Download working memory.

CHAPTER 12
Learning
and Memory
Learning deficiencies, dementias and Intellectual Disorders
Memory loss and aging
• For many years
– researchers believed deficits in the elderly caused by a substantial loss
of neurons, especially from the cortex and the hippocampus.
• More recent investigations
– the number of hippocampal neurons was not diminished in aged rats
– Even rats with memory deficits show little neuronal loss
– What neuronal loss occurs from cortical areas was relatively minor.
• BUT: certain circuits in the hippocampus do lose synapses
and NMDA receptors as animals age.
dementias
• Dementia
– ubstantial loss of memory and other cognitive abilities
– Typically in elderly
– 50% of those over 80 show some signs of dementia
• Alzheimer’s disease
– most common cause of dementia is
– characterized by progressive brain deterioration, impaired memory, loss of other
mental abilities.
– earliest and most severe symptom = impaired declarative memory.
– Language, visual-spatial functioning, and reasoning are particularly affected
– Behavioral problems such as aggressiveness and wandering away from home.
– Alzheimer’s affects nearly 10% of people over 65 years of age, and nearly half of
those over 85.
• Other dementias:
– Frontal-temporal dementia; Lewy Body Dementia
– Vascular dementias
– Dementias from illness such as stroke/heart attack
Brain changes in dementia
• There are two notable characteristics of the Alzheimer’s brain,
though they are not unique to the disease.
– Plaques
– Neurofibrillary tangles
• Plaques = clumps of amyloid,
– a type of protein Beta Amyloid peptide, which congregates together
– cluster among axon terminals
– interfere with neural transmission and are toxic to the neuron
• neurofibrillary tangles
– Abnormal accumulations of the protein tau
– form complexes inside neurons.
– Tangles are associated with the death of brain cells.
Dementia and brain
changes
• In the Alzheimer’s brain,
– gyri are smaller
– sulci are wider than in the normal brain.
• Pathology of Alzheimers believed to be death of groups of
neurons particularly in the nucleus basialis
– Because of their location, they effectively isolate the hippocampus from
its inputs and outputs,
– Particularly affect ACETYLCHOLINE neurons, but also serotonin
and norephinephrine neurons.
– this partially explains the early memory loss.
• Plaques and tangles in the frontal lobes account for
– additional memory problems
– attention and motor difficulties.
Figure 12.15 Alzheimer’s brain (left)
and a normal brain
The illustrations show the most obvious
differences, the reduced size of gyri and
increased size of sulci produced by cell
loss in the diseased brain.
Ach and memory
• Acetylcholine:
– Neural systems in various parts of the brain that produce acetylcholine are critical
for cognitive functions
– including attention and learning.
– Degredation of Ach:
•
Ach----------------------Acetate + Choline
AChE
(acetylcholine esterase)
Enzyme
• Acetylcholine-releasing neurons are among the victims of
degeneration in Alzheimer’s disease.
• The majority of treatment efforts have focused on restoring
acetylcholine functioning.
– E.g., cognex (Tacrine), aricept (Donezepil), exelon
– Also use anti-inflammatories early on, such as ibuprofen
Drugs for dementia
• Currently five drugs approved by the FDA for the
treatment of Alzheimer’s.
– Four of them improve acetylcholine neurotransmission by
preventing the breakdown of acetylcholine at the synapses.
– drugs provide only modest relief for both memory and behavioral
symptoms in mild cases of Alzheimer’s
– little or no help when degeneration is advanced.
• Other drug treatment
– Psychotropic drugs to control behavioral symptoms, reduce
hallucinations
– Antiseizure medications to control onset of seizures
– tranqulizers
Newer dementia drug
• Memantine
– The fifth dementia drug
– first approved for use in patients with moderate and severe symptoms.
• Some neuron loss in Alzheimer’s occurs when dying neurons
trigger the release of the excitatory transmitter glutamate.
– The excess glutamate overstimulates NMDA receptors and kills
neurons, a phenomenon known as excitotoxicity.
– Memantine limits the neuron’s sensitivity to glutamate, reducing
further cell death.
• Studies indicate moderate slowing of deterioration and
improvement in symptoms.
KorsAKoff’s syndrome
• Korsakoff’s syndrome
– Another form of dementia is, brain deterioration
– almost always caused by chronic alcoholism.
• The deterioration results from a deficiency in the
vitamin thiamine (B1), which has two causes:
1. The alcoholic consumes large quantities of calories in
the form of alcohol in place of an adequate diet.
2. The alcohol reduces absorption of thiamine in the
stomach.
KorsAKoff’s syndrome
• The most pronounced symptom : anterograde amnesia
– retrograde amnesia is also severe.
– Impairment is to declarative memory, while nondeclarative memory
remains intact.
• Several brain changes:
– hippocampus and temporal lobes are unaffected.
– mammillary bodies and the medial part of the thalamus are reduced in
size
– structural and functional abnormalities occur in the frontal lobes.
• Thiamine therapy can relieve the symptoms if the disorder is not
too advanced,
• Brain damage itself it irreversible.
KorsAKoff’s symptoms
• Confabulation
– Some Korsakoff’s patients show a particularly interesting characteristic in
their behavior
– Many other dementia patients, particularly frontal-temporal lobe also show
this
– They fabricate stories and facts to make up for those missing from their
memories.
– Depends on abnormal activity in the frontal lobes; confabulating patients
usually have lesions there.
• Confabulating amnesic patients
– Trouble suppressing irrelevant information they have learned earlier.
– Why? confabulation is due to an inability to distinguish between current
reality and earlier memories.
What is Intelligence?
• Intelligence is
– the ability to reason,
– to understand,
– to profit from experience.
• Binet, 1905: Intellingence tests for educational purposes
– Large sample average levels or norms
– Mental age vs. Chronological Age
• The measure of intelligence is typically expressed as the
intelligence quotient (IQ).
– (Mental age /chronological age) * 100
– Currently: IQ norm = 100;; Standard deviation = 15 poins
– 68% of people have IQ between 85 and 115
• Remember: IQ = score on test!
What is Intelligence?
• Wechsler Intelligence tests
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Several types of these tests
Wechsler Adult Intelligence Scale : WAIS-III
Wechsler Intelligence Scale for Children: WISC-IV
Wechsler Preschool and Primary Scale of Intelligence: WPPSI
 Divides test up by age groupings and by type of task:
– Verbal scales
– performance scales
Kinds of Intelligence
• Spearman’s G: general intelligence- just one kind
• Crystallized Intelligence:
– Skills, knowledge
• Fluid Intelligence
– Information processing
– Reasoning ability
– Memory
• Sternberg: practical and emotional intelligence
– Every day living skills
– Ability to perceive, process, use emtions
The Biological
Origins of Intelligence
• Intelligence research has tended to rely on data obtained from
individuals with compromised intelligence, particularly those
with frontal lobe damage
• Frontal lobe damage :
– impairs general intelligence more than performance on traditional IQ
tests,
– These tests emphasize crystallized intelligence (skills and information
learned earlier).
– Makes sense: Frontal areas involved in working memory and executive
control of problem solving
The Biological
Origins of Intelligence
• Brain size itself does not determine intelligence.
• What IS important? Ratio of the brain’s size to body size.
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Using ratio adjusts for the proportion of the brain to body size
Adjusts brain area needed for managing the body
Tells us how much is left over for intellectual functions.
Ratio for humans is one of the highest.
• MRI Twin studies: Is intelligence “genetic”
– Fraternal versus identical twins
– General intelligence correlated with both volume of gray matter and the
volume of white matter.
– Volume of gray matter in the frontal area appears to be particularly
important to general intelligence.
Rate of processing
important
• IQ scores also correlated with nerve conduction velocity
– Nerve conduction velocity: Speed with which nerve impulses transmitted
• Related to size of axon
• Degree of myelination, etc.
– Higher IQ correlated with faster nerve conduction velocity
– How examine? Speed of processing tasks on intelligence tests.
• People with higher IQ scores excel on tasks in which stimuli
presented for an extremely short interval and on tasks that require
choices.
– Both tasks: processing speed is important
– Assume that higher nerve conduction velocity contributes to the more
intelligent person’s superior performance.
– Thus: processing speed factors into IQ
Nerve conduction speed:
increased efficiency
• How make brain more efficient?
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greater efficiency through enhanced myelination of its neurons.
Also insulates neurons form each other.
reduces “crosstalk” that would interfere with accurate processing.
Remember, though: brain not have to be optimal or perfect, just
“good enough”
• Humans have a greater proportion of white matter
(myelinated processes) to gray matter than other animals
– appears IQ is related to the degree of myelination among individuals.
– Animals such as elephants, marine mammals, dogs, other nonhuman
primates also have high degree of myelination
– Sea Aplysia has No myelination!
Working memory
• Increased nerve conduction velocity may particularly enhance efficiency of
working memory.
– Working memory correlated with white & gray matter volume,
– Similar to correlation of white/gray matter and general intelligence
– Indeed, working memory correlated with intelligence!
• Working memory:
– limited capacity: 7+/- 2
– Contents decay rapidly (>20 seconds).
– Must get info into long term memory quickly and efficiently
• Individuals with rapid neuronal conduction can:
– complete manipulations more quickly
– transfer information to long-term memory faster
– All before decay occurs or short-term storage capacity is exceeded.
Issues with low nerve
conduction speed
• With low nerve conduction velocity:
– information in STM or working memory is lost; person must restart the
process
– Similar to when try to solve a problem and you not very alert
– You have to review information over and over because you can’t store it
– Takes LONGER to process similar amount of information.
• Higher IQ correlated with use of less brain energy
– lower rate of glucose metabolism during a challenging task
– Remember is correlational, not causal
– “hard” tasks not as hard; brain works less
– Does support model of brain efficiency = higher intelligence
The Brain areas implicated
in Intelligence
• Linguistic
– left frontal
– Left temporal lobes.
– Language based
• Logical-mathematical
•
•
Spatial ability depends on the interaction of somatosensory and visual
functions with parietal structures,
Mostly right hemisphere.
• Spatial
– Mathematical ability in humans
– depends on two distinct areas of the brain:
• left frontal region
• both parietal lobes.
Inheritability of
intelligence
• Intelligence has a heritability of around 50%
– At least 50% of variance for intelligence due to inherited traits
– Suggests large contribution of environment, however
– Most important is likely the interaction between heredity and
environment
• Documented genetic influence on several of the functions that
contribute to intelligence:
– working memory,
– processing speed
– reaction time in making a choice.
Inheritability of
intelligence
• Genetic factors appear to be slightly more important than
environmental:
– Most differences among individuals accounted for by genetic factors.
– Estimated heritabilities in one twin study were
• 90% for brain volume
• 82% for gray matter
• 88% for white matter.
• General intelligence has higher heritability than more specific
abilities
– Less heritability for verbal and spatial abilities
– Book suggests this provides additional argument for a biological basis for
g factor or general intelligence factor
– Individual variations may influence specific intelligences
Mental Retardation
• Limitations in intellectual functioning and adaptive skills
– Two models: developmental and Different
– are individuals jus slow to learn (hence word retarded) or are they
different physically (assume damage to brain produces different
functioning).
• Levels of Retardation
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Mild: IQ of 50 to 70
Moderate: IQ of 35 to 49
Severe: IQ of 20 to 34
Profound: IQ less than 20
Developmental disabiliteis
and mental retardation
• The criteria for retardation =arbitrary, and based on
judgments about the abilities required to get along in our
complex world.
– In 1978, then 1994 the American Psychiatric Association set the
criteria for retardation as a combination of an IQ below 70 points and
difficulty meeting routine needs like self-care.
– Prior to that, cut off was 85
– “cured” thousands of individuals
• Not only is any definition arbitrary, but it is situational and
cultural as well.
– A person considered retarded in our society might fare reasonably well
in a simpler environment.
– 6-hour retarded child
Developmental disabiliteis
and mental retardation
• MANY causes of retardation
• Retardation can be inherited or due to improper cell division
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Fragile X
Tay Sachs
Williams Syndrome
Prader Willy
Down Syndrome: 3 instead of 2 of the 21 chromosome
Phenylketonuria or PKU:
• genetic condition in which there is a a toxic accumulation of phenylalanine
• Faulty enzyme affects metabolism, causes neuron death
• Retardation can be caused by diseases contracted during infancy
– Meningitis; infection, etc.
– prenatal exposure to viruses such as rubella (measles).
Developmental disabiliteis
and mental retardation
• Can be due to teratogen exposure
– Maternal alcoholism is now the leading cause of mental retardation
– Other drugs
• Can be caused by prematurity
– 50% of preterm infants have significant disability
– Two most common: Cerebral palsy and mental retardation
• What about autism?
– Used to be generically called retardation
– Now identify it as separate disorder
– Many of individual who would have been diagnosed as retarded are now
labeled autistic
Down syndrome
• Down syndrome usually caused by
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the presence of an extra 21st chromosome,
Mosaicism: chromosome splits into many small parts
Trisomy 21: chromosonal split resembles presence of 3 21st chromosomes
Related to maternal age, but not necessarily caused by age
• Typically results in individuals with IQs in the 40 to 55 range.
– Early intervention critical
– Early that begin intervention, typically higher the IQ
• Amyloid precursor protein gene that involved in early-onset
Alzheimer’s disease is located on chromosome 21
– was discovered because Down syndrome individuals also develop amyloid plaques.
– 95% of people with Down syndrome have the entire extra chromosome
– In a few cases: only an end portion is present, and attached to another chromosome.
Other causes of
retardation
• Traumatic Brain Injury
– Occurs prenatally, at birth or in first few days/weeks of life
• Anoxia
• Stroke
• Other brain injury
– Results in brain that does not follow typical course of development
• Hydrocephalus
– Water on the brain; occurs when cerebrospinal fluid builds up in the cerebral
ventricles.
– The increased fluid volume crowds out neural tissue, usually causing
retardation.
– Hydrocephalus can be relatively easily treated if caught early
• installing a shunt that prevents the accumulation of the excess cerebrospinal fluid.
• Eliminate or greatly reduce likelihood of long term brain damage
autism
• Autism is a disorder that typically includes
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compulsive, ritualistic behavior
impaired sociability
Language deficits
Often to usually: mental retardation.
• Autism is now combined category for what used to
be 5 autism spectrum disorders
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Autism, classic autism, high functioning autism
Autistic Disorder
Asperger Syndrome or Asperger's Disorder
Pervasive Developmental Disorder (PDD),
Autism Spectrum Disorder (ASD).
Autism
• Autism:
– Disorder of attention, socialization, intellectual functioning
– Poor social interactions and lack of pretend play
• Does not make friends
• Does not play interactive games
– Affects verbal and nonverbal communication
• develops language slowly or not at all
• Does not adjust gaze to look at objects that others are looking at
– Often lack sense of “self”
• Does not refer to self correctly (for example, says "you want water" when the child
means "I want water")
• Does not startle at loud noises
– Has heightened or low senses of sight, hearing, touch, smell, or taste
• Slower processing speed (sort of)
– Often very low functioning in terms of academic and daily living skills
– But: may show remarkable talent in a single area
Autism: Common core of
impairment
• Whether retarded or not, autistic individuals share a common
core of impairment in
– Communication: often difficulty with communication
– Imagination: very literal
– Socialization: poor social skills
• May be mute or show delayed language development
– have trouble understanding verbal and nonverbal communication.
– Again, very literal and concrete
• Much of social behavior problem may be because autistic
person lacks a theory of mind
– ability to attribute mental states to oneself and to others.
– An individual with autism cannot infer what other people are thinking.
Theory of mind
• Two hypotheses as to how we develop a theory of
mind.
– “theory theory:” We build hypotheses over time based on our
experience.
– Simulation theory: We gain insight into people’s thoughts and
intentions by mentally mimicking the behavior of others.
• Data tends to support simulation view:
– Existence of mirror neurons
– Poor imitation skills in individuals with autism
– Very different from Williams syndrome, another genetic form of mental
retardation.
How does poor mirror
function affect intelligence?
• Impaired mirror functions reduces the autistic person’s
ability to
– Empathize
– learn language through imitation.
• For example, some individuals with autism show no
mirror neuron activity while
– imitating facial expressions
– or when observing a model’s hand movements.
• Other studies show reduced activation in the inferior
frontal cortex and motor cortex,
– Suggests weakness in the dorsal stream connections
– Provide important input to those areas containing mirror neurons.
Brain areas affected
in autism
• Subtle but widespread brain anomalies have been found,
• Especially in the
– brain stem,
– the cerebellum,
– temporal lobes.
– The location of damage is inconsistent, which may mean only
that there are various pathways to autism.
• What causes these brain defects?
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is uncertain,
at least we know they occur early, during brain development
So: know where and when to look for the answer.
NOT caused by parental rejection!
Williams syndrome
•
Another form of mental retardation; typically moderate to severe retardation
•
Is genetic misfiring: occurs randomly: deletion of approximately 25 genes from the 7th
chromosome
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Symptoms:
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Personality traits:
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include delayed speech early on, then exceptional speech
Strong learning by hearing; mimicking
Developmental delays, learning disorders and ADD
Variety of physical problems
very friendly
trusting strangers
fearing loud sounds or physical contact
being interested in music
Interestingly: studies suggest that individuals with Williams Syndrom have a greater
number of mirror neurons (compared to typically developing individuals)
Bottom line
• Use it or lose it!
– Staying active keeps neural circuits active
– Staying active enables brain to continue to make new connections
• General health important
– Healthy people show less cognitive decline
– Diet, exercise, general health contribute to brain health
• What you start with is important
– If have higher cognitive function, will maintain throughout life time
– Have more to work with, more to “lose”
• Most critical: using what you do have and maintaining it
– Maintaining what cognitive abilities you do have
– Making the most out of what abilities you have
– Taking care of your brain!