The Biology of Behavior

Chapter 2

Searching for the biology of “self”

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Is our identity in the heart? In the brain? In the whole body?

Biological Psychologists explore the associations between body, mind, and behavior.

Overview: What We Have in Mind

Building blocks of mind: Neurons and how they communicate (neurotransmitters)

Systems that build the mind: Functions of Parts of the Nervous system

Supporting player: the slower-communicating Endocrine system (hormones)

Tools for examining the brain and its activities More primitive and advanced brain structures

Neural and Hormonal Systems

Neurons and Neuronal Communication:The Structure of a Neuron

There are billions of neurons (nerve cells) throughout the body.

Action potential:a neural impulse that travels down an

axon like a waveJust as “the wave” can flow to the right in a stadium even though the people only move up and down, a wave moves down an axon although it is only made up of ion exchanges moving in and out.

The neuron

receives signals

from other neurons; some are telling it to

fire and some are telling it

not to fire.

• When the threshold is reached, the action potential starts moving.

• Like a gun, it either fires or it doesn’t; more stimulation does nothing.

• This is known as the “all-or-none” response.

The action

potential travels

down the axon

from the cell body

to the terminal

branches.

The signal is transmitted to another cell. However, the

message must find a way to cross a gap

between cells. This gap is

also called the synapse.

How neurons communicate(with each other):

When does the cell send the action potential? When it reaches a threshold.

The threshold is reached when excitatory (“Fire!”) signals outweigh the inhibitory (“Don’t fire!”) signals by a certain amount.

The synapse is also known as the “synaptic junction” or “synaptic gap.”

The SynapseThe synapse is a junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron.

Neurotransmitters

Neurotransmitters are chemicals used to send a signal across the synaptic gap.

Reuptake: Recycling Neurotransmitters [NTs]

Reuptake: After the neurotransmitters stimulate the receptors on the receiving neuron, the chemicals are taken back up into the sending neuron to be used again.

Seeing all the Steps TogetherNeural Communication:

Some Neurotransmitters and Their FunctionsNeurotransmitter Function Problems Caused by Imbalances

Roles of Different Neurotransmitters

Serotonin Affects mood, hunger, sleep, and arousal

Undersupply linked to depression; some antidepressant drugs raise serotonin levels

DopamineInfluences movement, learning, attention, and emotion

Oversupply linked to schizophrenia; undersupply linked to tremors and decreased mobility in Parkinson’s disease and ADHD

Acetylcholine (ACh)

Enables muscle action, learning, and memory

ACh-producing neurons deteriorate as Alzheimer’s disease progresses

Norepinephrine Helps control alertness and arousal

Undersupply can depress mood and cause ADHD-like attention problems

GABA gamma-aminobutyric acid

A major inhibitory neurotransmitter

Undersupply linked to seizures, tremors, and insomnia

GlutamateA major excitatory neurotransmitter; involved in memory

Oversupply can overstimulate the brain, producing migraines or seizures; this is why some people avoid MSG (monosodium glutamate) in food

Serotonin pathways

Networks of neurons that communicate with serotonin help regulate mood.

Networks of neurons that communicate with dopamine are involved in focusing attention and controlling movement.

Dopamine pathways

Divisions of the Nervous System

The Inner and Outer Parts of the Nervous System

The Central Nervous System (CNS), the brain and spinal cord, is the body’s decisionmaker.

The Peripheral Nervous System (CNS), gathers information from the body and sends CNS decisions out to the body.

Types of NeuronsSensory

neurons carry messages IN

from the body’s tissues and

sensory receptors to the

CNS for processing.

Motor neurons carry instructions

OUT from the CNS out to the body’s tissues. Interneurons (in the

brain and spinal cord) process information between the sensory

input and motor output.

The Peripheral Nervous System

The Autonomic

Nervous System:

The sympathetic NS arouses

(fight-or-flight)

The parasympathetic

NS calms(rest and digest)

Neural Networks

These complex webs of interconnected neurons form with experience.

Remember: “Neurons that fire together, wire together.”

Interneurons in the SpineDecisions made without the brain

Your spine’s interneurons trigger your hand to pull away from a fire before you can say OUCH!

This is an example of a reflex action.

The brain finds out about the reflex after it happens.

The Endocrine System

The endocrine system: a set of glands that produce chemical messengers called hormones.

The Body’s “Slow but Sure” Endocrine Message System The endocrine system sends

molecules as messages, just like the nervous system, but it sends them through the bloodstream instead of across synapses.

These molecules, called hormones, are produced in various glands around the body.

The messages go to the brain and other tissues.

Pituitary gland

The pituitary gland is the “master gland” of the endocrine system.

It is controlled through the nervous system by the nearby brain area--the hypothalamus.

The pituitary gland produces hormones that regulate other glands.

Tools of Discovery and Brain Structures

What We’ll See:How we learn about the brain: Scans and moreThe primitive, life-sustaining, inner parts of the brain: The brainstem and

limbic systemHigher Brain structure that help us think and act: The Cerebral Cortex

Monitoring activity in the brainTools to read electrical, metabolic, and magnetic

activity in the brain:

EEG: electroencephalogram

MRI: magnetic resonance imaging fMRI: functional MRI

PET: positron emission tomography

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An EEG (electroencephalogram) is a recording of the electrical waves sweeping across the brain’s surface.An EEG is useful in studying seizures and sleep.

EEG: electroencephalogram

The PET scan allows us to see what part of the brain is active by tracing where a radioactive form of glucose goes while the brain performs a given task.

PET: positron emission tomography

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MRI (magnetic resonance imaging) makes images from signals produced by brain tissue after magnets align the spin of atoms.The arrows below show ventricular enlargement in a schizophrenic patient (right).

MRI: magnetic resonance imaging

Functional MRI reveals brain activity and function rather than structures.

Functional MRI compares successive MRI images taken a split second apart, and shows changes in the level of oxygen in bloodflow in the brain.

fMRI: functional MRI

The Brain: Less Complex Brain Structures

Our tour of the brain begins with parts of the human brain found also in simpler animals; these parts generally deal with less complex functions:

Brainstem (Pons and Medulla)

Thalamus

Reticular Formation

Cerebellum

Limbic System

The Brainstem: Pons and Medulla

The Base of the Brainstem: The Medulla

The medulla controls the most basic functions such as heartbeat and breathing.

Someone with total brain damage above the medulla could still breathe independently, but someone with damage in this area could not.

The Thalamus The thalamus is the

“sensory switchboard” or “router”: All sensory messages, except smell, are routed through the thalamus on the way to the cortex (outer brain).

These messages cross over from one side of the body to the opposite side of the brain.

The crossover

Reticular (“net-like”) Formation

The reticular formation is a nerve network in the brainstem.

It enables alertness (arousal); stimulating this makes us wide awake.

It also filters incoming sensory information and relays it to other brain areas.

The cerebellum helps coordinate voluntary movement such as playing a sport.

Cerebellum (“little brain”)

The cerebellum has many other functions, including enabling nonverbal learning and memory.

emotions such as fear and aggression.

basic drives such as hunger and sex.

the formation of episodic memories.

The hippocampus (“seahorse”) processes conscious, episodic

memories. works with the amygdala to

form emotionally charged memories.

The Amygdala (“almond”) consists of two lima bean- sized

neural clusters. helps process emotions,

especially fear and aggression.

The Limbic (“Border”) SystemThe limbic system coordinates:

The Amygdala: Enabling two different responses to threat

Electrical stimulation of one area of a cat’s amygdala provokes aggressive reactions.

If you stimulate a different part of the amygdala and put the cat in a cage with a mouse, the cat will cower in terror.

lies below (“hypo”) the thalamus.

regulates body temperature and ensures adequate food and water intake (homeostasis), and is involved in sex drive.

directs the endocrine system via messages to the pituitary gland.

The Hypothalamus:Thalamus

Riddle: Why did the rat cross the grid? Why did the rat want to get to the other side?

The Hypothalamus as a Reward Center

Pushing the pedal that stimulated the electrode placed in the hypothalamus was much more rewarding than food pellets.

Review of Brain Structures

Higher Brain, Split BrainTopics for your cortex to process:

Cerebral Cortex Structure: The Lobes

The motor and sensory strips and association areas

Brain Plasticity Functioning of he

right and left hemispheres from cases of the divided and intact brains

The Cerebral Cortex:

300 billion synaptic connections

The brain has left and right hemispheres

The outer grey “bark” structure that is wrinkled in order to create more surface area for 20+ billion neurons.

Organized into 4 lobes in each of two hemispheres.

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The Lobes of the Cerebral Cortex: Preview

Frontal Lobes

Parietal Lobes

Occipital Lobes

Temporal Lobes

involved in speaking and muscle movements and in making plans and judgments

include the sensory cortex

include the visual areas; they receive visual information from the opposite visual field

include the auditory processing areas

Input: Sensory cortex (Left hemisphere section receives input from the body’s right side)

Output: Motor cortex (Left hemisphere section controls the body’s right side)

Functions of the Brain: The Motor and Sensory Strips

Axons receiving motor signals FROM the cortex

Axons sending sensory

information TO the cortex

Sensory Functions of the Cortex

The sensory strip deals with information from touch stimuli.

The occipital lobe deals with visual information.

Auditory information is sent to the temporal lobe.

The Visual Cortex

This fMRI scan shows increased activity in the visual cortex when a person looks at a photograph.

Association function of the cortexMore complex animals have more cortical space devoted to integrating/associating information

Case study: Phineas Gage

In a work accident, a metal rod shot up through Phineas Gage’s skull, destroying his eye and part of his frontal lobes. After healing, he was rude, odd, irritable, and unpredictable.

Possible explanation for the change in personality: Damage to his frontal lobes hurt his ability to inhibit emotions and impulses.

Whole-brain Association Activity

Whole-brain association activity involves complex activities which require communication among association areas across the brain such as: memory language attention meditation and spirituality consciousness

This 6-year-old had a hemispherectomy to end life-threatening seizures; her remaining hemisphere compensated for the damage.

Plasticity: The Brain is Adaptable

If the brain is damaged, especially in the general association areas of the cortex: the brain does not repair

damaged neurons, BUT it can restore some functions

it can form new connections, reorganize, reassign brain areas to new functions.

Some neurogenesis, production of new brain cells, helps rebuild

Brain Studies

Researchers have studied the impact of this surgery on patients’ functioning.

Split-

To end severe whole-brain seizures, some people have had surgery to cut the corpus callosum, a band of axons connecting the hemispheres.

Separating the Hemispheres:Factors to Keep in Mind

Each hemisphere controls the opposite side of the body AND is aware of the visual field on that opposite side.

Without the corpus callosum, the halves of the body and the halves of the visual field do not work together.

Only the left half of the brain has enough verbal ability to express its thoughts out loud.

Split visual field

Each hemisphere perceives the half of the view in front of you that goes with the half of the body that is controlled by that hemisphere.

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Divided Awareness in the Split BrainTry to explain the following result:

The divided brain in action

Talent: people are able to follow two instructions and draw two different shapes simultaneously

Drawback: people can be frustrated that the right and left sides do different things

Our Two Hemispheres

Lateralization (“going to one side”)The two hemispheres serve some different functions. How do we know about these differences? Brain damage studies revealed many functions of

the left hemisphere. Brain scans and split brain studies show more about

the functions of the two hemispheres, and how they coordinate with each other.

• Thoughts and logic

• Language: words and definitions

• Pieces and details

• Feelings and intuition

• Language: tone, inflection, context

• Wholes, including the self

The intact but lateralized brainRight-Left Hemisphere Differences

Left Hemisphere Right Hemisphere

Behavior Genetics and Evolutionary Psychology

Behavior Genetics: Predicting Individual Differences

More ways of exploring the origins of the biology of behavior:1. Understanding genes 2. Twin and adoption

studies 3. Gene/environment

interactions4. Evolutionary

Psychology

Behavior geneticists

study how heredity and environment

contribute to human differences.

Let’s start by looking at GENES.

Genes are parts of DNA molecules, which are found in chromosomes in the nuclei of cells.

DNA (Deoxyribonucleic Acid)

GENES:The Building Blocks of Heredity and Development

Genes are parts of DNA molecules, which are found in chromosomes in the nuclei of cells.

GENES:The Building Blocks of Heredity and Development

Chromosomes are made of DNA, which are made of genes.

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Chromosome: threadlike structure made largely of DNA

molecules

DNA: a spiraling, complex molecule containing

genes

Chromosomes and Inheritance The human genome includes 46

chromosomes in 23 sets matched sets; each chromosome has the same gene locations.

This includes the X and Y chromosomes, not a matched set in males, who are missing some genes on the Y.

A biological parent donates half his/her set of chromosomes to his/her offspring.

We received half a set of chromosomes from each biological parent.

The Human Genome:20,000 to 25,000 Genes Human genomes are so nearly

identical that we can speak of one universal human genome.

Yet tiny genetic differences make a difference. If there is a: .001 percent difference in

genome, your DNA would not match the crime scene/you are not the baby’s father.

0.5 to 4 percent difference in genome, you may be a chimpanzee.

50 percent difference in genome, you may be a banana.

The genome: an organism’s entire

collection of genes

How Genes Work Genes are not blueprints;

they are molecules. These molecules have

the ability to direct the assembly of proteins that build the body.

This genetic protein assembly can be turned on and off by the environment, or by other genes.

Any trait we see is a result of the complex interactions of many genes and countless other molecules.

Or vary the genes in the same environment?

Next step for behavior geneticists:Controlling Variables

Can we design an experiment to keep genes

constant and vary the environment and see what

happens?

Twin and Adoption StudiesTo assess the impact of nature and nurture, how do we examine how genes make a difference within the same environment? study traits of

siblings vs. identical twins

see if the siblings vary more than twins

Fraternal and Identical Twins

Fraternal “twins” from separate eggs are not any more genetically alike than other siblings.

Identical twin: Same sex only

Fraternal twin: Same or opposite sex

Twin and Adoption StudiesHow do we find out how the same genes express themselves in different environments?We can study the traits of identical twins as they grow up, or if they were raised separately (e.g., the Minnesota Twin Family Study).

Identical vs. Fraternal TwinsStudies of twins in adulthood show that identical twins are more alike than fraternal twins in: personality traits such as

extraversion (sociability) and neuroticism (emotional instability).

behaviors/outcomes such as the rate of divorce.

abilities such as overall Intelligence test scores.

Critiques of Twin Studies1. In the more recent years of the

Minnesota Twin Family Study, twins have known about each other and may influence each other to be more similar.

2. Coincidences happen; some randomly chosen pairs of people will have similar traits.

3. Environments may be similar; adoptive families tend to be more similar than randomly selected families in education, income, and values.

Studies of Identical Twins Raised ApartSimilarities found in identical twins despite being raised in different homes: personality, styles of

thinking and relating abilities/intelligence

test scores attitudes interests, tastes specific fears brain waves, heart

rateBUT none of these factors explains, better than the genetic explanation, why fraternal twins have more differences than identical twins.

Searching for Parenting Effects:Biological vs. Adoptive RelativesStudies have been performed with adopted children for whom the biological relatives are known.Findings: Adopted children seem to be more similar to their genetic relatives than their environmental/nurture relatives.

Given the evidence of genetic impact on how a person turns out,

does parenting/nurture make any difference?

Does the home environment have any impact?

Despite the strong impact of genetics on personality, parenting has an influence on:

religious beliefs values manners attitudes politics habits

Parenting Does Matter

Gene-Environment Interaction: genes turn each other on and off in response to environmental conditions

Epigenetics: The study of how this happens: The environment acts on the surface of genes to alter their activity

How does the interaction of genes and environment work?

Example in animals: shortened daylight triggers animals to change fur color or to hibernate

Example in humans: obesity in adults can turn off weight regulation genes in offspring

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Some topics: Natural selection and

adaptation Evolutionary success may help

explain similarities An evolutionary explanation

of human sexuality

Evolutionary Psychology: Understanding Human Nature

Evolutionary psychology is the

study of how evolutionary

principles help explain the origin and

function of the human mind, traits, and

behaviors.

We have been talking so far about human differences; we may now seek insight in the ways in which humans are alike.

Begin with a species’ genome, which contains a

variety of versions of genes that shape traits.

Conditions make it difficult for

individuals with some traits (some versions of those genes) to survive long enough to

reproduce.

Other individuals thus have their

traits and genes “selected” to spread in the population.

Evolutionary Psychology: Natural Selection: How it Works

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Dmitri Balyaev and Lyudmila Trut spent 40 years selecting the most gentle, friendly, and tame foxes from a fox population, and having those reproduce.

As a result, they were able to shape avoidant and aggressive creatures into social ones, just as wolves were once shaped into dogs.

Artificial SelectionThe Domesticated Silver Foxes

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Example: Why does “stranger anxiety”

develop between the ages of 9 and 13 months? Hint: in evolutionary/survival terms, humans are learning to walk at that time.Infants who used their new ability to walk by walking away from family and toward a lion might not have survived to reproduce as well as those who decided to stay with parents around the time they learned to walk.

How might evolution have shaped the human species?

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Why do people so easily acquire a phobia of snakes, more easily than a phobia of cars?

An evolutionary psychologist would note that snakes are often poisonous……so, those who more readily learned to fear them were more likely to survive and reproduce.

Evolutionary Psychology’s Explanation of Biologically Driven Phobias

Critiquing Evolutionary Psychology

“You’re just taking current

reality and constructing a way you could have predicted

it.” This is hindsight

reasoning and unscientific.

“You’re attributing too much to genes rather than the

human ability to make choices about social behavior.”

Response: yes, but there are predictions made about future behavior using this reasoning.

Response: yes, but our evolutionary past does not prevent our ability to act differently; “is” does not equal “ought.”

Evolution: Theory Evolution is a scientific theory

(NOT a “guess” and not a hypothesis, but something more): a coherent set of principles that fits very well with the accumulated evidence.

Parts of the evolutionary story may conflict with other stories of origins and change over time.

Is there room for overlap and agreement?

Possible areas of consensus, with or without evolution: The human mind

and body seems almost “designed,” by evolution or other forces, to have certain traits and abilities.

Nurture may shape us, but we seem to start out with some sort of human nature.