Hypothalamus Nuclei & Limbic System & Memories 😊

Hypothalamus Nuclei → Mneumonic = The CAR

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Nucleus
Function
Anterior nucleus
sweating, vasodilation (cooling)
Regulates sexual behaviour.
Contains osmoreceptors.
Posterior nucleus
shivering, curling (Heating)
Lateral nucleus
Thirst & hunger, Anger
Stimulated by Ghrelin
Ventromedial nucleus
Satiety.
Stimulated by Leptin
Ventral Tegmental area (midbrain) → Trophy
Medial forebrain bundle (hypothalamus) → Medal
Reward center

The VTA initiates dopamine release in response to rewarding stimuli, and the MFB serves as a major pathway for these signals to areas like nucleus accumbens and prefrontal cortex.
Suprachiasmatic nucleus
Biological/circadian rhythm.
give signal to → Pineal gland → Melatonin
SupraOptic
SAD
ADH Release
ParaOptic/Paraventricular
POX
Oxytoxin

Supra and ParaOptic Nucleus
Posterior Pituitary area appears Hotspot on T1W MRI
d/t stored hormones
PreOptic
Thrist, sexual function, GnRH
If not releasing → Kallman syndrome
Pre op - have sex and thirst
Ventrolateral preoptic nucleus.
Sleep Center
Sleepy eyelids → infront of eyes → pre optic
Medial preoptic nucleus
Thermoregulation in anterior region
Mammillary body.
Role in Memory
Applied Aspect (Wernicke-Korsakoff Syndrome)
Periaqueductal gray matter (hypothalamus).
Punishment center.
Stimulation causes rage.
Page to punish
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Thalamic Nuclei Mnemonics - The Car

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  • Hypothalamopituitary axis involves
    • Hypothalamus
    • Anterior Pituitary
    • Adrenal Cortex.

Temperature Regulation

  • Anterior Nucleus
    • Analogy: Car's front fan.
    • Function: Produces cooling.
    • Body: Cools the body. Lowers body temperature.
    • Sweating, vasodilation, thirst (osmocoreceptor).
  • Posterior Nucleus
    • Analogy: Car's rear heat exhaust.
    • Function: Releases heat.
    • Body: Controls heat production. Increases body temperature.
    • Shivering, vasoconstriction, increased urinary frequency.

Feeding and Satiety

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  • Lateral Nucleus
    • Analogy: Fuel tank opening on the car's side.
    • Body: Thirst and Hunger center.
    • To increase food intake:
      • Neuropeptide Y (NPY) & Agouti related peptide (AgRP) act on Lateral nucleus.
      • Lateral nucleus releases Orexin neurotransmitter.
  • Medial Nucleus (or Ventromedial Nucleus)
    • Analogy: The fuel tank itself inside the car. When full, the car is satiated.
    • Body: Satiety center.
    • To decrease food intake:
        • Ventromedial nucleus (satiety center) acted on by
          • Alpha melanocyte stimulating hormone (MSH) &
          • Cocaine amphetamine regulated Transcript (CART)
          • Eating Skin and Cocaine causes satiety

Regulation of Sleep & Wakefulness

  • Wake / Arousal State:
    • Lateral nucleus: Orexin.
    • Posterior nucleus: Histamine.
  • Sleep Center: 
    • Ventrolateral pre-optic nucleus.

Hormonal Regulation & Rhythms

  • Suprachiasmatic Nucleus
    • Analogy: Looking up (supra) from a car without a roof, seeing the sun and stars.
    • Body: Regulates circadian rhythms.
      • Dominant pacemaker / master clock:
        • Suprachiasmatic nucleus (SCN).
        • Synchronizes 24 hr bodily functions.
        • Controls cortisol production.
  • Supraoptic Nucleus
    • Analogy: Looking through the car's windshield (optic view). Rain (water) hits it, wipers activate.
    • Body: Releases ADH (Antidiuretic Hormone).
      • ADH controls water balance/osmolality.
      • Promotes water reabsorption in kidneys (distal convoluted tubule, cortical collecting tubule).
  • Paraoptic / Paraventricular nucleus
    • Analogy: Someone (e.g., girlfriend) sitting next to (para) you in the car, visible in your vision (optic).
    • Body: Releases Oxytocin.

Inhibitions of Pituitary hormones by hypothalamus

  • Dopamine (from arcuate nucleus):
    • Inhibits prolactin secretion from Anterior Pituitary
    • Tonic Inhibition
    • We get dopamine from arcade
        • Arcade → Dopamine
        Arcade → Dopamine
  • Somatostatin (from periventricular nucleus):
    • Inhibits growth hormone (GH) secretion
    • But control over GH is primarily stimulatory
      • (via growth hormone-releasing hormone, GHRH)
      • rather than inhibitory.

Role in Memory

  • Involves mammillary body.

Applied Aspect

  • (Wernicke-Korsakoff Syndrome):
    • Chronic alcoholism → Impaired memory (due to degeneration of mammillary bodies).

Wernicke's Encephalopathy

  • Symptoms (Mnemonic: GOA):
    • G: Global Confusion.
      • Mammillary bodies/Papez circuit
    • O: Ophthalmoplegia
      • 6th nerve palsy → most common
    • A: Ataxia.
      • Cerebellar neurons
  • Cause:
    • In acute thiamine deficiency.
      • e.g., those receiving dextrose infusion
      • without prior thiamine supplementation.
  • Neuropathology:
    • Lesions in
      • Mammillary bodies >>>
      • Hippocampus
      • Thalamus
      • Hypothalamus
  • Treatment: Thiamine Supplementation.
    • Reversible with early treatment
    • Rapid response is expected.
  • No response suggests
    • Pellagric encephalopathy
    • treat with Niacin
Wernicke Terms
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Wernicke pupil
• OT lesion
Wernicke Korsakoff syndrome
• In Alcoholics
• D/t Thiamine deficiency
• CAS → Confusion, Ataxia, Squint

Korsakoff Syndrome

  • Develops from chronic, untreated thiamine deficiency.
  • Leads to nerve atrophy.
  • Affected: mammillary bodies > Frontal lobes
  • Symptoms:
    • Impaired recent memory.
      • Anterograde amnesia >>
      • Retrograde amnesia.
    • Confabulation:
      • Making stories to fill memory gaps.
    • Sensory agnosia
  • Cause: Thiamine (Vitamin B1) deficiency.
  • Treatment:
    • Thiamine supplementation.
      • 100 mg,
      • 2-3 times/day for 3-12 months.
  • Prognosis:
    • Irreversible.
    • Full recovery in only 20% of patients.

Limbic System

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Structures related to emotions

  • Generation of emotions: Limbic system / Limbic Cortex
    • Aka Smell brain/rhinencephalon.
    • Emotions, smell & memory.
    • Oldest part of human body in terms of evolution.
    • Rim of cortical tissue.
  • Regulation of emotions: Frontal lobe.
  • Window of limbic system
    • Amygdala
    • Genesis of emotions / seat of emotions

Alexithymia

  • Inability to express or understand emotions

Clinical Aspects (Lesions)

Klüver-Bücy syndrome

  • Lucy
  • Lesion at Bitemporal region, amygdala →
    • Visual agnosia (Objects not recognized on sight).
    • Hypermeteramorphosis
      • Compulsion to explore environment
    • Placidity
      • No tears / anger
    • Hyperorality / Hyperphagia
      • Indiscriminate habit of eating
    • Hypersexuality
    • Sham Rage

Sham Rage

  • Sham rage = Aggressive, rage-like behaviour without actual provocation.
  • In healthy individual:
    • Cerebral cortex inhibits
      • Hypothalamus (especially dorsomedial nucleus)
      • Result: Sham rage not seen
  • On decortication (removal of cerebral cortex):
    • Inhibitory control from cortex is lost.
    • Hypothalamus acts unopposed
    • Result: Sham rage is seen

Mesial temporal lobe epilepsy

  • Lesion at Medial temporal lobe → No explicit memory
    • Complex partial seizure.
    • Uncinate fits (Smell / taste hallucination).
    • Deja vu (Unfamiliar environment seems familiar).
    • Jamais vu (Familiar environment seems unfamiliar).
        • Mesial temporal lobe sclerosis Sea horse
        Mesial temporal lobe sclerosis
        Sea horse

Papez Circuit – (Posterior to anterior)

  • Present in both sides of the brain
  • Connects memory & emotion of limbic system.
      1. Hippocampal formation
          2. ↓ via Fornix
      1. Mammillary bodies
          2. ↓ via Mammillothalamic tract
      1. Anterior nucleus of the thalamus
          2. ↓
      1. Cingulate gyrus
          2. ↓ via Cingulum
      1. Entorhinal cortex
        →         projects back to hippocampus
Pointed structure → Mammillary Body
Pointed structure → Mammillary Body
 

Structures in Memory and associated functions

Area
Functions
Prefrontal Cortex
• Anterior frontal lobe
• Executive functions:
• Planning, decision-making
• Working Memory (Short term) → Eg: Phone numbers
Anterior nucleus of thalamus
• Recent memories
• Relay station in the limbic circuit.
Amygdala
• Associates memory with emotions
• Especially fear
• Applied: Kluver - Bucy syndrome
• though not part of original Papez circuit, it's a part of limbic system
Hippocampal formation
• Memory encoding.
• Anterograde amnesia
↳ Lesions in hippocampus or Papez circuit.
Mamillary bodies
• Recollective memory
• Degeneration → Wernicke-Korsakoff psychosis
• (seen in alcoholics)
Parietal Association Cortex
• Spatial awareness
• Damage can cause hemispatial neglect.
• Parietal - Periphery - spatial awareness

Inferior parietal lobule
• Hand eye coordination

Superior Parietal lobule
• A/w Tactile agnosia
Temporal Association Cortex
• Memory, object recognition, and language comprehension.
• Includes Wernicke’s area on the dominant hemisphere.
Inferior Temporal Cortex
• Face recognition by sight
↳ Prosopagnosia
Limbic Association Area
• Part of limbic lobe;
• Connects with hippocampus and amygdala
• Involved in emotion, motivation, and memory.
Entorhinal cortex
(of limbic cortex)
• Associates memory with smell
• Also in Spatial memory
• Interface between hippocampus and neocortex.
  • Lesion: Prosopagnosia → Loss of recognition of faces
    • Fusiform Gyrus → Temporo occipital lobe
    • Mnemonic: Cant recognise face after using Pro Soap (Prosop - Agnosia) → IT jobs

Alzheimer’s disease

Structure
Braak Staging
Example Symptom
Entorhinal Cortex
I–II (earliest)
Forgetting recent events (e.g., breakfast)
Hippocampus
III–IV (next)
Cannot recall recent conversation
Nucleus Basalis
Early–mid, with cortical spread
Poor attention

Memory Types

By Duration:

Type of Memory
Duration
Area Involved
Working memory
↳ Eg Phone numbers
18–20 seconds
• Prefrontal cortex
Immediate memory
ã…¤
• Assessed by Digital Subtraction test
Short-term memory
Seconds to minutes
(0.5 - 5 mins)
• Ventral hippocampus (CA1 neuron).
Long-term memory
Weeks to months
• Stored: Neocortex
• Conversion: hippocampus
• [via Long Term Potentiation (LTP)]

Lesions in hippocampus 

  • Anterograde amnesia
  • Inability to form new long term memories.
  • Intact memories:
    • Recent
    • short term
    • procedural
    • past

By Recall:

Hippocampus
Hippocampus
Concept
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Definition / Key Point
Priming
Neocortex 
• Exposure to a stimulus (clue)
• Example: Clue triggers retrieval of a related memory
Explicit Memory
(Declarative)
Hippocampus,
Medial Temporal Lobe
• Needs conscious processing:
• E.g., first day of college, Words, rules, language
• Ex (explicit) Gf memories →
• Campusil (Hippocampus) poi,
• Mani Temple (Medial Temporal) il poi

Ex: Semantic memory
• General knowledge and facts about the world
• Sem exam → semantic → GK
Implicit Memory
(Non-declarative)
Striatum
• Unconscious recall of information or Skill memory
• Without awareness
• No hippocampus/ conscious processing needed.
• Reflex-like: Brushing teeth, cycling, procedural tasks
• Implicit → Vaishna → Sthree (Striatum)
Associative Learning
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• Forming associations between stimuli and responses
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