Article 3: The cognitive neuroscience of ageing (Grady) Flashcards
intro
- Old problems with episodic memory, working memory, attention, task switching, more prone to distraction, slower processing speed
- Maintained with age: semantic memory, emotional regulation etc
- fMRI: age related differences in brain activities
- reasons for increased brain activity with age might be: compensation, lack of efficiency, dedifferentiation
- change in brain structure/neurotransmitters?
- Undetected illness?
- BOLD
Compensation in the older brain
• Higher use of brain areas (frontal lobes) than young compensation
• More PFC activity visual impairment
• Bilateral (old) vs unilateral (young)
• Inhibition studies
• Critic: other work over recruitment not helpful
• Additional activity not always compensatory
• “partial compensation hypothesis”
• compensation-related utilization of neural circuits hypothesis’ (CRUNCH)
= more neural resources are recruited by older adults at low levels of cognitive load — that is, when tasks are easier — than by younger adults, who do not need them, At higher levels of load, this compensatory mechanism is no longer effective, leading to equivalent or less activation in older adults relative to young adults.
• At higher levels of load, this compensatory mechanism is no longer effective, leading to equivalent or less activation in older adults relative to young adults.
Dedifferentation
- Experiment: implicit to explicit memory old less distinctive patterns of activity in all except PFC and parietal
- age differences in autobiographical and episodic memory but maintained, or even increased, semantic memory with age.
- or even increased, semantic memory with
- less selective responses to specific categories of visual stimuli have also been reported and are associated with measures of task switching and working memory in old adults
- young adults have activation patterns that are typically quite selective for the particular stimulus features or task demands involved, whereas in older adults activation can be much less distinct, which is consistent with the idea of dedifferentiation across cognitive processes
- adaptation fusuiformis less differentiation old
Brain networks and functional connectivity
- young: load-dependent increases in activity in PFC, old: always
- old: deficient ability to dynamically modulate network connectivity
- episodic memory: older adults compensate for hippocampal deficits by relying more on the parahippocampal cortex.
- successful memory encoding in older adults might be mediated by similar posterior- to-anterior shifts in the functional connectivity of memory-related regions in the MTLs.
- weakened functional connectivity between PFC and parietal regions may explain the reduced ability of older adults to attend to and make use of stimuli in the environment.
- task-relevant functional connections between specific brain regions can be disrupted with age and that these disruptions have a negative impact on task performance.
- Default network resting, spontaneous thought lower activity with age
Factors influencing brain activity
• Changes with ageing:
Grey matterreduced volume, thinning cortex, esp. frontal lobes
• White matter
• Reduction in neurotransmitter binding potential
• Reduction in receptor density
For dopamine and serotonin
• Risk of Alzheimers etc increases
Brain structure
- Volume of white matter and hippocampus decrease
- relationship between age reductions in grey matter volume of a region in the right middle frontal gyrus (MFG) and brain activity In older adults, right MFG volume was not positively correlated with activity in any regions that showed correlations in young adults, but was negatively correlated with activity in several regions, including the parahippocampal cortex older adults with larger right MFG volume may be better able to compensate for the effects of age on this region by modifying activity in other brain regions to help memory retrieval.
• relation between brain activity and grey matter volume in younger and older adults across the whole brain structural age changes may account for some, but not all, of the differences in brain activity between older and younger adults age differences in brain structure can influence the relationship between activity in task-related brain regions and behaviour, indicating a complex interplay between structure and function.
Dopamine
• rewardstriatum
• old: less striatum activation during reward anticipation, weaker relationship between striatum activity and dopamine levels in midbrain
neurotransmitter changes with age affect everyday decisions
• non-reward dopamine: COMT enzyme thought to regulate dopamine levels in PFC
• Val, Met
• Methigh dopamine
• Vallow dopamine
• Met carriers: no age difference in brain activity, Val carriers do
Specific genes
• some of the agerelated differences seen in brain activity during varying cognitive loads (FIG. 2) may be due to alterations in dopaminergic neurotransmission.
• age differences in dopamine synthesis capacity, as with binding potential, influence functional activity in multiple brain circuits that are relevant for working memory performance
Risk factors for Alzheimer’s disease: apolipoprotein E.
- memory reduction seen 6 years before Alzheimers diagnosis
- . Some studies have reported greater activation in memory-related areas, notably the hippocampus, in healthy old adults who were ε4 carriers compared with non-carriers of the ε4 allele162–164, and even in young ε4 carriers relative to non-carriers165, suggesting an increase in demand on these regions before the appearance of any symptoms of memory lossdebateable
- APOE genotype influences age-related changes in brain function, and the altered task-related brain activity in ε4 carriers may reflect the increased vulnerability of these individuals to Alzheimer’s disease pathology and cognitive decline.
- over-recruitment of brain activity in older ε4 carriers is enhanced in those with greater physical activity168.
Risk factors for Alzheimer’s disease: mild cognitive impairment
- individuals with MCI have greater activation in the MTLs during memory tasks relative to healthy older controls
- These studies point towards specific processing deficits as well as an impairment in the ability to respond to increases in cognitive demand as potential explanations for MTL over-recruitment in MCI.
- continuum of effects due to age and neuropathological brain changes, perhaps because both ageing and risk of dementia can affect cognition in a general way that impairs the ability to respond to increasing cognitive demand.
- MCI affects larger scale brain networks.
- compensatory response to dysfunction in the MTLs
- DN activity and functional connectivity in older samples might be a useful marker for predicting cognitive decline.
nfluence of training on the ageing brain
- how short-term behavioural training can affect brain activity in older adults?
- Training: reduced age differences in brain activity that were apparent before training1
- direct role for training in influencing both brain function and behavior
- increased brain activity after even limited training could be a result of the adoption of a different strategy, whereas decreased brain activity after training is more likely to be due to a practice-related increase of efficiency on a task
Conclusion
• compensation: over-compensation interpreted as compensation ( with positive AND negative correlation of brain activity and behavior)
better definition of compensation needed
• 3 different types of compensation:
1. : attempted compensation: recruitment of additional neural resourcesincreased brain activity, no link to behavior
2.: successful compensation: increased brain activity leads to better task performance
3.: unsuccessful compensation: worse task performance
• Term compensations could be used only for when old recruit brain activity not seen in young and engagement of that area only improves performance for old, not young
• Use of lifespan studies
• ageing is influenced by a large number of factors that vary from individual to individual, including genetics and life experiences
• current trend is to include an assessment of multiple influencing factors and multiple measures of brain structure and function
