W6L2 - Neuroanatomy & Biochemistry of Memory Flashcards
What are extra-temporal connections to the MTL
- Papez Circuit
- Frontal Lobes
- Dienecephalon
What is the Limbic System and what does it regulate
Limbic System = Amygdala + Papez Circuit
- Emotional expression and experiences
What is the role of the Amygdala in memory? What happens if it’s leisoned?
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)
What are the parts of Papez Circuit (in order)
- Hippocampus
- Fornix
- Mamillary Body - Part of Hypothalamus
- Anterior Thalamus Nuclei - Part of Thalamus
- Cingulate Gyrus
[Closed Circuit]
What is the role of the Papez Circuit in memory? Lesion to which part is memory most reliably imparied?
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
What does the Frontal Lobe contain
- Posterior Frontal Lobe
- Motor and premotor cortex
- Motor programming
- Anterior Frontal Lobe
- Prefontal cortex
- Cognitive Control Processes
Leision of Frontal Lobes in Memory
- 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
Where are the rich connections in frontal lobes connected to
Rich reciprocal connections:
- ) Within frontal lobes itself
- ) With MTL (hippocampus, neocortical association areas, etc)
(With hippocampus via fornix)
What is the Dienecephalon
Dienecephalon = Thalamus + Hypothalamus
What does the hypothalamus contain? Hence?
- Mamillary bodies (In Papez Circuit)
- Impairment = loss of declarative memory (relational)
What does the thalamus contain
- ATN (Papez Circuit)
- Mammillo-thalamic tract (MMT): Connects ATN with hipocampus
- Medio Dorsal Nuclei (MDM) / Dorsal Medial Nuclei
- Internal Medullary Lamina (IML) / Midline
Which parts of leisons of thalamus most likely to cause memory loss
Anterior and Medial
- More likely
- Most connected to frontal lobes
- Anterior (part of Papez circuit)
- Medial
Posterior and Lateral
- Less likely
Damage of mammillo-thalamic tract (connects ATN to hippocampus) and ATN
Declarative (Relational memory)
Damage of Medio Dorsal Nucleus (MDN) and/or Internal Medullary Lamina (IML) damage; but spared mammillo-thalamtic tract (MTT)?
Specific retrieval difficulties
- Impaired Recall
- Preserved Recognition
- Top Down cannot recall, but can recall under prompt
Damage of Medio Dorsal Nucleus (MDN) and Intralaminar/Midline Nucleus?
Medio Dorsal Nucleus
- Deficits in selecting the appropriate information to be retrieved
- ‘Active retrieval’
Intralaminar/Midline
- Deficits seen in semantic memory, memory retrieval
Summary of leisions of the 3 areas
- 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
Biochemistry: What does learning require
Synaptic Plasticity
Biochemistry of synapses change to alter the effect on post-synaptic neuron
What is LTP
Long-term increase in excitability of a neuron (B) to a particular synaptic input caused by repeated high frequency activity of that input (A)
What is Hebb’s Law. What does it describe
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
Evidence for LTP
- Baseline EPSP measured for single electrical stimulus
- 100 electrical stimuli delivered rapidly
- Increased EPSP for subsequent single electrical stimulus
- LTP
Biochemically, how does LTP cause synaptic changes? Describe the changes at the level of the pre and post-synaptic
(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
Sites of LTP (Where it occurs)?
- ) Hippocampus (esp. dentate gryus + CA1), entorhinal cortex
- ) Others: Frontal Lobes, Thalamus, Amygdala, Visual Cortex
What are 3 other mechanisms of neural plasticity
- ) Long term depression
- ) Habituation
- ) Sensitization
How does Long Term Depression affect neural plasticity
Low frequency stimulation at synapse decrease synaptic strength
How does Habituation affect neural plasticity
Repeated stimulation reduces strength of synaptic response (Reduced NT release)
Note: Repeated but neutral
How does Sensitization affect neural plasticity
Single noxious stimulus causes exaggerated synaptic response to repeat presentation of noxious stimulus
