Limbic System

Question 1

Cortical structures:

Answer 1

parahippocampal, cingulate and dentate gyri; hippocampus, subiculum, entorhinal cortex, and orbitofrontal cortex

Question 2

structure components: Nuclei

Answer 2

hypothalamus (including mammillary body), amygdala, anterior nucleus of the thalamus

Question 3

fibre tracts

Answer 3

fornix (including fimbria of hippocampus), and fornical (hippocampal)commissure, cingulum, uncinate fascicle

Question 4

limbic lobe

Answer 4

(Broca’s concept) is mainly an anatomical concept restricted to the cor8cal mantle of the telencephalon (not subcor&cal nuclei or fibre systems) that surrounds (borders) the diencephalon
composed of the fornicate gyrus (cingulate gyrus + parahippocampal gyrus) fornicate gyrus (from latin: fornicatus = arched)

Question 5

limbic function

Answer 5

• learning and memory

- control of emo&ons and ins&nc&ve behavior

Question 6

CONCEPT/structure of limbic structures

Answer 6

• analyses stimuli (sensory input) for emotional significance
• stores emotional memory
• tags/colours sensory input with emotional component and impacts cognitive responses that is required for normal social behaviour and survival

Question 7

Summary of the simplified organisa8on of sensory input and motor output

Answer 7

§ Limbic loop tags sensory input with emotional component
§ Emotionally touching experiences get attention and tend to be well remembered (= memorized)
§ Motivational state (e.g. interest or fear) dictates behaviour

Question 8

structure components: cortices:

Answer 8

~ cingulate & parahippocampal gyri, orbitofrontal cortex, subcallosal area (septal areas)
~ hippocampal formation (hippocampus proper + dentate gyrus + entorhinal cortex + subiculum)

Question 9

association fibres of limbic system

Answer 9

§ Cingulum (fascicle): is located in cingulate and parahippocampal gyri and connects cortical structures of both gyri
§ Uncinate fascicle: connects temporal with frontal lobe (orbitofrontal cortex)

Question 10

short term memory

Answer 10

§ Important for daily life as it enables us to retain what someone has said just long enough to reply
§ The prefrontal cortex mediates short-term memory
§ contains at least 3 components:
1) verbal information (present in posterior parietal cortex and Broca’s area)
2) visual information (present in frontal cortex)
3) spatial informa&on (present in prefrontal subregions)

Question 11

Long-term memory

Answer 11

Short-term memory can be transferred to form long-term memory
§ Hippocampal formation transfers short-term memory into long-term

Question 12

Long term memory: Explicit memory (declarative memory) conscious processing

Answer 12

• Episodic memory (personally experienced events)
• Semantic memory (facts & general knowledge)
• Stored in most association cortical areas but requires hippocampus

Question 13

Long term memory: Implicit memory (nondeclarative memory) unconscious processing

Answer 13

Memories of skills and habits (know-how memory)
- Stored in motor cortex, basal ganglia, cerebellum
Memories of emotions Classical & operant conditioning, priming
- processed by amygdala

Question 14

ENTORHINAL CORTEX

Answer 14

§ The hippocampal formation receives major input through the entorhinal cortex (door to the limbic loop)
§ The hippocampal formation sends major output to the entorhinal cortex

Question 15

The parahippocampal gyrus

Answer 15

§ It is also referred to as the hippocampal gyrus (old nomenclature)
§ It is located in basal medial temporal lobe
§ It contains, in its anterior portion, the entorhinal cortex and uncus (the “hook”)
§ Deep inside, it houses the subiculum, hippocampus, & dentate gyrus (not shown here)
§ Posteriorly, it is con&nuous with the lingual gyrus (no clear identifiable border between the two gyri)

Question 16

Anatomy of the entorhinal cortex

Answer 16

in par&cular, it is located in the anteriormost portion (rostral 1/3) of the parahippocampal gyrus
§ important structure for learning, memory, and spatial navigation
§ It contains so-called grid cells for spatial navigation
§ It is first site to be affected in Alzheimer’s disease
§ It provides the largest fibre input to the hippocampus

Question 17

The hippocampus location

Answer 17

§ It lies in the floor of the inferior horn of the lateral ventricle
§ It is located in mediobasal part of the temporal lobe deep inside the parahippocampal gyrus

Question 18

hippocampus function

Answer 18

Hippocampus is an important structure for:
- declarative (explicit) memory (e.g. history and facts)
- contains so-called place neurones that help to map and remember places (spatial memory; navigation) - contains so-called time neurones that help to remember the flow of events in distinct experiences
§ It transfers short-term memory (specifically the “when” and “where” of memory) into the long-term memory (“keyboard” versus “hard disk” analogy)

Question 19

Hippocampal formation

Answer 19

hippocampus proper + dentate gyrus + entorhinal cortex + subiculum

Question 20

§ Hippocampal sector CA1

Answer 20

is very sensitive for hypoxia (could be affected in patients with cardiovascular
or respiratory diseases; e.g. cardiac infarction or stroke)

Question 21

Hippocampal CA2 subfield

Answer 21

is involved in seizure (epilepsy) generation

Question 22

The dentate gyrus

Answer 22

§ The dentate gyrus is the only site in the human CNS where adult neurogenesis takes place

Question 23

limbic circuit

Answer 23

relationship between emotion and memory
Hippocampus> fornix> mamillary body (part of hypothalamus)> thalamus (anterior nucleus)> cingulate gyrus & parahippocampal gyri
(~ entorhinal cortex) (including the fibre tract cingulum)

Question 24

Structures of parahippicampal gyrus

Answer 24

The anterior portion of parahippocampal gyrus contains the entorhinal cortex and the uncus
§ the subiculum & dentate gyrus (looks like teeth row) are visible deep inside the parahippocampal gyrus
§ The uncus contains the semilunar gyri (amygdala is found deep inside the semilunar gyrus)

Question 25

fornix

Answer 25

The fornix (yellow) stretches as a C-shaped bundle of neuronal fibres below the corpus callosum (blue) § The fornix connects each hippocampus with one mammillary body (of the hypothalamus)
§ The two fornices (or two hippocami) are interconnected by the fornical (hippocampal) commissure
§ The septum pellucidum (red) spans between the fornix (yellow) and the corpus callosum (blue)
§ Septum pellucidum is a vertically oriented membrane that separates the two lateral ventricles

Question 26

Functions of Amygdala:

Answer 26

It analyses environmental stimuli for emotional significance (friendly or hostile) to generate appropriate responses; for instance
- if friendly, it is able to develop emotional apachment to stimulus
- if hostile, it generates perception of fear and may triggers ‘fight or flight’ responses via hypothalamus
(“danger [detector] alarm system of the body”);
§ stores emotional memories of fear

Question 27

Summary of major limbic structures:

1. Fornicate gyrus (= cingulate & parahippocampal gyri)

Answer 27

Limbic nuclei:
1. Amygdala (in temporal lobe)
Limbic Fibre tracts:
1. Fornix (= continuation of fimbria of hippocampus & includes fornical commisure)

Question 28

Summary of major limbic structures:
Hippocampal formation (= composed of hippocampus proper, dentate gyrus, entorhinal cortex (or parahippocampal gyrus) & subiculum)

Answer 28

Limbic nuclei:Hypothalamus
(= includes the mammillary body)
Limbic Fibre tracts: 2. Cingulum (located within the fornicate gyrus)

Question 29

Summary of major limbic structures:

3. Orbitofrontal cortex (part of prefrontal cortex)

Answer 29

Limbic nuclei: 3. Anterior nuclei of the thalamus

Limbic Fibre tracts: 3. Uncinate fascicle (connects frontal and temporal limbic structures)