• memory of how to do things and/or associations made with particular events, ideas, actions, etc.
• Think skills and habits like riding a bike or emotional responses (coordinated by the cerebellum)
• Involves neocortex, striatum, amygdala, cerebellum, and reflexive pathways

• memories of facts and events
• think about facts like 1st US president or remembering your mom's birthday and associated events
• Relies on the medial temporal lobe (hippocampus)

Henry Molaison

• A patient case study that has led us to much of what we know about the hippocampus and memory
• Received bilateral hippocampectomy in order to suppress seizures (a procedure that is no longer done on patients)
• Following procedure, experienced complete anterograde amnesia as well as extensive retrograde amnesia.
• This procedure only affected declarative memory (he could still memorize new motor programs)
• Showed that hippocampus did not serve purpose in memory retrieval or storage
• Serves purpose in making new memories (declarative)

• an inability to form new memories; a symptom experienced by H.M. following his surgery

• an inability to recall previously-made memories
• H.M. experienced this as he could only recall memories a certain time prior to his surgery

• hippocampus is located medial to this structure
• temporal lobe is bilateral structure located lateral to diencephalic structures
• 2 lateral ventricles (one for each side of brain) surrounding diencephalon

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located ventral to the hippocampus

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• located medially to the temporal horn of the lateral ventricle
• has a main purpose in formation of new declarative memories as evidenced by bilateral lesion in H.M.
• Also known as "Ammon's Horn" (cornu Ammonis); contains regions C1-C4 (C4 considered part of dentate gyrus)

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• otherwise known as just dentate
• curved layers of hippocampal tissue that contain granule cells/cortex
• Takes form of "C" shape facing in towards C4

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• cortex that projects to entorhinal cortex
• projects information from association cortices of temporal, parietal, and frontal lobes to the entorhinal cortex and vice versa

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• similar to parahippocampal cortex in its purpose
• projects to entorhinal cortex 
• sends information from association cortices (temporal, parietal, frontal) to the entorhinal cortex and vice versa

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• cortical region between entorhinal cortex and CA1 of hippocampus

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• cortical area between subiculum and parahippocampal and perirhinal cortices

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• separates subiculum from the dentate

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1. hippocampus located between dentate and subiculum
2. as temporal cortex expands, hippocampus curls and folds in on itself creating C shape
3. Dentate pulls away from hippocampus and curves around C4 in C shape that conforms to edge of C4

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• layers of dentate and hippocampus are phylogenetically older than neocortex (3 vs. 6 layers)
• Molecular layer - apical dendrites of pyramidal cells
• Pyramidal layer - cell bodies of pyramidal cells
• Polymorphic layer - axons and basilar dendrites of pyramidal cells

• similar to hippocampus in having 3 layers and being phylogenetically older than neocortex
• molecular layer - apical dendrites of granule cells
• granule cell layer - cell bodies of granule cells
• polymorphic layer - axons and basilar dendrites of granule cells 

• main excitatory neurons in the hippocampus (CA1-CA4)
• Glutaminergic

• excitatory neuron in dentate
• glutaminergic

• Various types of GABAergic neurons in the hippocampus and dentate

• projections from cortical association areas of parietal, temporal, and frontal lobes project to the parahippocampal and perirhinal cortices
• parahippocampal and perirhinal cortices project to entorhinal cortex through two different pathways
• Entorhinal cortex projects to
  • dentate gyrus through pyramidal cells
  • hippocampus through neuromodulatory cholinergic and monoaminergic (DA,NE,5-HT) cells
• PH+PR→ER→DG+H

• perforant, mossy fiber, and schaffer collateral pathway

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• Pyramidal cells of the Entorhinal Cortex (cell bodies in EC pyramidal cell layer)
• Axons (in the polymorphic layer) project to the dentate gyrus
• Go through the hippocampal sulcus (perforate)

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• dentate granule cells (granule cell layer) projects to CA3 pyramidal cells (axons in polymorphic layer)
• axons appear mossy

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• Pyramidal cells in CA3 (Pyramidal Cell layer) project to CA1 pyramidal cells (axons in polymorphic layer, bodies in pyramidal cell layer)

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1. Association cortices of temporal, parietal, and frontal lobes project to parahippocampal and perirhinal cortices
2. Parahippocampal and perirhinal cortices project to entorhinal cortex
3. Entorhinal cortex sends excitatory projections to dentate gyrus through pyramidal cells (Perforant)
   • hippocampus also receives cholinergic and monoaminergic neuromodulatory input
4. Dentate gyrus sends excitatory projections to CA3 through granule cells (Mossy Fiber)
5. CA3 sends excitatory projections to CA1 (Schaffer Collaterals)
6. CA1 pyramidal cells send projections to subiculum
7. Subiculum pyramidal cells send projections to entorhinal cortex

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• Hippocampal information related to association cortex inputs follows the same pathways back through the parahippocampal and perirhinal cortices to the association cortices
• CA1 and subiculum pyramidal neurons → forebrain and diencephalic structures
• CA3 pyramidal neurons→contralateral hippocampus
• Involves Alveus, fimbria, fornix, and hippocampal commissure

• Alveus

• CA3 → hippocampal commissure through fimbria/fornix → contralateral hippocampus
• CA1 and subiculum → alveus → fimbria → fornix → forebrain and diencephalon
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• Decline in mental ability that is severe enough to interfere with daily life; can be associated with hippocampal problems
• Alzheimer's Disease share symptoms with dementia

• common, chronic, progressive degenerative disorder that causes problems with memory and other symptoms of dementia
• Foreshadowed by MCI ("mild cognitive impairment")
• Gross brain deterioration
• Amyloid Plaques
• Neurofibrillary tangles (NTFs)

• difficulty performing more than one task at a time, problem-solving deficits, trouble remembering recent conversations or events
• this is an early indicator of alzheimer's but is also prevalent in natural aging

• Alzheimer's patients experience significant neuron loss resulting in slow loss of cognitive and eventually vital processes
• Results in noticeable brain shrinkage
• Primary sensory cortices are the last to go as even most late stage Alzheimer's patients are able to smell/taste/touch 

• β-amyloid(A-β) is normal protein in brain usually broken down to harmless metabolites
• In Alzheimer's patients, these β-amyloid proteins coalesce into large plaques which can be found between neurons in the brain and around blood vessels