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For our biological foundations of memory class I prepared a 15 minute talk to present some of the symptoms, as well as neurological and cognitive manifestations of Alzheimers disease. I conclude by evaluating ERP work in Alzheimer's patients to further research on memory encoding and old/new effects.
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Memory Deficits in
Alzheimer's Disease
Image: http://www.caregivingclub.com/wp-content/uploads/2012/11/Memory-Loss-dreamstime_m_15669472-2.jpg
Consumer Reports Best Buy Drugs (2012)
Alzheimers Disease Symptoms
• Earliest symptom = episodic
• Encoding new information (Delis et al, 1991)
• Delayed Recall Effects (Think Old/New effects) (Welsh et al, 1991)
• Mild Cognitive Impairment (MCI)
• Atrophy of relevant brain areas
– Responsible for consolidation and retrieval
– Mesial Temporal Regions
Image: http://arealmummydiary.files.wordpress.com/2013/08/image-3.jpg
Preclinical SymptomsSmall, Herlitz and Bäckman, 2004
• Episodic Memory Deficits
– General in Nature
• I.e. Both verbal and non verbal materials
• Across Retention Interval
• Across conditions (i.e. cued/free recall, recognition)
• Mediated by Cognitive Support
Image: http://arealmummydiary.files.wordpress.com/2013/08/image-3.jpg
Cognitive Support
• Recognition tasks have the most cognitive support
• Small et al, 1997 (See Small, Herlitz and Bäckman, 2004)
– Tested memory tasks to see which predicted onset of AD
• Significant effects in:recall of unlimited words
• Recall of organisable words
• Word and face recognition After multivariate analysis, only these two were significant predictors of a diagnosis.
Unsupported
Supported
Deficits typical of ageing
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Old/New Effects
• Study context defined as ‘source’
• In healthy participants, trials may be contaminated by other recollective experiences
• However: AD begins with impaired recollection
Familiarity - NEW Recollection – OLD
Recognition without retrieval of ‘study context’ (source)
Recognition including recall of ‘study context’
Hypothesis Rationale(Tendolkar et al, 1999)
• Measured ability to recognise previously studied words and
recollect study context
• If AD patients cannot recollect contextual information, ERP
old/new effect should be less contaminated by recollective
processes than in healthy subjects.
• Therefore: ERP readings should be more purely related
to familiarity.
Methods: Study Phase
• 10 Study phases of 10 words
• 500ms duration (5.5s interval)
• Participants instructed to memorise word and presentation colour
BOOK WINDOW
Methods: Test Phase
• 50% of words OLD; 50% of words NEW
• Participants asked to respond if they had seen the word prior
• For words judged ‘old’, participants then asked to name the presentation colour
HOUSE BOOK
Results
AD Patients Controls
Impairment to recollect study context
Sustained old/new effect
Correctly recognised ‘old’ words more positive only between 300-500ms
Peaks over frontal scalp Left temporo-parietal and frontal sides
The ERP’sFAMILLIARITY = NEWRECOLLECTION = OLD
Frontal peaks should give a more pure version of familliarity…But do they?
The OLD’s in Alzheimers are wherein they have defied the nature of their illness.
(Tendolkar et al, 1999)
And Therefore..?
• Hippocampal atrophy to blame for lack of temporoparietal old/new effect?
• Symptoms typical of AD
• But… why could patients with AD still encode some things with a flat-line ERP during the encoding of OLD items?
What does the competition say?
• Debate as to whether semantic and episodic memories are tightly related (Tulving) or dissociated (Hodges & Graham)
• An episode cannot be recounted first without going through semantic memory (Tulving, 1995; Tulving & Markowitsch, 1998)
See Overman and Becker (2004)
Discussion
• Is this a ‘process based dissociation’
– What is a process based dissociation?
– What aboutthis model from Tulving that suggests it isconnected?
References
Consumer Reports Best Buy Drugs. (2012). Evaluating Prescription Drugs to Treat: Alzheimer’s
Disease. Retrieved from http://www.consumerreports.org/health/resources/pdf/best-buy-
drugs/AlzheimersFINAL.pdf
Keller, S. S., Mackay, C. E., Barrick, T. R., Wieshmann, U. C., Howard, M. A., & Roberts, N. (2002).
Voxel-based morphometric comparison of hippocampal and extrahippocampal
abnormalities in patients with left and right hippocampal atrophy. Neuroimage, 16(1), 23-
31.
Overman, A. A., & Becker, J. T. (2004). Information Processing Deficits in Episodic Memory in
Alzheimer’s Disease. In R. Morris, J. Becker (Eds.), Cognitive Neuropsychology of Alzheimer’s
Disease (pp. 120-140). New York: Oxford University Press Inc.
Small, B. J., Herlitz, A., & Bäckman, L. (2004). Preclinical Alzheimer’s Disease: Cognitive and
Memory Functioning. In R. Morris, J. Becker (Eds.), Cognitive Neuropsychology of
Alzheimer’s Disease (pp. 120-140). New York: Oxford University Press Inc.