Limbic Flashcards
what does the limbic system do
-processes emotion and related brain activity, memories, environmental cues and state of the individual
-act on this info to maximise survival strategies
eg.
sensory input into cerebral cortex
leads to
reaction/response
-fight/flight, freeze, rest and digest
-heart rate, sweating, resp. rate, defecation, micturition, evacuation, facial expression
what are the core processing components of the limbic system
amygdala
hippocampus
septal area
thalamus
limbic cortex
what are the effectors (output) of the limbic system
hypothalamus
brain stem structures
what are important white matter bundles found in the limbic system
what do they connect to
STRIA TERMINALIS
FORNIX
amygdala via stria terminalis
hippocampus via the fornix to mammillary bodies
where is the amygdala found
grey matter
in anterior TEMPORAL lobe
tail of caudate nucleus and rostral to hippocampus
with nuclei (central, corticomedial, basolateral)
what is Kluver-bucy syndrome
rare syndrome in humans produces behavioural impairment
associated with damage to the anterior temporal lobes
what are common effects of kluver-bucy syndrome
hyperorality
lack of fear
less common
-hypersexuality
-visual agnosia
-xs attentiveness to visual stimuli
-memory loss
-enhanced aggressino
-seizures
-dementia
what are causes of kluver-bucy syndrome
treatment
herpes encephalitis
trauma
tumours
hypoxia
pick’s disease
symptomatic
may use psychotropic medicatoins
what is Urbach-Wiethe disease
what is main symptoms
temporal lobes have calcification causing amygdala to degenerate
rare recessive genetic disorder
NO FEAR
difficulty building memories
defect in judgement in facial expressions
what happens if there is electrical stimulation of the amygdala
anxiety and fear
what does fear activate in the brain (fMRI)
central nucleus
bed nucleus of stria terminalis (BST)
what are the functions of the nuclei in the amygdala
sensory input into basal lateral nuclei
output from central nucluus
corticomedial receives olfactory input (not very well developed)
what happens in creating an emotional response eg. snake in room
stimulus
-fast track via thalamus to amygdala (lateral nuclei) does not reach consciousness– rapid response (may SAVE LIFE)
-longer route via cerebral cortex (realise theyre not as bad)
concept (idea of snake)
-cerebral cortex
context
-HIPPOCAMPUS (space/time)
input-lateral
output-central
what does subliminal mean
below consciousness
how does amygdala learn a modified fear response
fear stimulus to a noise (eg.)
Pavlovian type learning experience
then dont need fear stimulus just noise to elicit fear
where does the amygdalas output go
(main output)
stria terminalis to hypothalamus and brain stem
reward centre in septal area and BST
what are the direct outputs from the amygdala to the brain stem
Periaqueductal grey matter
locus coeruleus
parasympathetics
ventral tegmental area
drive autonomic response
what is a summary of the amygdala
controls emotional reactions (threat/fear)
via effectors (hypothalamus, brain stem through to autonomic nervous system, endocrine and motor system)
emotional learning resetting according to threat level and experience
it does simple codes of value (good/bad) for a threat/emotional trigger
-more refined mechanism for evaluating the survival value of emotional response
which part of the cingulate gyrus is found in the limbic cortex
-anterior cingulate cortex
-anterior portion of middle cingulate cortex
(also posterior cingulate cortex)
INVOLVED IN EMOTIONS
what does the anterior cingulate area encode
and what does it do in response to amygdala
happiness
sadness
fear
emotional memory
pain/anticipated pain
unpleasant experiences
TOP-DOWN INFLUENCE–RECONDITIONS AMYGDALA
eg. next time see snakes– reconditioned to not freak out so much
-computes relevance/outcome (appropriate behaviour)
-provides conflict resolution)
-part of pain network
does cingulate gyrus drive motor functions from motor cortex
yes
drives OWN responses via the brainstem and hypothalamus
direct connections to brain stem
either through amygdala or separately
motor reactions complex and context dependent– approach/avoidance behaviour, desire to leave room, vocalisation, facial expression, kissing, lip puckering, pushing
specific zone for driving face muscles
direct outputs from ACC to autonomic system
summary of anterior cerebral cortex
- Has reciprocal connections with the amygdala
- Heavy direct connections to autonomic centres
including brainstem (bypass amygdala) - Classified as the primary limbic cortex
- Attentional system, monitors conflict and
resolves it - Pain activates complex interaction with
emotion here - Motivates behaviours, mediates orientation
towards or away from emotional stimuli - Recodes value of stimulus on amygdala
what does the insula do
works with the ACC in evaluating emotional contexts- role in EMPATHY
light up in pain and others pain
- Anterior portion considered to work with the ACC
- Input -> Visceral sensory information including pain (like distended tummy- pain)
- Patients with lesions have defects including in
awareness of other people’s pain (empathy) - Classified as limbic “sensory” cortex
EMOTIONAL AWARENESS
difference between amygdala and ACC
amygdala-simple emotion codes
ACC- recodes amygdala
-modify good/bad
-drive motor responses directly
-avoidance mechanisms
-work with insula
they are the processes of emotion
What happens in PTSD to limbic system
- Part of ACC is hypo-responsive in PTSD
- Reduction in size of ACC
- Amygdala becomes hyper-responsive to trauma related stimuli
- Top-down control of Amygdala by ACC is therefore missing in PTSD
what are the effectors of the limbic system
what do they do
hypothalamus
locus coeruleus
periaqueductal grey
dorsal raphe nucleus
mediate emotional reactions via ANS
modulating learning/memory
what is the major limbic system effector
hypothalamus
direct input:
limbic cortex, amygdala
input from:
olfactory, sensory systems, viscera, retina, internal signals
outputs:
brainstem, spinal cord
autonomic
endocrine
behavioural
basic homeostasis
what is the locus coeruleus
a midbrain nucleus involved in physiological responses to panic and stress
generates huge blanket of noradrenaline neuron fibers
-ALERTNESS, WAKEFULNESS (eg. if see snake need to be alert)
promote anxiety and formation of emotional memories (projections from LC to amygdala)
projections to hypothalamus maintain arousal
projections FROM PAG selects fight or flight mode
what are the different PAG pathways
amygdala communicates with PAG to do different things
ventrolateral PAG– vagal path (parasympathetic in FREEZING)
dorsolateral PAG– LC and BSTem (fight or flight)
projects to nucleus of solitary tract, dorsal nucleus of vagis, intermediolateral column
intensity different pathways
far vs close snake
gauge extent of response
far:
less serious with PAG
-striatum involved (initiating movement) CG through basolateral amygdala to striatum
-independent to PAG
close
-central amygdala drives PAG and other brainstem centres to panic/freeze mode
-autonomic nervous system engaged
what is the dorsal raphe nucleus
project an ascending system
projects to and receives from amygdala and ACC
regulate dynamic mood state
theory of 5HT and depression/mood
high levels of 5HT=MANIA
low levels of 5HT=DEPRESSION
what are the changes that occur in limbic system structures in established depression
-reduced metabolism in ACC
-reduced size of ACC
-amygdala hyperactive and medial output region increased in size
what is the connection with 5HT processing and a predisposition to depression?
In normal individuals with:
* Variant polymorphism in 5HT transporter gene (5HTT)
* Diminishes transcription efficiency and expression
* Possible increased risk of depression (especially in reaction to previous stress)
* Reduced communication between ACC and amygdala
* Reduced size of amygdala and increased reactivity of amygdala to emotional stimuli
reward centre and depression
- Amygdala pathways partially overlap with those that regulate reward
- Reward centres are located in the NUCLEUS ACCUMBENS and prefrontal area
- Amygdala is connected to the ventral striatum (Nuc accumbens) via stria terminalis
- In some types of depression blunted activation of the reward centres
- Suggests targets for deep brain stimulation nucleus accumbens
what is the role of the hippocampus and the limbic system
and where is it located
CONTEXT VERY IMPORTANT
indirect influence on emotion
-important in establishing EPISODIC MEMORY
SPATIAL AND TEMPORAL EMOTION WITH
-emotional
-sensory
-cognitive information
to establish new episodic memory
This framework allows the experience to be stored in such a way that it can be later
retrieved as a conscious recollection of that experience.
very close to amygdala
looks like a seahorse
deep in temporal lobes
elongate structure in the floor of the lateral ventricle
output is fornix
what makes up the hippocampal formation
hippocampus and associated cortex (parahippocampal gyrus)
around hippocampus:
perirhinal cortex
neocortex
entorhinal cortex
parahippocampal cortex
what is the main gateway of the hippocampal formation
entorhinal area (for input with the neocortex)
bring in sensory input
what are some major clues to the function of the hippocampus
EARLY hippocampal damage difficult to remember events of their daily lives, but seem to have an
intact semantic memory, being able to learn school subjects such as languages and acquiring factual
knowledge
Patients with hippocampal damage can retain memories of events that occurred years before to
the onset of their brain damage.
Sparing of remote memory - undergoes consolidation gradient, memories gradually become
independent of hippocampus as they are consolidated in other brain regions (neocortex).
Hippocampal amnesic patients displayed a deficit in their ability to imagine new experiences. This
inability to construct from its individual components a mental narrative may reflect the synthetic
defect (episodic memory amnesia)
what is involved in declarative memory
episodic memory (recollection about a specific event in one’s past, tied to a specific time and place)
AND
sematic memory (general knowledge about the world)
What are place cells (found in the hippocampus)
what do other cells do
provide clue about importance of spatial information - become active when in a certain area- recording spatio info
other cells response to other modalities such as odours, tactile info, timing to give overall picture of context
CA3- temporary consolidation
CA1- more permanent consolidation
what are the 3 inputs into hippocampus (through related cortex for memory processing)
- Dorsal stream processes spatial context culminates in PARAHIPPOCAMPAL CORTEX
SCENE RECOGNITION, LOCATION, TEMPORAL CONTEXT
- Ventral stream processes object recognition and culminates in PERIRHINAL CORTEX
OBJECT, FACE RECOGNITION, CONCEPTUAL IDENTITY, SALIANCE
- Rostral hippocampus processes interoceptive signals for emotional and motivational modulation
EMOTIONAL INFORMATION
- and 2. go to caudal hippocampus
-processes exteroceptive signals for scene learning
What diseases is atrophy of the hippocampus found in
alzheimers
hypertension
depression
epilepsy
cushings
stress
genetic disorders
chronic alcohol use
sensitive to stress (GLUCOCORTICOIDS)
ISCHAEMIA SENSITIVE
WHAT IS WILLIAMS SYNDROME
(1/10,000 births) genetic deletion syndrome in which there is
developmental hippocampus effects
what is Wernicke’s- Korsakoff syndrome
thiamine deficient alcohol related hippocampal damage
decrease in hippocampal learning
what is the fornix
(arch)- white matter bundle
output structure of hippocampus
project to mammillary bodies which is connected to the anterior nucleus of the thalamus
what are the functions of the fornix
language
visiospatial
emotional/motivational learning
scene learning
output segregated according to hippocampus processing
what happened to patient who had glioma in LV that obliterated fornix
clear memory defect and delayed recall
