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Building brains > Limbic system & hippocampus > Flashcards

Limbic system & hippocampus Flashcards

1
Q

What is the limbic system?

A

A series of anatomically connecte CORTICAL & SUBCORTICAL STRUCTURES that collectively play a role in the way we experience & repond to:
- Emotional
- Social
- Motivational
stimuli, as well as learning & memory

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2
Q

What are the 3 componenets of an emotional state?

A
  • Autonomic responses
  • Subjective feelings
  • Cognition
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3
Q

Give examples of autonomic responses

What is the main area that controls this?

A

Increased HR or sweating

Hypothalamus

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4
Q

What are subjective feelings?

What is the main area that controls this?

A

Unconscious

Amnygdala, cingulate gyrus

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5
Q

What is cognition?

What is the main area that controls this?

A

Conscious thougths about the experience

Cortex

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6
Q

What are the subcortical structures of the limbic system?

A
  • Amygdala & stria terminalis
  • Hypothalamus
  • Septa nuclei
  • Olfactory bulbs
  • Hippocampus
  • Thalamus (anterior)

(This is in order, rememember it in this order & u are good)

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7
Q

What are the cortical structures of the limbic system?

A
  • Cingulate gyrus
  • Parahippocampal gyrus
  • Orbitofrontal cortex
  • Sensory association cortices
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8
Q

What is the “king of the limbic structures”

A

The Amygdala!

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9
Q

What is the role of the Amygdala?

A

Fear, strong emotions (e.g. anger), including pleasure

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10
Q

Where is the Amygdala located?

A

It is located in the temporal lobe, it is the most anterior aspect of the temporal lobe

(abt the size of an almond so pretty small)

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11
Q

What connection comes out of the amygdala & where does it go to?

A

The stria terminalis comes out of the amygdala

Projects to hypothalamus & nuelcues accumbens

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12
Q

What is the stria terminalis & where is it located?

A

It is a white matter structure

It follows the pathway of the fornix, moves in a posterior direction & shifts superiorally & it begins to move anterirorally, curling up & over the thalamus

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13
Q

What does the stria terminalis make connections to?

A

Part of the basal ganglia called the nucleus accumbens & the hypothalamus

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14
Q

What is the hypothalamus role in the limbic system?

A

Autonomic NS regulation, aggression, as well as endocrine functions:
(- Temp
- Hunger
- Weight
- Sleep
- Reproduction)

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15
Q

What does the Septal nuclei do?

A

Regulates hypothalamic aggression

(Now known that they regulate the hypothalamus → brain has so many built in mechanisms for reversing aspects of control

This makes sense bc if something goes wrong somewhere the brain has ways of overcoming & compensating this.)

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16
Q

Where is the Olfactory bulb located?

A

In the human brain they’re tucked up beneath the frontal lobes

(Massive in the rodent brain for obvious reasons)

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17
Q

Where does the olfactory bulb in the limbic system connect to & why is this important?

A

Important in limbic system

Have connections to the Amygdala –> bc smells can be correlated w emotion & memory

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18
Q

Where is the hippocampus loacted & what does it connect to?

A

In temporal lobe & has a lot of connections w the Amygdala (in rodents pretty large)

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19
Q

What is the role of the hippocampus in the limbic system?

A

Role in emotion & helps us to navigate around our environment

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20
Q

If u move in a posterior direction thru temporal lobe, what does the hippocampus become?

A

The fornix

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21
Q

Where is the cingulate gyrus found?

A

Found next to the cingulate sulcus that runs along the middle of the brain, parallel with the corpus callosum

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22
Q

Now please go over the structures of the limbic system & where they are located on the brain!!!

A

High chance you will be asked to label some of these

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23
Q

What are the 2 structures that are connected to the hippocampus?

A

The fornix & mammillary bodies

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24
Q

As we move in a posterior direction from the hippocampus, what is found here?

A

The fimbria

(Just means fringe = on the fringe of the hippocampus)

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25
Q

What is the crus?

A

It is the main part of the fornix (past the fimbria)

(They are the legs of the crus = latin for leg)

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26
Q

What happens at the fornix body?

A

The 2 legs (crus) connect & form the commisural fibre

Share info here

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27
Q

What happens at the colum of the fornix?

A

Once fornix has connected in the middle it will divide into the columns

These make connections to the mammillary bodies

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28
Q

What are the 6 key structures making up the fornix?

A
  • Hippocampus
  • Fimbria
  • Crus
  • Fornix body (commisural)
  • Column
  • Mammillary bodies

(These are in order, remember them in this order)

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29
Q

What is the septal nuclei a good landmark for?

A

For where the fornix seperates into the mammillary bodies

(Located in the middle between the lateral ventricles)

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30
Q

Pls study the structures of the limbic systems brain scan

A

Key structures will probs be asked to label them

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31
Q

What is the role of the cingulate gyrus?

A

COgnitive, attentional & emotional processing

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32
Q

What is the role of the parahippocampal gyrus?

A

Memory encoding

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33
Q

What is the role of the fornix?

A

Projects to the mammillary bodies (from hippocampus)

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34
Q

What is the role of the mammilothalamic tract?

A

Projects to anterior nucleus of the thalamus

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35
Q

What si the James Lange theory (1884)?

A

Proposed that the physiological status of the body triggers the conscious experience of emotion

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36
Q

What is the Cannon Bard theory?

A

Proposed that the physiological state & emotional state were occuring simultaneously

(This came AFTER James Lange theory)

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37
Q

How did Cannon Bard prove his theory & disprove James Lange?

A

He & a PhD student got come cats & removed the cortex of the cats

Cats survived & seemed normal, however very subtle stimuli caused ‘sham rage’

PROVED: you don;t need cortex to experience emotion

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38
Q

What areas did Cannon Bard say mediate aggression?

A

The thalamus & hypothalamus mediate aggression & this process is potentiated when the cortex is lost (cat can’t mediate its behaviour)

39
Q

What later proved Cannon Bard’s theory?

A

Swiss pyschologist stimulated cat’s hypothalamus

Cats exhibited sham rage again = solidifies Cannon’s theory

40
Q

What did septal nuclei stimulating experiments generally find?

What conclusions were drawn from this?

A

That if u stimulated the septal nucleus u get a calm animal

Theory was septal nucleus was regulating hypothalamic control –> this was the case

41
Q

How did a modern paper prove that the septal nuclei regulates hypothalamic aggression?

A

Used optogenetics

  • Take a virus, remove its DNA + CHR2 DNA –> fuse CHR2 to yellow fluorescent protein & inject into septal nucleus
  • The CHR2 receptor will DEPOLARISE cells when activated by LIGHT
  • Light stimulation of the lateral septal nuclei STOPPED ATTACKS
    (e.g. put a grp of male mice together & whenever the light was turned on the attack stopped)
42
Q

Summarise the Papez circuit:

A

The cingulate gyrus recieves stimuli from the sensory association cortex

It projects to the parahippocampal gyrus & the hippocampus processes this info

Info is fed back to the cingulate via the mammillary bodies & anterior nucleus of the thalamus

43
Q

What did Papez name his circuit & what did he centre his theory around?

A

He called it the limbic loop

He thought the hippocampus was at the centre of the limbic system (was very hippocampus focussed & built his theory around this)

44
Q

What is the primary cause of Kluver-Bucy syndrome?

A

Herpesviral encephalitis

(Kluver-Bucy is extremely rare in humans)

45
Q

List some symptoms of Kluver-Bucy syndrome:

A
  • Placidity - poor response to emotional stimuli incl reduced fear
  • Difficulty w memory
  • Hypersexuality
  • Visual agnosia - inability to recognise familiar objects or faces
  • Hyperphagia - over eating, and/or the compulsion to place and/or examine objects w the mouth
46
Q

How did Kluver & Bucy discover Kluver-Bucy syndrome?

A

Kluver & Bucy were removing temporal lobes of monkeys & they started exhibiting strange behaviours after this.

They were no longer afraid of anything & became rlly docile, hungry, putting odd things in their mouths & they were hypersexual

47
Q

List the structures of the Papez circuit:

A
  • Hippcoampus & parahippocampal gyrus
  • Fornix (connects)
  • Mammillary bodies & hypothalamus
  • Anterior thalamic nuclei
  • Cingulate gyrus
  • Seonsory association cortex
48
Q

4 main theories you need to know!

James-Lange theory

Cannon-Bard theory

Papez circuit

Kluver-Bucy syndrome

A

James-Lange theory –> Proposed cortex elicits a conscious emotional response after receiving physiologicla stimuli

Cannon-Bard theory –> proposed emotions & physiological states were a simultaneous process (importance of thalamus & hypothalamus)

Papez circuit –> attributed emotional expression to the structures in the circuit

Kluver-Bucy syndrome –> caused by removal of temporal lobes & it’s discovery supported Papez theory

49
Q

What did Paul MacLean (1950s) do?

A

He expanded on the Papez circuit

& coined the limbic system

(He recognised that Papez’s circuit is still valid but has just added a few more branches –> more refined)

50
Q

How did Paul MacLean expand on the Papez circuit?

A

He added & recognised the importance of the:

  • Orbitofrontal cortex
  • Amygdala
  • Nucleus accumbens

(He was undoubtedly influenced by all the experiments on the hypothalamus, amygdala & septal nuclei)

51
Q

What did Paul MacLean realise about the amygdala?

A

That it is anatomically connected to the Hippocampus & the Hypothalamus (via the stria terminalis)

52
Q

What did Paul MacLean realise about the parahippocampal gyrus?

A

He added connections between parahippocampal gyrus & the cingulate gyrus

Also between cingulate gyrus & sensory association cortices too

53
Q

What do amygdala lesions produce in animals?

A

Tameness & fear

(This idea was used in experiments to understand its role & location in the limbic system)

54
Q

What causes Urbach-Wiethe disease & what does it do?

A

Is a rare genetic disorder

Cause = calcification of the amygdala

Symptoms = Patients unable to recognise fearful faces

55
Q

What does modern neuroimaging tell us about the amygdala?

A

The techniques confirm the Amygdala is active when ppl see fearful faces

56
Q

What did fear conditioning experiments in rondents tell us?

(Amygdala)

A

Highlighted the importance of the Amygdala w respect to LEARNING to FEAR stimuli

(Also plays a role in other emotions: anger & pleasure)

57
Q

What did LeDoux do?

A

He discovered the concept of fear conditioning

Used rodents & fear conditioned them - soem of them he lesioned the amygdala

58
Q

What was LeDoux’s process of fear conditioning?

A
  • Put rat in the box & play a loud scary sound –> rat experiences a little bit of an inc in BP & a little bit of freezing behaviour where they are very still & nervous
  • Then they give the loud noise & pair it with a foot shock which stings a little. BP skyrockets & lots of freezing behaviour
  • The more & more u do this you no longer need the shock, just the sound & the rat will experience the rise in BP & the freezing behaviour
59
Q

What was the result of fear conditioning in rodents which LeDoux had lesioned their amygdala?

A

They would never learn to be afraid of tbe sound even after being shocked

(Showed us it’s important to be afraid of things)

60
Q

Where do dopaminergic neurones in the midbrain project to?

A

The amygdala, Orbitofrontal cortex & nucleus accumbens

(Release dopamine to the limbic structures - part of the mesolimbic reward system)

61
Q

What does dopamine mediate?

A

The pleasurable aspects of reward

62
Q

Where are the dopaminergic neurones in the midbrain?

A

Located in the ventral tegmeantal area

(where our dopamine producing cells are in the substantia nigra)

63
Q

What is the mesolimbic reward system?

A

A group of cells in the VENTRAL TEGMENTAL area (in substantia nigra) in the midbrain that produce dopamine

Projects to the amygdala, OFC & nucleus accumbens

Dopamine mediates the pleasureable aspects of reward

64
Q

What does the dopamingergic mesolimbic reward system do?

A

(Same as the mesolimbic reward system jsut another name)

Modulates the pleasurable experience associated w reward

65
Q

What are the 2 main types of memory?

A
  • Declarative/explicit memory
  • Nondeclarative/implicit memory
66
Q

What is declarative/explicit memory?

A
  • Semantic e.g. facts, ppl, places & things
  • Episodic e.g. personal experience
67
Q

What is nondeclarative/implicit memory?

A
  • Procedures, skills, habits
  • Conditioning

(Things we don’t have to think about actively - skills or habits that you have)

68
Q

Who helped us to understand the types of memory?

A

HM

Surgeon was supposed to take out the hippocampus & the parahippocampal gyrus but it turns out the surgery was more anterior than thought so it also took out the amygdala & the posterior aspects of the hippocampus & parahippocampal gyrus were left in tact

He couldn’t form new memories - jsut procedural & semantic only

69
Q

What area of HM’s brain was removed & what did this result in?

A

Area removed = hippocampus & para-hippocampal gyrus

Resulted in = anterograde amnesia

70
Q

What memories was HM capable of?

A

Couldn’t form new memories but was capable of:

Acquisition of SEMANTIC & PROCEDURAL memories

71
Q

What is the hippcoampus composed of?

A
  • Dentate gyrus
  • Subiculum
  • Cornu Ammonis (CA)

(Shaped like a seahorse ;l

72
Q

Where is the hippocampus located?

A

Medial anteriorr aspect of temporal lobe

73
Q

What does the structure of the hippocampus look like & what are the parts?

A

Like 2 interlocking C shapes

1st = is the dentate gyrus
2nd = CA (Cornu Ammonis - don’t rlly need to know full name)

(Interlocking C shapes are actually a row of cell bodies)

74
Q

How many CA regions are there?

A

Approx 4

75
Q

What is the order of the 2 interlockign C shapes in the hippocampus?

A

Inside to out

Dentate gyrus
CA4
CA3
CA2
CA1

76
Q

What comes after the CA(1) region of the hippocampus (working outwards)?

A

The subiculum & then entorhinal cortex

77
Q

How many layers does the hippocampal cortex have?

A

Only 3 layers (not 6)

(The CA & dentate gyrus have these 3 layers each)

78
Q

What are the 3 cortex layers of the CA region called?

A

1 - Polymorphic

2 - Pyramidal (This is the layer that mkaes the charateristic C shape)

3 - Molecular

79
Q

What are the 3 cortex layers of the dentate gyrus?

A

4 - Polymorphic

5 - Granular (Very densely packed in this layer)

6 - Molecular

80
Q

What happens to the hippocampal cortex when you move out to the subiculum?

A

It transitions (from 3 layers) to the standard 6 layered entorhinal cortex

81
Q

What is Long Term Potentiation (LTP)?

A

The cellular basis by which memories are stored = LTP

82
Q

What was Bliss & Lomo’s experiment on LTP & what did they discover?

A

→ They had rabbits & put electrodes into the entorhinal cortex & electrically stimulating it via the perforant path

→ However the recording electrodes were placed in the CA1 region.

→ This showed that although they were stimulating the entorhinal cortex, they could read the postsynaptic responses in the CA1 region

→ The postsynaptic responses were lasting (long term) & enhanced (potentiated), called LTP

83
Q

What did Bliss & Lomo’s experiment show?

A

That the brain is able to make changes in its organisation & in response to stimulation → the concept of plasticity

Has been suggested to be a cellular model by which memories are formed

84
Q

What is the order of info being processed in the hippocampus?

A

→ Perforant path stimulates granular cells in the dentate gyrus

→This then stimulates the mossy fibres which project to the CA3 layer

→ CA3 layer has schaffer collaterals which project to the CA1 layer

→ Finally, the CA1 pyramidal cells project to the subiculum

85
Q

What was the first evidence that the hippocampus plays a role in spatial memory?

A

Came from the discovery of PLACE CELLS

86
Q

What are place cells?

A

Hippocampal cells that fire depending on the location of the organism in the environment

(aka GPS of the brain)

87
Q

What area of the brain plays a role in spatial memory?

A

The hippocamus

88
Q

How was it discovered that the hippocampus plays a role in spatial memory?

A

→ Had rats & used a plus maze & they put some tasty rat food in there, there’s things all around the room that they can see that they can use to navigate to the food

→ They put electrodes into the brains of rats & they could measure up to 50 cells at the same time.

→ They let the rat go round & get the food out the maze and what they noticed was when the rats were in certain locations in the maze, only certain cells would fire

→ e.g. in the second diagram (refer to lecture) when the rat was staying in the left side, cell C was firing, whereas when the rat was approaching his target, cell D was firing

89
Q

What did lesion studied of the hippocampus show that it was important for?

A

Additional evidence that the hippocampus plays a role in COGNITIVE MAPS came from lesion studies

(Morris tested this)

90
Q

What was the set up of Morris’ experiment on spatial memory?

A
  • A vat with opaque liquid in like milk or something non toxic to rats & there’s an escape platform in there, the goal is to find the escape platform.
  • There’s objects around the room & the rat will see these when on the escape platform, so when they repeat it the next day they’ll recognise the things in the room and remember where to go
  • Use cues in the room to guide them to the platform (spatial nav) → called the Morris water maze
91
Q

How did the Morris water maze work when the hippocampus was lesioned?

A

Normally the rat would be able to find the platform every time after 1 or 2 goes (could rememeber where it was)

When hippocampus was lesioned no matter how amny times the rat couldn’t remember & would swim around randomly until it found the platform

92
Q

Where does adult neurogenesis occur in the hippocampus?

A

In the sub-granular zone of the dentate gyrus

(It is 1 of 2 brain structures that has the ability to generate new neurons)

93
Q

Describe how adult neurogenesis can occur in the hippocampus:

A

→ Quiescent undifferentiated STEM CELLS (nesting, sox-2, GFAP) activate & give rise to fast PROLIFERATING cells (nestin, sox-2)

→ NEUROBLASTS (doublecortin) reflect the commitment towards NEURONAL LINEAGE

→ Immature neurons begin to MATURE & extend DENDRITES into the MOLECULAR LAYER & the AXONS project into the CA3 region

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