Neuropsychology of Amnesia PowerPoint Presentation

Slide 1 -

Neuropsychology of amnesia Lecture (Chapter 9) Jaap Murre murre@psy.uva.nl

Slide 2 -

In this lecture We will review basic aspects of amnesia We will try to locate memory in the brain and relate brain lesions to amnesia We will make a start with dementia, looking at progressive semantic dementia

Slide 3 -

Before we embark on our study of amnesia What types of memory are there? If amnesia is a form of memory loss, what is forgetting?

Slide 4 -

Forms of memory: Larry Squire’s memory taxonomy

Slide 5 -

Forgetting There is currently no theory that explains why we forget Forgetting seems to follow rather strict rules, but even these have not been fully explored It is postulated that very well rehearsed knowledge will never be forgotten (Harry Barrick’s ‘permastore’)

Slide 6 -

Before looking at the anatomy and clinical aspects of amnesia We will review a connectionist model of amnesia It will not be necessary to review the technical aspects of this model The model may help you to get an overall idea of what amnesia is

Slide 7 -

We will focus on some important characteristics Anterograde amnesia (AA) Implicit memory preserved Retrograde amnesia (RA) Ribot gradients Pattern of correlations between AA and RA No perfect correlation between AA and RA

Slide 8 -

The French neurologist Ribot discovered more than 100 years ago that in retrograde amnesia one tends to loose recent memoriesMemory loss gradients in RA are called Ribot gradients

Slide 9 -

x retrograde amnesia anterograde amnesia lesion present past Normal forgetting

Slide 10 -

An example of retrograde amnesia patient data Kopelman (1989) News events test

Slide 11 -

Neuroanatomy of amnesia Hippocampus Adjacent areas such as entorhinal cortex and parahippocampal cortex Basal forebrain nuclei Diencephalon

Slide 12 -

The TraceLink model is an abstraction of these areas Link system (hippocampus) Trace system (neocortex) Modulatory system (basal forbrain)

Slide 13 -

The position of the hippocampus in the brain

Slide 14 -

There are two hippocampi in the brain!

Slide 15 -

Parahippocampal gyrus and other structures

Slide 16 -

Connections to and from the hippocampus

Slide 17 -

Anatomy of the hippocampus

Slide 18 -

ppt slide no 18 content not found

Slide 19 -

Connectivity within the hippocampus

Slide 20 -

Hippocampus has an excellent overview of the entire cortex

Slide 21 -

Diencephalon: dorsomedial nucleus and the mammillary bodies

Slide 22 -

Connectionist modelling Based on an abstraction of the brain Many simple processors (‘neurons’) Exchange of simple signals over connections (‘axons and dendrites’) Strength (‘synapse’) of the connections determines functioning of the network Such neural networks can be taught a certain range of behaviors

Slide 23 -

Example of a simple heteroassociative memory of the Willshaw type 1 1 0 1 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 0 1 0 1 0 0 0 1 0 1 1 0 0 1 0 1 1 1 0 0 1 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

Slide 24 -

Example of pattern retrieval 1 1 1 1 1 1 1 1 1 0 0 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 3 2 2 3 3 2 1 0 0 1 1 0 Sum = 3 Div by 3 = (1 0 0 1 1 0)

Slide 25 -

Example of successful pattern completion using a subpattern 1 1 1 1 1 1 1 1 1 0 0 1 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 1 1 2 2 1 1 0 0 1 1 0 Sum = 2 Div by 2 = (1 0 0 1 1 0) 1

Slide 26 -

Example graceful degradation: small lesions have small effects 1 1 1 1 1 1 1 1 1 0 0 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 3 2 1 2 3 1 1 0 0 0 1 0 Sum = 3 Div by 3 = (1 0 0 1 1 0)

Slide 27 -

Trace-Link model: structure

Slide 28 -

System 1: Trace system Function: Substrate for bulk storage of memories, ‘association machine’ Corresponds roughly to neocortex

Slide 29 -

System 2: Link system Function: Initial ‘scaffold’ for episodes Corresponds roughly to hippocampus and certain temporal and perhaps frontal areas

Slide 30 -

System 3: Modulatory system Function: Control of plasticity Involves at least parts of the hippocampus, amygdala, fornix, and certain nuclei in the basal forebrain and in the brain stem

Slide 31 -

Stages in episodic learning

Slide 32 -

Retrograde amnesia Primary cause: loss of links Ribot gradients Shrinkage

Slide 33 -

Anterograde amnesia Primary cause: loss of modulatory system Secondary cause: loss of links Preserved implicit memory

Slide 34 -

Semantic dementia The term was adopted recently to describe a new form of dementia, notably by Julie Snowden et al. (1989, 1994) and by John Hodges et al. (1992, 1994) Semantic dementia is almost a mirror-image of amnesia

Slide 35 -

Neuropsychology of semantic dementia Progressive loss of semantic knowledge Word-finding problems Comprehension difficulties No problems with new learning Lesions mainly located in the infero-lateral temporal cortex but (early in the disease) with sparing of the hippocampus

Slide 36 -

Semantic dementia in TraceLink Primary cause: loss of trace-trace connections Stage-3 (and 4) memories cannot be formed: no consolidation The preservation of new memories will be dependent on constant rehearsal

Slide 37 -

Severe loss of trace connections Stage-2 learning proceeds as normal Stage 3 learning strongly impaired Non-rehearsed memories will be lost No consolidation in semantic dementia

Slide 38 -

Clinical presentation of amnesia Age Degenerative disorders Vascular disease Anoxia Korsakoff (vitamin B deficiency)

Slide 39 -

Clinical presentation of amnesia (con’d) Focal brain damage Closed-head injury Transient global amnesia (TGA) Electroconvulsive therapy Psychogenic (functional) amnesia

Slide 40 -

Rehabilitation of amnesia There is no known treatment Compensation will, thus, help the patient best: ‘memory book’ electronic agenda Errorless learning is pioneered by Alan Baddeley and Barbara Wilson

Slide 41 -

Comments on the chapter Very few people now believe that the amygdala plays a role in episodic memory Most neurologists now accept the existence of focal retrograde amnesia (Kapur, 1993) Animal studies (rats, primates) show clear evidence of Ribot gradients in the range 30 to 100 days

Slide 42 -

Next lecture Implicit memory Dementia