W6L1 - HM and Temporal Lobes

Question 1

What does HM have initially

Answer 1

Severe epilepsy

Question 2

What are epilepsy seizures caused by? What is the biochemistry behind it?

Answer 2

Cause

• Sudden excitation in groups of neurons,
• With a loss of inhibitory potential

​​Biochemistry

• Seizures decreases GABA
  
  • Inhibitory: GABA
    
    • Nervous system stability
  • Excitation: Glutamate
    
    • Increases spread of excitation

Question 3

Definition of Temporal Lobe Epilepsy (TLE)

Answer 3

Recurrent unprovoked seizures originating from medial or lateral temporal lobe

Question 4

What are the types of seizures caused by TLE

Answer 4

• Simple partial seizures
  
  • Without loss of awareness
• Complex partial seizures
  
  • With loss of awareness

Question 5

What is the most common pathphysiology of TLE. Onset and Phyisology?

Answer 5

Most common: Hippocampal sclerosis (HS)

Onset

Early in life: About 20-years-old

Physiology

• Neuronal loss
• Gliosis
  
  • Excess growth of glial cells after neuronal cell loss occurs in a region

Other aetiologies include past infections, tumours and vascular malformations

Question 6

What happens to seizures when a leisoned hippocampus is surgically removed

Answer 6

Surgical removal of hippocampus cures or reduce seizures

Question 7

How many gyri and sulci of the Temporal Lobe

Answer 7

Gyrus

• Superior Temporal Gyrus
• Middle Temporal Gyrus
• Inferior Temporal Gyrus

Sulcus

• Superior Temporal Sulcus
• Inferior Temporal Sulcus

Question 8

Where is the hippocampus located

Answer 8

Within parahippocampal gyrus, which is at the MTL

Question 9

What is the parahippocampal gyrus posterior to

Answer 9

• Anterior
  
  • Perihinal
• Middle
  
  • Entorhinal (Links to hippocampal formation)
• Posterior
  
  • Parahippocampal Cortex

Question 10

What did HM undergo. Which parts of his brain was removed

Answer 10

• Bilateral resection of extensive amount of medial temporal tissue
• Amygdala, Hippocampi, part of parahippocampal gyrus

Question 11

What did HM retain after surgery

Answer 11

Retained

• Normal attention span
• Normal Intelligence
• Retrograde memory recovered over time
• Procedural memory

Question 12

What is the difference between retrograde amnesia and anterograde amnesia

Answer 12

• Retrograde: Impairment for memory PRIOR to injury
• Anterograde: Impairment for memory AFTER injury

Question 13

What condition did HM have after surgery

Answer 13

Severe antereograde amnesia

• Particularly declarative memory

Question 14

What is the difference between declarative and procedural memory

Answer 14

• Declarative
  
  • Conscious access to information learnt previously
• Procedural
  
  • “Muscle Memory”/”How To” (e.g., playing piano)

Question 15

DId HM lose declarative/procedural memory. How do we know?

Answer 15

• Declarative
  
  • Severely impaired
    
    • Could not remember home
    • (but) Remember that his mother died
• Procedural
  
  • Retained
    
    • Able to learn new skills and normal performance on procedural memory task (star)

Question 16

What did HM tell us about memory?

What did he NOT teach us?

Answer 16

• MTL is essential for memory function
  
  • More essential for anterograde than retrograde memory
  • More essential for declarative than procedural memory (distinction between Declarative and Procedural memory)

Note: He didn’t teach much about the semantic memory system

Question 17

Anatomy of Memory: What have we learnt since HM. What is functional asymmetry?

Answer 17

• Intact memory function relies on a neuroanatomical network
• Temporal Lobes (TL) are the ‘engine’ of memory
• Functional Asymmetry
  
  • Material-specific deficits
    
    • Left MTL lesion: Verbal memory impariment
    • Right MTL lesion: Visual or Non-Verbal memory impairment

Question 18

What is the hippocampus also known as

Answer 18

Cornu Ammonis (Ammon’s horn): CA1 to CA3

Question 19

What is the Hippocampal formation?

Answer 19

Hippocampus (CA3 - CA1) and related parts

• Dentate Gyrus
• CA3 - CA1
• Subiculum

Question 20

What is the schematic representation and processes of the MTL

Answer 20

Unimodal/Polymodal Association [Sensory]

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Perihinal Cortex + Parahippocampal Cortex

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Entorhinal Cortex > Other direct projections

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Hippocampal Formation (From dentate gyrus)

• Information is integrated in sensory systems,
  sent to hippocampal formation for long-term
  storage
• Memories can then be accessed by reciprocal
  connections between hippocampal formation
  and temporal neocortex

Question 21

What is the role of Hippocampal Formation and what are the 2 theories on its role

Answer 21

Hippocampal formation and surrounding structures:

• Learning and consolidating novel information
  
  • Particularly for relational memory tasks

1. ) Consolidation Theory: Squire
   * After a period of consolidation, information can be retrieved INDEPENDENTLY of hippocampal formation involvement
2. ) Multiple Trace Theory (MTT): Mosocvitch
   * Retrieval of episodic experiences ALWAYS INVOLVE hippocampal formation

Question 22

What are paired association learning task. What is the brain structure required to do this task?

Answer 22

Remember an association between arbitrary (unrelated) pieces of information

Hippocampal formation