Limbic system: Memory and emotion (8.5) Flashcards
Describe the position, basic components and basic connections of the limbic system
Position: Part of the cerebrum. Just beneath the cerebral cortex, on either side of the thalamus, within the telecephalon and dicephalon. Comprised of structures from the temporal, parietal and frontal lobes.
Basic components:
- Hippocampus
- Amygdala
- Cingulate gyrus
- Hippocampal formation - hippocampus and parahippocampus
- Entorhinal cortex
- Anterior thalamus and hypothalamus
- Mammillary bodies
- Fornix
- Nucleus accumbens septi shell (the core is part of the basal ganglia): Allows us to receive a pleasurable experience e.g. during eating/sex.
Basic connections:
Outline the various roles of the limbic system
*Combines higher mental functions and primitive emotions*
Generates unconscious responses in response to multiple inputs - relies heavily on sensory input.
- Emotion and motivation (sexual desire, appetite)
- Visceral responses to emotion (autonomic/endocrine responses)
- Memory formation → implicated in compulsive behaviours and addiction
- 5 Fs: Feeding (hunger), fighting (emotional response/anger), forgetting (memory), family (sexual production/maternal instincts) and fornicating (sexual reproduction)
The limbic lobe is formed from which structures?
Cingulate gyrus: Part of the cerebral cortex but is deep to the surface of the brain
Hippocampal formation: Hippocampus and parahippocampus
Describe the position and basic components of the hippocampal formation
Function: Involved in the formation of new memories
Position: Associated with the inferior temporal lobe and the inferior horn of the lateral ventricle
Basic components:
- Hippcampus
- Dentate gyrus
- Entorhinal cortex
- Parahippocampal gyrus
Outline the general role of the hippocampus in memory formation
Left hippocampus: Memories involving language
Right hippocampus: Memories involving spatial tasks
Anterior hippocampus: Short term memory formation
Anterior hippocampus is supplied by the anterior choroidal artery (branch of internal carotid artery) - infarct to this region leads to anterograde amnesia
Posterior hippocampus: Long term memory formation
Outline where memories are stored and explain the consequences of a lesion to the anterior hippocampal region
Outline the general role and inputs to the amygdala
Clinical link: Explain the consequence of damage/over stimulation of the amygdala
General role: Analysis of afferent information and co-ordination of emotions, responses and behaviours
Inputs:
- All sensory areas
- Hypothalamus
- Prefrontal cortex
- Limbic areas
Clinical Link
Damage/underactive amygdala - Kluver-Bucy syndrome
- Docile, loss of fear and anger
- Increased appetite
- Visual agnosia
Overactivity of amygdala
- Anxiety states/anger/agression/defensive
Outline the general role of the cingulate gyrus and the outcome of lesions to the area
- Processing memories and long term memory storage - Papez Circuit
- Cardiorespiratory, digestive, bladder control and visceral response to emotion for sad events - autonomic area
- Happy events are also modulated in the cingulate gyrus but there is no autonomic response
- Emotional modulation of pain and of the amygdala (suppresses aggressive behaviour)
-
Learning, emotions and memory.
- A positive emotional response promotes learning
- Perceptions, self-awareness and motivation
Clinical link
Lesions to the cingulate gyrus cause an indifferent response to painful/emotional stimuli.
Flatness, low motivation, schizophrenia and tactless behaviour may be observed.
Outline the different types of memory
Short term memory: Short duration of retention < 1 hour
Long term memory: Declarative/explicit (recall of a fact) or procedural/implicit (learned skills)
Outline the functions of the hypothalamus
Maintenance of homeostasis and hormone release (endocrine)
- Temperature, appetite, thirst, blood pressure and HR
- Pituitary hormones
- Sexual arousal
- Mood
- Autonomic nervous system
- Circadian rhythm
Which neurotransmitters have been implicated in the degeneration of the limbic system?
Serotonin: Raphe nucleus to the hippocampus via the medial forebrain bundle (MFB), also to the nucleus accumbens and frontal cortex
Decreased levels: Depression, Alzheimer’s
Increased levels: Anxiety
Dopamine: Ventral tegmental area (VTA) to the prefrontal cortex and septum.
Decreased levels: Parkinson’s, depression
Increased levels: Mania, Schizophrenia
Norephinephrine: Locus ceruleus and raphe nuclei to the limbic system and pre-frontal cortex
Decreased levels: Depression
Increased levels: Anxiety, mania, schizophrenia
**Conditions are related to ventriculomegaly, relative to the cortex (as the limbic system degenerates)
Reduced size of limbic system → reduced function and altered neurotransmitter production
State the components of the limbic system which are involved in reward
Septal nuclei: Pleasure
Nucleus accumbens: Dopamine activated reward centre, provides an intense sense of well being
Prefrontal cortex: Social centre
These areas prompt seeking behaviour (due to positive association with the action). This can be implicated in substance abuse and addictive behaviour.
Outline the neurotransmitters implicated in addictive behaviour
Neurotransmitter: Area of release, function, areas of action
Outline the consequences of mammillary body damage
Korsakoff’s Psychosis - Severe thiamine (B1) deficiency
☆ Often associated with alcoholism
Consequences: Mammillary body damage, projecting to the anterior nucleus of the thalamus
Signs and symptoms: Anterograde and often retrograde amnesia; insertion of fabricated memories (confabulation); lack of insight/apthy; nystagmus; ataxia
