Lecture 6.2 Flashcards
limbic system 3 main functions
- controls endocrine system (hypothalamus)
- involved in memory encoding and retrieval (hippocampus)
- integrates and produces homeostatic responses to environmental stimulus (cortex)
what does the limbic system control about the endocrine system
influences many aspects of emotional behavior (fear, anger, sexual behavior, appetite and eating behavior, sleep, addiction and motivation, social cognition)
how are the three functions of the limbic system related
in order to have an appropriate emotional response (amygdala) to environmental stimuli we need to be able to store and retrieve memories of our previous experiences
other names for limbic lobe
cingulate cortex/cingulate gyrus
Broca’s contribution to discovery of limbic system
pointed out horseshoe shaped circular rim of cortex that surrounded the junction between the diencephalon and cerebral hemispheres
- based on anatomical, not functional specifications
James Papez’s contribution to limbic system discovery
proposed that there is an emotional system that links the cortex to the hypothalamus where the type and intensity of emotion is determined by the activity of the cingulate cortex and expression of the emotion is governed by endocrine system
Papez circuit
- cingulate cortex projects to hippocampus
- which projects to the hypothalamus
- which projects to the thalamus
- which projects back to cingulate cortex
limbic system role in emotion and cognition
- integrates emotional states with cognitive processes
- involved in the regulation of emotional responses, formation and retrieval of memories, decision-making, and social interactions
limbic system integration with other brain regions
- highly interconnected with other brain regions, including the prefrontal cortex, sensory cortices, and brainstem
- allows for a complex interplay between emotional, cognitive, and physiology processes
limbic system network perspective
- functional network more than a distinct anatomical entity
- components participate in broader neural circuits that support a range of behaviors, from emotional regulation to cognitive functions
core limbic system structures
- limbic cortex (limbic lobe/cingulate gyrus)
- hippocampus
- amygdala
- prefrontal cortex
- mammillary bodies
- hypothalamus
- septal nuclei
current view on limbic system
- no single neural system produces all emotional states
- different emotions depending on on different neural circuits but they all converge in the cortex for higher processing/awareness
- limbic system translates sensory data from cortex into motivational forces that produce human behaviors
what is the “ring” of cortex tissue associated with limbic function
cingulate, parahippocampal, & entorhinal cortex
how does limbic system connect pre-frontal/association cortex and lower limbic structures
2-way communication to control behavioral responses
what does ablation of some limbic cortex areas result in
persistent changes in an animal’s behavior
hippocampus role
encoding & consolidating info from short-term to long-term memory, memory retrieval, and spatial memory/nav
what does the hippocampus consist of
hippocampus and parahippocampal gyrus
where does the hippocampal gray matter lie
on the floor of the inferior horn of the lateral ventricle
what is the alveus formed by
formed of axons leaving the hippocampus along the surface of the hippocampus that form the fornix
what is the fimbria formed by
axons of the alveus coming together to form a larger white matter tract called the fimbria
what is the fornix formed by
the fimbria from the left and right hemispheres come together at the commissure to form an even larger white matter tract called fornix
fornix
C-shaped bundle of white matter fibers that arise from neurons in the hippocampus and are its major output tracts
- carries some afferent tracts into the hippocampus from the diencephalon and forebrain
what does cutting the fornix result in in humans
memory loss
- some debate over what type of memory is affected, but typically it’s episodic father than semantic or spatial knowledge
major white matter output from hippocampus
fornix
hippocampus axons projection path
alveus —> fimbria —> fornix
hippocampul commissure
part of the fornix that transmits information from either side of the brain
- bridge between the hemispheres
what does the parahippocampal gyrus contain
entorhinal cortex
entorhinal cortex function
provides most of the input to the hypothalamus
hippocampal formation
hippocampus (dentate gyrus + CA1 to CA4 - where neuron cell bodies are located), the entorhinal cortex, and the rest of the parahippocampal gyrus
perforant path
the primary source of external input to the hippocampus from the entorhinal cortex
what role does the entorhinal cortex-hippocampus system play
declarative (autobiographical/episodic) memory and spatial memory formation, consolidation, and optimization during sleep
where do the hippocampal outputs reach
amygdala, mammillary bodies, thalamus, hypothalamus, and the cingulate and frontal cortex
two distinct divisions of hippocampus
dorsal/posterior hippocampus, ventral/anterior hippocampus
dorsal/hippocampus main functions
- spatial learning and memory
- context encoding
- place memory
ventral/anterior hippocampus main functions
- emotional behaviors
- stress response system
- HPA axis negative feedback
hippocampal place cells
specialized neurons in the dorsal hippocampus, mainly CA1 and CA3 that play a crucial role in spatial memory and navigation
which cells are associated with encoding the “cognitive map” of an environment
place cells
when do place cells increase their firing rate
when an animal is in a particular location that corresponds to their place field
when do place fields form
when an animal is introduced to a new environment
how does the size of hippocampal place fields change
increases dramatically from the dorsal region to the ventral hippocampus
declarative or explicit memory
a form of long-term memory used to recall everyday facts and knowledge
spatial memory
a part of declarative/explicit memory for recalling locations
episodic memory
a part of declarative/explicit memory for recalling events
semantic memory
a part of of declarative/explicit memory for recalling facts
procedural/implicit memory
a part of long-term memory: previous experiences help the performance of a task without conscious awareness
what functions is procedural/implicit memory associated with
- skills and habits
- emotional associations
- conditioned reflexes
retrograde amnesia
cannot remember events prior to brain damage
anterograde amnesia
cannot remember events that occur after brain damage
functions associated with amygdala
- social interactions
- anxiety
- aggression
- fear
- addiction/emotional rewards
what does the amygdala respond to
emotionally salient stimuli
three groups of amygdala
- basolateral nuclei (BLA)
- central nuclei (CEA)
- medial nuclei (MEA)
basolateral nuclei function
communicated bi-directionally w/ brain regions affecting cognition, motivation, and stress responses including prefrontal cortex, hippocampus, nucleus accumbens and hindbrain regions
central nuclei function
connections with hypothalamus and periaqueductal gray controlling body’s physiological emotional response
medial nuclei function
interconnected with olfactory system; associated with olfactory memory, social behavior, aggression
valence meaning
emotional value associated with a stimulus, which can be positive (rewarding) or negative (threatening)
which part of amygdala encodes emotional valence of stimuli
basolateral amygdala
where does the basolateral amygdala send out projections to in order to stimulate approach or defensive behaviors
nucleus accumbens (reward/approach/pleasure), central amygdala (defensive reaction/threat avoidance), ventral hippocampus (anxiety behaviors)
what kind of memory does the amygdala activity affect
episodic autobiographical (EAM) memory
- encodes, stores, and retrieves EAM memories
what does amygdala valence coding do
emotionally “charge” cues so that events of a specific emotional significance can be more rapidly retrieved
how is the amygdala connected to the hippocampus
strengthens learning and memory in the hippocampus
which kinds of memories are better remembered than others
negative memories > positive memories > neurtral memories
how can PTSD result
amygdala-enhanced memories as a result of traumatic experience
pre-encounter threat imminence
increased predator potential
pre-encounter state
anxiety
pre-encounter antecedent stimuli
past experiences w/ predation or threates
pre-encounter consequent behaviors
- stretched approach
- alterations in meal patterns
- retreat to next
pre-encounter neuroanatomy
- prefrontal cortex
- ventral
- hippocampus
post-encounter threat imminence
predator deteccted
post-encounter state
fear
post-encounter antecedent stimuli
detection of a predator or imminent threat
post-encounter consequent behaviors
- freezing
- thigmotaxix
post-encounter neuroanatomy
- amygdala
- ventral PAG (midbrain)
circa-strike threat imminence
predator makes contact
circa-strike state
panic
circa-strike antecedent stimuli
a striking predator is making or is about to make physical contact
circa-strike consequent behaviors
- audible vocalizations
- vigorous escape attempts
- Protean movement (zig zag running)
circa-strike neuroanatomy
dorsal PAG with sensory inputs from the superior colliculus
prefrontal cortex roles
- decision making
- planning and organizing
- impulse control
- attention and focus
- working memory
- social behavior
- emotional regulation
amygdala emotion generation
experiencing something emotional activates amygdala, triggers immediate intense emotional response
prefrontal cortex emotion regulation
manage emotions; “brake” on the amygdala, helping calm down, think logically, and respond appropriately
ucinate fasciculus
prefrontal cortex - amygdala white matter pathway
prefrontal cortex - amygdala balance
- prefrontal cortex controls impulsive reactions from amygdala, making sure emotional responses are balanced and appropriate
- if amygdala is overactive, emotions take over
- prefrontal cortex inhibits amygdala
how to strengthen prefrontal cortex - amygdala pathway
exposure therapy and fear extinction in PTSD or phobia therapies
mammillary bodies location
- part of the diencephalon
- paired nuclei that bulge anteriorly from the hypothalamus
mammillary bodies general function
relay station in olfactory pathways, hippocampus, and other cerebral memory processing areas
- memory formation
what part of the brain are the mammillary bodies part of
diencephalon (hypothalamus)
what are the mammillary bodies connected to
- hippocampus via fornix
- anterior thalamic nuclei via mammillothalamic tract
- tegmentum (reticular formation) via mamillotegmental tract
what is Wernicke-Korsakoff Syndrome caused by
thiamine deficiency
role of the hypothalamus in the limbic system
- contains many connections with neural circuits that regulate emotions and the body’s physical response
- produces many bodily autonomic responses associated with emotions; unconsciously controls endocrine glands
septal nuclei projections
- receive afferent connections from other limbic structures (hippocampus, amygdala, and hypothalamus)
- send efferent projections to hippocampus, thalamus, ventral tegmental area, and hypothalamus
septum pellucidum
thin, almost transparent membrane running down middle of brain from corpus callosum to hippocampus white matter tracts of fornix
septum pellucidum location
- forms part of the walls of the lateral ventricles
- connected to bottom of corpus callosum
- made up of thin two-layered structure consisting of nerve fiber bundles and blood vessels
- surrounded by septal nuclei
septal nuclei function
feelings of social connectedness and bonding
- maternal behaviors
where does septal nuclei converge
lateral septum in regulation of maternal behaviors
