Post on 26-Dec-2015
Chapter 12
Learning and Memory across
the Lifespan
12.1
Behavioral Processes
3
12.1 Behavioral Processes
• The Developing Memory: Infancy through Adolescence
• Learning and Memory in Everyday Life— Can Exposure to Classical Music Make Babies Smarter?
• Sensitive Periods for Learning
• The Aging Memory: Adulthood through Old Age
4
Developing Memory in Infancy: Some Learning Can Occur Before Birth!
• Gestational age (GA)—time since conception.
• By 25 weeks GA, enough development in fetus’s brain and sense organs to perceive.
• In studies (play sounds to human fetus): Fetus (34–36 weeks GA) moved in response to a
sound; habituated (reduced response) by trial 13.
Moved to 2nd stimulus; habituated by trial 11.
Back to 1st stimulus; habituated by trial 8.
5Adapted from Hepper & Shahidullah, 1992.
Habituation to Sound (in 10 Human Fetuses)
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Short pause
Long pause
Long pause
Unfamiliar story plays
Familiar story plays
Familiar story plays
Time (sec.)
Polygraph recording of sucking on
nipple
Details of DeCasper & Spence (1986) paradigm:
Before birth, infants were played familiar story in mother’s voice; memory for story was tested after birth by playing recordings of this story or unfamiliar story while infants sucked on artificial nipple.
Infants tend to suck in bursts punctuated by pauses (interburst intervals, IBIs). First, researchers took baseline measurements of average IBI. Then, conditioned some infants that long IBIs would be reinforced with familiar story while sucking; short IBIs would be punished with unfamiliar story while sucking. (Other infants in counterbalanced conditioning, short intervals were punished.)
Fig
ure ad
apted
from
Fig
ure 1 o
f DeC
asper &
Sp
ence, 1986.
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Conditioning and Skill Learning in Young Children
• Explosion of learning in first few years of life! Most learning present in adults, present in infants.
But, perceptual and motor systems immature.
Until input/output systems mature, infants cannot fully learn or express.
8
Rovee-Collier Studies
• (1993) Rovee-Collier studied instrumental conditioning in infants: 2-month-old infants learned to kick to move a
colorful mobile (hung over the crib).Illustrates instrumental conditioning.
With no reminders, Infants remembered foot-kick technique for 1–3 days.
With reminders, up to 21 weeks.
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Rovee-Collier Studies
• If crib liner with new pattern was used, babies didn’t kick. Illustrates context-dependent
learning.
Co
urt
esy
of
Ca
roly
n R
ove
e-C
olli
er
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Infants and Classical Conditioning
• Other studies show infants have basic components of classical conditioning. Human and rat infants learned delay eyeblink conditioning.
But, use more trials than adults of their species.
Trace conditioning improved from infancy to early adulthood.
Shows that, with more mature development, organism can learn more efficiently (under increasingly difficult conditions).
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Development of Episodic and Semantic Memory
• Elicited imitation—infants’ ability to imitate an action at a later time. From single observational learning training session.
• In study, 10-month-olds are shown how to operate a toy puppet. 4 months later, showed more interest in the puppet than
control group (same age, no prior showing).
At 5 years, showed more interest and dexterity with the puppet than control group, though most could not recall previous exposure.
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Development of Episodic and Semantic Memory
• In study, 4-, 6-, and 8-year-olds taught 5 facts from an experimenter and 5 from a puppet. One week later, 6- and 8-year-olds recalled and
recognized more facts than 4-year-olds.
6- and 8-year-olds had better recall of source, with more intra-experimental errors (i.e., knew it was learned in experiment, confused source).
4-year-olds made more extra-experimental errors (i.e., thought learning was outside experiment, for example at school).
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Episodic Memory in Children
Data from Drummey & Newcombe, 2002.
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Development of Working Memory
• Working memory lifespan progression: English-speaking children 5–6 years can hold average digit
span of 3–4 digits in working memory.
By 9–10 years, can hold 5–6 digits.
By 14–15 years, can hold 7 digits (adult average).
Similar working memory progression seen with words and visual patterns.
• Why fewer for children? Lack of exposure.
Children’s performance improves with familiarity.
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0
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5
6
7
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5 6 7 8 9 10 11 12 13 14 15
Age (years)
Mea
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igit
s
GirlsBoys
Memory for digit span increases with age (reach adult levels by about age 12 or 13); no significant gender difference.
Figure plotted from data in Gardner, R. (1981). Digits forward and digits backward as two separate tests: Normative data on 1567 school children. Journal of Clinical Child Psychology, Summer 1981, 131–135.
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Learning and Memory in Everyday Life— Can Exposure to Classical Music
Make Babies Smarter?
• Limited intellectual benefits from exposure to classical music (no true “Mozart effect”). Research shows little evidence that supports benefits;
zero evidence that the effect lasts longer than 10–15 minutes.
• So, why did scores increase? Music may “prime” or prepare brain regions for abstract
spatial reasoning or mental imagery.
Music may improve mood and subsequent performance.
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Sensitive Periods for Learning
• Sensitive periods—time ranges during which learning is enhanced or possible.
• Examples: In male sparrows, 30–100 days is a sensitive
period for song learning.
In cats, 3 weeks to 60 days is a sensitive period for visual development.
But, for monkeys, all of the first 6 months are important for visual development.
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Sensitive Periods for Learning
• In study of 28 human infants who had cataract surgery at age 1 week to 9 months: ACUITY improved significantly over 1 month, with
some improvement apparent after as little as 1 hour of visual input.
Unlike older children, improvement was the same for eyes treated for monocular and binocular deprivation.
Visual input necessary for postnatal improvement; its onset initiates rapid functional development.
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Imprinting
• Imprinting—phenomenon in which some species (e.g., newborn goslings, turkeys, sheep, deer, buffalo) form a social bond with the first object they see. Imprinting involves critical
period for permanent change to occur.
http://www.youtube.com/watch?v=LGBqQyZid04
Thomas D. McAvoy/ Time Magazine
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Social Attachment Learning
• Primates do not appear to imprint, but there is evidence of sensitive period for social attachment.
• In study, Harry Harlow rears rhesus monkeys isolated from mothers; in adolescence moved to group cages, show social retardation. For rhesus monkeys, first months = sensitive period
for learning social interactions.http://www.youtube.com/watch?v=An02zCsVEpY
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Social Attachment Learning
• Sensitive period for social attachment in humans? Consider children under Ceausescu regime (1970s): Romanian children (RC) reared from infancy (up
to 42 months) in depriving institutions, then placed in UK adoptive homes.
Compared with nondeprived UK-born children adopted before 6 months.
past
http://www.youtube.com/watch?v=rXivHuugp3c
presenthttp://www.youtube.com/watch?v=FWKQNMZa--Y&feature=related
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Social Attachment Learning
• Findings: RC tested at time of entry to UK; showed developmental
impairment in cognitive function.
Tested again at 4 years; all RC show improvement.RC adopted before aged 6 months showed normal cognitive and social functioning.
But, RC adopted at 6 months or later still showed some cognitive deficits, mild social problems.
Suggests biological programming or neural damage from institutional deprivation; varied outcomes related to early environmental stimulation.
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A Sensitive Period in Humans
Data from Rutter et al., 1998.
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Aging Memory: Adulthood to Old Age
• Working memory capacity is particularly vulnerable in old age.
• Average STM capacity for digits drops from 7 (in early to middle adulthood) to 6–6.5 in elderly adults.
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Conditioning and Skill Learning Decline—But Well-Learned Skills Survive
• Learning decline begins around age 40–50 in humans. Also seen in elderly rabbits, rats, and cats.
• However, well-established, highly practiced skills tend to be maintained or improved (chess and bridge experts).
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Conditioning and Skill Learning Decline—But Well-Learned Skills Survive
• In studies: Eyeblink conditioning
may take twice as many trials in elderly.
Skill learning for rotary pursuit task and computer use take more time.
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(B) Rotary pursuit skill learning
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18-29 30-39 40-49 50-59 60-69 70-70
Age (in years)
Tri
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to C
rite
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(A) Eyeblink classical conditioning
Mea
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ista
nce
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vere
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Classical conditioning and skill learning decline with aging.(A) Plotted from data in Solomon et al., 1989, Table 1. (B) From Kausler, D. (1994). Learning and Memory in Normal Aging. New York: Academic Press, p. 38 fig 2.4 (top), which cites adapted from Ruch, 1934.
Age (in years)
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Episodic and Semantic Memory: Old Memories Fare Better than New Learning
• Healthy elderly adults tend to retain semantic knowledge, and recall many episodic memories.
• In paired associates test: Elderly may be able to recognize words or images
previously studied.
May have difficulty with recall.
May recall more information if given more time or allowed to self-pace rate of presentation.
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Paired associate learning is impaired in elderly adults relative to young adults when items are presented at a rate of one every 1.5 seconds; impairment decreases if presentation rate is slowed. Recall best when learning is self-paced, though elderly subjects never quite reach same performance as young subjects.
From D. Kausler (1994) Learning and Memory in Normal Aging, NY: Academic Press, p. 88, which cites adapted from Canestrari, 1963, Table 2.
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12.1 Interim Summary
• Just about every kind of learning and memory observed in adults can also be observed in very young children. Some simple kinds of learning (e.g., habituation,
recognition) can be observed before birth.
Other kinds of memory (particularly episodic and working memory) may be present at a very young age, but do not fully mature until late childhood or adolescence.
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12.1 Interim Summary
• Development of learning and memory abilities at least partially reflects brain development.
• Sensitive periods = time windows early in life when certain kinds of learning advance most rapidly. Includes imprinting, social attachment learning.
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12.1 Interim Summary
• Many kinds of learning and memory show some decline in healthy aging. Working memory is especially vulnerable.
In other memory domains (e.g., skills, conditioning, episodic and semantic memory) old, well-formed memories tend to survive well; may be harder to acquire new memories.
12.2
Brain Substrates
34
12.2 Brain Substrates
• The Genetic Basis of Learning and Memory
• Neurons and Synapses in the Developing Brain
• Gender Differences in Brain and Behavior
• The Brain from Adulthood to Old Age
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The Genetic Basis of Learning and Memory
• DNA—material in cell nucleus; instructions for replication. Looks like twisted ladder; sides = sugar and
phosphate molecules, rungs = base pair.
Four kinds of DNA:Adenine
Thymine
Cytosine
Guanine
36
The Genetic Basis of Learning and Memory
• DNA organized into chromosomes. Humans have 23 chromosome pairs (one set from each
parent).
23rd pair determines gender.XX = female
XY = male
• Chromosomes subdivided into genes— segment of DNA with information for building proteins from amino acids. Probably 20,000 to 25,000 genes in humans.
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Genes and DNA
CN
RI/
Ph
oto
Re
se
arc
he
rs,
Inc
.
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Genetic Variation among Individuals Affects Innate Learning Abilities
• Mutation—accidental changes in DNA sequence. Possibly from outside causes (e.g., radiation, viral
infection) or copying error.
• Mutations can: Be harmless.
Lead to cell malfunction, disease, death.
Be beneficial to the species.New characteristics for reproduction or survival.
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Genetic Variation among Individuals Affects Innate Learning Abilities
• Because of mutation over time, most genes have alleles—naturally occurring variations. e.g., eye color
Bey2: blue-blue Bey2: BROWN-blue
Bey2: blue-blue
Bey2: BROWN-blue
Bey2: blue-blue
Bey2: BROWN-blue
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Genetic Variation among Individuals Affects Innate Learning Abilities
• Brain function also influenced by variations; can affect learning and memory.
• Examples: BDNF protein (the Val allele) may facilitate long-
term plasticity.
Tyr allele (variant of His allele on 5-HT2AR gene) results in less-efficient serotonin receptors. Perform slightly worse on delayed word recall task.
41
Genetic Influences on Learning and Memory in Humans
(a) Data from Egan et al., 2003; (b) adapted from de Quervain et al., 2003.
42
Selective Breeding and Twin Studies
• Tryon (1940): Can animals be bred for learning ability? Bred discrete groups of maze-bright and maze-
dull rats in 7 generations.By 7th generation, maze-bright offspring
routinely out-perform rats bred from maze-dull line.
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Da
ta s
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wn
are
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po
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se
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0.
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Selective Breeding and Twin Studies
• Multiple genes control characteristics of learning ability. No single gene.
• Human twin studies suggest that over half of the variation in memory scores may be genetic. Identical twins have more similarity than fraternal.
45
The Influence of Environment
• Rats raised in enriched environment (good sensory stimulation) have more dendrites and synapses. Males had the most growth
in visual cortex.
Female rats had the most growth in frontal cortex.
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Neurons and Synapses in the Developing Brain
• Neurons are overproduced, then weeded out.
• Neurogenesis (neuron birth) = most active during prenatal development; continues to a limited degree throughout life. Not uniform throughout brain; some neurons form
earlier than others.
47
Neurons and Synapses in the Developing Brain
• In early development, glia guide cell migration; produce molecules that modify growth of axons and dendrites. Some glia (oligodendrocytes) produce myelin
sheath, from birth to 18 years.
• Neurotrophic factors (e.g., BDNF protein) help cells properly locate and specialize. Without these chemical compounds, about 1/3 of
neurons die (apoptosis), a natural phenomenon.
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Neurons and Synapses in the Developing Brain
• Synapses are also formed, then pruned.
• Synaptogenesis (formation of new synapses)—begins during gestation, but most active after birth to about age 6. Tiny dendrite spines come and go; if stimulated by
neurotransmitters, synapses may form.
Unused synapses die (pruning).
New synapses may strengthen during non-REM sleep and unused may die during REM sleep.
49
Most synapses Occur on Dendritic Spines
(a) Adapted from Hof & Morrison, 2004; (b) adapted from Trachtenberg et al., 2002.
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Sensitive Periods for Learning Reflect Sensitive Periods for Neuronal Wiring
• Neural pathways (and specific receptors) may develop rapidly during sensitive periods.
• Apoptosis may then clean up neurons not used in in this sophisticated development.
51
The Promise of Stem Cells for Brain Repair
• Young brains = highly plastic; older brains less able to adjust.
• Can stem cells be integrated into adult brains? Stem (especially from fetal tissue) cells have
ability to develop into many cell types.e.g, skin, liver, brain cells
Fetal stem cell transplant research still preliminary.Tried in Parkinson’s disease patients.
New neurons do not cure the underlying disease.
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Embryonic Stem Cell Transplants in Brains of Parkinson’s Patients
Adapted from Freed et al., 2001.
53
Gender Differences in Brain and Behavior
• In studies: Women often perform better than same-aged men on:
List recall.
Story recall.
Memory for object location.
Men can outperform women in maze learning.
Men and women studied a fictitious town map:Men tended to learn a route more easily.
Women remembered more landmarks.
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Gender Differences in Brain and Behavior
• Male and female rats also show gender differences.
• Sex hormones may contribute to gender-based learning differences.
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Effects of Sex Hormones on Brain Organization
• Puberty—body’s physical change to sexual maturity in adolescence. Surge in release of sex hormones.
Primarily estrogens in woman, androgens in men (especially testosterone).
In mammals and birds, testosterone surges in female fetuses and even more in male fetuses just before birth.
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Effects of Sex Hormones on Brain Organization
• During infancy, testosterone influences sex differences in brain development. Larger in women:
Lateral frontal cortex
Language areas (supramarginal gyrus)
Hippocampus
Larger in men:Visual and spatial processing areas
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Effects of Sex Hormones on Adult Behavior
• Gender differences in memory performance appear after puberty from circulating estrogen and testosterone.
• Estrogen stimulates adult rats’ neuronal growth and synaptic plasticity (LTP), especially in the hippocampus.
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Effects of Sex Hormones on Adult Behavior
• Estrogen may increase verbal learning; testosterone may increase spatial learning. But, relationship between sex hormones (especially
testosterone) and learning is complex.
• Studies show male-to-female transsexual persons taking estrogen scored higher on paired-associate task. Compared to similar group who had not yet started
estrogen treatment.
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Adulthood to Old Age: Parts of the Aging Brain Lose Neurons and Synapses
• Slow human brain shrinkage, including the cerebellum, begins in young adulthood. By age 80, average adult loses about 5 percent of brain
weight.
• Studies show: Cerebellum-dependent classical eyeblink conditioning
slows with age.
However, there is little loss of hippocampal neurons in the healthy elderly.
Reductions in neurons = disease warning signs.
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Neuron Loss in Prefrontal Cortex of Aging Monkeys
Adapted from Smith et al., 2004.
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Synaptic Connections May Be Less Stable in Old Age
• Barnes (et. al.) suggest total number of neurons, synapses does NOT decrease; rather, decrease in ability to maintain changes in synapse strength. Rat and monkey studies suggest that synapses may be
less stable in old age.
In studies, young rat and an old rat learned a figure 8-shaped maze. In second session, hippocampal LTP in the old rat was unstable.
Instability could contribute to spatial and episodic memory declines.
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Hippocampal Neurons Encoding Location in Old and Young Rats
(b–e) adapted from Barnes et al., 1997.
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New Neurons for Old Brains? Adult Neurogenesis
• Adult brain may be able to grow new neurons. Adult neurogenesis has been studied (and reliably
observed) in birds, fish, amphibians, reptiles.
• Neurogenesis in mammals? Studies show limited neurogenesis in brains of
adults macaque monkeys and human cancer patients.
Most new neurons die within a few weeks.
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12.2 Interim Summary
• Development of learning and memory abilities at least partially reflects brain development. Temporal and frontal cortex are among the last
brain areas to fully mature.May help explain why memory processes
dependent on these areas are among last to reach full adult potency.
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12.2 Interim Summary
• Genes play a large role in determining learning and memory abilities. Enriched environment studies show that experiences
can also impact brain organization and an individual’s abilities.
• Before birth, the brain overproduces neurons and synapses. Unnecessary neurons and synapses are gradually
eliminated.
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12.2 Interim Summary
• Sensitive periods may reflect times when external inputs can easily and profoundly alter brain connectivity. After sensitive period, large-scale organization of
brain area in question may be fixed, and further learning (of the kind in question) may be limited to fine-tuning.
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12.2 Interim Summary
• Sex hormones, like estrogen and testosterone, can influence development and performance. Leads to gender differences among adults in
various kinds of learning and memory.
Influence on developing brain leads to gender differences even in very young individuals.
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12.2 Interim Summary
• Working memory declines in healthy aging. Vulnerability may reflect normal frontal cortex
shrinkage in healthy aging.
• Pattern of memory loss in healthy aging may reflect loss of neurons and synapses. Also, may reflect decrease in ability to maintain
changes in synapse strength.Thus, newly encoded information may be lost.
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12.2 Interim Summary
• New neurons produced throughout the lifespan. But, particularly in humans, there is as yet little
evidence that adult neurogenesis could provide large-scale replacement for damaged or aging neurons.
12.3
Clinical Perspectives
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12.3 Clinical Perspectives
• Down Syndrome
• Alzheimer’s Disease
• A Connection between Down Syndrome and Alzheimer’s Disease?
• Unsolved Mysteries—Treating (and Preventing) Alzheimer’s Disease
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Down Syndrome
• Down syndrome—congenital form of mental retardation which occurs equally in girls and boys. Retarded speech and language
development; low IQ scores.
Usually caused by trisomy 21 (extra copy of a chromosome 21).
During embryo formation, parent’s (usually mother’s) chromosome fails to split properly.
La
ura
Dw
igh
t
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Brain Abnormalities and Memory Impairments
• In Down syndrome, brain size may be average at birth, but growth in some areas (e.g., hippocampus, frontal cortex, cerebellum) may be stunted.
• Individuals tend to have profound deficits in hippocampal-dependent memory abilities. Young adults with Down syndrome performed at the 5-
year-old level on mental abilities tasks.
Also, performed much worse on hippocampal-dependent memory tasks.
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Hippocampal-DependentLearning and Down Syndrome
Data from Vicari, Bellucci, & Carlesimo, 2000).
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Figure summarizes performance on battery of tests that require hippocampal function (like list learning and spatial learning) compared with a battery of tests that require prefrontal function (like working memory). Adapted from Pennington et al., 2003, Figure 2.
Brain Abnormalities and Specific Memory Impairments in Down Syndrome
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Animal Models of Down Syndrome
• Mice bred for segmental trisomy (Ts65Dn mice) showed deficits in hippocampal-dependent tasks (e.g., location of maze goal).
• Enriched environment improved spatial memory in female Ts65Dn mice. Exacerbates impairment in Ts65Dn males.
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Alzheimer’s Disease
• Alzheimer’s Disease (AD)—a form of progressive cognitive decline from accumulating brain deterioration.
• AD affects about 4.5 million people in U.S. As many as 50 percent of people over age 85 are
afflicted.
http://www.youtube.com/watch?v=7-P9lbTJ9Hw
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Progressive Memory Loss and Cognitive Deterioration
• AD progression: Earliest symptoms of AD occur in episodic
memory, such as forgetting recent visitors.
Later, there are declines in semantic memory (e.g., forgetting familiar names, locations).
Next, conditioning and skill memory deteriorate.
In late-stage AD, there is often a lack of awareness and daily living skills.
http://www.youtube.com/watch?v=oTEbq4h-kvQ
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Patients with AD show marked impairment in many forms of memory, including list learning. Over three trials with a 10-word list, AD patients recall fewer items than same-aged healthy controls; after a 10 minute delay, the patients recall almost none of the studied words.
Adapted from Figure 1 of Moulin et al. (2004).
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Healthy Elderly
Early AD
1 2 3 Delay
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Plaques and Tangles in the Brain
• Amyloid plaques = deposits of beta-amyloid (abnormal byproduct of amyloid precursor protein, or APP; kills adjacent neurons). Plaques are fairly evenly distributed across cerebral cortex.
• Neurofibrillary tangles = collapsed protein scaffolding within neurons. Early in AD, accumulate in hippocampus and MTL, relating
to semantic and episodic memory deficits.
Hippocampal shrinkage = early AD warning sign.
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Plaques and Tangles—Hallmarks of Alzheimer’s Disease
(a) Cecil Fox/Science Source/ Photo Researchers. (b) Adapted from Figure 3 of Hardy & Gwinn-Hardy, 1998.
a) Amyloid plaque (dark center spot) surrounded by residue of degenerating cells.
b) Neurofibrillary tangles (seen as darkened areas).
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Plaques and Tangles in the Brain
• Verification of presence of plaques and tangles (to confirm AD diagnosis) can only happen at autopsy. 10 to 20 percent of “probable AD” diagnoses (based
on MRI, PET, lumbar puncture, etc.) are incorrect.
Many other conditions (some treatable) mimic AD, so better diagnostic test needed.
e.g., vitamin B deficiency, hypothyroidism, depression
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Genetic Basis of Alzheimer’s Disease
• Several genes implicated in AD.
• Most progress understanding genetic cause of early-onset AD (begins at 35–50 years). Less than 1 percent of AD cases = early-onset.
Caused by genetic mutations, which are autosomal dominant (meaning, just one mutated gene from either parent will trigger early-onset AD).
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Connection Between Down Syndrome and Alzheimer’s Disease?
• Chromosome 21 (implicated in Down syndrome) contains APP (implicated in AD).
• By age 35–40, adults with Down syndrome develop neural plaques and tangles.
• Half of Down syndrome patients show memory decline and other symptoms of AD; other half do NOT show cognitive decline. Why? Unclear. Explanation will help in understanding
both pathologies.
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Unsolved Mysteries—Treating (and Preventing) Alzheimer’s Disease
• Cholinesterase inhibitors treat forgetfulness and anxiety. Inhibiting breakdown of neurotransmitter
acetylcholine (depleted in patients with AD).
• Memantine blocks glutamate receptors. May help protect neurons from glutamate-
mediated damage, slow cognitive decline.
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Unsolved Mysteries—Treating (and Preventing) Alzheimer’s Disease
• Risk factors for AD include: Type-II diabetes
High LDL (“bad” cholesterol)
Previous head injury
Stroke
High blood pressure
• High levels of cognitive activity may slow AD symptoms.
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12.3 Interim Summary
• Down syndrome = condition in babies born with extra copy of chromosome 21.
• Children with Down syndrome have cognitive impairments. Includes memory impairments.
• Some brain areas tend to be abnormally small. Includes hippocampus, frontal cortex, cerebellum.
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12.3 Interim Summary
• In Alzheimer’s disease, plaques and tangles accumulate in the brain. Memory symptoms are prominent early in the disease.
Consistent with finding that hippocampus and nearby MTL areas suffer pathology early in disease.
• Several genes may contribute to an individual’s risk for the common, late-onset form of the disease.