Limbic System Flashcards
Cortical structures:
parahippocampal, cingulate and dentate gyri; hippocampus, subiculum, entorhinal cortex, and orbitofrontal cortex
structure components: Nuclei
hypothalamus (including mammillary body), amygdala, anterior nucleus of the thalamus
fibre tracts
fornix (including fimbria of hippocampus), and fornical (hippocampal)commissure, cingulum, uncinate fascicle
limbic lobe
(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)
limbic function
- learning and memory
- control of emo&ons and ins&nc&ve behavior
CONCEPT/structure of limbic structures
- 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
Summary of the simplified organisa8on of sensory input and motor output
§ 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
structure components: cortices:
~ cingulate & parahippocampal gyri, orbitofrontal cortex, subcallosal area (septal areas)
~ hippocampal formation (hippocampus proper + dentate gyrus + entorhinal cortex + subiculum)
association fibres of limbic system
§ 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)
short term memory
§ 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)
Long-term memory
Short-term memory can be transferred to form long-term memory
§ Hippocampal formation transfers short-term memory into long-term
Long term memory: Explicit memory (declarative memory) conscious processing
- Episodic memory (personally experienced events)
- Semantic memory (facts & general knowledge)
- Stored in most association cortical areas but requires hippocampus
Long term memory: Implicit memory (nondeclarative memory) unconscious processing
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
ENTORHINAL CORTEX
§ 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
The parahippocampal gyrus
§ 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)
Anatomy of the entorhinal cortex
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
The hippocampus location
§ 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
hippocampus function
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)
Hippocampal formation
hippocampus proper + dentate gyrus + entorhinal cortex + subiculum
§ Hippocampal sector CA1
is very sensitive for hypoxia (could be affected in patients with cardiovascular
or respiratory diseases; e.g. cardiac infarction or stroke)
Hippocampal CA2 subfield
is involved in seizure (epilepsy) generation
The dentate gyrus
§ The dentate gyrus is the only site in the human CNS where adult neurogenesis takes place
limbic circuit
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)
Structures of parahippicampal gyrus
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)
fornix
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
Functions of Amygdala:
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
Summary of major limbic structures:
1. Fornicate gyrus (= cingulate & parahippocampal gyri)
Limbic nuclei:
1. Amygdala (in temporal lobe)
Limbic Fibre tracts:
1. Fornix (= continuation of fimbria of hippocampus & includes fornical commisure)
Summary of major limbic structures: Hippocampal formation (= composed of hippocampus proper, dentate gyrus, entorhinal cortex (or parahippocampal gyrus) & subiculum)
Limbic nuclei:Hypothalamus
(= includes the mammillary body)
Limbic Fibre tracts: 2. Cingulum (located within the fornicate gyrus)
Summary of major limbic structures:
3. Orbitofrontal cortex (part of prefrontal cortex)
Limbic nuclei: 3. Anterior nuclei of the thalamus
Limbic Fibre tracts: 3. Uncinate fascicle (connects frontal and temporal limbic structures)
