The Three Amnesias Russell M Bauer Ph D

The Three Amnesias Russell M. Bauer, Ph. D. (DON’T BELIEVE H IS LIES)

Multiple Forms of Memory

“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

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

Clinically Relevant Dimensions of Human Memory Performance Immediate-recent-remote Encoding-storage-retrieval Material, modality specificity Tests vs. processes

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

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 << immediate memory (forgetting)

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 << recognition (also true of shallow encoding), inconsistent errors

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

Temporal Lobe Pathology Associated with Herpes Simplex Encephalitis

The Case of Henry M (H. M. )

Bauer, Grande, & Valenstein, 2003

Integrated Circuitry Linking Temporal, Diencephalic, and Basal Forebrain Regions

Two Limbic Circuits Anterior Thalamus Cingulate Gyrus Dorsomedial Thalamus Mamillothalamic Tract Mammilary Bodies Fornix Hippocampus Medial (Papez) Orbitofrontal Amygdalofugal pathways Uncus Amygdala Lateral

CA 3 CA 1 DG subic

Delayed Nonmatching to Sample

Delayed Nonmatching to Sample, multiple trials, trial-unique objects

6 -8 weeks postsurgery 2 years postsurgery

Zola-Morgan & Squire, 1990

Bauer, Grande, & Valenstein, 2003

Zola-Morgan & Squire, 1990

Two Limbic Circuits and the Two-system theory of amnesia Anterior Thalamus Cingulate Gyrus Dorsomedial Thalamus Mamillothalamic Tract Mammilary Bodies Orbitofrontal Amygdalofugal pathways Fornix Uncus Hippocampus Amygdala PRPH Medial (Papez) Lateral

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

Mamillary Body Lesions in a case of Korsakoff’s Disease

Graff-Radford, et al, 1990

Two Limbic Circuits and the Two-system theory of amnesia Anterior Thalamus Cingulate Gyrus Dorsomedial Thalamus Mamillothalamic Tract Mammilary Bodies Fornix Hippocampus Medial (Papez) Orbitofrontal Amygdalofugal pathways Uncus Amygdala Lateral

Two Potential Lesion Scenarios in Diencephalic Amnesia

Basal Forebrain Syndromes • Anterior Communicating Artery (ACo. A) infarctions – prominent anterograde, variable retrograde amnesia – prominent confabulation – frontal extension of lesions • Basal forebrain and cholinergic projections to hippocampus

Basal Forebrain Anatomy

Two Limbic Circuits Anterior Thalamus Cingulate Gyrus Dorsomedial Thalamus Mamillothalamic Tract Mammilary Bodies Fornix Hippocampus Medial (Papez) Orbitofrontal Amygdalofugal pathways Uncus Amygdala Lateral

Two Potential Lesion Scenarios in Basal Forebrain Amnesia

Two Limbic Circuits Anterior Thalamus Cingulate Gyrus Dorsomedial Thalamus Mamillothalamic Tract Mammilary Bodies Fornix Hippocampus Medial (Papez) Orbitofrontal Amygdalofugal pathways Uncus Amygdala Lateral Bauer, Grande, & Valenstein, 2003

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