Limbic system Flashcards
What is the function of the limbic system?
- Processing and responding to pain and intense emotions e.g fear, anger, joy
- Regulation of visceral responses to emotion (autonomic responses to stress)
- Helps regulate other body processes e.g. sleep, appetite, sexual function
- Important roles in memory, motivation anf learning
What are the components of the limbic system?
- Limbic cortex : ring of cortex formed by cingulate gyrus, hippocampus and parahippocampal gyrus
- Subcortical nuclei: amygdala, nucleus accumbens, septal nuclei, hypothalmus
- Receives many inputs from elsewhere in the brain and many outputs
What is the papez circuit?
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- Plays a key role in the formation of memories
- Hippocampus is the start and end of the circuit. Fornix connects hippocampus to hypothalamus
What are the links between the hypothamus to the limbic structures?
- Influences and regulates:
- release of pituitary hormones
- reproductive system function
- Bonding
- Thermoregulation
- Appetite and thirst
- Cardiovascular and autonomic function
- Mood
- Circadian rhythm, sleep/wake cycle
What is the role of the hippocampus?
- works with other medial temporal lobe structures to form new memories
- substances in CSF can affect memory formation
What is short term memory?
- recalled minutes, hours after a stimulus
- Working memory: conscious ability to manipulate information held in short-term memory
- problem solving, reasoning
- Awareness of emotional or social cues during conversations
- Working memory controlled by lateral prefrotntal cortex and association areas od temporal and parietal lobes
What is long term memory?
- Long-term memory: recalled weeks, months, years after a stimulus with structural changes in neurons e.g. protein synthesis, increased synaptic strength, increased neuronal excitability
- Declarative (explicit) memory: can be put into words
Semantic memory: common knowledge e.g. names of countries
Episodic memory: personal experiences e.g. a party you attended
Non-declarative (implicit) memory: semi-automatic learning
Procedural memory: learning and performing motor skills (‘muscle memory’) - Amnesia is the loss of declarative memory
- Retrograde amnesia = unable to remember events from before an injury
- Anterograde amnesia = unable to remember new events after an injury
Procedural memory is unaffected but unable to recall practicing tasks or skills
What is declarative memory?
- Encoding : processing info into a representation of a memory
- Improved by paying attention, mood, drawinf connections between information - Consolidation
- Stabilising memories
- Synaptic connections become stronger with repeated activation (long-term potentiation)
- Medial temporal lobe directs storage of memories across large networks of neurons elsewhere- engrams (basic unit of memory) - Retrieval
- Accessing and using memories in different ways : recall , recognition
- Prefrontal cortex and cingulate cortex play key roles e.g. learning
- Important for learning e.g. spaced retrieval practice
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What is the role of the medial temporal lobe ?
- Plays a major role in memory and connections to many other structures
- Lateral/ prefrontal cortex : keeps working memory on task involved in processing and retrieving declarative memory
- Association areas in temporal, parietal and occipital lobes : declarative memory and integrating sensory perceptions
- Cingulate cortex : helps direct attention and processes emotions in relation to memory, especially anterior cingulate cortexx
- Cerebellum and striatum (basal ganglia) : procedural memory e.g. learning how to play a musical instrument. Adjusting and refining movvements
- Thalamus : anterior nuclei have a key role in episodic memory
How does the hippocampus work with other medial temporal lobe structures?
- ## helps to form new memories
What can bilateral lesions of the anterior hippocampus can cause anterograde amnesia?
- Ischaemia (due to stroke), epilepsy, encephalitis, anoxia
- Impaired formation of new memories
- Recall of long term memories unaffected
- Patient will not be able to recall new memories that have occured post-injury
- Recall of long -term memories not dependent on the hippocampus
- Posterior hippocampus helps to encode memories for long term storage elsewhereem but does not help with recall
What is the role of the left and right hippocampus in relation to declarative memory?
- Left hippocampus = helps to encode verbal memories
- Right hippocampus = helps to encode spatial memories
- London taxi drivers have greater right posteriorr hippocmapal volume, but reduced anterior volume
What is the blood supply to the hippocampus?
- Anterior choroidal artery branches
- Some branches from posterior cerebal artery posterior hippocampus
- Clinical revelance : temporal lobe epilepsy surgery
What is the cingulate cortex?
Key part of Papez circuit — receives projecting fibres from anterior
nucleus of thalamus and is continuous with parahippocampal gyrus
Perception of pain and role in ernotional regulation
Learning and memory — positive emotional responses promote learning
Autonomic area — specifically related to visceral responses that occur
during sad ernotional states
Other roles in bladder control, speech, executive function
Links to insular cortex — self-awareness, interoception
Role in mood disorders like depression. Cingulate cortex lesions or
reduced activity can cause indifference to pain or ermtional stimuli - flattened affect, low motivation
Blood supply = anterior cerebral artery
What is the amygdala (amgydaloid nucleus)?
- Located more anteriorly in medial temporal lobe
- Extensive connections to and from other parts of the limbic system - helps react to the world around you, e.g , threats
- Processing fearw, stressful stimuli
- Overactivity = anxiety, aggression, defensiveness
- Connections to autonomic and endocrien pathways e.g. increase HR
- Role in appetite
- Helps regulate sexual function (especially restraint)
- Blood supply = antrerior choroidal artery
