w2: Ageing II Flashcards
How do we study the ageing brain?
-post-mortem (problem- low sample size)
- neuroimaging techniques (CT, MRI, fMRI, PET)
changes in the human brain
- weight of brain decreases up to 10%
- weight of brain relative to body weight stays relativelly stable from age 20+
changes in human brain: ageing
Brain Volume
Cerebral cortex as a whole decline:
- 0.12% per year in younger adults.
- 0.35% per year in adults over 53 years of age.
Strong differences between regions:
- Some show a relatively steep decline.
- Others have a relatively stable volume over time.
changes in human brain: ageing
Grey Matter
brain areas that reduce and stay stable in size
Brain regions that reduce in volume with age:
- Caudate nucleus.
- Lateral prefrontal cortex.
- Cerebellar hemispheres
- Hippocampus.
Brain regions with minimal reduction or stable volume with age:
- Primary visual cortex
- Entorhinal cortex
Age related atrophy of grey matter differs across regions.
- The frontal lobes show the most atrophy. Between 0.9% and 1.5% per year.
- The parietal lobes show the second most atrophy per year. 0.34% and 0.9% per year.
Decline becomes steeper with increasing age.
Example: hippocampus.
- 0.86% per year in whole sample.
- 1.85% per year after the age of 70.
changes human brain: ageing
white matter
Throughout the entire brain
Greatest while matter loss in frontal regions.
- White matter loss is more extensive than grey matter loss.
Anterior to posterior gradient (from front of brain to the back of brain- ie. down hairline)
changes in brain: ageing
brain cavity and CSF
Between ages of 20 and 50 the brain occupies 90% of the cranial cavity.
Thereafter: the brain occupies progressively less space.
- Increase in the volume of cerebrospinal fluid.
- Widening of the sulci.
changes during ageing
Neurotransmitters
in case of dopamine
Two main families of dopamine receptors
- D1
- D2
Aging: loss of D1 and D2 receptor binding
- Decrease 7-10% per decade.
Dopamine transporter.
- 4.4% to 8% per decade.
Anterior-posterior gradient.
Neurotransmitter: loss of receptors and transporters
are the structural changes of influence on cognition?
yes!
significant correlation b/w decline in brain structure and cognitive functioning.
- Representations are generally well maintained at older ages, but some knowledge is either lost (especially with lack of practice) or becomes inaccessible.
- Control processes develop at different ages and also decline differentially, depending in part on the brain areas involved.
which domains decline
Ageing and Cognitive Decline
significantly decline
- speed of processing
- Working Memory
- LTM
- STM- but less than ^^
verbal knowledge = intact, increases for some people.
Functional Challenges in the brain
- Neuronal activity associated with cognition shows both age-related decreases as well as increases.
- Young adults and older adults (partly) recruit different areas of the brain for the same tasks.
Refer to age related:
- Compensation
- Adaptation
Age-related functional activations
pattern 1
Posterior-Anterior shift ageing (PASA)
PASA refers to a functional shift in brain activity from posterior (back) regions to anterior (front) regions with increasing age.
decreased activation in **posterior regions **(e.g., occipital and parietal lobes), which are typically involved in sensory and perceptual processing.
increase in activation in **anterior regions **(e.g., prefrontal cortex), which are involved in executive functions like planning, decision-making, and working memory.
shift = compensatory mechanism, old brains recruit frontal regions to compensate for decline in sensory + cognitive processing.
PASA suggests that ageing is accompanied by a redistribution of brain activity, reflecting attempts to maintain cognitive function
Age-related functional activations
pattern 2
Hemispheric Asymmetry Reduction in Older Adults
(HAROLD)
HAROLD describes a reduction in the typical functional asymmetry of brain activity in older adults, where tasks that usually activate one hemisphere begin to engage both hemispheres.
young adults, cognitive tasks ie. memory = laterised activity
older adults, same task = bilateral
bilateral activation is thought to compensate for declining efficiency in one hemisphere by engaging the corresponding regions in the opposite hemisphere.
- HAROLD reflects the brain’s capacity to reorganise itself to counteract age-related decline, particularly in tasks requiring memory, language, and attention.
explainations PASA+ HAROLD
compensation + dedifferentiation account
-
Compensation: bilateral activity is associated with successful cognitive performance. Found in high-performing rather than low-performing older adults.
2.** Dedifferentiation account: **more widespread activation reflects an age-related difficulty in engaging specialised neural mechanisms.
cognitive ageing theories
Sensory Deficit Theory
Age-related deficits in sensory processing play a major role in age-related cognitive decline.
Older adults show considerable deficits in:
- Visual processing
- Auditory processing
Strong correlations between age-related differences in sensory processing and cognitive performance
cognitive ageing theories
Resource Deficit Theory
**Aging is associated with a reduction in the amount of attentional resources
- Result: deficit in demanding cognitive tasks **
- Deficits are smaller when environment provides support
Support: when attentional resources are reduced in younger adults, they tend to show cognitive deficits that resemble those of older adults.
Also support from neuroimaging studies:
- *Attention relies strongly on the prefrontal cortex (PFC)
Older adults tend to show decreased activation in a part of PFc that is activated during attention tasks in young adults*.
Older adults tend to shoe a more bilateral pattern of PFC activity during attention tasks.
HAROLD
cognitive ageing theories
Speed Deficit Theory
speed processing = refers to how quickly the brain can encode, interpret, and respond to information.
With age, the brain’s neural pathways and communication efficiency decline, leading to slower processing.
slowing of processing speed impacts other cognitive domains such as memory, problem-solving, and reasoning.
Limited Time Mechanism:
Because processing speed is slower, older adults may not have enough time to complete all the necessary mental operations before new information is presented or before they must respond.
Simultaneity Mechanism:
As processing takes longer, it becomes harder for older adults to hold earlier steps of a task in working memory while engaging in subsequent steps. This impacts their ability to integrate information effectively.
mechanisms speed deficit theory
White Matter Deterioration:
The myelin sheath, which insulates axons and facilitates fast signal transmission between neurons, deteriorates with age.
This deterioration reduces the speed and efficiency of neural communication, particularly in areas of the brain associated with complex cognitive tasks.
Increased Neural Network Demand:
As the brain ages, it compensates for declining efficiency in certain areas by recruiting additional neural networks to support cognitive performance.
This compensatory mechanism often increases cognitive load and slows down overall processing speed because it requires additional time and resources for task execution.
cognitive ageing theories
Inhibitory Deficit Theory
Age-related cognitive decline is due to a decline in the inhibitory control of working memory contents.
- When inhibitory control fails, goal-irrelevant information gains access to working memory.
- Result: mental clutter, which impairs working memory
Support: older adults
- Better remember disconfirmed solutions
- Better remember to-be-forgotten information
-Older adults show weaker activity than younger adults in inhibitory control regions
- Older adults show **greater activity in regions that are supposed to be inhibited than younger adults. **
model that combines it all
Scaffolding Theory of Ageing and Cognition (STAC model)
STAC model: accounts for the possibility of both deficient and preserved performance on cognitive tasks:
- Acknowledge that the aging brain must adapt to neural challenges including atrophy
- To cope: the brain builds alternative neural circuitry, or scaffolds
- Scaffolds: represent compensatory strategies and allow older adults to maintain a high level of activation.
Model is not specific to old age, but to the life span the brain is confronted with cognitive challenges.
Cognitive Reserve
individual differences in cognitive processes or neural networks underlying task performance allow some people to come better with the decline in brain structures than others
mesures of cognitive reserve
intelligence (crystallised intelligence)
level of education
work level
literacy
integrity of social relations
activites in spare time
+ve and -ve influences on cognitive reserve
+ve
- mental stimulation
- active lifestyle
- social stimulation
- cognitive remediation
-ve
- poor education
- mood disturbance
- poor nutrition
- alcohol/drug abuse
- poor health
low vs high cognitive reserve
**People with a low cognitive reserve **
- Show relatively *early a decline in cognitive performance *relative to the decline in brain structures.
People with a high cognitive reserve
- Show relatively late a decline in cognitive performance relative to the decline in brain structures