Hippocampus: Memory And Amnesia Flashcards
What is lambic
It is an anatomical term, not really a functional term
Limbic structures
Structures bordering the ventricular system and midline, including cingulate cortex, primary olfactory cortex, parahippocampal gyrus, amygdala, hippocampus, septum
Limbic system
Phrase commonly used to refer to lambic regions and related tracts, but often used incorrectly to suggest a single functional system or to include regions that are not limbic
Is the basal forebrain part of the limbic system
No
Limbic structures in the medial temporal lobe
Uncus
Parashippocampal gyrus
Isthmus of cingulate gyrus
Limbic structures in the subcortical medial temporal lobe
Amygdala, within uncus
Hippocampus (within PH gyrus)
How does the hippocampus sits _______ to inferior horn of the lateral ventricle
Medial and ventral
Amygdala sits ______ to hippocampus
Mostly rostral
Amygdala in relationship to the hippocampus
Amygdala extends caudally and just superior/dorsal to hippocampus
Entorhinal cortex
Tail of the seahorse
- parahippocampal gyrus
- subiculum
Hippocampus proper
- hippocampus
- dentate
What is the hippocampal complex derived from
Folding of cortex
What layers are the hippocampal complex made up of
- polymorphic layer
- pyramidal cell layer
- molecular layer
How do signals travels in the hippocampal complex
Cortex-entorhinal-dentate-hippocampus(CA2)-CA1-subiculum-cortex
Comes in through cortex and back out to different part of cortex
What is the tri synaptic circuit of the hippocampal complex
Takes info from the cortex and back out to the cortex.
Long term memory
What is the cellular/circuit basis of memory
Tri synaptic circuit of the hippocampal complex
Promotes long term memory of information for single sensory modality or can promote multi sensory memories
Tri synaptic circuit of the hippocampal complex
What does the hippcampal complex receive input from
Amygdala and sensory/association neocortex
Where does the hippocampal complex send projections to
Amygdala and sensory/association neocortex
What is the output to the fornix from the hippocampal complex
Hypothalamic nuclei of all kinds
- behavioral
- hormonal
- unconscious involuntary responses
Out put to fornix
Mediated hippocampal regulation of feeding, reproductive behavior, stress hormone release
Memory consolidation
- when first meeting a future friend, reciprocal connections between cortical regions processing faces and voices are initially very weak, unlikely to activate each other
- repeated meetings with friend repeatedly strengthens reciprocal connections. Hippocampus is required for this strengthening of synspases
- after memory consolidation, exposure to voice alone will re-activate memory of face without hippocampal participation
What is required for strengthen of synapses when repeatedly meeting a friend and becoming familiar with their face
Hippocampus
Hippocampus drives changes in wiring
After you have seen your friend so many times, what role does the hippocampus play in recognition of friend
None. After memory consolidation, exposure to voice alone will reactivate memory of face without hippocampal participation
Declarative long term memory
- Explicit=conscious/effortful
- faces, events
- hippocampus/cortex
Non declarative long term memory
-implicit=unconscious/automatic
Procedural non declarative long term memory
Skills/habits
- basal ganglia
- cerebellum
Associative learning non declarative long term memory
Conditioning
-cortex and amygdala sometimes
Examples of declarative memory
- who is US president
- what is your home address
- how did you get here for your appointment
- what did you do yesterday? On your last birthday
Skills that become second nature or motor habits
Procedural memory
Natural examples of procedural memory
- Tennis forehand/backhand volley
- driving manual transmission
- following a routine path through building
Lab tests for procedural memory
- read backwards text as if viewed in mirror; copy test backwards (does not require hippocampus)
- Mirror drawing
- tower of hanoi disk puzzle
Procedural memory tasks in the lab
Normal subjects show improved performance with training and long term memory (they retain good performance later)
Mirror drawing test
- tests procedural memory
- subject must trace between narrow lines
Tower of hanoi puzzle
Sequential moves of disks with a goal of re-stacking them in same order on a different peg
Medial temporal lobe removal of HM
- had extensive medial temporal lobe removed to help seizures
- immediate anterograde amnesia
- retrograde amnesia
- preserved general intelligence
- no changes in personality or motivation
Anterograde amnesia
Forgets everything after several minutes
- cant recognize family or anyone
- no recell or awareness of events more than several minutes ago
Declarative memory loss
Retrograde/anterograde amnesia
HM’s procedural memory
- was intact because you don’t need hippocampus for that
- during each days training, HM shows steady reduction in errors. Also when returning the next day to continue trading in, the Indian error rate is still low, indicating intact long term procedural memory, despite no episodic memory training
HM intact procedural memory and the tower of hanoi puzzle
HM has to move 31 discs instead of just 3, and reaches top score after just 2 days and still good at it one year later
First to study HM and gain insight into neural basis of declarative memory
Dr. Brenda Milner
-mentee Suzanne Corkin also helped
Is amygdala needed for memory
No
Lesions of only hippocampus vs lesions of amygdala
Lesions of only hippocampus Reproduce amnesic syndrome, whereas lesions only of amygdala do not proceed amnesia
What does amygdala do
Can enhance or impair declarative memory for information from emotionally charged events. Amygdala also mediates simpler forms of learning/memory
Concept of memory storage
Consensus is that storage and recall of information occurs in same region of cortex as original sensory processing. Recall of visual info occurs in visual cortex, auditory recall in auditory cortex, verbal recall in Wernicke’s speech comprehension area, etc
Concept of memory consolidation
Hippcampal function and connectivity with cortical areas is required to induce changes in cortex that allow for memory storage and retrieval. Later hippocampus is no longer needed to recall information: cortical regions can ref-activate each other without help from the hippocampus
What does hippocampus specialize in and is an exception to the rule for memory consolidation
Specializes in spatial information processing and is required for storage and retrieval f spatial information (navigating to parked car, to home, etc)
Lesion to hippocampus
Anterograde amnesia, retrograde amnesia
Sparing of oldest memories
What is the hippocampus required for
- new infor to be stored in cortex (lesion=anterograde amnesia)
- recent past info to be permanent stored in cortex (lesion=retrograde amnesia)
What is hippocampus NOT required for
Memory storage or recall for remotes (older) events (lesion=sparing of oldest memories)
