circuit theory, takeoff point for limbic system theory. (LeDoux; Emotional Brain, 90)

Limbic System Structures Connected to Hypothalamus

All of the limbic system structures are strongly connected to the hypothalamus, which regulates bodily functions. Although the limbic system does not consists of a universally accepted set of structures, I’ll use this set, which seems reasonable to me. (Norden, Understanding the Brain, 90)

· Hypothalamus

· Amygdala

· Ventral Tegmental Area (VTA)

· Nucleus accumbens

· Hippocampus

· Orbitofrontal cortex

· Dorsolateral prefrontal cortex

Limbic System Structures Connected to the Forebrain

All of the limbic system structures are strongly connected to the forebrain. Any events that arise in the limbic system are swiftly announced in the forebrain. Conversely, cognitive thoughts that might have an emotional impact are linked to the limbic.

Visual thalamocortical pathway, interaction with emotional pathways - (illustration) (Johnston; Why We Feel, 114)

Limbic System

Neural processing of emotions begins with the limbic system, a number of interconnected subcortical regions around the hypothalamus. One major pathway from the limbic system via the hypothalamus is responsible for physiological adjustments to the body, such as changes in heart rate or blood pressure. A second output pathway, common to all feelings, is the pleasure pathway, which ultimately releases dopamine onto the nucleus accumbens. The dopamine pathway to the nucleus accumbens is closely associated with the control of motor behavior and is correlated with hedonic tone that is a fundamental aspect of all feeling states. Limbic system outputs influence two major arousal systems of the brain, and these pathways provide a mechanism by which feelings can modulate cortical arousal. (Johnston; Why We Feel, 119)

Visual thalamocortical pathway, interaction with emotional pathways - (illustration) (Johnston; Why We Feel, 114)

Specific portions of the limbic system project to different areas of the cingulate gyrus, allowing different patterns of limbic activity to generate qualitatively different emotional feelings and bias cognitive processes. (Johnston; Why We Feel, 119)

Amygdala is the part of the limbic system most specifically involve with emotional experience. (Kandel; Principles of Neural Science, 988)

 

Dopamine onto the Nucleus Accumbens, Reward feelings.

Release of dopamine onto the nucleus accumbens appears to underlie all reward feelings. (Johnston; Why We Feel, 116)

Cocaine causes a massive release of dopamine onto the nucleus accumbens, and the user experiences a sudden 'rush' of extreme pleasure. (Johnston; Why We Feel, 116)

 

Emotions as Fixed Action Patterns (FAPs) (Llinás 155)

Emotions are internally generated intrinsic events, excellent examples of premotor templates in primitive form. (Llinás; I of the Vortex, 57)

Motor FAPs of relatively primitive animals are accompanied by a well-defined emotional component. (Llinás; I of the Vortex, 157)

Exclusively human FAPs: laugh, crying

Neurotransmitters

Dopamine potently augments the drive to obtain a rewarding stimulus, but it is not directly responsible for the hedonic experience itself. (Nature, Vol 443, 21 September 2006, p.289)

 

 

Access Consciousness and Feelings (Koch; Quest for Consciousness, 238)

 

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Neural processing of emotions, limbic system, interconnected subcortical regions around the hypothalamus; pleasure pathway, releases dopamine onto the nucleus accumbens. (Johnston; Why We Feel, 119)

Suggestion: Output from the limbic system provides the major source of arousal responsible for the formation of large neural gestalts. (Johnston; Why We Feel, 125)

 

Emotion

Fear

Anticipation of Pleasure

Neural Correlate

Amygdala

Nucleus Accumbens

 

Basic Emotions

Primary emotions - (diagram) (Damasio; Descartes’ Error, 132)

Primary emotions (happiness, sadness, anger, fear, disgust, surprise) (Johnston; Why We Feel, 88)

Children's facial expressions are automatic and controlled by subcortical centers within the extra-pyramidal motor system. (Johnston; Why We Feel, 101)

Primary emotions may be common to many species; secondary feelings appear to be a consequence of the unique history of humans. (Johnston; Why We Feel, 100)

Bodily expressions (especially of the face) occurring emotions are similar in people around the world. Goose bumps, a mild form of piloerection in humans, occur as a vestige of the more dramatic displays in our mammalian cousins. Innate emotions, some have older evolutionary histories than others. Innate emotions, universal facial expressions that are similar across many different cultures. (LeDoux; Emotional Brain, 109-112)

 

 

Return to — Emotion

Link to — Consciousness Subject Outline

Further discussion — Covington Theory of Consciousness