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
Regulates emotional expression & experience
What is the role of the Amygdala in memory. Some examples
Emotionally arousing experiences (Joy? Fear?)
– Classical fear conditioning
Leision of Amygdala in Memory
- Loss of conditioned fear and impairment of new
fear learning - Reduced memory for emotionally laden events
What is the role of the Papez Circuit in memory.
Declarative Memory
What are the parts of Papez Circuit (in order)
1) Hippocampus >
2) Fornix >
3) Mamillary Body (part of Dienecephalon Hypothalamus ) >
4) Anterior Thalamus Nuclei (part of Dienecephalon Thalamus) > Cingulate Gyrus
Closed Circuit
Leision of Papez Circuit in Memory
Declarative memory impairment (esp. poor relational
memory/encoding)
Where is leision of Papez Circuit most servere
When hippocampus or Anteior Thalamus Nuclei (ATN) are lesioned
What is the role of the Frontal Lobes in memory.
- Developing and implementing strategies for appropriate memory ENCODING and RETRIEVAL
Leision of Frontal Lobes in Memory
1.) Impairment in developing and implementing strategies for appropriate memory
ENCODING and RETRIEVAL
2.) Impairment in remembering contextual details e.g.
source of information, chronological order of
memories (DLPF)
3.) Confabulation – production of statements involving
bizarre distortions of memory
What does the Frontal Lobe contain
Posterior Frontal Lobe: Motor Cortex (Motor & Premotor)
Anterior Frontal Lobe: Cognitive Control Processes (PFC)
Where are the rich connections in frontal lobes connected to
Rich reciprocal connections:
- ) Within frontal lobes itself (DLPFC, AFPC, VLPFC, MPFC)
- ) With MTL (hippocampus, neocortical association areas, etc)
What is the Dienecephalon
Dienecephalon = Thalamus + Hypothalamus
What does the hypothalamus contain. And hence?
Mamillary bodies (Also in Papez Circuit)
Hence, impairment = loss of declarative memory (esp. relational)
What does the thalamus contain.
ATN (Papez Circuit)
Medio Dorsal Nuclei (MDM)
Internal Medullary Lamina (IML)
Which parts of leisons of thalamus most likely to cause memory loss
Anterior and Medial more likely. Posterior & Lateral less likely
Damage of mammillo-thalamic tract (connects anterior thalamus to hippocampus)
Amnesic Type - Relational memory
Damage of Medio Dorsal Nucleus (MDN) and/or Internal Medullary Lamina (IML) damage; spared mammillo-thalamtic tract (MTT)
Specific retrieval difficulties (preserved recognition) - Top Down cannot recall, but given prompt can.
Damage of Medio Dorsal Nucleus (MDN)
Deficits in selecting the appropriate information to be retrieved – ‘Active retrieval’
Damage of Intralaminar/Midline
Deficits also in selecting appropriate information, but more so seen in semantic memory
Summary of leisions of the 3 areas
1.) Papez’s circuit lesion => impaired relational
memory/encoding (hippocampal type of amnesia)
- ) 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
What is 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 to a particular synaptic input caused by repeated high
frequency activity of that input
What is Hebb’s Law
When an axon of cell A…excites cell B by repeatedly firing it, change takes place in 1/both cells to increase A’s efficiency
Evidence for LTP
1.) Baseline EPSP measured for single electrical stimulus
2.) 100 electrical stimuli delivered rapidly
3.) Increased EPSP for subsequent single
electrical stimulus (LTP)
Biochemically, how does LTP cause synaptic changes?
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
Where does synaptic change occur
- ) Hippocampal Formation: 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 via. reduced NT release
How does Sensitization affect neural plasticity
Single noxious stimulus causes exaggerated synaptic response to repeat presentation of noxious stimulus
