7 - The aging brain Flashcards
Name the 4 lobes.
1) Frontal lobe
2) Parietal lobe
3) Temporal lobe
4) Occipital lobe
Explain the role of the frontal lobe.
- Its main role is executive functioning, along with decision making, planning, imagining the future
-
Motor cortex: movement
→ part of the frontal cortex
→ helps to plan, control and execute voluntary movement
→ the point where the motor cortex and the somatosensory cortex meet is the central sulcus – forms a boundary between the frontal and the parietal lobes
Explain the role of the parietal lobe.
- Directs goal orientated movement
→ p.ex: grasping an object -
Somatosensory cortex: sensory information
→ p.ex: temperature, taste, touch, movement from the rest of the body
Explain the role of the temporal lobe.
- Hearing, language, and music
- lies below the lateral fissure (boundary between the temporal and the frontal and parietal cortex)
- the underside of each temporal lobe plays a crucial role in memories
Explain the role of the occipital lobe.
- Visual processing
→ processes imagines from the eyes and links that information to images stored in memory
What are the largest and second largest parts of the brain?
1) Cerebrum: This is the 4 lobes
2) Cerebellum: Processes and regulates signals between other parts of the brain and body
What are the 3 ways we talk about the brain (its orientation)?
1) Anterior vs. Posterior (front vs. back)
2) Lateral vs. medial (sides vs. middle)
3) Dorsal vs. Ventral (top vs. bottom)
What is white matter?
- Part of the brain’s composure
- Is made up of nerve fibres and forms tracts that send information through the brain
- Made up of bundles of axons (which also gives it its white colour)
- Wrapped in myelin which gives the tissue its white colour (axons pathways) and provides insulation for the axon and helps nerve signals travel faster and farther (signal transmission)
- Axons may be short (like signals from one cell to another), and its less than a hair-width away; or can be very long (signals from the brain all the way down the spinal cord)
- Makes up 60% of the brain
What is grey matter?
- Part of the brain’s composure
- Is made up of cell bodies and is where processing of information occurs
- The dendrites receive messages from other cells
→ dendrites: end portion of nerves
→ they extend out of the cell body like the branches of a tree and receive these messages
→ signals pass from the dendrites through the cell body and may travel away from the cell body down an axon or axon terminals then to another neuron - Is grey because that section of the nerve lacks the fatty material called myelin
- The cerebral cortex (or gray matter) makes up the outer layer of the brain
→ these are the 2 ways we can refer to the outer layer - 40% of the brain
What are ventricles?
- Part of the brain’s composure
- Filled with cerebrospinal fluid (CSF) which cushions the brain and spinal cord
→ CSF is manufactured in the ventricles, which allows the brain to move and expand without pushing too much on the skull
→ CSF washes out waste and impurities and delivers nutrients
→ measure of atrophy, because as grey matter shrinks, the ventricles get larger
→ white space in the middle: for people with dementia, this space expands, which means you have less grey and white matter, but more CSF
___ matter deals with signal transmission, while ___ matter deals with information processing.
White; grey
Numerous changes in the brain are observed in aging including..
→ Decreased white and gray matter volume
→ Alterations in functional connectivity
→ Increases in vascular lesions
→ Changes in protein composition
→ Reductions in neural activity and blood flow
What are reductions in white matter with age attributed to (structural brain changes)?
Reductions in white matter with age are attributed to factors such as myelin degeneration, axonal loss, and reduce white matter integrity (white matter reductions does just naturally decline with aging, part of normative aging)
Explain the white matter structural brain changes with age.
- Most changes are often observed in areas involved with complex functions
→ frontal white matter tracts which connect the frontal lobe to other brain regions especially show degeneration, which can impact cognitive and motor functions due to disrupted communication between brain regions - WM reductions are quite variable within and between people
→ the extent and rate of WM changes vary significantly
→ not everyone experiences the same degree of white matter loss, some people may have minimal or no WM loss
→ BUT, when losses are extreme, that’s when there’s a significant decline - These losses are linked to widespread cognitive deficits
→ cognitive impact of WM with aging is actually quite broad, however, WM is mainly involved with processing speed, which is a major area that is affected because the role of WM is to facilitate communication between regions (frontal cortex relies heavily on white matter tracts)
→ declines here can lead to difficulties with goal setting, organizing thoughts, adapting to changing situations, the ability to make well-considered decisions and control impulses may also be affected
→ older adults may thus experience delay in responding to tasks
Explain the grey matter structural brain changes with age.
- Reductions in grey matter volume are attributed to reduced synaptic densities (connections between neurons)
- GM reductions do not occur at the same rate between young and older adults in different areas
→ so a reduction in these means reduction in the amount of cell bodies throughout the brain
→ there’s a steady decline from 200 to 100 in synaptic density
→ its expected that if we live to 130, we would reach the same density as people with alzheimer’s disease - GM reductions do not occur in everyone (or at the same rate in everyone)
→ reductions in brain volume is observed in some areas, more than others including the prefrontal cortex and the medial temporal lobe structures
→ reductions also differ between people
→ some will have an accelerated loss in GM, and some will have limited loss - GM volume loss is associated with cognitive deficits – but the cognitive deficit is specific to the area of loss
→ p.ex: we can do paper tasks that look at executive functioning and if people score very very low, if we do an MRI, we’ll be able to see a reduction in GM in the frontal lobe
What is a super-ager?
“super-agers” are older adults who don’t have much changes as they age; thus, they don’t lose a lot of GM or WM that we would see in the normal aging process
What occurs to the grey matter in the lateral prefrontal cortex with age?
There is a general decrease here across age, BUT it is a wide range, i.e., some older adults have significant decline, while others have are above the mean of decline
What occurs to the grey matter in the primary visual cortex with age?
The decline is not as bad here as it is in the lateral prefrontal cortex, so there is no real reduction in the visual cortex; i.e., no change in visual processing as we age.
What occurs to the grey matter in the hippocampus as we age?
As we get older, the hippocampus experiences the most decline in aging, and it’s very steady after the age of 30
Older adults typically show a __% volume loss in the whole brain and hemisphere.
15%
Older adults show a 22% volume loss in the ___ lobes.
Frontal
What hemisphere shows more decreased volume with age?
- The left hemisphere is more decreased in volume than the right
→ older men will typically show greater decreases in volume in left hemisphere and frontal left hemisphere than older women, indicating the larger left hemisphere is largely contributed to selective atrophy of the left frontal lobe in older men
The peak rate of growth for grey matter occurs at ___; while the peak of grey matter volume occurs at ___.
6 months; 6 years old.
Ventricle volume steadily increases after __ years of age.
40;
→ Coincides with maximum loss of gray and white matter starting around 40
→ Total cerebrum volume peaked just before the onset of puberty
What are vascular lesions?
- Refers to abnormal changes or damages to blood vessels in the body, including those in the brain, which can disrupt blood flow; in the brain, if they’re in vascular regions they can lead to problems like stroke, hemorrhages and reduced blood supply
What are the risk factors of the appearance of vascular lesions (i.e., due to risk factors such as…)?
- Appearance of vascular lesions due to risk factors such as smoking, high blood pressure, & drinking alcohol (because they appear in the vascular system
→ as we get older (60+) if they still have these vascular risk factors, the chances of having lesions is very high leading to decline, which can lead to dementia
How are vascular lesions associated with dementia? With alzheimers disease?
Dementia:
- Brain damage from lesions due to impaired blood flow to the brain (causing dementia)
- With vascular dementia, we see that these lesions are all over the brain
Alzheimers:
- in alzheimers disease, they tend to be most prominent in the posterior regions
Elaborate on white matter lesions.
- often indicate cortical vascular disease
- atrophy (decline in brain regions, both generalized or specific) is at least strongly associated with dementia
- these are areas of demyelinated cells found in the brain
Elaborate on large cortical infractions (lesions).
- Cerebral infarction, area of necrotic tissue death resulting from blockage or narrowing in the arteries supplying blood and oxygen to the brain
Elaborate on microbleeds (lesions).
- Small chronic brain hemorrhages
- Likely caused by structural abnormalities of the small vessels of the brain
- Structural abnormality of the small vessel
Elaborate on multiple lacunar infarcts (lesions).
- Grey spots; most common type of stroke or blockages within the brain
- Result of these infarcts leading to blockages is that the small penetrating arteries that provide blood to the brain’s structures are impacted
- Stopping the regulation of blood flow within the brain; impacting specific parts of the brain getting oxygen
What are the changes in protein composition that influence brain health and function?
- Many changes in proteins and enzymes change influence brain health and function
- Changes in protein and enzymes are not always structural changes
- Common increases in amyloid-beta and tau proteins occur with age (moderate amounts)
→ the increases seen with age are common, however a certain level of increase is seen in people with alzheimers - May have specific directionality of accumulation in the brain (starting in temporal lobe and then spreading out)
- Can lead to dementia and cause severe deficits in cognitive functioning
