Clinically Relevant Functional Neuroanatomy

2: Neuroanatomy of Memory

Russell M. Bauer, Ph.D.University of Florida, USA

Vivian Smith Summer Institute

23 June, 2006

The Three Amnesias

Russell M. Bauer, Ph.D. (DON’T BELIEVE HIS LIES)

Multiple Forms of MemoryMultiple Forms of Memory

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

Integrated Circuitry Linking Temporal, Diencephalic, and Basal Forebrain Regions

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

Hippocampus

Mammilary Bodies

Anterior Thalamus

Cingulate Gyrus

Fornix

Mamillothalamic Tract

Amygdala

Dorsomedial Thalamus

Orbitofrontal

Uncus

Two Limbic Circuits

Medial (Papez) Lateral

Amygdalofugal pathways

DG

CA3CA1

subic

Bauer, Grande, & Valenstein, 2003

Delayed Nonmatching to Sample

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

6-8 weeks postsurgery 2 years postsurgery

Zola-Morgan & Squire, 1990

Anterior Posterior

Bauer, Grande, & Valenstein, 2003

Zola-Morgan & Squire, 1990

Murray & Richmond, Curr Opin Neurobiol, 2001

-perirhinal cortex obviously important in memory, but also apparently important in fine-grained visual discrimination

Hippocampus

Mammillary Bodies

Anterior Thalamus

Cingulate Gyrus

Fornix

Mamillothalamic Tract

Amygdala

Dorsomedial Thalamus

Orbitofrontal

Uncus

Two Limbic Circuits and the Two-system theory of amnesia

Medial (Papez) Lateral

Amygdalofugal pathways

PRPH

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

Lesion Profile in a Case of Thalamic Amnesia

Graff-Radford, et al, 1990

Hippocampus

Mammillary Bodies

Anterior Thalamus

Cingulate Gyrus

Fornix

Mamillothalamic Tract

Amygdala

Dorsomedial Thalamus

Orbitofrontal

Uncus

Two Limbic Circuits and theTwo-system theory of amnesia

Medial (Papez) Lateral

Amygdalofugal pathways

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

Hippocampus

Mammillary Bodies

Anterior Thalamus

Cingulate Gyrus

Fornix

Mamillothalamic Tract

Amygdala

Dorsomedial Thalamus

Orbitofrontal

Uncus

Two Limbic Circuits

Medial (Papez) Lateral

Amygdalofugal pathways

Hippocampus

Mammillary Bodies

Anterior Thalamus

Cingulate Gyrus

Fornix

Mamillothalamic Tract

Amygdala

Dorsomedial Thalamus

Orbitofrontal

Uncus

Two Limbic Circuits

Medial (Papez) Lateral

Amygdalofugal pathways

Bauer, Grande, & Valenstein, 2003

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

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