How do some older individuals with Amyloid Plaques maintain normal cognition? Nature Neuroscience.Sept14.2014

16.09.2014

Accumulation of Amyloid B peptide is considered as an early event in Alzheimer’s disease.(AD). It is intriguing that some older people with extensive deposits of these peptides do not go on to have AD. fMRI studies show that they may have increased neural activity during cognitive activity than young people or older people without plaques. Is this increased activity beneficial ?

Jeremy A Elman and team of researchers at University of California adopted an f MRI task to look at the relationship between fMRI activation and amount of memory detail for an encoded stimulus.

22 healthy young adults and 59 older people with normal cognition participated in this study. 33 of the older adults had no brain A Beta peptide and 16 had these deposits. Subjects then studied pictures of scenes (under fMRI) and after 15 minutes they were tested for ‘gist memory’ ( i.e. the central meaning of the scene). They viewed written descriptions of scenes and had to state whether these descriptions matched the scenes previously seen. Memory richness was tested by asking true false questions about the scenes.Brain activations during encoding for items subsequently remembered during the gist task (hits) were assessed.

Results: Young people showed greater increases in activity with more details remembered within task-positive areas. Old individuals without plaques demonstrated relatively little modulation in task-positive regions, they showed greater deactivation with more recalled details in the task-negative network, as compared to young subjects. Old subjects with plaques showed stronger parametric effects than those without in parietal and occipital cortex, particularly in the right hemisphere. They showed reduced deactivation in task-negative regions, but increased activation in task-positive regions related to more detailed memory encoding.  

Conclusion: Authors conclude that increased neural activity in those with brain Aβ is a beneficial process that reflects neural plasticity and is a compensatory function. It is also thought that these compensatory mechanisms could eventually fail.

Comments: If we could further understand how these compensatory mechanisms work, opportunities may arise to prolong or augment them.

Summary of the article:

Neural compensation in older people with brain amyloid-β deposition.

Elman JA, Oh H, Madison CM, Baker SL, Vogel JW, Marks SM, Crowley S, O’Neil JP, Jagust WJ.

Nat Neurosci. 2014 Sep 14. doi: 10.1038/nn.3806. [Epub ahead of print]

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