Clinically Relevant Functional Neuroanatomy

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The Three Amnesias
Russell M. Bauer, Ph.D. (DONT BELIEVE HIS LIES)
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Multiple Forms of Memory
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Core Features of Amnesia

• anterograde amnesia defect in new learning
• retrograde amnesia/remote memory disturbance
  defect in retrieving old memories
• spared memory abilities attention span,
  psychometric intelligence, and nondeclarative
  forms of memory are generally spared

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The Human Amnesic Syndrome

• Impaired new learning (anterograde amnesia),
  exacerbated by increasing retention delay
• Impaired recollection of events learned prior to
  onset of amnesia (retrograde amnesia), often in
  temporally graded fashion
• Not limited to one sensory modality or type of
  material
• Normal IQ, attention span, nondeclarative forms
  of memory

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Clinically Relevant Dimensions of Human Memory
Performance

• Immediate-recent-remote
• Encoding-storage-retrieval
• Material, modality specificity
• Tests vs. processes

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Encoding

• Definition process of transforming to-be
  remembered in formation into memorable and
  retrievable form
• Encoding I bringing information-processing
  capacity to bear on stimuli
• Encoding II ability to use the results of E-1
  mnemonically
• Relevance levels-of-processing accounts of
  memory (memory as by-product of information
  processing)
• Clinical manifestation poor immediate
  (superspan) recall

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Consolidation/Storage

• definition process of making new memories
  permanent
• basis anatomic and physiological changes at
  cellular level hippocampal system important
• when? during study-test interval
• duration hours? days? years?
• clinical symptom delayed memory ltlt immediate
  memory (forgetting)

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Retrieval

• definition process of locating, selecting, and
  activating a memory representation
• basis re-enactment of pattern of excitation
  occurring at encoding
• when? at point of test
• clinical symptom recall ltlt recognition (also
  true of shallow encoding), inconsistent errors

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Medial Temporal Syndromes

• Anoxic-hypoxic syndromes
• cardiac arrest
• CO poisoning
• Amnesia associated with ECT
• CNS Infections (Herpes)
• MTS and complex-partial epilepsy
  (material-specific)
• Early AD

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Temporal Lobe Pathology Associated with Herpes
Simplex Encephalitis
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The Case of Henry M (H.M.)
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Bauer, Grande, Valenstein, 2003
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Integrated Circuitry Linking Temporal,
Diencephalic, and Basal Forebrain Regions
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Two Limbic Circuits
Anterior Thalamus
Dorsomedial Thalamus
Mamillothalamic Tract
Mammilary Bodies
Cingulate Gyrus
Orbitofrontal
Amygdalofugal pathways
Fornix
Uncus
Hippocampus
Amygdala
Lateral
Medial (Papez)
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CA3
CA1
DG
subic
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Bauer, Grande, Valenstein, 2003
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Delayed Nonmatching to Sample
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Delayed Nonmatching to Sample, multiple trials,
trial-unique objects
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6-8 weeks postsurgery
2 years postsurgery
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Zola-Morgan Squire, 1990
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Bauer, Grande, Valenstein, 2003
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Zola-Morgan Squire, 1990
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Two Limbic Circuits and the Two-system theory of
amnesia
Anterior Thalamus
Dorsomedial Thalamus
Mamillothalamic Tract
Mammilary Bodies
Cingulate Gyrus
Orbitofrontal
Amygdalofugal pathways
Fornix
Uncus
Hippocampus
Amygdala
PRPH
Lateral
Medial (Papez)
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Diencephalic Syndromes

• Korsakoff Syndrome associated with ETOH abuse or
  malabsorption
• prominent encoding deficits
• role of frontal pathology
• Vascular disease
• Thalamic trauma

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Mamillary Body Lesions in a case of Korsakoffs
Disease
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Lesion Profile in a Case of Thalamic Amnesia
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Graff-Radford, et al, 1990
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Two Limbic Circuits and the Two-system theory of
amnesia
Anterior Thalamus
Dorsomedial Thalamus
Mamillothalamic Tract
Mammilary Bodies
Cingulate Gyrus
Orbitofrontal
Amygdalofugal pathways
Fornix
Uncus
Hippocampus
Amygdala
Lateral
Medial (Papez)
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Two Potential Lesion Scenarios in Diencephalic
Amnesia
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Basal Forebrain Syndromes

• Anterior Communicating Artery (ACoA) infarctions
• prominent anterograde, variable retrograde
  amnesia
• prominent confabulation
• frontal extension of lesions
• Basal forebrain and cholinergic projections to
  hippocampus

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Basal Forebrain Anatomy
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Two Limbic Circuits
Anterior Thalamus
Dorsomedial Thalamus
Mamillothalamic Tract
Mammilary Bodies
Cingulate Gyrus
Orbitofrontal
Amygdalofugal pathways
Fornix
Uncus
Hippocampus
Amygdala
Lateral
Medial (Papez)
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Two Potential Lesion Scenarios in Basal Forebrain
Amnesia
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Two Limbic Circuits
Anterior Thalamus
Dorsomedial Thalamus
Mamillothalamic Tract
Mammilary Bodies
Cingulate Gyrus
Orbitofrontal
Amygdalofugal pathways
Fornix
Uncus
Hippocampus
Amygdala
Lateral
Medial (Papez)
Bauer, Grande, Valenstein, 2003
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Key Points

• Extended memory system including hippocampus,
  amygdala, and basal forebrain
• We (basically) understand anatomy, now we need to
  understand computation
• Notion of distinct subtypes of amnesia generally
  less favorable now than 10 years ago
• Certain structures are wired for associational
  processing these structures are reciprocally
  connected to cortical processors