W6L1 - HM and Temporal Lobes Flashcards
1.) Understanding the contribution of HM 2.) Understanding the neuroanatomy of the temporal lobe memory system 3.) Understanding the function of the temporal lobe memory system
What does HM have initially
Severe epilepsy
What are epilepsy seizures caused by? What is the biochemistry behind it?
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
- Inhibitory: GABA
Definition of Temporal Lobe Epilepsy (TLE)
Recurrent unprovoked seizures originating from medial or lateral temporal lobe
What are the types of seizures caused by TLE
- Simple partial seizures
- Without loss of awareness
- Complex partial seizures
- With loss of awareness
What is the most common pathphysiology of TLE. Onset and Phyisology?
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
What happens to seizures when a leisoned hippocampus is surgically removed
Surgical removal of hippocampus cures or reduce seizures
How many gyri and sulci of the Temporal Lobe
Gyrus
- Superior Temporal Gyrus
- Middle Temporal Gyrus
- Inferior Temporal Gyrus
Sulcus
- Superior Temporal Sulcus
- Inferior Temporal Sulcus
Where is the hippocampus located
Within parahippocampal gyrus, which is at the MTL
What is the parahippocampal gyrus posterior to
- Anterior
- Perihinal
- Middle
- Entorhinal (Links to hippocampal formation)
- Posterior
- Parahippocampal Cortex
What did HM undergo. Which parts of his brain was removed
- Bilateral resection of extensive amount of medial temporal tissue
- Amygdala, Hippocampi, part of parahippocampal gyrus
What did HM retain after surgery
Retained
- Normal attention span
- Normal Intelligence
- Retrograde memory recovered over time
- Procedural memory
What is the difference between retrograde amnesia and anterograde amnesia
- Retrograde: Impairment for memory PRIOR to injury
- Anterograde: Impairment for memory AFTER injury
What condition did HM have after surgery
Severe antereograde amnesia
- Particularly declarative memory
What is the difference between declarative and procedural memory
- Declarative
- Conscious access to information learnt previously
- Procedural
- “Muscle Memory”/”How To” (e.g., playing piano)
DId HM lose declarative/procedural memory. How do we know?
- Declarative
- Severely impaired
- Could not remember home
- (but) Remember that his mother died
- Severely impaired
- Procedural
- Retained
- Able to learn new skills and normal performance on procedural memory task (star)
- Retained
What did HM tell us about memory?
What did he NOT teach us?
- 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
Anatomy of Memory: What have we learnt since HM. What is functional asymmetry?
- 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
- Material-specific deficits
What is the hippocampus also known as
Cornu Ammonis (Ammon’s horn): CA1 to CA3
What is the Hippocampal formation?
Hippocampus (CA3 - CA1) and related parts
- Dentate Gyrus
- CA3 - CA1
- Subiculum
What is the schematic representation and processes of the MTL
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
What is the role of Hippocampal Formation and what are the 2 theories on its role
Hippocampal formation and surrounding structures:
- Learning and consolidating novel information
- Particularly for relational memory tasks
- ) Consolidation Theory: Squire
* After a period of consolidation, information can be retrieved INDEPENDENTLY of hippocampal formation involvement - ) Multiple Trace Theory (MTT): Mosocvitch
* Retrieval of episodic experiences ALWAYS INVOLVE hippocampal formation
What are paired association learning task. What is the brain structure required to do this task?
Remember an association between arbitrary (unrelated) pieces of information
Hippocampal formation
