78 - Limbic System

Question 1

Introduction to emotion

Answer 1

Emotion is a combination of powerful subjective feelings and associated physiological states. Subjective feelings are explicit conscious awareness, such as fear, anxiety,
happiness. Physiological states are implicit, unconscious, autonomic, endocrine and somatic motor reactions and responses.

Because of these properties of emotion, the neurobiological system that mediates emotions
needs to be able to interact with both cortex and systems that regulate these physiological states.

Question 2

Limbic system

Answer 2

The limbic system is a convenient way of describing several functionally and anatomically interconnected nuclei and cortical structures that are located in the telencephalon and diencephalon.

Question 3

Functional properties of the limbic system

Answer 3

• Highly interconnected
• Highly modulated
• Emotional (Affective) responses
      - fear
      - rage
      - pleasure
      - motivation
• Critical for certain types of memory
• Homeostasis
     - reproductive drive
     - eating/drinking behaviors
     - endocrine control
     - autonomic regulation
• Dysfunction results in psychiatric disorders and dementia

Question 4

Main components of the limbic system

Answer 4

• Limbic cortex (a ring of cerebral cortex that surrounds subcortical limbic structures)
      − Anterior cingulate cortex (Acc)
     − Orbitofrontal, medial prefrontal cortex (mPFC)
     − Insula
• Hippocampus
• Amygdala
• Septal nuclei
• Thalamus
     − Anterior nucleus
     − Mediodorsal nucleus
• Nucleus Accumbens (NAcc)
• Basal forebrain
• Olfactory system
• Hypothalamus

Question 5

Connectivity and Functional Hierarchy

Answer 5

• Reciprocal connections
• Primary output (Hypothalamus)
• Functional Hierarchy
− Hypothalamus: governs and monitors internal homeostasis and basic needs such as hunger and thirst.
− Higher order limbic nuclei (Amygdala, hippocampus, etc): achieve some awareness of external reality and begin to form memories.
− Limbic Cortex: more efficiently, effectively, and safely satisfy limbic needs and impulses; associated with the conscious, rational mind.

Under certain circumstances, emotions can hijack the logical mind, and the limbic system can overturn the neocortex

Question 6

Modulation via neurotransmitters

Answer 6

• Norepinephrine
• Serotonin
• Dopamine
• Acetylcholine

Question 7

Where does norepinephrine act?

Answer 7

Locus ceruleus (LC)

Question 8

Where does serotonin act?

Answer 8

Raphe nuclei

Question 9

Where does dopamine act?

Answer 9

Mesolimbic system
− Ventral tegmental area (VTA) –> NAcc, mPFC, septal nuc.
− Nigrostriatal projection: Substantia nigra –> striatum

Question 10

Where does acetylcholine act?

Answer 10

− Nucleus basalis –> hippocampus, neocortex

− Septal nucleus –> hippocampus

Question 11

Describe the overall role of the hypothalamus

Answer 11

Governs and monitors internal homeostasis and basic needs such as hunger and thirst. Mediates raw and reflexive emotionality: pleasure, displeasure, rage, and
aversion.

Question 12

Four zones of hypothalamus

Answer 12

• Lateral zone
• Periventricular zone
• Medial zone
• Posterior zone

Question 13

Lateral zone nuclei

Answer 13

• lateral preoptic area

- lateral hypothalamic nuclei

Question 14

Lateral zone behavioral function

Answer 14

• motivation (self-stimulation)
• emotion (rage)
• Food & Water intake

Question 15

Periventricular zone nuclei

Answer 15

• periventricular nuc.& arcuate nuc.
• suprachiasmatic nuc.
• premamillary nuc.
• ventromedial nuc.
• paraventricular nuc.
• supraoptic nuc.

Question 16

Periventricular zone behavioral function

Answer 16

• pituitary regulation (Ant.&Post)
• CRH, TRH, GH-RH, LH-RH, DA
• diurnal rhythm
• GH-RH, glucose metabolism
• oxytocin, vasopressin

Question 17

Medial zone nuclei

Answer 17

• medial preoptic nuc.
• dorsomedial nuc.
• anterior nuc.
• ventromedial nuc.

Question 18

Mecial zone behavioral function

Answer 18

• temperature regulation
• sexual differentiation & behavior
• food intake
• nutrient balance

Question 19

Posterior zone nuclei

Answer 19

• posterior nuc.
• supramammillary nuc.
• mammillary bodies

Question 20

Posterior zone behavioral function

Answer 20

• cardiovascular regulation
• respiratory regulation
• temperature regulation

Question 21

What are the characteristics of the hypothalamus?

Answer 21

• Primary output of limbic system
• Primitive, similar through evolution
• Fully functional at birth
• Highly involved in all aspects of
     − emotional responses
     − reproductive drive
     − endocrine
     − hormonal regulation
     − autonomic function
     − eating, drinking, sleeping
• Exerts influence through synaptic connections and circulation
• Sexual dimorphism

Question 22

Describe the relationship between the hypothalamus and the autonomic nervous system (ANS)

Answer 22

• Hypothalamus controls emotion expression through ANS.
• Intense activity of the sympathetic division prepares animal to fully utilize metabolic and other resources in challenging or threatening situations.
• Conversely, activity of the parasympathetic and enteric divisions promotes
a build up of metabolic reserves.

Question 23

Describe the basic function of the amygdala

Answer 23

Amygdala is the integrative center for emotions, emotional behavior, and
motivation

Question 24

Components of the amygdala

Answer 24

~ 10 distinct nuclei; can group into 3 functional sets

1. Corticomedial nucleus
2. Basolateral nucleus
3. Central nucleus

Question 25

Connections of the amygdala

Answer 25

Connections define its function. The amygdala receives sensory information directly from the various sensory systems that process the external world. The output of amygdala are the systems involved in the emotional reactivity.

Question 26

Major inputs of the amygdala

Answer 26

Sensory cortex Sensory thalamus Associative cortex Prefrontal cortex

Question 27

Major outputs of the amygdala

Answer 27

Hypothalamus Thalamus Basal ganglia

Question 28

Functional properties of the amygdala

Answer 28

Functional Properties • Fear, anxiety; aggression • Interpretation of facial expression, particularly fear • Mediating conditioned fear response (learning) • Stimulation of the amygdala produces a perception of familiarity • Motivation & reinforcement to fear behaviors (via nucleus accumbens) • Homeostasis (neuroendocrine control)

Question 29

Describe the amygdala role in fear, anxiety and aggression

Answer 29

Fear, anxiety; aggression − Profound lesion to the amygdala → flat affect, docile behavior − Other brain regions involved in regulation of emotion processing

Question 30

Describe the amydala role in mediating conditioned fear responses (learned fear)

Answer 30

Mediating conditioned fear response (learning) − Best understood through animal studies of Pavlovian fear conditioning − When a conditional stimulus (neutral, CS) is repeatedly paired with a unconditional stimulus (aversive, US. For example, foot shock), over time the animal begin to respond to the neutral stimulus with fear behaviors. − Underlying neural circuit: Synaptic connections of sensory inputs to amygdala neurons are strengthened; Amygdala outputs to hypothalamus activate the visceral motor effector system to prepare body for an action.

Question 31

What three processes is the hippocampus involved in?

Answer 31

- Sensory processing - Homeostasis - Learning and memory

Question 32

Sensory processing by the hippocampus

Answer 32

Sensory processing – Novelty detection – Spatial organization

Question 33

Homeostasis by the hippocampus

Answer 33

Homeostasis – Regulation of HPA axis • ↑ [glucocorticoid receptors] in CNS • toxic effects of stress (cortisol)

Question 34

Learning and memory in the hippocampus

Answer 34

``` Learning & Memory – Long-term synaptic plasticity • explicit memory – Spatial context and surroundings • place cells – Contextual regulation to amygdala-mediated fear processing ```

Question 35

What processes target the hippocampus?

Answer 35

Aging and stress

Question 36

Function of the frontal cerebral cortex

Answer 36

The role of the cerebral cortex in emotional behaviors is complex where many exceptions and contradictions appear to exist, illustrating our poor understanding.

Question 37

How does the frontal lobe play a role in restraint?

Answer 37

- Judgement - Foresight - Perseverance - Delayed gratification - Inhibition of socially unacceptable behavior - Self-governance - Concentration

Question 38

How does the frontal lobe play a role in initiative?

Answer 38

- Curiosity - Spontaneity - Motivation - Drive - Creativity - Personality - Mental flexibility

Question 39

How does the frontal lobe play a role in order?

Answer 39

- Abstract thinking - Working memory - Perspective - Planning - Insight - Organization - Sequencing

Question 40

How does the frontal lobe play a role in cortical regulation of the fear response?

Answer 40

Medial prefrontal cortex projecting to amygdala

Question 41

What is empathy?

Answer 41

Understanding emotion in others

Question 42

Limbic system "mirror neurons"

Answer 42

The concept of the mirror neuron originates from a phenomenon that a subset of neurons in the premotor region are activated when a monkey performs an action itself and when it observes another living creature perform that same action. Thus we understand the actions (emotion) of others possibly by activating our own neural representation of these actions (emotion).

Question 43

Empathy for pain

Answer 43

The neural substrate for empathic experience does not involve the entire “pain matrix.” Only that part of the pain network associated with its affective qualities, but not its sensory qualities, mediates empathy.

Question 44

Manifestations of prefrontal cortex lesion

Answer 44

* Apathetic * Impulsive * Poor judgment * Depressive behaviors * Mania

Question 45

What are the four components of the brain reward system?

Answer 45

``` • Nucleus accumbens • Frontal cortex • Ventral tegmental area (VTA) • Dopamine ```

Question 46

Describe the process of the brain reward system

Answer 46

1. Underlying circuits: the reinforcement limbic loop 2. Elements of this loop are modulated by the dopaminergic system. 3. Dopamine from ventral tegmental area (VTA) to nucleus accumbens serves as the reward signal 4. Under normal physiological conditions, emotional processing in the limbic system can signal the presence of rewards and can promote the activation of motor programs to acquire the beneficial rewards. Natural rewards include food, water, sex, love, nurturing etc.

Question 47

Drug addiction in relation to emotional reinforcement

Answer 47

Addiction highlights the vulnerability of emotional neural circuits to dysregulation when they are exposed to drugs.

Question 48

Effect of drug addiction on the limbic system

Answer 48

- Drugs of abuse, including cocaine, heroin, alcohol, opiates, marijuana, nicotine, and their synthetic analogs act on elements of the limbic circuitry by altering the neuromodulatory influence of dopamine. - Addiction dampens the response of reward circuitry to natural rewards, and intensifies the response to addictive drugs, resulting in “hypofrontality” – reduced cortical control of emotional behaviors.