03-10-23 - The limbic system, emotion, the hypothalamus, appetites Flashcards
Learning outcomes
- List the main core components of the limbic system.
- Appreciate their role in emotion, emotion driven behaviour and emotional memory.
- Describe the location, structure, function and inputs of the amygdala and outline Kluever-Bucy syndrome..
- Be aware that the amygdala stores simple codes for emotions and can establish memory for these.
- Describe functions of the cingulate gyrus and be aware of relationship with the amygdala and of its outputs to the motor system and brain stem.
- Outline the roles of the limbic system effectors.
Physically, what is the limbic system?
What does it form?
What are 4 general functions of the limbic system?
What are 8 functional roles of the limbic system?
What are 3 ‘philosophical’ functions of the limbic system?
- The limbic system is a system of interconnected discrete structures within the brain and brain stem largely forming a ring around the corpus callosum
- 4 general functions of the limbic system:
1) Emotion and motivation - puts a value on things
2) Appetitive behaviour
3) Endocrine function
4) Autonomic nervous system control - 8 functional roles of the limbic system:
1) Eating / Drinking
2) Fighting/killing
3) Sex drive
4) Enjoyment
5) Fear / anxiety
6) Autonomic preparation
7) Memory formation and recall
8) Expression of emotion - 3 ‘philosophical’ functions of the limbic system:
1) Relates the person to their environment with reference to past experience, current requirements and present situation.
2) Engages the person with the environment by employing motivation, behaviour and emotions mixed with memory
3) The assignment of value Physically: Fear, Dread, Foreboding, Joy, Eagerness, Flight or Flight
What are the 4 categories of limbic system functions?
- 4 categories of limbic system functions:
1) Emotions and drives via the amygdala
2) Homeostasis and motivation (autonomic and neuroendocrine) via the hypothalamus
3) Olfaction via the olfactory cortex
4) Memory via the hippocampus
Label the cortical structures of the limbic system (in picture)
Label the subcortical structures of the limbic system (in picture)
Where is the amygdala found?
What are 3 roles of the amygdala?
What have Experiments with auditory Pavlovian signals been used to demonstrate?
- The amygdala is found at the anterior tip of the hippocampus.
- 3 roles of the amygdala:
1) Provides an emotional component to experiences & memory
2) Provides the ability to recognise fear and emotions in others
3) Provides an appreciation of innate (baby precipice) and learned fear and has extensive connections with all cortical association areas allowing integrative function
- Experiments with auditory Pavlovian signals with rabbits and rats have demonstrated the range of sensory input in learned fear
Describe the fear condition experiments with Little Albert.
Where does social conditioning such as this occur?
What can we learn from these experiences?
- Fear condition experiments with Little Albert:
- Cruel experiments in which little Albert was conditioned with noise to fear rats and rabbits (John Watson at Johns Hopkins)
- We learn from, and fear to make mistakes which have adverse effects
The Amygdala - connectivity & function.
Where do the most significant afferents to the amygdala come from?
Where do the most significant efferents of the amygdala go to?
What info is the amygdala sending/receiving with these afferents and efferents?
Describe the outcome of the ablation of the amygdala in Macaque Monkeys.
- The Amygdala - connectivity & function
- Most significant afferents to the amygdala are from frontal temporal and parietal lobes receiving cognitive information
- Most significant efferent’s are to the hypothalamus and limbic cortex providing emotional cognisance, and visceral/homeostatic information
- Ablation of the amygdala in Macaque Monkeys produces a lack of fear such that they no longer function within the parameters of the group
- They were constantly attacked for taking food from a superior, or mating with inappropriate partners, as they were unable to learn despite vicious attacks (losing ability to sense emotion in others)
- These monkeys also display unusual tameness, - as do rats and humans following bilateral amygdalotomy
The amygdala and fear.
Describe Ekman’s six types of universal facial expression (in picture).
Describe the effects of lesions of the amygdala in humans?
What does electrical stimulation of the amygdala result in?
When will FMRI show increased activity in the amygdala?
- The amygdala and fear
- Ekman’s six types of universal facial expression (in picture)
- Lesions in the human amygdala gives a loss of recognition of fear and anger in other peoples faces, these subjects however can usually recognise the other 4 Ekman emotion types (sad happy disgust surprise and anger)
- Other modalities such as vocalisation can also be misunderstood
- Electrical stimulation of the amygdala (as well as the anterior hypothalamus & the PAG) causes anxiety, agitation and aggression in humans (fight or flight response activated)
- FMRI shows increased activity in the amygdala when fearful faces are shown as compared to other emotions
What is Kluver-Bucy syndrome?
What are 4 signs/symptoms of Kluver-Bucy syndrome?
- Bilateral temporal lobe lesions in all mammals produce a range of symptoms known as Kluver-Bucy syndrome
- 4 signs/symptoms of Kluver-Bucy syndrome:
1) Visual recognition impairment for fear in others (form of visual agnosia)
2) Heightened sexual appetite (Hypersexuality)
3) Flattened emotions
4) Oral tendencies (Hyperorality)
* Wanting to put things in their mouth
The Amygdala and unconscious reactions.
What reaction can be shown in arachnophobics and ophidophobics?
Who does not show this reaction?
How is this reaction achieved?
- The Amygdala and unconscious reactions
- Arachnophobics and ophidophobics show a skin conductivity reaction to seeing camouflaged spiders or snakes, before they are aware they are there
- Those with no fear of spiders do not show this response to spiders and vice versa for snakes
- This reaction represents a fast sub-cortical route for visual information which connects the thalamus to the amygdala and then to the hypothalamus, which allows for a much faster response, allowing a memory to be made quickly
- Input goes into the eye, up to the lateral geniculate ganglion of the thalamus, goes back to the occipital lobe, where the data is decoded and constructed
- Once we decide what that thing is, the information goes to the hippocampus, and starts to form a memory of the snake and the fact it frightens you
What is the main effector of the limbic system?
- The main effector of the limbic system is the hypothalamus, as it has a mass of outputs as well as inputs
What are 5 inputs (afferents) to the hypothalamus?
- 5 inputs (afferents) to the hypothalamus:
1) Neocortex
2) Pain & sensory integration in brainstem nuclei
* Hunger and pain
3) Spinal cord
4) Amygdala
* Memory with emotion
* Can summon fear by recalling frightening things that affect the hypothalamus, which leads to shivers/sweating
5) Eyes - Danger/beauty
What are the 6 efferents (outputs) to the hypothalamus?
- 6 efferents (outputs) to the hypothalamus:
1) Neocortex (another name for cortex)
* For motivational strategies
* I want to get this food, how will I get to it
2) Pain & sensory integration in brainstem nuclei
* Dulling pain/hunger
* Descending pain reduction system that originates at the PAG (periaqueductal gray)
* This will feed down and can turn off pain coming in the spine by sending down opiates
3) Anterior and posterior Pituitary
* Hormone release
4) Amygdala
5) Medulla
* Vomiting and respiration etc
* Can detect disgust in things
6) Spinal cord
* Visceral motor function
What are 4 parasympathetic outputs in the hypothalamic circuit?
What are 3 sympathetic outputs in the hypothalamic circuit?
Where do all efferent targets feedback to?
What is the purpose of this?
- 4 parasympathetic outputs in the hypothalamic circuit:
1) Viscera
2) Heart
3) Gut
4) Trachea - 3 sympathetic outputs in the hypothalamic circuit:
1) Viscera
2) Blood vessels skin
3) Exocrine glands etc - All efferent targets feed back to the limbic system to provide information about environments both internally and externally.
- This prepares the body for fight or flight by systemic arousal - triggered by an emotion derived from a situation
What are the 3 types of effects exerted by the hypothalamus?
- 3 types of effects exerted by the hypothalamus:
1) Vegetative functions
* Cardiovascular regulation;
* Thirst
* Appetites
* Temperature - blushing pallor
* Sexual excitement
2) Endocrine functions
* Control over anterior pituitary gland hormone release through the connecting blood supply
3) Behavioural functions
* General level of activity up to and including ‘rage’ for pursuit of food, water, sex etc;
* Ingestion/disinterest in/of food
* Fear and punishment behaviour
* Increased sexual drive
Where does the mesolimbic dopamine system (or reward system) originate?
What 5 places does the limbic reward system project to?
How are drugs of abuse and the limbic reward system linked?
Describe 4 steps in the limbic reward system
- The mesolimbic dopamine system (or reward system) originates in the ventral tegmental area of the midbrain
- 5 places does the limbic reward system project to:
1) Medial prefrontal cortex (mPFC)
2) Amygdala
3) Hippocampus
4) Nucleus accumbens
5) Ventral pallidum - Drugs of abuse such as psycho stimulants (e.g. cocaine) opiates (e.g. heroin) , ethanol cannabinoids and nicotine are currently thought to have a final common dopaminergic pathway feeding into the limbic system
- 4 steps in the limbic reward system:
1) The ventral segmental area (to do with motivations and addictions) has dopaminergic pathways that feed into the MPFC, Amygdala, and hippocampus
2) This excites those areas, which feed into the nucleus accumbens via glutamatergic pathways
3) The nucleus accumbens makes decisions about how to achieve that pleasure again, and helps the brain find strategies to do things
4) The nucleus accumbens will generate signals via GABAergic pathways to excite the ventral pallidum, then the mediodorsal thalamus in order to stimulate the MPFC again e.g in smokers stimulates the MPFC to find ways to get more nicotine
What is the anterior insular cortex?
What is its role?
How is Huntington’s disease linked with the anterior insular cortex?
- The anterior insular cortex is part of the fold of the main mantle of the brain
- It provides introspection which allows the interpretation of sensation as joy or disgust e.g seeing something disgusting that makes you nauseous is mediated by this area
- Patients with Huntington’s disease (a progressive frontal cortex degenerative disease) show impairment of visual characteristics associated with disgust.
- The extent of the impairment is dependent of the amount of damage to the anterior insular cortex and the reduction in its activity
The limbic system and pain. What structures associated with pain does the limbic system interconnect with?
How is the PAG (periaqueductal grey able to reduce pain?
What does electrical stimulation of PAG result in?
How can this be blocked?
What does the perception of pain depend on?
How does the placebo effect alter the perception of pain?
- The limbic system and pain
- The limbic system interconnects with structures involved in pain and pain perception such as the PAG (periaqueductal grey)
- The PAG is able to reduce activity in the ascending pain pathway, its effects are agonised by endorphins and so opiates.
- Electrical stimulation of PAG produces analgesia which can be blocked by nalaxone (Opioid receptor blocker)
- Electrical stimulation of PAG can also produce aggression
- The perception of pain is dependent on the perception of the circumstances.
- Sadistically inflicted pain stimuli hurt more than accidentally inflicted pain stimuli from a friend
- The placebo effect can alter the perception of pain - saline injections or a parental kiss can reduce pain
- Pain relief is blocked by nalaxone
What 2 parts of the limbic system are affected by depression?
- 2 parts of the limbic system are affected by depression:
1) The ventromedial portion of the prefrontal cortex
2) The cingulate gyrus
The limbic system and depression.
How is the ventromedial portion of the prefrontal cortex affected by depression?
How is this area of the brain affected in bi-polar sufferers?
How is the proposal that this portion of the brain plays a role in depression reinforced?
- The limbic system and depression
- The ventromedial portion of the prefrontal cortex has a reduced activity
- This area is normally associated with goal setting, forward planning, and ascribing meaning to perceptions.
- The ventromedial prefrontal cortex has reduced mass in individuals with familial depression – mass reduction is from loss of glial cells not neurones.
- In bi-polar sufferers, this portion of the brain is virtually inactive during depression (no meaning to life) and hyperactive during manic phases (high significance of ordinary occurrences - hyperfixation)
The limbic system and depression.
How is the cingulate gyrus affected by depression?
How is this area affected in bi-polar patients?
What is the role of the cingulate gyrus (CG)?
What are 5 other conditions the CG is involved in?
- The limbic system and depression
- The cingulate gyrus shows abnormal activity during clinical depression.
- Generally, the activity in the cingulate gyrus becomes reduced during depression
- In bi-polar patients the anterior portion becomes more active during depression and less active during manic periods (opposite to ventromedial cortex)
- Normal function of the CG is complex but is thought of as a straddle between emotion and cognition.
- Can focus a patient on their pain for example.
- 5 other conditions the CG is involved in:
1) Implicated in aspects of Schizophrenia
2) Involved in transient
3) Mood swings
4) Depression and
5) Anxiety disorders
Imbalances of what 3 limbic neurotransmitters are involve d in depression?
What drug is used to correct imbalances in serotonin levels?
What are Elevated blood glucocorticoid levels are a response?
Describe the pathway by which this occurs and how it can cause depression (5 steps)
- Imbalances 3 limbic neurotransmitters are involved in depression:
1) Serotonin
2) Dopamine
3) Norepinephrine - Antidepressants such as Prozac (fluoxetine) are marketed as correcting perceived
imbalances in serotonin levels - The true imbalances may actually lie in receptor expression as well as neurotransmitter
release - Elevated blood glucocorticoid levels are a response to exposure to prolonged stressors
- The glucocorticoids themselves aren’t the cause of stress, but stress can lead to the modulating system of the glucocorticoids being broken
- Mechanism by which this occurs:
1) The pituitary releases ACTH which signals the adrenal glands to release glucocorticoid - Prep for fight or flight.
2) Glucocorticoid is detected by the hippocampus which then activates the hypothalamus into releasing corticotrophin releasing hormone (CRH).
3) CRH causes release of adrenocorticotrophic Hormone (ACTH) which causes the release of more glucocorticoids.
4) Normally cortical receptors feed back into the system blocking production of CRH but left unchecked (as in people with depression) this results in excess glucocorticoids
5) Increased glucocorticoids affects the expression of serotonin receptors leading to depression and possible suicide risk
What can overactivity of the limbic system cause?
Who pioneers the frontal lobotomy?
What did this procedure involve?
How was the frontal leukotomy performed?
Describe this procedure.
What 4 ways did frontal leukotomies affect the patient?
- As the limbic system provides the emotional aspects of cognitive function
- Over activity of certain elements can cause medical conditions; such as prolonged anxiety states
- Egas Moniz pioneered the frontal lobotomy (Nobel Prize 1949 for psychosurgery).
- The aim was to separate the limbic cortex at the level of the frontal lobes
- The frontal leukotomy was performed under local anesthesia.
- The “leukotome” was inserted into the brain at approximate angles
- When in place, a wire “knife” was extended and the handle rotated in order to lacerate a portion of the brain
- The picture depicts a horizontal slice of the brain (parallel to the top of the skull) with Moniz’s estimate of the extent of the damage done by the procedure.
- 4 ways did frontal leukotomies affect the patient:
1) Disinhibition
2) a lack of forward planning
3) Lowered executive function
4) Lowered multitasking abilities.
