Unit 10 - Limbic System

Question 1

limbic system - general location

Answer 1

“Limbus” means rim or border – and in this case it’s referring to the set of connected structures along the medial surface of the cerebrum, including cingulate gyrus, and connecting through continuously, to the medial temporal lobe (parahippocampal gyrus)

Question 2

Function of limbic system

behaviours it is involved in

Answer 2

The limbic system is the seat of emotion, pain, reward and basic survival functions

For example, it functions critically in survival behaviours such as feeding, fight or flight response, aggression and the expression of emotion, as well as pleasure, fear, affection, and memory

plays a role in autonomic, behavioural and endocrine aspects of sexual response

Question 3

features of some subregions of nuclei

Answer 3

3 layered - phylogenetically older cortices

likely involved in less evolved behaviours

Question 4

External input to papez circuit

Answer 4

Via our sensory cortices (olfactory, somatosensory, vision, auditory)

+ cortical areas that integrate sensory modalities - insula

Question 5

functions influenced by limbic system

Answer 5

Social cognition, facial recognition or valence appraisal (i.e. whether something is positively or negatively valanced), can all be processed and interact with the limbic system to determine our subjective emotional experience and dictate our expressive behaviours in response

Question 6

Papez circuit as an anatomical substrate

Answer 6

anatomical substrate for convergence of cognitive, cortical activities, emotional experience, and expression

Question 7

What runs in the cingulate gyrus

Carries info via ______ to the ______

Answer 7

Cingulum bundle

carries information via the lingual gyrus to the parahippocampal gyrus (just medial to hippocampus proper)

Question 8

Where is the amygdala

Answer 8

Anterior and slightly superior to the head (or anterior-most part) of the hippocampus

Question 9

Main output tract of the hippocampus

Answer 9

Fornix

Question 10

Main output tract of amygdala

Answer 10

While it has a more direct route to the frontal cortex, it is stria terminalis

Question 11

Where do the outputs of the hippocampus and amygdala converge

Where do these structures feed info to

Answer 11

These outputs converge on an inferior frontal area, including structures of the hypothalamus (including mammillary bodies, septal area, and the bed nucleus of the stria terminalis)

These structures then feed to the sub-genual cingulate cortex closing the circuit

Question 12

Overview of Papez circuit

Answer 12

Cingulum → parahippocampal gyrus and entorhinal cortex

Hippocampus → via fornix terminating in the septal area and mamillary bodies

Mamillary bodies → via mamillothalamic tract to the anterior nucleus of the thalamus

Amygdala → via stria terminalis to the BNST

BNST, amygdala & septal area and hypothalamus all relay to the subgenual cingulate closing the circuit

Question 13

Name the parts of the cingulate gyrus

Answer 13

Question 14

Where does the cingulate gyrus receive input from

Answer 14

wide-spread areas of association cortices, and is consistently demonstrated to be involved in pain related activation through measurements made of regional cerebral blood flow derived from water PET, or from measuring the blood oxygen-level dependent (BOLD) signal derived from functional MRI

Question 15

Cingulum bundle

where do the fibres project to

Answer 15

refers to the underlying pair of association white matter tracts beneath each cingulate gyrus, or deep to them, in each hemisphere

fibres project to the entorhinal cortex of the temporal lobe and the hippocampal formation

Question 16

Cingulotomy

Answer 16

a lesion surgically made in the cingulum tract

This procedure is used to treat severe depression and OCD

Question 17

What is the subgenual part of cingulate implicated in

Answer 17

BA 24

mood regulation, and a successful site of deep brain stimulation in treatment refractory depression

Question 18

DBS for bipolar disorder

Answer 18

Between anterior and dorsal cingulate

Question 19

What gyrus is found in close proximity to the cingulate

Answer 19

Curves continuous with the lingual gyrus inferior to the splenium and ultimately with the parahippocampal gyrus

Question 20

Location of hypothalamus

Answer 20

hippocampus proper is a long sausage shaped structure lying in the inferior horn of the lateral ventricle, in an antero-posterior orientation (in green)

Question 21

Input to hippocampus proper

Answer 21

derives from fibres emanating from the parahippocampal gyrus, passing through and area more specifically referred to as the entorhinal cortex and finally, the subiculum, before forming CA1 subregion of the hippocampus

Question 22

Separation between ventricle space and cisternal CSF

Answer 22

Thin layer of pia mater

Question 23

parts of hippocampus

Answer 23

CA1

CA2

CA3

CA4

Dentate gyrus

Question 24

What is hippocampus implicated in

Answer 24

disruptions to memory – amnesia

Question 25

Output of hippocampus

Answer 25

gathers fibres and thickens as you move posteriorly to form the alveus

Alveus forms fimbria which eventually forms the fornix

Question 26

Short term memory

Answer 26

Usually refers to minutes or hours

An example of short-term memory is working memory – refers to ability to hold in mind or pay attention to or manipulate several pieces of information at once

Question 27

Long term memory

Answer 27

Long term memories can be declarative (can put them into words), or non-declarative (there is a certain amount of learning that you’re only partially aware of or are that partially accessible to consciousness)

Types of declarative memory are semantic or episodic

Semantic are facts and information and episodic would be your personal record of your day-to-day events

An example of a non-declarative or implicit memory, would be procedural memory – important when learning a motor skill

Question 28

Bilateral hippocampal lesions

Answer 28

Anterograde amnesia

Lose the ability to form new memories with a particularly large deficit in episodic memories

procedural memory is usually normal, which means it is still possible to learn new skills, for instance it would be possible to train a person with medial temporal lobe amnesia to play the piano, but they would not be aware that they had received any lessons

Question 29

Retrograde amnesia

Answer 29

Some pre existing memories may also be lost following hippocampal damage

occasionally extending over several years

Question 30

Possible function of hippocampus in storage of memories

Answer 30

hippocampus may therefore store memories temporarily prior to consolidation in the neocortex

Question 31

Alzheimer’s disease

Answer 31

there is severe degeneration of the hippocampus and entorhinal cortex, which is associated with profound disturbance of episodic memory and spatial navigation – forgetting recent conversations or getting lost in familiar places

Question 32

fornix

parts

where does it arise from

Answer 32

Alveus, fimbria, crura, commissure, body, columns

Arises from hippocampus

Question 33

Alveus → fimbria → crura → commissure → body → columns

Answer 33

origin of the fornix is the alveus (slim white matter band running into the fimbria)

The fimbria of the fornix (the small flap in the image) runs along the length, antero-posteriorly, of the hippocampus, thickening as it forms the crura of the fornix

Crura (meaning “legs”) are connected to the hippocampus laterally in the temporal lobes and running superiorly, meet at a superior location where they connect in the form of the commissure of the fornix (hippocampal commissure)

This commissure lies superior to the thalami nuclei and inferior to the isthmus of corpus callosum

Anterior to the commissure it the body of the fornix and is more medial in its location, and descends mid-sagittally before separating into columns – one pair more anterior to the anterior commissure and one pair posterior to the anterior commissure

The columns of the fornix run along the base of septum pellucidum

Finally as it descends, the columns of the fornix branch to the septal area, when anterior to anterior commissure or to the mamillary bodies when they are posterior to the anterior commissure

Question 34

Where do the columns of the fornix divide

Answer 34

In a location superior to anterior commissure

Septal area is anterior to lamina terminalis - contains the anterior commissure

Question 35

Anterior commissure

Answer 35

tightly packed ovoid bundle of fibres – they cross the midline in the upper portion of lamina terminalis to interconnect the olfactory bulbs and the temporal lobes

Question 36

Input to septal area

Role of septal area

Answer 36

septal area receives input from the habenula via stria medullaris and also via the fornix

It plays a key role in regulating the hippocampal activity associated with memory and spatial navigation, as well as being involved in pleasure and reward, along with the nucleus accumbens

Question 37

Where do the mamillary bodies run

Role of mamillary bodies

Answer 37

project onward toward the anterior nucleus of the thalamus via the mammillothalamic tract – represents the main way in which the amygdala and hippocampus are connected to the thalamus

The tract appears to also play a role in spatial navigation

Question 38

Bilateral lesioning of amygdala results in

Answer 38

Docile and passive behaviour

Question 39

Amygdalum =

where does the amygdala lie

Answer 39

Almond shaped

lies near the anterior pole of the temporal lobe

It is slightly medial and anterior to the anterior limit of the hippocampus. It is both anterior and superior to the inferior horn of the lateral ventricle (locate ventricle space first)

Question 40

What is the amygdala implicated in

Answer 40

Anxiety disorders

Disorders of olfaction, detecting danger, sexual behaviour and Kluver-Busy Syndrome

Question 41

Kluver Busy Syndrome symptoms

Answer 41

Involves lesions of the medial temporal lobe that include the amygdala

In humans, this syndrome involves docility, hypersexuality and visual agnosia (inability to recognise objects)

Question 42

Role of amygdala in healthy human cognition

Answer 42

amygdala appears to be vital to learning the emotional significance of a stimulus, such as a negative stimulus in the environment, and includes healthy responses of anger, fear, recognition of facial expressions and social cognition

Question 43

Where is the amygdala located

Answer 43

Question 44

Structure of amygdala

Answer 44

13 subnuclei

Question 45

Large lateral subnucleus of amygdala

Answer 45

receives input from sensory cortices

Question 46

Basal subnucleus of amygdala

Answer 46

acts as an output to the peri-aqueductal grey of the brainstem

Question 47

Peri-aqueductal gray

Answer 47

gray area encircling the cerebral aqueduct of the midbrain and somewhat in the pons as well, involved in ascending anxiety related system and pain system

Question 48

layers of subnuclei

Answer 48

paleocortex – 3 layered cortical areas as opposed to the usual 6 layered cortex

This 3-layered cortical areas were present 250million years prior to the emergence of mammals

It’s a structure that is well-developed at birth with phylogenetically older nuclei showing synaptogenesis earlier

, it is though that the interplay balance with orbitofrontal cortex plays a role in anxiety disorders

Question 49

Range of anxiety disorders

Answer 49

broad range and include generalised anxiety specific phobias, such as agoraphobia (fear of being outdoors), panic disorder, PTSD

Question 50

Output tract of the amygdala

Where does it project to

Answer 50

Stria terminalis

Projects to bed nucleus of stria terminalis (BNST)

amygdala does have a secondary output tract that more directly reaches the frontal cortices (green in the image) – called ventral amygdalofugal pathway

• more ventral route and more direct and has connections with the periaqueductal gray, thalamus, hypothalamus, septal nuclei, nucleus accumbens and basal forebrain

Question 51

Location of BNST

Answer 51

bilateral, lateral to columns of fornices, and inferior and lateral to the inferior tip of the lateral ventricle, and superior to the anterior commissure

Projects onwards to anterior hypothalamus