Memory 2

Question 1

What are extra-temporal connections to the MTL?

Answer 1

1. Papez Circuit
2. Frontal Lobes
3. Dienecephalon

Question 2

What is the Limbic System and what does it regulate?

Answer 2

Limbic System = Amygdala + Papez Circuit

• Emotional expression and experiences

Question 3

What is the role of the Amygdala in memory? What happens if it’s leisoned?

Answer 3

Role of Amygdala

• Memory for emotionally arousing experiences (Not necessarily fear)
  
  • Fear conditioning
  • Rich representations of emotional experiences

Lesioned

• Loss of conditioned fear
• Impairment of new fear learning
• Reduced memory for emotionally laden events (Not necessarily fear)

Question 4

What are the parts of Papez Circuit (in order?

Answer 4

1. Hippocampus
2. Fornix
3. Mamillary Body - Part of Hypothalamus
4. Anterior Thalamus Nuclei - Part of Thalamus
5. Cingulate Gyrus

[Closed Circuit]

Question 5

What is the role of the Papez Circuit in memory? Lesion to which part is memory most reliably imparied?

Answer 5

Declarative Memory

General View

• Relational memory/encoding, similar to MTL
• Most reliable when hippocampus or ATN are leisoned. But other parts also cause relational damage
  
  • Damage tend to be spread anyways

Question 6

What does the Frontal Lobe contain?

Answer 6

• Posterior Frontal Lobe
  
  • Motor and premotor cortex
  • Motor programming
• Anterior Frontal Lobe
  
  • Prefontal cortex
  • Cognitive Control Processes

Question 7

Leision of Frontal Lobes in Memory?

Answer 7

• Impairment in developing and implementing strategies for appropriate memory encoding and retrieval
• Impairment in remembering contextual details (DLPFC)
  
  • E.g., Sources of information, chronological order of memories
• Confabulation (VLPFC)
  
  • Production of statements involving bizarre distortions of memory

Question 8

Where are the rich connections in frontal lobes connected to?

Answer 8

Rich reciprocal connections:

1. ) Within frontal lobes itself
2. ) With MTL (hippocampus, neocortical association areas, etc)

(With hippocampus via fornix)

Question 9

What is the Dienecephalon?

Answer 9

Dienecephalon = Thalamus + Hypothalamus

Question 10

What does the hypothalamus contain? Hence?

Answer 10

• Mamillary bodies (In Papez Circuit)
  
  • Impairment = loss of declarative memory (relational)

Question 11

What does the thalamus contain?

Answer 11

1. ATN (Papez Circuit)
2. Mammillo-thalamic tract (MMT): Connects ATN with hipocampus
3. Medio Dorsal Nuclei (MDM) / Dorsal Medial Nuclei
4. Internal Medullary Lamina (IML) / Midline

Question 12

Which parts of leisons of thalamus most likely to cause memory loss?

Answer 12

Anterior and Medial

• More likely
• Most connected to frontal lobes
  
  • Anterior (part of Papez circuit)
  • Medial

Posterior and Lateral

• Less likely

Question 13

Damage of mammillo-thalamic tract (connects ATN to hippocampus) and ATN affects what type of memory?

Answer 13

Declarative (Relational memory)

Question 14

Damage of Medio Dorsal Nucleus (MDN) and/or Internal Medullary Lamina (IML) damage; but spared mammillo-thalamtic tract (MTT) affects memory how?

Answer 14

Specific retrieval difficulties

• Impaired Recall
• Preserved Recognition
  
  • Top Down cannot recall, but can recall under prompt

Question 15

Damage of Medio Dorsal Nucleus (MDN) and Intralaminar/Midline Nucleus affects memory how?

Answer 15

Medio Dorsal Nucleus

• Deficits in selecting the appropriate information to be retrieved
  
  • ‘Active retrieval’

Intralaminar/Midline

• Deficits seen in semantic memory, memory retrieval

Question 16

Summarise lesions of the 3 areas.

Answer 16

• Papez’s circuit lesion
  
  • Impaired relational memory/encoding (Similar to MTL)
• Frontal Lobes
  
  • Impaired ability to organise the encoding, retrieval and maintenance of memories
• Dorso-medial, intralaminar and midline nuclei
  
  • Impaired memory due to reduced mental flexibility and inappropriate selection of information retrieval

Question 17

Biochemistry: What does learning require?

Answer 17

Synaptic Plasticity

Biochemistry of synapses change to alter the effect on post-synaptic neuron

Question 18

What is LTP?

Answer 18

Long-term increase in excitability of a neuron (B) to a particular synaptic input caused by repeated high frequency activity of that input (A)

Question 19

What is Hebb’s Law? What does it describe?

Answer 19

When an axon of cell A…excites cell B by repeatedly firing it, change takes place in 1 or both cells to increase A’s efficiency

• Describes long-term potentiation

Question 20

Evidence for LTP?

Answer 20

• Baseline EPSP measured for single electrical stimulus
• 100 electrical stimuli delivered rapidly
• Increased EPSP for subsequent single electrical stimulus
  
  • LTP

Question 21

Biochemically, how does LTP cause synaptic changes? Describe the changes at the level of the pre and post-synaptic.

Answer 21

(Glutamate)

Pre-Synaptic

• Increased glutamate by pre-synaptic terminal button

Post-Synaptic

• New receptors
• Increased receptor sensitivity to glutamate
• Increase protein synthesis in post-synaptic dendrites

Question 22

Sites of LTP (Where it occurs)?

Answer 22

1. ) Hippocampus (esp. dentate gryus + CA1), entorhinal cortex
2. ) Others: Frontal Lobes, Thalamus, Amygdala, Visual Cortex

Question 23

What are 3 other mechanisms of neural plasticity?

Answer 23

1. ) Long term depression
2. ) Habituation
3. ) Sensitization

Question 24

How does Long Term Depression affect neural plasticity?

Answer 24

Low frequency stimulation at synapse decrease synaptic strength

Question 25

How does Habituation affect neural plasticity?

Answer 25

Repeated stimulation reduces strength of synaptic response (Reduced NT release)

Note: Repeated but neutral

Question 26

How does Sensitization affect neural plasticity?

Answer 26

Single noxious stimulus causes exaggerated synaptic response to repeat presentation of noxious stimulus