Download Gluck_OutlinePPT_Ch02

Chapter 2
The Neuroscience
of Learning and
Memory
BRAIN FACTS
•
Weighs 3 to 3.5 lbs
•
•
10% of the cells are
neurons (100 billion)
Uses 20% of the
body’s energy
•
30,000 neurons fit on
the head of a pin
Needs 8 gallons of
blood per hour
•
Neurons make 1,000
to 20,000 connections
Consumes 1/5 of the
body’s oxygen
•
Needs 8 glasses of
water per day
•
•
•
Synaptic permutations
2
2.1
A Quick Tour of
the Brain
2.1 A Quick Tour of the Brain
•
The Brain and the Nervous System
•
Observing Brain Structures and Function
4
Neuroscience and the Brain
•
Neuroscience—study of the nervous
system, especially the brain
•
Neuroscientists believe the brain is the seat
of learning and memory.
5
The Nervous System
•
Nervous system—distributes and
processes information.
Central nervous system (CNS)—brain and
spinal cord
Peripheral nervous system (PNS)—nerve fibers
that connect CNS to rest of body
•
Neurons—nerve fibers, collect and
process incoming information.
6
Nervous
Systems
7
8
The Human Brain
•
Cerebral cortex—tissue covering top and
sides of brain.
Divided into four lobes:
Frontal (plan and perform actions)
Parietal (sensory)
Temporal (hearing)
Occipital (vision)
Subcortical structures—under cerebral cortex
Thalamus, basal ganglia, hippocampus, amygdala
involved in learning and memory.
9
The Human Brain
•
Cerebellum—behind cortex
Important for coordinated movement
Involved in learning that requires physical action.
•
Brainstem—connects brain to spinal cord.
Key in regulating automatic functions (e.g.
breathing, body temperature)
10
The Visible Surface of
the Human Brain
© Visuals Unlimited, Ltd.
11
The Human Brain
12
Human Subcortical Structures
•
Thalamus—receives sensory
information; relays it to brain.
•
Basal ganglia—involved
in learning skilled
movements.
•
Hippocampus—linked
to learning new facts,
memory.
•
Amygdala—linked to
emotion.
13
Comparative Brain Anatomy
•
Study of similarities and differences among
organisms’ brains
•
Vertebrates
Have both CNS and PNS.
Differ in overall brain size and brain structure size.
•
The complex relationship between brain
size and learning capacity needs further
research.
14
Comparative Brain Anatomy in
Several Vertebrate Species
15
Learning without a Brain
Invertebrates:
With recognizable,
decentralized, brains
(e.g. octopus, bee).
Capable of maze learning,
learning by observation
With no recognizable brain
(e.g. jellyfish, worm)
Mauro Fermariello/Photo Researchers
•
Can learn to avoid negative stimuli.
•
Simple invertebrate nervous systems are
useful in research.
16
Observing Brain Structure and Function:
The Dark Ages of Brain Science
To detect brain damage:
Look through
hole in skull.
Remove brain.
•
Franz Joseph Gall
(1758–1828)
Pseudoscience of
phrenology
© Charles Walker/Topfoto/The Image Works
•
17
Structural Neuroimaging:
Looking inside the Living Brain
•
Structural Neuroimaging—modern
methods to see brain size/shape, structures,
lesions
Computed tomography (CT)—takes many Xrays from different angles.
Forms a three-dimensional representation of body
structures, such as the brain.
Magnetic resonance imaging (MRI)—uses
changes in magnetic field to generate image;
magnet aligns atoms in brain or body.
More popular than CT
18
MRI Images
Custom Medical Stock
Photography
Scott Camazine/Photo
Researchers, Inc.
19
2.1 Interim Summary
•
Central nervous system (CNS) = brain and
spinal cord
•
Peripheral nervous system (PNS) = sensory
and motor neurons
•
Brain connects to PNS to control behavior.
Most connections pass through spinal cord.
20
2.1 Interim Summary
•
Vertebrate brain organized into:
Cerebral cortex
Frontal, temporal, parietal, and occipital lobes
Cerebellum
Brainstem
•
Cerebral cortex structures are specialized:
Process sensory information.
Generate motor outputs.
21
2.1 Interim Summary
•
Animals with simple nervous systems can
learn.
Study “simpler” nervous systems to learn how
vertebrate (even human) brains work.
•
Early study of the brain:
Phrenology: relate personality/mental abilities to
size and shape of skull.
Study brain anatomy by examining post-mortem
healthy or abnormal brains after death.
22
2.1 Interim Summary
•
Modern structural brain imaging techniques
(e.g., MRI and CT):
Provide ways to look at the physical structure of
living brains
Cause no harm.
Lesions/abnormalities may be visible on images.
23
2.2
From Brain to
Behavior
2.2 From Brain to Behavior
•
Information Pathways in the Central
Nervous System
•
Observing Brain Systems in Action
•
Unsolved Mysteries—What Do Functional
Imaging Methods Really Measure?
25
Brain Function
•
Brain systems are specialized for specific
functions.
•
Some localization of brain function:
Many functions may depend on a single brain area.
One function may rely on many brain areas.
26
Information Pathways in the CNS
•
Reflex—an involuntary, automatic
response to a stimulus (“hardwired”).
Newborn sucking reflex
Newborn palmar grasp reflex
Human knee-jerk reflex
Eye blink reflex
27
Reflexes Present at Birth
28
Behavior Without the Brain:
Spinal Reflexes
•
Bell-Magendie law of neural specialization
Spinal cord has two parallel nerve systems.
Sensory nerves—sensory information from PNS to
spinal cord
Motor nerves—motor signals from spinal cord to
muscles
•
Charles Sherrington (1857–1952)
Simple “spinal reflexes” combine into complex
movements.
29
Behavior
Without the
Brain:
Spinal
Reflexes
30
Incoming Stimuli:
Sensory Pathways into the Brain
•
Primary sensory cortices are the first stage
of sensory processing.
•
More advanced processing occurs
in adjacent
cortical regions.
31
Outgoing Responses:
Motor Control
•
Primary motor cortex gets input from frontal
lobes, cerebellum, basal ganglia, brainstem:
Sends output to the spinal cord via the brain stem.
Spinal cord activates motor fibers that control
muscles.
32
Motor Control:
How to Pick Up a Coffee Cup
33
Observing Brain Systems
in Action
•
Human neuropsychology—studies
relationship of brain function to behavior.
Generally, studies case studies of patients with
brain damage.
Cognitive testing may guide patient rehabilitation
and provide further knowledge of normal brain
function.
34
Experimental Brain Lesions
•
Research on animal brains:
Follow strict ethical guidelines.
Carefully lesion or deactivate animal brain
regions.
Create animal “models” of human patients.
Animal lesions more precise.
•
Coordination of human and animal studies
provide better view of brain and behavior.
35
Memory and the Brain
•
Karl Lashley (1890–1958)
•
Conducted brain lesion studies to find
location of engram (physical change in
brain, basis for memory).
•
Theory of equipotentiality—brain acts a a
whole to store memories (no single area).
36
Functional Neuroimaging:
Watching the Brain in Action
•
Functional Neuroimaging—shows activity
or function of the living brain.
Positron emission tomography (PET)—
measures brain activity by detecting positrons.
M.E. Raichle, Mallinckrodt of Radiology, Washington University School of Medicine
37
Functional Neuroimaging:
Watching the Brain in Action
•
Difference image—subtract image of a
relaxed, baseline brain from the image of a
brain engaged in specific activity.
Images show which brain regions change or
remain constant.
Also made using functional MRI (fMRI).
PET and fMRI produce similar, but not exact,
imaging of brain’s localized use of oxygen.
38
Comparing PET
and fMRI
Custom Medical Stock Photography
Adapted from Devlin et al., 2002.
39
Unsolved Mysteries:
What Do Functional Neuroimaging
Techniques Really Measure?
•
fMRI reflects local blood oxygenation.
•
PET reflects blood flow or glucose
utilization.
•
Assumption is that neurons in highly active
brain areas use more oxygen (seen on
fMRI), which required more blood flow to
supply this oxygen (seen on PET).
40
Unsolved Mysteries:
What Do Functional Neuroimaging
Techniques Really Measure?
•
fMRI and PET images can be different.
Very active neurons may not need additional
oxygen.
Blood flow increase may be utilized for more
functions than oxygenation.
•
Neuroscientists need to be careful in
imaging interpretations.
41
Electroencephalography:
Charting Brain Waves
•
Electroencephalography (EEG)—
electrodes on scalp measure roar of axons
firing in brain areas.
Form two-dimensional “brain wave.”
•
Event-related potentials (ERPs)—
averaged EEGs from a repeated event
Can measure changes in brain activity during
learning and memory tasks.
42
Phanie/Photo Researchers, Inc.
EEG and
Learning-Related Changes
(b) Adapted from Tremblay and Kraus, 2002.
43
2.2 Interim Summary
•
Reflexes = hardwired (unlearned) responses.
Sherrington and other early neuroscientists
believed complex learning was built up from
combinations of simple spinal reflexes.
•
Bell and Magendie = propose/demonstrate
parallel fiber systems.
Carry sensory information into spinal cord.
Commands go from the spinal cord out to
muscles and organs.
44
2.2 Interim Summary
•
Sensory information is (initially) processed in
brain’s cortical regions.
•
Regions are specialized:
Primary auditory cortex (A1) for sounds
Primary visual cortex (V1) for sights
Primary somatosensory cortex (S1) for touch
•
Regions transmit signals to other brain
areas for further processing.
45
2.2 Interim Summary
•
Primary motor cortex (M1): outputs guide
coordinated movements.
Portion of motor cortex devoted to a given body
part reflects (innate or learned) degree of motor
control for that part.
•
Human and animal brain lesions reveal:
Brain function.
Neurobiology of learning and memory.
46
2.2 Interim Summary
•
Lashley conducts early brain lesion studies.
Brain’s engram = physical trace of a memory
Not stored in a single place; rather, a function of the
whole brain.
•
Modern brain studies show localized
evidence of engrams.
Particularly in subcortical structures (e.g.,
cerebellum)
47
2.2 Interim Summary
•
Functional neuroimaging methods (e.g.,
fMRI and PET):
Track brain activity indirectly.
Measure increases or decreases in brain’s blood
flow during task performance.
Create difference image to identify more (or less)
active brain areas.
48
2.2 Interim Summary
•
Electroencephalography (EEG):
Detect electrical activity (“brain waves”).
Electrodes placed on scalp.
Brain waves = summed electrical charges of many
neurons.
•
Event-related potentials = EEG recordings
averaged across many repeated stimulations.
Allow enhanced detection of electrical signals.
49
2.3
Learning and
Synaptic Plasticity
2.3 Learning and
Synaptic Plasticity
•
The Neuron
•
Measuring and Manipulating Neural Activity
•
Synaptic Plasticity
51
The Neuron
•
Dendrites—inputs; receive signals.
•
Cell body (soma)—integrates dendrite
signals.
•
Axons—transmit information.
•
Glia cells—give functional and structural
support to neurons.
52
Biophoto Associates/Photo Researchers
The Neuron
53
The Synapse:
Where Neurons Connect
•
Synapse—gap between neurons; pass
chemical signals across (neurotransmitters)
•
Presynaptic neuron—sending neuron
•
Postsynaptic neuron—receiving neuron
•
Receptors—molecules specialized to
received specific neurotransmitters
54
Dennis Kunkel/Phototake
The
Synapse
55
Information Flow across a Synapse
56
Neuromodulators:
Adjusting the Message
•
Neuromodulators—alter how neurons
exchange messages.
Some neurons (especially in the brain stem)
release chemicals into broad areas to affect
many neurons simultaneously.
e.g., acetylcholine
•
Change the conditions for neural firing.
57
Measuring and Manipulating
Neural Activity
•
Neurophysiology—study of neural
activation.
•
Single-cell recording—
researchers implant
electrodes into
an animal’s brain,
which are held in
place by a hat-like
“head stage.”
electrode
58
Stimulating Neurons into Activity
• Researchers
can deliberately stimulate
neurons to observe corresponding
behavior.
A way to map cortical areas (homunculus)
Transcranial magnetic stimulation (TMS)
involves placing a magnet on the skull.
59
The British Museum, Natural History
Homunculus and Motor Cortex
60
Manipulating Neuronal Function
with Drugs
Drugs—chemicals that change the body’s
biochemical functioning
• Subunit Pharmacology
• Can affect:
•
Neurotransmitter release.
Neural firing.
e.g., morphine can fit into opioid receptors.
Neurotransmitter reuptake.
61
Synaptic Plasticity
•
Synaptic plasticity—ability of synapses to
change with experience
•
According to Donald Hebb, the connection
between two contiguously firing neurons
will strengthen.
62
Long-Term Potentiation
•
Long-Term Potentiation (LTP)—synaptic
transmission is sensitized by recent
experience.
Occurs in many brain regions of many
organisms.
•
What is the relationship of LTP to learning?
Drugs that block LTP can impair learning.
Rats bred to produce more LTP are better
learners.
63
Long-Term Potentiation
64
Associative
Long-Term
Potentiation
65
How is LTP Implemented in
a Neuron?
•
Postsynaptic receptors may become more
responsive and fire more easily for hours.
•
Presynaptic neurons may release more
neurotransmitter for hours.
•
Postsynaptic neurons may permanently
change.
66
Long-Term Depression
•
Long-Term Depression (LTD)—Neurons
that do not fire together become disengaged.
•
Possible reasons:
Decrease in postsynaptic receptor responsiveness
Decrease in presynaptic neurotransmitter release
Long-term structural changes in neurons and
synapses
67
2.3 Interim Summary
•
Neurons:
Dendrites collect signals (input).
Axon transmits messages (output).
•
Neuronal communication occurs across
synapses (tiny gaps).
Presynaptic (sending) neuron releases
neurotransmitter (chemical message) into synapse.
Message activates receptors on postsynaptic
(receiving) neuron.
68
2.3 Interim Summary
•
Single-cell recordings monitor and record
single neurons as they become active (“fire”).
Implanted electrodes deliver electrical charges that
stimulate a neuron into activity.
Observe evoked behavior.
•
Drugs alter body’s biochemical functioning.
Brain-affecting drugs increase or decrease transfer
of information between subsets of neurons.
69
2.3 Interim Summary
•
Learning requires physical changes in neural
circuits.
Physical changes affect firing behavior.
Changes involve neuron’s shape/size and/or
number of neuronal connections.
•
Synaptic plasticity = ability of synapses to
change with experience.
Strengthening or weakening connections
influences firing.
70
2.3 Interim Summary
•
Long-term potentiation (LTP): transmission
becomes more effective with experience.
Hebb’s rule: Synapses strengthened by conjoint
presynaptic and postsynaptic neuronal activity.
“neurons that fire together, wire together”
•
Long-term depression (LTD): transmission
becomes less effective with experience.
Weakens neuronal connections.
71