Anatomy and function of the Limbic system Flashcards
What is the Limbic system involved in
Emotions
Reward driven activity: feeding and sex
Motivation
Social behaviours: friend and foe
Memory of environment and experience
How does the limbic system function
Links to other key brain regions
Output to hypothalamus, sensory and motor and frontal regions to achieve survival
What is the Limbic system transitional between
Subcortical nuclei and Neo-cortex
What are the subfields of the hippocampus
Dentate gyrus
CA3
CA1
Subicular cortex
What is the basic circuit of the hippocampus
1) sensory information from multiple cortical areas
2) flows to Entorhinal cortex
3) Then Dentate gyrus
4) Then CA3
5) Then CA1
6) Then Subiculum
7) Then back to Entorhinal cortex
What allows memory formation in the hippocampus
There are connections between the inhibitory and excitatory neurons in the hippocampus
What is the function of the septal nuclei (which is connected to the hippocampus)
Have a role in the theta rhythm of the hippocampus which plays a role in behaviour
Where does sensory information enter the hippocampus and where does it go
From throughout cortex via entorhinal cortex> perforate path to dentate gyrus
What are the outputs of the hippocampus
Via Subiculum and entorhinal cortex to neocortex
Via fornix to
- septal region
- mamillary bodies
- hypothalamus
- median forebrain bundle
Non pharmacological treatment for severe or treatment resistant depression
Electroconvulsive therapy
-General anaesthetic and muscle relaxant, electricity given to produce a controlled generalised epileptic seizure. Course of up to 12 treatments
-It is vagal nerve stimulation and deep brain stimulation
Another non-pharmacological treatment for depression
Transcranial magnetic stimulation
-Magnets focussed byt do not penetrate far into brain so can be targeted at front-limbic circuits implicated in depression
What is cognitive behaviour therapy
Tackles reasons why depression or anxiety are still present, not what caused them
How to use CBT in thinking patterns in depression
Tackle:
- Nagative automatic thoughts- based on unhelpful thinking styles e..g. black and white thinking
- Assumptions ‘if something happens then I am good/bad/unloved etc’
- rigid beliefs
How to use CBT in behaviour in depression
Set tasks to increase confidence and interest each day
How to use CBT in problem solving in depression
Define a spefici problem into one or more solvable problems
Inputs Of hippocampus
Sensory info from throughout cortex via entorhinal cortex > perforate pathway to dentate gyrus
Modulatory inputs from septal nuclei, brainstem nuclei influence the overall functioning
What are other important connections of hippocampus
Amygdala and thalamus
What are the two types of Declarative memory
Semantic: the Eiffel towel is in Paris (fact)
Episodic: I kissed my lover under the Eiffel tower
What type of memory is associated with the hippocampus
Episodic memory
What does removal of hippocampus lead to
Profound deficit in episodic memory
Preserved procedural memory
Preserved memory of events before surgery
What can damage to hippocampus lead to
Temporal lobe epilepsy
What are the inputs of the amygdala
Olfactory bulb
Prefrontal cortex
Hippocampus and
Entorhinal cortex
Sensory thalamus and cortex
Viscerosensory cortex
How can the effector region of the amygdala generate an autonomic response for fear
via Sympathetic and parasympathetic NS
How can the effector region of the amygdala generate hormonal responses to fear
Through HPA axis
How can the effector region of the amygdala generate a modulatory response
via modulatory systems using
NE
5-HT
DA
ACh
What does the basal nucleus of the amygdala have a role in
regulation via prefrontal cortex
reward behaviours via ventral striatum
What is the lateral nucleus in amygdala responsible for
Sensory information
Where is the effects of most of the outputs of the amygdala from
central nucleus
How do the outputs of the amygdala reach the brainstem
Stria terminalis > hypothalamus > brainstem > BNST > accumbens
What is an example of a fear conditioning pathway
e.g. If a rat was exposed to a noise when it is electrocuted, it would eventually show a fear response even with just a noise (no electric shock necessary)
Mechanism behind the fear conditioning pathway
The stimulus and the fearful thing pathways eventually become linked in the central nucleus so therefore only one is needed to make a fear response
What is Kluver-Bucy syndrome
What are the symptoms
Large bilateral anterior temporal love resections removing amygdala, hippocampus and surrounding temporal lobe
Very docile-no longer aggressive towards keepers
- Indiscriminant sexual activity
- Lost ability to visually discriminate edible from inedible
- A breakdown of visual input to channeling drives
What is Urbach Wiethe disease
Bilateral amygdala lesions
-Normal ability to recognise familiar faces, happy, sad, angry, surprise, disgust face
- Unable to recognise fear face
- No fear of other things
- Cannot learn fearful associations
What do specialised circuits linking sensory input to in amygdala
Link sensory input with their emotional value
What do the outputs of the amygdala use to cause behaviour
brainstem and hypothalamic mechanisms
What is the neurotransmitter involved in the reward circuit
Dopaminergic neurons
*Where is the reward circuit
Ventral tegmental area to nucleus accumbens
Where is the Nucleus accumbens
Ventral area of nucleus accumbens
When do midbrain dopaminergic neurons show brief bursts of activity
After rewarding stimuli like food or sex
Stimuli which PREDICTS reward (such as smelling food)
Is the midbrain dopaminergic neurons correlated with ‘liking’ or ‘wanting’
Wanting, not liking
When do midbrain dopaminergic neurons show Tonic (base level firing)
Motivation
What receptors are involved in reward pathway
D1
What does an absence of reward after stimulus predicting a reward produce
A drop in DA neural firing
Where are pleasure hotspots
IN nucleus accumbens and Orbitofrontal cortex
Where is the dopaminergic circuit
From the Substantial Nigra to the Dorsal Striatum (caudate and putamen)
What is the ventral striato-pallidal circuit involved in
Reward
What is the route of ventral striato-pallidal circuit
VTA
- ->Ventral Striatum
- ->Ventral Pallidum
- -> Thalamus MD
- -> LImbic and prefrontal cortex
When is the Cingulate cortex arisen
When is there an over activity in OCD
Handline conflicting information (such as the word RED written in green)
Monitoring error
Arousal
-Over activity in OCD
What dysfunction is seen in depression
Complex network of limbic-striatum-frontal cortex
What are the different components of depression and which part of the brain is responsible for these
Amygdala-anxiety
Hippocampus- memory deficits
Reward circuits- anhedonia and motivation
Frontal lobe- motivation, decision making
Striatum- motor slowing
What is the Meso-Limbic DA circuit
Where does it receive inputs from
key motivation and reward pathway
Inputs from VTA to Nucleus accumbens and basal forebrain
What is pre-frontal cortex important in
What disorders are associated with it
Decisions about reward and appetite
Motivation and regulation of behaviour
Disorders can include psychiatric and personality disorders
What does the septal nuclei connected to the hippocampus have a role in
Producing theta rhythm
