Limbic System Flashcards
what are the core structures of the limbic system?
hippocampus
amygdala
cingulate gyrus
fornix
mamillary bodies
what are additional structures often included in the limbic system?
hypothalamus
anterior nucleus thalamus
which structures connect to the limbic system?
frontal cortex
basal forebrain
septal nuclei
nucleus accumbens
what is the mesolimbic dopamine system?
Connects the limbic system to the nucleus accumbens that is responsible for the brain’s reward center that releases dopamine when we experience pleasure and regulates what is real and worth reacting to versus what is irrelevant or imagined
what can too much dopamine in the temporal gyrus lead to?
Too much dopamine can cause misinterpretation of neutral stimuli, leading to delusions or hallucinations
what is the papez circuit?
loop-like pathway that connects structures in the limbic system, allowing information to flow between areas involved in memory, learning, and emotion
Hippocampus→Fornix→Mammillary Bodies (in Hypothalamus)→Anterior Nucleus of the Thalamus→Cingulate Gyrus→Back to the Hippocampus
what can disruptions in the papez circuit cause?
amnesia
what does the hypothalamus coordinate?
hormonal, autonomic responses and stress responses related to reward and motivation
what is the function of the Hippocampus?
Located in the temporal lobe, helps convert short-term memories into long-term memories and encodes and retrieves personal (episodic) and pattern-based memories
***(Long-term memories are not stored in the hippocampus but distributed across different parts of the cortex)
what is the function of the anterior nucleus of the thalamus?
acts as a relay hub, passing memory-related signals between the mammillary bodies and cingulate gyrus
what is the function of the cingulate gyrus?
- connects the limbic system (emotion) to higher cognitive functions (thinking, awareness)
- role in the conscious experience of emotions and how we process pain perception
- helps us assign emotional significance to memories
what is the function of the amygdala?
strongly connected to the hippocampus, links emotions to memories, helps store emotionally charged memories, such as those related to fear, trauma, or pleasure and establishes emotional associations with pain (unconscious bias)
what is the function of the parietal lobe?
process new sensory information and connects it with retrieved memories
** integrate old memories with new experiences
what is the role of the Prefrontal Cortex?
directs attention to important information decides what is worth remembering (factual information, events, experiences) but without attention new information is not stored properly
declarative (explicit) vs non-declarative memory (implicit)
- declarative: episodic and semantic memory (events and facts)
- nondeclarative: skills, habits, emotional memory, conditioned reflexes
what is the CA1 region of the hippocampus sensitive to?
O2 deprivation and is critical to memory consolidation
what is the primary site of Long Term Potentiation?
Hippocampus
what is Long Term Potentiation?
strengthens the connections between neurons (synaptic plasticity), allowing short-term memories to be consolidated into long-term memories
how does repeated stimulation in a presynaptic neuron cause Long Term Potentiation?
- presynaptic neurons release a lot of glutamate which binds AMPA and NMDA receptors allowing more Na⁺ and Ca2+ in
- Increased calcium activates the CREB which promotes the production of more AMPA & NMDA receptors
- Stronger synapses = More efficient signal transmission = Long-term memory formation
how does CREB organize how memories are stored?
based on context, time, or categories (“chunking”)
where does the mammillothalmic tract project to?
anterior nucleus of the thalamus
what is Wernicke’s encephalopathy?
neurological disorder caused by thiamine (Vitamin B1) deficiency, most commonly seen in chronic alcohol use disorder (AUD). It primarily affects the mammillary bodies, thalamus, and temporal lobe, leading to memory impairment (anterograde amnesia) and confusion.
why is it imporant to catch Wernicke’s Encephalopathy early?
it is reversible with thiamine treatment (Vitamin B1) but if untreated, it progresses to Korsakoff’s syndrome, a more severe, irreversible memory disorder
what is the function of the Frontal Cortex?
Deliberate retrieval of factual (semantic) memory and storage of facts, knowledge, and general information
what is the function of the Cerebellum?
Stores procedural (motor) memory for learned tasks and stores muscle memory, so skills become effortless over time
the connection of the Amygdala to the hypothalamus allows for ?
amygdala detects threats and triggers fear responses by communicating with the hypothalamus to activate the autonomic nervous system
An overactive amygdala is associated with
excessive fear responses, anxiety disorders, phobias, and PTSD (Post-Traumatic Stress Disorder).
lesions to the amygdala are associated with
- Loss of fear responses
- Risk-taking behavior
- Impaired emotional learning
Kluver-Bucy Syndrome
rare neurological disorder caused by bilateral damage to the amygdala, often due to:
Temporal lobe tumors
Severe seizure disorders
Infections such as HSV (herpes simplex virus) encephalitis
how might reduced amygdala activity contribute to antisocial personality disorder (APD) and psychopathy?
Deficient amygdala function is associated with a lack of empathy, remorse, and fear.
- Individuals with APD or psychopathy may have reduced emotional responses to threats or distress in others, increased risk-taking and impulsive aggression and difficulty recognizing fear or emotional cues in faces
why might some people find stress rewarding?
individuals experience pleasure or excitement from stress or high-risk situations due to strong amygdala connections with the reward system (dopamine system)
What are the effects of temporal lobe damage due to surgery or viral encephalitis?
Temporal lobe damage, often due to HSV encephalitis or surgery, leads to severe amnesia, emotional changes, impulsivity, and limbic seizures.
Are memory lapses always a sign of an underlying pathology?
No, memory lapses are common, especially with normal aging, certain medical conditions and everyday cognitive errors that happen to everyone
what is amnesia?
Partial or total loss of memory for a duration of time
what is retrograde amnesia?
Loss of older or previous memories but possess capacity to encode new ones
what is anterograde amnesia?
Loss of new memories and lose ability to encode but retain old memories
what is dissociative amnesia?
Loss of memory of specific (often traumatic) event
- “Memory gaps” ~ covered in psychiatry section
what type of amnestic syndromes would a Stroke (Infarct) or Traumatic Brain Injury (TBI) cause?
sudden onset and persistent memory loss
what type of amnestic syndromes would a Seizure or Mild Concussion cause?
sudden onset and complete recovery
what type of amnestic syndromes would drug-induced memory impairment cause?
sudden onset and complete recovery if the drug is STOPPED
what are drugs that can cause reversible memory issues?
- Benzodiazepines: enhance GABA activity, leading to sedation and memory loss
- Drugs with antimuscarinic (anticholinergic) properties: more common in the elderly
what type of amnestic syndromes would Wernicke’s Encephalopathy or Herpes Simplex Virus (HSV) Encephalitis cause?
Gradual onset, variable recovery
what type of amnestic syndromes would Alzheimer’s Disease, Other Dementias, and Neurodegenerative Disorder cause?
Gradual onset, progressive worsening
Long term chronic Alcohol use disorder causes irreversible damage leading to
- atrophy of mammillary bodies & anterior thalamus
- significant retrograde and anterograde amnesia
- “Confabulation” is common (fill in memory gaps & past history with untrue ‘stories’)
- Korsakoff’s psychosis
Korsakoff’s psychosis
irreversible neuropsychiatric disorder caused by long-term alcohol abuse, often following Wernicke’s encephalopathy
- causes hallucinations & altered reality increased susceptibility to seizures and significant damage & disability
there is no cure for chronic AUD but what is the treatment plan?
medications including:
Antipsychotics
Cognitive Enhancers
Anti-Seizure Medications
what are seizures?
temporary dysfunction of the brain caused by excessive and synchronized electrical activity of cortical neurons
what are acute seizures?
triggered by an underlying abnormal physiological event or medication and not necessarily linked to chronic epilepsy
what is status epileptics?
prolonged seizure lasting more than 5 minutes or multiple seizures without full recovery between episodes
* can be life threatening
what is epilepsy?
A neurological disorder characterized by recurrent, unprovoked seizures
what are the acute causes of seizures?
- infections or high fever
- metabolic abnormalities (hypoglycemia)
- brain injury or bleeding
- triggers if susceptible (Flashing lights, sleep
deprivation) - medications/drugs of abuse (usually induce
generalized seizures) - drug withdrawal in chronic users
what are the two types of seizures?
generalized and focal (partial)
what are the types of generalized seizures?
- Absence Seizure: brief staring spells that originate in the Thalamus and affects consciousness without motor involvement
- Tonic-Clonic Seizure: stiffening of the muscles (body becomes rigid) then rhythmic jerking movements of the limbs.
what is a focal (partial) seizure?
the most common type of seizure often originating in the temporal lobe and limbic system
* muscle twitching, unusual smells/tastes, or déjà vu sensations
Absence seizures result from
abnormal thalamocortical activity, driven by T-type calcium channel dysfunction.
what are the causes of chronic seizures?
- Epilepsy
- Brain tumors
- Traumatic Brain injury (TBL-long-term damage)
- Stroke (areas like temporal lobe)
- AUD with long-term damage
- Underlying disorders that increase susceptibility
- Autism Spectrum Disorders
- Down’s Syndrome
- Neurodegenerative diseases
