lecture 24: aging and neurodegeneration Flashcards
Adult plasticity
although the large scale synaptic dynamics found during development are
not present in the adult brain, there is still plenty going on at the synaptic level. One classic
example comes from the Barn owl.
Barn owls use their visual and auditory senses
for hunting and locating prey. Within the owl’s
brain (area called the tectum), the auditory and
visual pathways converge to create a map that
links sound and vision and contain neurons that
respond to both visual stimulation in a certain
area of visual space AND a specific time
discrepancy between the right and left ears.
There are some cells that represent the visual/
auditory space right in front of the animal - cells
that respond to the center of the visual field and
a 0 µs interaural delay and other cells that
represent the sides (e.g. cells that respond to to the left side of the visual field and a short
50-100 µs interaural delay where the sound reaches the left ear first).
Baby barn owls fitted with prisms that shift the visual world (left or right) can rewire that
map and adjust to the new visual setup (presumably an evolutionary adaptation due to
variation in skulls size/shape). In laboratory experiments, this rewiring becomes less and
less effective as the animal ages (typical for a ‘critical period’). Yet, scientists found old owls
could remap – they identified three factors that helped: 1. incremental learning, 2. previous
exposure and 3. increased motivation
Alzheimer’s disease
a neurodegenerative
disorder prevalent in the aging population.
Initial symptoms include gradual loss of
memory, impaired cognitive and intellectual
capabilities, and reduced ability to cope with
daily life. It is defined by the combined
presence of abundant amyloid plaques and
neurofibrillary tangles and eventual neuronal degeneration in postmortem brains.
Neurodegenerative disorder
disorder
characterized by progressive neuronal
dysfunction, including loss of synapses,
atrophy of dendrites and axons, and death of
neurons
Dementia
general term for a decline in memory or other thinking skills that impairs normal
life
Amyloid plaques
extracellular deposits consisting primarily of aggregates of pieces of amyloid precursor protein (APP) mostly the amyloid β protein, a ~40 amino acid peptide with a
strong tendency to form aggregates rich in β-pleated sheets. One theory is that the plaques
cause problems for the cells: possibly disrupting synaptic transmission and eliciting an immune
inflammatory response
Neurofibrillary tangles
an intracellular tangle of cytoskeletal elements, consisting of an abnormal accumulation of hyper-phosphorylated tau, a microtubule-binding protein that is highly enriched in axons
- Describe the critical period for visual and auditory alignment in the barn owl
- Give several examples how plasticity can be increased or critical periods can be extended/
reopened in adults
- Describe normal changes in the aging brain and possible avenues to prevent synaptic loss
- Describe the pathological changes that occur in Alzheimer’s disease
Sound localization as a model of adult plasticity
- Owls localize sounds by differences in the time at which sounds reach the two
ears (interaural time difference) - Amazing ability to detect interaural differences of just 10’s of microseconds!
- To catch its prey, the owl needs to make sure its EARS and EYES give it the same
information
Optic tectum (area in the midbrain)
has neurons
that respond to both visual and auditory stimuli.
* Specifically neurons that respond to the location of
visual stimuli and the interaural difference of auditory
stimuli.
Experimental manipulations to extend the critical period
Cause plasticity in adolescence. Fit young owl
with prisms during the critical period. Then
remove when adjustment is complete. When the
prisms are re-fit in adulthood, there is much
greater remapping than if the they are first fit in
adulthood.
* Incremental learning. There is much more
remapping if prisms of increasing strength are fit
successively than if full-strength ones fit all at
once.
* Increased motivation/attention. The initial
experiments were done in a laboratory, where the
owl didn’t benefit from remapping. Results were
different when the owl had some reason to care
about the outcome…
the aging brain shows some
evidence of changes
Vocabulary and other “crystallized” knowledge
increases
* Decreases in working memory and
cognitive abilities (with variation)
Loss of synapses/synaptic “integrity” with aging brain
Decreased numbers of spines and synapses in the CNS
