Lecture 19: Limbic System Flashcards
What led to the limbic system?
The search for cortical representation of feeling
What is the overall idea behind the limbic system?
Emotionally significant stimuli activate sensory pathways that trigger the hypothalamus (controls the ANS) to modulate heart, blood pressure and respiration
What are the main structures of the limbic system?
- Hippocampal formation
- Amygdala
- Hypothalamus
- Cingulate gyrus
- Anterior, Lateral Dorsal and Dorsal medial nuclei of the thalamus
- Limbic association cortices
What makes up the hippocampal formation?
Hippocampus, fornix and dentate gyrus
What does dysfunction to any structure of the limbic system cause?
Psychiatric disorders
What is the amygdala involved in?
The formation and storage of information related to emotional events, long term memory formation and recognizing danger or fear
Which lobe does the amygdala sit in?
In the frontal lobe
What does the amygdala have a hardwired connection to?
The hypothalamus, the hippocampus and the nuclei involved in reward and emotional response
What helps us to:
- Form and store information related to emotional events
- Facilitate long term memory formation
- Help us recognize when we are in danger or fearful of something?
The amygdala
What does the Amygdala do?
Helps us to:
- Form and store information related to emotional events
- Facilitate long term memory formation
- Help us recognize when we are in danger or fearful of something?
What does injury to the amygdala affect?
- Memory formation
- Emotional sensitivity
- Learning and retention
- Depression
- Anxiety
Injury to where effects:
- Memory formation
- Emotional sensitivity
- Learning and retention
- Depression
- Anxiety
The amygdala
What happens when animals have their amygdala’s removed?
The animals become very docile
A lesion to where can cause animals to become very docile?
The amygdala
How was the amygdala found to be an emotionally aggressive area of the brain?
Animals with their amygdala removed became very docile
What does the Amygdala sit anterior to?
The hippocampus
What sits anterior to the hippocampus?
The amygdala
What is the Fornix?
The connection of the hippocampus to the hypothalamus
What is the connection of the hippocampus to the hypothalamus?
The Fornix
What is the Stria Terminalis?
The connection of the amygdala to the hypothalamus
What connects the amygdala to the hypothalamus?
The stria terminalis
What does the limbic system being a circuit allow us to do?
Start anywhere
What is the Hippocampus?
A large nucleus in the parahippocampal gyrus with multiple functions
What is the large nucleus in the parahippocampal gyrus known as?
The hippocampus
What is the main function of the hippocampus?
Converts short term memory to long term memory
Where does the hippocampus have its cell bodies?
In the hippocampal formation
What has its cell bodies in the hippocampal formation?
The hippocampus
Where does the hippocampus extend its axons to?
The hypothalamus
What are the two axons of the hippocampus to the hypothalamus?
Fimbriae and fornix
What are fimbriae and fornix?
Axons from the hippocampus to the hypothalamus
What is the crus?
Where the two fornices from the hippocampus come together
What is the body of the fornix?
The midline structure that makes up the lateral ventricle
Where does the hippocampus end?
At the mamillary bodies
What synapses at the mamillary bodies?
The hippocampal axons
In the limbic circuit where does it go from the hippocampus?
The Mamillary bodies
In the limbic circuit, where does it go from the mamillary bodies?
The thalamus
Where does the tract from the mamillary bodies synapse in the thalamus?
Anterior or lateral dorsal or medial dorsal nuclei of the thalamus
What synapses at the anterior, lateral or medial dorsal nuclei of the thalamus?
The mamillary bodies
Where do axons from the thalamus project to in the limbic system?
The cingulate gyrus
What lobes are part of the cingulate gyrus?
The frontal and parietal lobe
Where do axons go from the cingulate gyrus in the limbic system?
To all over the brain
What is the order of limbic projects starting with the hippocampus?
- Hippocampus
- Mamillary bodies
- Thalamus
- Cingulate gyrus
- Widespread throughout the brain
What does the Fornix do?
Connects the hippocampus to the hypothalamus
What is the most anterior part of the hippocampus?
The pes hippocampus
What is the pes hippocampus?
The most anterior part of the hippocampus
What sits underneath the fornix?
The third ventricle
What is the Dentate gyrus a part of?
The hippocampus
What are the output regions of the dentate gyrus?
CA regions
What do the cell bodies of the dentate gyrus communicate with?
Different CA regions
Where do CA regions send their axons out as?
The fornix
What is the Perforant pathway?
The pathway that the entorhinal cortex used to project to the dentate gyrus of the hippocampus
How does the entorhinal cortex project to the dentate gyrus of the hippocampus?
Via the perforant pathway
What is the entorhinal cortex?
The region around the hippocampus
How is the hippocampus affected in people with Alzheimer’s?
People with Alzheimer’s have atrophies hippocampi
Where is the limbic association cortex located?
On the medial surface of the frontal, parietal and temporal lobes
What is located on the medial surface of the frontal, parietal and temporal lboes?
The limbic association cortex
What is the limbic association cortex?
The areas that the limbic system is projecting to
What did Papez suggest?
The limbic lobe forms a neural circuit that provides the neuroanatomical basis for the elaboration of emotions
What did Papez suggest emotion is?
Not a function of any specific brain center but a circuit that involved for basic structures interconnected through several nervous bundles
What are the nervous bundles involved in the limbic system suggested by Papez?
- Hypothalamus with mamillary bodies
- Anterior thalamic nucleus
- Cingulate gyrus
- Hippocampus
How did Papez propose that the cortex influences the hypothalamus?
Through connections of the cingulate gyrus and hippocampus
What is the Limbic circuit of Papez?
A work flow from the cingulate gyrus back to the hippocampus that explains the hippocampus
What are the steps in the Papez circuit starting with the hippocampus?
- Hippocampus goes along the fornix to the hypothalamus and mammillary bodies
- From the mamillary bodies to the thalamus through the mammillothalamic tract
- From the thalamus to the cingulate gyrus
- From the cingulate gyrus to the cortex
- From the cortex back to the cingulate gyrus and to the hippocampal formation
In the circuit of Papez, where does it go after the hippocampus?
From the hippocampus going along the fornix it goes to the hypothalamus and mammillary bodies
In the Papez circuit, what happens after reaching the hypothalamus and mammillary bodies?
It goes via the mammillothalamic tract to the thalamus
What does the Fornix do?
Carries information from the hippocampus to the hypothalamus and mammillary bodies
What carries information from the hippocampus to the hypothalamus and mammillary bodies?
The fornix
What does the mammillothalamic tract do?
Carries information from the mamillary bodies to the thalamus
What tract carries information from the mamillary bodies to the thalamus?
The mammillothalamic tract
Where is information from the thalamus first carried in the circuit of Papez?
It is carried from the thalamus to the cingulate gyrus
Where is information from the cingulate gyrus first carried in the circuit of Papez?
It is carried from the cingulate gyrus to the cortex
Where is information from the cortex carried in the circuit of Papez?
It is carried back to the cingulate gyrus
Where is information from the circuit of Papez carried after returning to the cingulate gyrus?
It is carried via the cingulum to the hippocampus
What is the cingulum?
The tract that carries information from the cingulate gyrus to the the hippocampus
What tract carries information from the cingulate gyrus to the hippocampal formation?
The cingulum
What is the second version of the limbic circuit called?
The Paul Mclean version
What was left out in the circuit of Papez?
The amygdala
What did the Paul Mclean version of the limbic circuit add?
Amygdala
What is the difference between the circuit of Papez and current version?
In the current version, both the hippocampus and the amygdala both talk to the hypothalamus. And the hypothalamus can go straight to the prefrontal cortex or through the cingulate gyrus to the prefrontal cortex
Overall what are the differences in the circuit of papez and the current version?
- Hippocampus and amygdala both send inputs to the hypothalamus
- Hypothalamus can go straight to the prefrontal cortex or through the cingulate gyrus to the cortex
What neural body did the Paul Mclean circuit (current limbic circuit version) add?
The amygdala
What are the bodies in the current limbic circuit starting with the entorhinal cortex?
- Entorhinal cortex or periamygdaloid
- Hippocampus
- Mammillary bodies
- Thalamus
- Cingulate gyrus
- Cortex
- Cingulate gyrus
- Hippocampus or entorhinal cortex
What is the Periamygdaloid?
Area around the amygdala
Starting at the Entorhinal cortex or periamygdaloid where does the current limbic circuit go?
To the amygdala
From the amygdala in the current limbic circuit, where does it go?
To the hippocampus
What are the two routes to the hippocampus in the current limbic circuit?
- From the entorhinal cortex or periamygdaloid to the hippocampus
- Amygdala to the hippocampus
Where does the limbic circuit go after reaching hippocampus in the current system?
To the mammillary bodies
Where does the current limbic circuit system go after reaching the Mamillary bodies?
The thalamus
What tract connects the mamillary bodies to the thalamus?
The Mammillothalamic tract
What does the Mammillothalamic tract do?
Connects the mamillary bodies to the thalamus in the limbic circuit
In the current limbic circuit where does it go after the Thalamus?
The cingulate gyrus
Where does the cingulate gyrus project to?
The Cortex and back to the hippocampus or entorhinal cortex
What does the Cingulum do?
Carries information from the cingulate gyrus to the hippocampus or entorhinal cortex
What do the amygdala and hippocampus work together to do?
Store memories with emotional links
What is the amygdala responsible for?
Love, anger, fear, sexual desire/arousal, preferences in food, preference in sexual partners
What happens if both amygdala are removed?
Animals show extreme docility
What is responsible for: Love, anger, fear, sexual desire/arousal, preferences in food, preference in sexual partners?
The amygdala
What is the hippocampal formation responsible for?
Learning and memory and storage of making short term to long term memories
What is responsible for learning and memory and storage of making short term to long term memories?
The hippocampal formation
What happens if the left hippocampus is damaged?
Auditory/vocal memory loss
What happens if both hippocampi are removed?
Anterograde amnesia
What causes auditory/vocal memory loss?
Damage to the left hippocampus
What causes anterograde amnesia?
Both hippocampi being removed
What two major limbic function do the hippocampal formation and amygdala mediate?
- Learning and Memory
- Emotions
What is the Amygdala?
Part of the limbic system most specifically involved with emotional experiences (learned emotion responses) and behavioural expression
What does stimulation of the amygdala cause?
Feeling of fear/aprehension
What do lesions to the amygdala in animals cause?
Tameness and fearlessness
What does the Hippocampal formation have an indirect role in?
Emotion
How does the hippocampal formation have an indirect role in emotion?
It is involved in explicit (declarative) memory, memory consolidation and learning from emotional experiences
What is the Lateral Amygdala linked to?
The neocortex
What is the Anterior Commissure?
The connection between the two amygdala
What is the connection between the two amygdala?
The anterior commissure
What is the Medial Amygdala linked to?
The striatum
What does the medial amygdala connect to?
The Motor and brainstem
What does stimulation to the hypothalamus cause?
Extreme pleasure
What does the Medial Forebrain bundle connect?
Connects the amygdala to the hypothalamus
What is the lateral hypothalamus known as?
The pleasure center
What is the Ventromedial hypothalamus known as?
The aversion center
Where is the pleasure center?
The lateral hypothalamus
Where is the aversion center?
The ventromedial hypothalamus
What are the reward centers of the brain?
The septal nuclei and nucleus accumbens
What are the septal nuclei and nucleus accumbens together?
The reward center of the brain
Where do the Septal Nuclei and Nucleus Accumbens project?
Throughout the hypothalamus and maintain connections with amygdala, hippocampus, cingulum and reticular formation
Where in the brain are the septal nuclei found?
In the frontal part of the frontal lobe
How do drugs affect the septal nuclei?
The trigger the release of dopamine at these centers
What can a bilateral lesion of the frontal gyri cause?
- Difficulties concentration
- Loss of initiative
- Apathy
- Cannot decide
What can a bilateral lesion of the orbital cortex cause?
- Unstable emotional behavior
- Loss of inhibition
- Inappropriate social behavior
What does bilateral of the temporal pole (amygdala and entorhinal cortex) cause?
- Removal of fearlessness
- But if you stimulate it: Anxiety, fear, panic
What does Bilateral lesion of the Parahippocampal gyrus cause?
No new memory
Where does the Limbic association cortex receive information from?
Higher order sensory areas, esp. the prefrontal cortex and the parieto-temporal-occipital (PTO) association cortex
Where does the limbic association cortex convey information from the cortex and PTO to?
The amygdala and the hippocampus
What does the Amygdala do when the limbic association cortex conveys information from higher-order sensory areas to it?
It uses the sensory information to link a particular stimuli with specific emotions
What does the Hippocampus do when the limbic association cortex conveys information from higher-order sensory areas to it?
It learns the more complex setting of the environment
What are the steps involving the hippocampal formation and amygdala when we have a stimuli?
- Information will be in the cortex
- Then will go to the PTO
- Information will then go to the limbic association cortex
- Then to the amygdala and hippocampus
What are the hippocampal afferents (what projects to the hippocampus)?
- reward centers
- Frontal lobe and parietal lobe vis cingulate gyrus
- Amygdala
What are the hippocampal efferents (where does the hippocampus project to)?
- Cell bodies in the CA region
- Mamillary bodies
- Cingulate gyrus and cortex
- Septal nuclei
- Amygdala
What are the amygdala afferents (what projects to the amygdala)?
- Higher order center in the temporal lobe and insula
- Different association cortices
- Olfacotry bulb
- Brainstem nuclei (NTS) - stretching of bowels
What are the two main Amygdala efferencts?
The Ventral Amygdalofugal pathway and the Stria Terminalis
What is the Stria Terminalis?
An axon tract that goes from the amygdala to the hypothalamus or the nucleus accumbens for reward
What is the Amygdalofugal pathway?
An axon tract that goes from the amygdala to the hypothalamus and thalamus reward centers of the brain and causes the fear response
What disorders is the amygdala strongly implicated in?
Mood disorders, including depression and anxiety and substance abuse
What is Kluver-Bucy syndrome?
When lesions to the amygdala cause fearlessness, docileness
What can damage to the hippocampus cause?
Severe anterograde amnesia and Alzheimer’s disease
What are the four major neurotransmitters in the limbic system?
- Dopamine
- Serotonin
- Norepinephrine
- Acetylcholine
Where does the dopamine in the limbic system come from?
The midbrain - substantia nigra, VTA
Where does Serotonin in the limbic system come from?
Reticular formation neurons - raphe
Where does Norepinephrine of the limbic system come from?
Involved in the reticular activating system – floor of 4th ventricle
Where does the Acetycholine in the limbic system come from?
The basal forebrain cholinergic neurons
Where are Dopaminergic projections in the limbic system from?
Midbrain Ventral Tegmental Area & SNc
What do Dopaminergic projections from from the midbrain VTA travel through to get to the limbic areas?
The medial forebrain bundle
Where do Dopaminergic projection in the limbic system go?
Limbic areas, amygdala and Hippocampal formation (involved in emotions, memory & learning)
What structures are apart of the Limbic association cortex?
Periamygdaloid cortex, parahippocampal gyrus, entorhinal cortex, cingulate gyrus and frontal region.
Where is the VTA?
In the midbrain
Where does the VTA project to?
The Medial forebrain bundle
Where does the medial forebrain bundle go to?
The nucleus accumbens, and then projects back to the thalamus and reward centers of the brain
What do drugs for schizophrenia do?
Block dopamine receptors
Where does serotonin in the limbic system come from?
The reticular formation (raphe nuclei)
What do serotonergic projections in the limbic system travel via?
The medial forebrain bundle
Where do serotonergic projections in the limbic system project to?
Amygdala, hippocampus, striatum & cerebral Cortex
What do drugs that block serotonin reuptake mechanisms (SSRIs) do?
Treat depression, anxiety and OCD
Where do Noradrenergic projections to the limbic system come from?
The Locus coeruleus
What do Noradrenergic projections in the limbic system travel via?
The medial forebrain bundle
Where do Noradrenergic projections in the limbic system project to?
Entire cerebral cortex, including limbic association areas, limbic structures
Where do Cholinergic projections to the limbic system come from?
Basal forebrain cholinergic neurons (incl. Nucleus Accumbens and Septal Nuclei)
What do cholinergic projections in the limbic system travel via?
Diverse pathways
Where do cholinergic projections in the limbic system project to?
Entire cerebral cortex, limbic association cortex, amygdala, hippocampal formation
What neurotransmitter is lost in Alzheimers disease?
Acetycholine
