Chapter 2

The Neuroscience of Learning and

Memory

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BRAIN FACTS

• Weighs 3 to 3.5 lbs

• 10% of the cells are neurons (100 billion)

• 30,000 neurons fit on the head of a pin

• Neurons make 1,000 to 20,000 connections

• Synaptic permutations

• Uses 20% of the body’s energy

• Needs 8 gallons of blood per hour

• Consumes 1/5 of the body’s oxygen

• Needs 8 glasses of water per day

2.1

A Quick Tour of the Brain

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2.1 A Quick Tour of the Brain

• The Brain and the Nervous System

• Observing Brain Structures and Function

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Neuroscience and the Brain

• Neuroscience—study of the nervous system, especially the brain

• Neuroscientists believe the brain is the seat of learning and memory.

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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.

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Nervous Systems

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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 cortexThalamus, basal ganglia, hippocampus, amygdala

involved in learning and memory.

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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)

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The Visible Surface of the Human Brain

© Visuals Unlimited, Ltd.

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The Human Brain

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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.

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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.

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Comparative Brain Anatomy in Several Vertebrate Species

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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)

Can learn to avoid negative stimuli.

• Simple invertebrate nervous systems are useful in research.

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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

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Structural Neuroimaging: Looking inside the Living Brain

• Structural Neuroimaging—modern methods to see brain size/shape, structures, lesions Computed tomography (CT)—takes many X-rays

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

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MRI Images

Custom Medical Stock Photography

Scott Camazine/Photo Researchers, Inc.

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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.

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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.

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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.

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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.

2.2

From Brain to Behavior

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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?

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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.

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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

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Reflexes Present at Birth

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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.

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Behavior Without the Brain: Spinal Reflexes

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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.

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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.

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Motor Control: How to Pick Up a Coffee Cup

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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.

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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.

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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).

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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

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• 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.

Functional Neuroimaging: Watching the Brain in Action

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Comparing PET and fMRI

Custom Medical Stock Photography Adapted from Devlin et al., 2002.

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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).

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• 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.

Unsolved Mysteries: What Do Functional Neuroimaging

Techniques Really Measure?

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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.

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EEG and Learning-Related Changes

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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.

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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.

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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.

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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)

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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.

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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.

2.3

Learning and Synaptic Plasticity

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2.3 Learning and Synaptic Plasticity

• The Neuron

• Measuring and Manipulating Neural Activity

• Synaptic Plasticity

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The Neuron

• Dendrites—inputs; receive signals.

• Cell body (soma)—integrates dendrite signals.

• Axons—transmit information.

• Glia cells—give functional and structural support to neurons.

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The Neuron

Biophoto Associates/Photo Researchers

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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

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The Synapse

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Information Flow across a Synapse

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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.

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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

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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.

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Homunculus and Motor Cortex

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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.

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Synaptic Plasticity

• Synaptic plasticity—ability of synapses to change with experience

• According to Donald Hebb, the connection between two contiguously firing neurons will strengthen.

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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.

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Long-Term Potentiation

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Associative Long-Term Potentiation

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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.

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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

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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.

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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.

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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.

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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.