Limbic System Flashcards
What are the general functions of the limbic system? (5)
- Plasticity/memory
- Responding to stressors
- Vigilance / attention
- Respond to emotional stimuli
- Classical conditioning (pavlovian)
The limbic system receives information and projects to multiple areas of the brain. What are these areas in general
Projects to and from the following:
- Where is the cingulate gyrus
- What does it do?
- What pathology is associated with damage to this structure?
- Superior to corpus callosum
- Relays info on error detection and reality testing to cortex
- Akinetic mutism
- Where is the amygdala?
- What does it do?
- What pathology is associated with damage to this structure?
- In front of hippocampus
- Emotional respose, particularly fear
- Kluver-bucy syndrome
- Where is the hippocampus?
- What does it do?
- What pathology is associated with damage to this structure?
- Seahorse shaped structure in medial temporal lobe
- Memory consolidation (declarative)
- Anterograde amnesia
- Where are the septal nuclei?
- What do they do?
- Near the nucleus accumbens, and at the inferior end of the septum pellucidum
- Signal pleasure when they are stimulated and rage when they are totally inhibited
- Where are the mamillary bodies?
- What do they do?
- What pathology is associated with damage to this structure?
- Under back end of hypothalamus
- Memory
- Wernicke-korsakoff (thiamine, vit B1, deficiency)
- Where is the ventral tegmental area?
- What does it do?
- What pathology is associated with damage to this structure?
- Medial to red nucleus and substantia nigra in midbrain
- Reward and motivation
- Addiction
- Where is the nucleus accumbens?
- What does it do?
- What pathology is associated with damage to this structure?
- Medial forebrain, where caudate and putamen meet
- Reward and motivation
- Addiction
What information is conveyed via the fornix?
Output from hippocampus to mamillary bodies, septal nuclei
Input to hippocampus from septal nuclei
Where is the stria terminalis located?
What information is conveyed via the Stria terminalis?
Between head of caudate and thalamus
Output from amygdala to basal gangia, septal nuclei, nucleus accumbens and hypothalamus
What information is conveyed via the mamillo-thalamic tract?
Output to various thalamic nuclei (particularly anterior thalamic nucleus)
What information is conveyed via the medial forebrain bundle?
Connects ventral tegmental area to nucleus accumbens, amygdala, septal nuclei and prefrontal cortex
What is declarative memory?
What is procedural memory?
What type of memory is consolidated in the hippocampus?
Facts, numbers, concepts
Processes, activities, actions
Declarative
The diagram below shows the entrohinal and perihinal cortices of the hippocampus. What is the significance of these areas?
EC connects to olfactory bulb
Both connect to higher order brain areas where long term memories are stored
Damage to these areas in early alzheimers can manifest as loss of anterograde amnesia
- What is kluver bucy syndrome?
- What symptoms would a person display?
- Significant damage to temporal lobes (medial temporal cortices –> limbic system)
- Symptoms:
- Anterograde and retrograde amnesia
- Hyperorality (oral exploration, putting odd things in mouth)
- Hypersexuality
- Placidity (very quiet when scolded)
- Hypermetamorphosis (strong reaction to visual stimuli)
- Visual agnosia (psychic blindness)
- Dietary changes (over eating and swallowing odd things)
What neurotransmitter is produced in the ventral tegmental area?
Dopamine
What is the mesolimbic system?
What is the mesocortical system?
Mesolimbic - dopaminergic projections from VTA to limbic structures (amygdala, septal nuclei, nucleus accumbens, hippocampus)
Mesocortical - dopaminergic projections from VTA to cortex
The medial forebrain bundle is a white matter tract that contains projections from the […] to the […] that are involved in regulating […]
VTA
Nucleus Accumbens
Reward
Medial Forebrain Bundle
Neurons in VTA release […] onto […] neurons in the nucleus accumbens, which then release […] back onto the VTA and the pallidum.
Dopamine
Medium spiny
GABA
Substance use disorders are thought to be maintained by what 2 processes?
- Reinforce effect of drug itself
- Aversive effects of withdrawl
**Long term use is thought to alter brain systems involved in normal reward processes
What effect do stimulants have on the limbic system?
Directly increase dopamine in nucleus accumbens from VTA
What effect do opoids have on the limbic system?
Inhibit GABAergic interneurons in VTA –> disinhibition of dopaminergic neurons –> increased secretion of dopamine
What effect does nicotine have on the limbic system?
Activates VTA by binding to nicotinic cholinergic receptors
What effect does alcohol have on the limbic system?
Inhibit release of GABA from interneurons in VTA leading to increased dopamine secretion
What effect does PCP have on the limbic system?
Non-competitive NMDA receptor agonist which reduces glutamatergic excitation of the Nucleus accumbens
What is anhedonia?
During withdrawl from drugs, many natural reinforcing stimuli (sex, foods, activities, exercise) that were normally pleasurable no longer are and there is a loss of interest in doing things
Explain what is being shown in this diagram.
CS = conditional stimuli –> a stimulus that a subject has been trained to associate with a reward (think Pavlov’s dogs)
Explain the limbic loop involving the limbic system and basal ganglia with respect to reward and habit formation in the context of pleasurable stimuli.
Pleasurable stimuli (food, water, drugs, sex) initially activate the loop in the cortex. These stimuli trigger an increased release of dopamine from the VTA to the nucleus accumbens and simultaneous activation of the amygdala. The nucleus accumbens then inhibits the pallidum and substantia nigra, which releases the mediodorsal nucleus of the thalamus from inhibition and increases thalamic output signaling pleasure.
If these pleasurable stimuli are preceeded by cues, people can learn that the cues predict the pleasurable reward, so they gain the ability to activate this loop in response to the cue alone via learning that takes place in the amygdala.
Explain this diagram.
What is sensitization to a drug?
Why is the dopamine system particularly vulnerable to sensitization?
Sensitivity increases with repeated use
It’s believed that there is expansion of dendrites on neurons in the nucleus accumbens in response to chronic exposure to a drug. This would increase a person’s reaction to the drug when taken and this is believed to be why a person can take a drug chronically and not “like” the drug but they will crave it more and more
Although the data is only suggestive at this time, oxytocin and vasopressin may be involved in activation of the mesolimbic systems reward pathways as well. Describe how this was discovered and how it works.
This was discovered by studying voles. Prarie voles are monogamous and biparental where as meadow voles are neither. When a naive pair of prarie voles initially meet, it was discovered that partner preference requires dopaming signaling through D2 receptors in the nucleus accumbens and continual bond formation requires D1 signaling in the nucleus accumbens.
Oxytocin and vasopressin are released from magnocellular neurons in the PVN and SON and affect distant targets but they are also released in some amount locally into the extracellular fluid and affect nearby neurons. It was discovered that inhibition of vasopressin in male prarie voles prevented pair bonding while inhibition of oxytocin in females prevented pair bonding. It is suggested that the local release of these 2 hormones may play a role in bonding behaviors in humans.
The amygdala is slightly […] to the hippocampus
Medial
Other than declarative memory, the hippocampus is important for […] types of learning and memory.
Spatial
What are the 3 nuclei of the amygdala?
What are the major inputs to the amygdala?
Sensory from thalamus
Cortex
Hippocampus
Explain this diagram
An emotional stimulus conveys informatin to thalamus –> thalamus can convey information directly to amygdala –> central nucleus of amygdala –> send afferent projections to mount coordinated behavioral, endocrine and autonomic response
The amygdala sends outputs to the bed nucleus and hypothalamus via the […]
Stria terminalis
The amygdala sends outputs to the cortex and PAG via the […]
Ventral amygdalofugal pathway
Explain pavlovian fear conditioning.
The CS and US arrive at the lateral nucleus of the amygdala at approximately the same time in order to establish the association.
In pavlovian fear conditioning, what happens if we continue to present the CS many times alone after the conditioning has occurred?
Extinction = NOT forgetting, but rather a new learned response that tells the subject not to respond with fear to the CS.
How are the prefrontal cortex and hippocampus involved in extinction of a fear response to the CS in pavlovian fear conditioning?
The prefrontal cortex realizes that the CS is no longer heralding the dangerous event, so it tells the amygdala to stop triggering a fear response by inhibiting the lateral nucleus of the amygdala.
The hippocampus provides contextual information to the central nucleus of the amygdala. Thus, if the fear in response to the CS is learned in a specific location, and the subject is then moved to a totally different environment and the CS is presented they will not respond because the hippocampus is telling the central nucleus of the amygdala that it’s not the same context so you don’t need to be afraid.
The amygdala is […] in people with PTSD
Hyperactive
The prefrontal cortex is […] in individuals with PTSD
Hypoactive –> less ability to extinguish fear response to CS
What is the basis of extinction training?
Repeated presentation of the fear stimulus (CS) without the US creates new learning. If it takes place in a safe context, the memory of the CS can be reconsolidated as a safe memory.
