Structure, function, & Neurochemisty

Question 1

What are the main structural changes to the brain as we age?

Answer 1

• Whole brain shrinkage/ventricular expansion at a rate of 3% per year
• Until 70-80 years old grey matter has a linear decline
• White matter is stable until 45 years and declines thereafter

Question 2

What are the changes in grey matter for different areas of the brain?

Answer 2

Decline per year, over 5 years:

• Frontal lobe: 0.91&
• Parietal lobe: 0.87%
• Temporal lobe: 0.69%
• Occipital lobe: 0.10%

Question 3

What are the 3 major trends in age-related functional reorganisation?

Answer 3

1. Increased anterior compared to posterior activity (e.g. PASA)
2. Loss of hemispheric specialisation (e.g. HARLOD)
3. Additional activity/over-activation (e.g. CRUNCH/STAC)

Question 4

What are the changes in energy consumption of the brain?

Answer 4

• Age-related metabolic reductions in frontal and temporal lobes by 13-24%
• Older adults have on average 8% lower cerebral metabolic rates for glucose than younger adults, in frontal and temporal grey matter
• Lack of change in cerebellum and occipital lobe, suggesting alterations in energy consumption are regionally specific

Question 5

Changes in BOLD: resting state networks?

Answer 5

• Decreased connectivity between regions of the Default Mode Network (DMN) e.g. medial prefrontal cortex and posterior cingulate cortex
• Not due to reduced grey matter volume
• Multiple potential sources of resting state activity change: abnormal structural connectivity, neurotransmission, and/or protein deposits

Question 6

Changes in BOLD: task-specific networks?

Answer 6

• Older adults show a decrease in connectivity between areas belonging to the same task-specific functional network but show increased connectivity between areas belonging to different functional networks

Question 7

Changes in BOLD: the vascular system

Answer 7

• Arterial stiffness/narrowing blood vessels leads to changes in pressure, cerebral hypoperfusion and ischemia
• Prefrontal cerebrovascular reactivity (CVR) decreases by 54% from ages 20-80 years
• There is a vascular component to dementia

Question 8

What are the changes in event-related potentials?

Answer 8

• No age differences in o-back, slower RT and more errors in 2-back task for older adults
• Delayed frontal N2, accompanied by attenuated and delayed P3a/P3b responses

Question 9

What are the changes in oscillations?

Answer 9

• Lower power in the frontal theta (6 Hz) and parietal alpha (9-11 Hz) frequency ranges in older versus younger adults. Particularly prominent reduction in theta power during the 2-back task.
• Less efficient front-parietal network synchronicity in older adults, which leads to deficits in identification and maintenance of task relevant stimuli