The Brain and Behavior

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					                                         The Brain and Behavior


                                                Phrenology
 Franz Gall
 A wrongheaded theory Despite initial acceptance of Franz Gall's speculations, bumps on the skull tell us
  nothing about the brain's underlying functions.
 Nevertheless, some of Gall's assumptions have held true. Different parts of the brain do control different
  aspects of behavior, as you will see throughout this chapter.

                              Discovering Psychology: The Behaving Brain
 This program discusses the structure and composition of the brain: how neurons function, how
  information is collected and transmitted, and how chemical reactions determine every thought, feeling,
  and action.
 http://learner.org/resources/series138.html#
                                          Neural Communication
 Biological Psychology
    branch of psychology concerned with the links between biology and behavior
    some biological psychologists call themselves behavioral neuroscientists, neuropsychologists,
      behavior geneticists, physiological psychologist, or biopsychologists
 Neuron
    a nerve cell
    the basic building block of the nervous system
                                        The Nervous System
 Major division - Central vs. Peripheral
    Central or CNS- brain and spinal cord
    Peripheral- nerves connecting CNS to muscles and organs

                                  The Central Nervous System Hierarchy

                                  Peripheral Nervous System
 3 kinds of neurons connect CNS to the body
    sensory

    m o to r

    interneurons

 Motor - CNS to muscles and organs
 Sensory - sensory receptors to CNS
 Interneurons: Connections Within CNS
    Most numerous in CNS



                                               Sympathetic
   “ Fight or flight” response
   Release adrenaline and noradrenaline
   Increases heart rate and blood pressure
   Increases blood flow to skeletal muscles
   Inhibits digestive functions

                                              Parasympathetic
   ― Rest and digest ‖ system
   Calms body to conserve and maintain energy
   Lowers heartbeat, breathing rate, blood pressure

                                            Autonomic System
 Two divisions:
    sympathetic

    Parasympatheitic

 Control involuntary functions
    heartbeat

    blood pressure

    respiration
    perspiration
    digestion
 Can be influenced by thought and emotion



                                           Neural Communication
 Dendrite
    the bushy, branching extensions of a neuron that receive messages and conduct impulses toward
      the cell body
 Axon
    the extension of a neuron, ending in branching terminal fibers, through which messages are sent to
      other neurons or to muscles or glands
 Myelin [MY-uh-lin] Sheath
    a layer of fatty cells segmentally encasing the fibers of many neurons
    makes possible vastly greater transmission speed of neutral impulses
                                            Neural Communication
 Action Potential
    a neural impulse; a brief electrical charge that travels down an axon
    generated by the movement of positively charges atoms in and out of channels in the axon‘s
      membrane
 Threshold
    the level of stimulation required to trigger a neural impulse
                                            Neural Communication
 Synapse [SIN-aps]
    junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving
      n e u ro n
    tiny gap at this junction is called the synaptic gap or cleft
 Neurotransmitters
    chemical messengers that traverse the synaptic gaps between neurons
    when released by the sending neuron, neuro-transmitters travel across the synapse and bind to
      receptor sites on the receiving neuron, thereby influencing whether it will generate a neural impulse




                                            The Firing of a Neuron:
                                        First Stage - Resting Potential
 Resting Potential - At rest the inside of the cell is at -70 microvolts
 With inputs to dendrites the inside becomes more positive and if resting potential rises above threshold
  an action potential starts to travel from cell body down the axon

                          Stage 3 – Repolarization, Hyperpolarization and the
                                            Refractory Period
 After depolarization potassium (K+) moves out restoring the inside to a negative voltage. This is called
  repolarization
 Repolarization leads to a voltage below the resting potential, called hyperpolarization
 Now neuron cannot produce a new action potential. This is the refractory period


                                             All-or-None Principle
 The all-or-none law is the principle that either a neuron is sufficiently stimulated and an action potential
  occurs or a neuron is not sufficiently stimulated and an action potential does not occur.
 Following the action potential, a refractory period occurs in which the neuron is unable to fire. During this
  thousandth of a second or less, the neuron repolarizes, that is, it reestablishes the resting potential
  conditions.
 Two factors affect the speed of the action potential.
    Axon diameter—thicker axons are faster.
        Myelin sheath—myelinated axons are faster.


                                         Neural Communication
 Transmission of information between neurons occurs in one of two ways.
    Electrical: Ion channels bridge the narrow gap between neurons; communication is virtually
     instantaneous.
    Chemical: A chemical substance diffuses across the synaptic gap from the presynaptic neuron to the
     postsynaptic neuron (over 99 percent of the synapses in the brain use chemical transmission).

                                           Neural Communication

                                          Chemical Transmission
 An action potential arrives at the axon terminals; these branches at the end of the axon contain tiny
  pouches or sacs called synaptic vesicles, which contain special chemical messengers called
  neurotransmitters.
 The synaptic vesicles release into the synaptic gap the neurotransmitters manufactured by a neuron,
  thus communicating information to other neurons and to the muscles.
 Synaptic transmission is the process in which neurotransmitters are released by one neuron, cross the
  synaptic gap, and affect surrounding neurons by attaching to receptor sites on their dendrites.
                                          Synaptic Transmission
 After synaptic transmission, the following may occur.
    Reuptake: the process by which neurotransmitter molecules detach from a postsynaptic neuron and
      are reabsorbed by a presynaptic neuron so they can be recycled and used again.
    Enzymatic destruction or breakdown.
 Each neurotransmitter has a chemically distinct, different shape. For a neurotransmitter to affect a
  neuron, it must exactly match the shape of the receptor site. Resembles a lock and key.


                                            Neural Communication
                                           Neurotransmitter Release
   Action Potential causes vesicle to open
                                               Locks and Keys
   Neurotransmitter molecules have specific shapes
                                      Excitatory and Inhibitory Messages
   A neurotransmitter communicates either an excitatory message or an inhibitory message to a
    postsynaptic neuron.
   An excitatory message increases the likelihood that the neuron will fire; an inhibitory message decreases
    the likelihood that it will fire.
   Depending on the receptor site to which it binds, the same neurotransmitter can have an inhibitory effect
    on one neuron and an excitatory effect on another neuron.
   On the average, each neuron in the brain communicates with 1,000 other neurons.


                                         Neural Communication
 Acetylcholine [ah-seat-el-KO-leen]
    a neurotransmitter that, among its functions, triggers muscle contraction
 Endorphins [en-DOR-fins]
    ―morphine within‖
    natural, opiatelike neurotransmitters
    linked to pain control and to pleasure
                                        Major Neurotransmitters
                             Major Neurotransmitters and their Functions
 Acetylcholine –
    affects memory; in Alzheimer‘s disease, there is nearly complete loss of the neurons that produce

     acetylcholine.

 Norepinephrine –
    contributes to arousal and is closely related to adrenalin.

    Approximately ½ of the norepinephrine is located near the reticular formation and controls

     wakefulness and sleep,
    Also involved in learning and mood.
 Norepinephrine seems to be involved in the activation of neurons throughout the brain. It is also involved
   when the body ―gears up‖ to face danger. It is closely related to adrenalin. Approximately ½ of the
   norepinephrine is located near the reticular formation and appears to control wakefulness and sleep, and
   is also involved in learning and mood. It increases heartbeat and seems to also be involved in the
   processes of learning and memory retrieval. It is also implicated in some mental disorders.

                             Major Neurotransmitters and their Functions
 Serotonin –
    different from some of the other neurotransmitters because one of the substances from which it is
     made comes directly from food.
    Carbohydrates increase the amount of tryptophan that is absorbed by the brain and it affects how
     much serotonin is produced in the brain.
    Malfunctions in the serotonin feedback system responsible for disturbances of mood and appetite in
     certain types of obesity, premenstral tension, and depression.
    Antidepressants like Prozac increase the availability of serotonin in certain regions of the brain.
     These drugs can help treat depression and other disorders
    It has also been implicated in aggression.
 Dopamine –
    is important for movement.
    Malfunctioning in the dopamine system can contribute to movement disorders including Parkinson‘s
     disease. Parkinson‘s is most common in elderly people, and available evidence suggests that it
     results from an inherited sensitivity to an as yet unidentified environmental factor or toxin. Treatment
     includes using drugs that enable neurons to make more dopamine or that stimulate dopamine
     receptors.

                              Major Neurotranmitters and their Functions
 GABA – gamma-amino-butyric-acid –
    is the major inhibitory neurotransmitter.
    Helps you calm down and fall asleep.
    A malfunctioning system can result in Huntington‘s disease an inherited disorder that results in the
     loss of many GABA – containing neurons. When they are lost the dopamine systems may run wild.
     The effects are in some ways the opposite of those with Parkinson‘s disease: Instead of being
     unable to begin movements, the victim is plagued by uncontrollable movement of the arms and legs.

 Glutamate – is the major excitatory neurotransmitter –
    used by more neurons than any other neurotransmitter.
    It‘s synapses are located mostly in the cerebral cortex and in the hippocampus.
    Glutamate strengthens the brain‘s ability to transfer messages from one neuron to another.
    It is believed that it could be the root of learning and memory.
    Over-activity of glutamate causes neurons to die. It literally ―excites neurons to death‖.
    Blocking glutamate receptors immediately after brain trauma can prevent permanent brain damage.

                             Major Neurotranmitters and their Functions
 Endorphins –
    The term refers to any neurotransmitter that can bind to the same receptors stimulated by opiates
     (i.e. morphine).
    These neurotransmitters are actually 100 times as strong as the chemically introduced opiates like
     morphine and heroin.
    The body relies on them to act as a pain reducer when injured.
    The introduction of synthetic opiates that mimic endorphins can disrupt the system that produces the
     endorphins and cause permanent damage.


                                         Alzheimer‘s Disease
 Deterioration of memory, reasoning and language skills
 Symptoms may be due to loss of ACh neurons

                                            Parkinson‘s Disease
 Results from loss of dopamine-producing neurons in the substantia nigra
 Symptoms include:
    difficulty starting and stopping voluntary movements

    tremors at rest
       stooped posture
       rigidity
       poor balance
                                           Parkinson‘s Disease
 Treatments:
    L -d o p a
    transplants of fetal dopamine-producing substantia nigra cells
    adrenal gland transplants
    electrical stimulation of the thalamus to stop tremors

                                         Neural Communication
                                                Hormones
 Released by organs, including the stomach, intestines, kidneys and the brain
 Also released by a set of glands called the endocrine system


                                        Hormones vs. Neurotransmitters
 Distance traveled between release and target sites
    hormones travel longer distances
    neurotransmitters - travel across a synaptic cleft (20 nm)
 Speed of communication
    hormones - slower communication
    neurotransmitters - rapid, specific action
                                                 Pituitary Gland
 ―Master endocrine gland‖
 Produces hormones that control hormone production in other endocrine glands
                                                 Pituitary Gland
 Also produces growth hormones
 Too little pituitary activity produces dwarfism
 Too much leads to gigantism
                                                 Pituitary Gland
 Also involved in breastfeeding
 Produces prolactin
    stimulates milk production
 Produces oxytocin
    involved in milk release
                                                 Adrenal Glands
 Involved in stress response
 Hormones released include:
    epinephrine (a.k.a. adrenaline)
    norepinephrine (a.k.a. noradrenaline)
                                                Endocrine Glands
 Thyroid gland - metabolism
 Pineal gland - sleep and wakefulness
 Pancreas - regulates blood sugar level
 Ovaries and testes - secrete sex hormones such as testosterone and estrogen
                                   Neural and Hormonal Systems: Summary
 Autonomic Nervous System
    the part of the peripheral nervous system that controls the glands and the muscles of the internal
      organs (such as the heart)
 Sympathetic Nervous System
    division of the autonomic nervous system that arouses the body, mobilizing its energy in stressful
      situations
 Parasympathetic Nervous System
    division of the autonomic nervous system that calms the body, conserving its energy
                                    Neural and Hormonal Systems: Summary
 Nerves
    neural ―cables‖ containing many axons
    part of the peripheral nervous system
    connect the central nervous system with muscles, glands, and sense organs
 Sensory Neurons
    neurons that carry incoming information from the sense receptors to the central nervous system
 Motor Neurons
    Neurons that carry outgoing information from the CNS to the other parts of the body
                                                The Brain
 Uses 20% of our available oxygen
 Uses most of the sugar we consume
 Weighs about 3 pounds
 Looks like a cauliflower
 Operates on the equivalent of 20 watts of electricity


   Electroencephalogram (EEG)
     an amplified recording of the waves of electrical activity that sweep across the brain‘s surface
     these waves are measured by electrodes placed on the scalp


 CT (computed tomograph) Scan
    a series of x-ray photographs taken from different angles and combined by computer into a
     composite representation of a slice through the body. Also called CAT scan.
                                                  PET Scan
 PET (positron emission tomograph) Scan
    a visual display of brain activity that detects where a radioactive form of glucose goes while the brain
     performs a given task.

                                                 MRI Scan
 MRI (magnetic resonance imaging)
    a technique that uses magnetic fields and radio waves to produce computer – generated images that
     distinguish among different types of soft tissue; allows us to see structures within the brain.

                                                The Cerebrum
 THE CEREBRUM IS THE CONTROL CENTER OF THE BRAIN.
 The LARGEST and most PROMINENT part of the Human
      Brain it represents 85% OF THE W EIGHT OF A HUMAN BRAIN.
 The Cerebrum is responsible for all the VOLUNTARY (CONSCIOUS) activities of the body.
 Is the site of intelligence, learning and judgement.
 Functions in language, conscious thought, memory, personality development, vision and other
  sensations.
 Cerebrum is divided into two hemispheres – left and right.




                                          The Cerebellum
 The CEREBELLUM
    SECOND LARGEST part of the Brain, and is located at the back of the Skull.
    COORDINATES MUSCLE MOVEMENTS.
    The Cerebellum coordinates and balances the actions of Muscles so that the body can move
     gracefully and efficiently.
    Cerebellum receives sensory impulses from muscles, tendons, joints, eyes, and ears, as well
     as input from other brain centers.
    Processes information about position and controls posture by keeping skeletal muscles in a
     constant state of partial contraction.

 The Cerebellum Coordinates rapid and ongoing movements. BALANCE, POSTURE, and
  COORDINATION
    Because the function of the Cerebellum is INVOLUNTARY (not under conscious control), learning a
     completely new physical activity can be very difficult.



                                    The Brain Stem
 The BRAIN STEM CONNECTS the BRAIN to the SPINAL CORD.
 THE BRAIN STEM, W HICH MAINTAINS LIFE SUPPORT SYSTEMS, CONSIST OF THE
  DIENCEPHALON, MEDULLA OBLONGATA, PONS, AND THE MIDBRAIN.
 THE BRAIN STEM CONTROLS VITAL BODY PROCESSES.
 THE MEDULLA CONTROLS INVOLUNTARY FUNCTIONS THAT INCLUDE, BREATHING, BLOOD
  PRESSURE, HEART RATE, DIGESTION, SW ALLOW ING, AND COUGHING
 Another important part of the Medulla is a GROUP of CELLS known as THE RETICULAR ACTIVATING
  SYSTEM or RETICULAR FORMATION (RAS).
 The Reticular Activation System (RAS) actually helps to alert, or awaken, the upper parts of the Brain,
  including the Cerebral Cortex.
 The RAS also helps to control respiration and circulation and serves as a filtering system for incoming
  sensory signals.


                                             Our Divided Brain
 Corpus Callosum
    largest bundle of neural fibers
    connects the two brain hemispheres
    carries messages between the hemispheres
                                              Corpus Callosum
 Major ( but not only) pathway between sides
 Connects comparable structures on each side
 Permits data received on one side to be processed in both hemispheres
 Aids motor coordination of left and right side


   What happens when the corpus callosum is cut?
   Sensory inputs are still crossed
   Motor outputs are still crossed
   Hemispheres can‘t exchange data
                                             The „Split Brain‟ studies
   Surgery for epilepsy : cut the corpus callosum
   Roger Sperry, 1960‘s
   Split Brain - a condition in which the two hemispheres of the brain are isolated by cutting the connecting
    fibers (mainly those of the corpus callosum) between them
   Special apparatus
       picture input to just one side of brain

       screen blocks objects on table from view



                                               Visual Pathways
 The Left visual field is processed in the Right Hemisphere and the Right Visual Field is processed in the
  Left Hemisphere.
                                      The Sensory and Motor Cortex
                                             Association Areas
 areas of the cerebral cortex that are not involved in primary motor or sensory functions
 involved in higher mental functions such as learning, remembering, thinking, and speaking

                                            The Story of Phineas Gage
                             Phineas Gage and His Physician John Harlow, M.D.
                                                 The Tamping Rod
   This is the bar that was shot through the head of Mr. Phineas P. Gage at Cavendish, Vermont, Sept. 14,
    1848. He fully recovered from the injury & deposited this bar in the Museum of the Medical College of
    Harvard University. Phineas P. Gage Lebanon Grafton Cy N-H Jan 6 1850 *
                                                    The Damage
   The skull and the path of the tamping iron
    There are three places where Gage‘s skull is damaged.
       There is a relatively small area under the zygomatic arch (or cheek bone) where the tamping iron first
        impacted.
       The second place is the orbital bone of the base of the skull behind the eye socket. After healing this
        area is about 1 inch wide by 2 inches in the anterior-posterior direction and must have been larger at
        the time of injury (upper left of a, below).
        The total area of bone damage caused by the tamping iron where it emerged is truly enormous. As
        can be seen in (b), there is an unhealed irregular, roughly triangular shaped area of total bone
        destruction at the top of the skull. Lying mainly to the left of the midline, it is about 2 inches wide and
        4 inches in circumference, and there is another on the lower left side about 2.7 inches in
        circumference. Between them there is a flap of frontal bone about 2.5 inches long and about x 2
        inches wide at the widest point (c). Behind the main area is a second flap of parietal bone about 2
        wide and 0.75 to 1.5 inches long. Harlow replaced both flaps; the rear (parietal) reuniting so
        successfully that it is actually difficult to see from outside the skull. In (c) it has been copied from a
        photograph of the underside of the skull and ‗pasted‘ to the outside.

                                                The Aftermath
 Some months after the accident, probably in about the middle of 1849, Phineas felt strong enough to
  resume work. But because his personality had changed so much, the contractors who had employed
  him would not give him his place again. Before the accident he had been their most capable and
  efficient foreman, one with a well-balanced mind, and who was looked on as a shrewd smart business
  man. He was now fitful, irreverent, and grossly profane, showing little deference for his fellows. He was
  also impatient and obstinate, yet capricious and vacillating, unable to settle on any of the plans he
  devised for future action. His friends said he was ―No longer Gage.‖
 As far as we know Phineas never worked at the level of a foreman again. According to Dr. Harlow,
  Phineas appeared at Barnum‘s Museum in New York, worked in the livery stable of the Dartmouth Inn
  (Hanover, NH), and drove coaches and cared for horses in Chile. In about 1859, after his health began
  to fail he went to San Francisco to live with his mother. After he regained his health he worked on a farm
  south of San Francisco. In February 1860, he began to have epileptic seizures and, as we know from the
  Funeral Director‘s and cemetery interment records, he died on 21st. May 1860 (not in 1861 as Harlow
  reported).
                                           Left Brain-Right Brain
HEMISPHERE DOMINANCE/SPECIALIZATION
 Research on split-brain patients has given a clear picture of the differences between the two brain
  hemispheres. The left hemisphere is specialized for language functions-speaking, reading, writing, and
  understanding language and for analytical functions such as mathematics. The right hemisphere is
  specialized for nonverbal abilities. These include musical abilities and perceptual and spatial skills (such
  as drawing geometric designs, working puzzles, painting pictures, and recognizing faces)
 Roughly 95% of all adults use the left side of the brain for speaking, writing, and understanding
  language. W orking with the right hemisphere is like talking to a child who understands a dozen words or
  so. To answer questions the right hemisphere must point to objects or make other nonverbal responses.

 Hemisphere
Specialization
                                                   Handedness
   Left-handedness

   What is it like to be left-handed? Most of you will not know since only a small portion, about 10% of the
    population is left-handed. Somewhat more males are left-handed.
    http://www.indiana.edu/~primate/lspeak.html


   The prevalence of right handedness probably reflects the left brain‘s specialization for language
    production. Evidence exists that the majority of humans have been right handed for at least 50
    centuries.
   It had been believed that children didn‘t express clear-cut handedness until age 4 or 5, but a recent study
    shows that hand preference for many children is stabilized by 18 mos.
   Most expressions of speech that refer to left-handedness are negative statements.
   Ex. Coming from left field.
          Left-handed compliment
          two left feet, left behind, left out,
   On the other hand, (no pun intended) we have the right way, right-hand man, righteousness, in his right
    mind….
   In the past, lefties have been accused of being stubborn, clumsy, maladjusted.
   http://jackie.freeshell.org/woh/language.htm
   http://jackie.freeshell.org/woh/superstitions1.htm
   The supposed clumsiness of left-handers is in reality a result of living in a right hand world. If it can be
    gripped, pulled, turned, folded, or held, its probably designed for the right hand. Even toilet handles are
    on the right side.

 Handedness Tests http://jackie.freeshell.org/woh/tests.htm
 Other handedness facts and puzzles http://www.drspock.com/article/0,1510,5815,00.html
                                        Famous Left-Handers
 Legendary Figures: Albert Einstein, Beethoven, Benjamin Franklin, Joan of Arc, Julius Caesar,
  Leonardo da Vinci, Mark Twain, Michelangelo, Napoleon, Pablo Picasso, Queen Victoria

   Actors and Comedic Talents: Anthony Perkins, Bruce W illis, Carol Burnett, Cary Grant, Christian
   Slater, Dan Aykroyd, Danny Kaye, David Letterman, David Spade, Demi Moore, Dennis Quaid, Diane
   Keaton, Dick Smothers, Dick Van Dyke, Don Rickles, Emma Thompson, Fran Drescher, Fred Astaire,
   Goldie Hawn, Harpo Marx, Henry Ford, Howie Mandel, Jason Alexander, Jason Bateman, Jay Leno,
   Jerry Seinfeld, Jim Carrey, Jim Henson, Joe Piscopo, Julia Roberts, Keanu Reeves, Kim Basinger, Lisa
   Kudrow, Luke Perry, Marcel Marceau, Marilyn Monroe, Mary-Kate Olsen, Matthew Broderick, Michael
   Landon, Michael Richards, Montel Williams, Morgan Freeman, Nicole Kidman, Oprah W infrey, Richard
   Dreyfuss, Robert DeNiro, Sarah Jessica Parker, Scott W olf, Sid Caesar, Telly Savalas, Tim Allen, Tom
   Cruise, Val Kilmer, Whoopi Goldberg

   Astronaut: Buzz Aldrin

   Musicians: Annie Lennox, Celine Dion, George Michael, Jimi Hendrix, Phil Collins, Paul McCartney,
   Seal, Sting


                                           Famous Left Handers
 Athletes:

 Baseball--Brady Anderson, Barry Bonds, Ty Cobb, Ken Griffey Jr., Tony Gwynn, Sandy Koufax, Babe
  Ruth, Casey Stengel, Ted Williams, W hitey Ford, Steve Howe, Randy Johnson

 Soccer--Pelé, Edson Arantes do Nascimento

 Olympians--Greg Louganis (diving), Mark Spitz (swimming), Bruce Jenner (decathlon), Dorothy Hamill
  (figure skating)

 Boxing--James "Gentleman Jim" Corbett, Marvin Hagler, Oscar de la Hoya

 Football--Mark Brunell, Gayle Sayers, Steve Young

 Basketball--Larry Bird, Nick Van Exel, Bob Lanier, Bill W alton

 Tennis--Jimmy Connors, John McEnroe, Martina Navratilova (ambidextrous)

 U.S. Presidents: James Garfield, Herbert Hoover, Harry S. Truman, Gerald Ford, Ronald Reagan,
  George Bush, Bill Clinton

   And...Kermit the Frog

              Is Left and Right Brain Specialization Reversed in Left-Handed Individuals?
 Not necessarily. Most people who use their left hand to write, hammer a nail, or throw a ball still have
   their language areas on the left side of the brain.
 95% OF RIGHT HANDERS WERE FOUND TO HAVE SPEECH LOCATED ON THE LEFT SIDE OF
   THE BRAIN AND ARE LEFT BRAIN DOMINANT
 70% OF LEFT HANDERS SHOW ED THE SAME PATTERN
 25% OF LEFTIES AND 3% OF RIGHTIES USE THEIR RIGHT BRAIN FOR SPEECH
 15% OF LEFTIES USE BOTH SIDES OF THE BRAIN FOR LANGUAGE PROCESSING
                                          Is Handedness Inherited?
IS HANDEDNESS INHERITED?
 There is no simple genetic code for handedness. Even identical twins aren‘t especially likely to share
   the same handedness.
      George Michel (1981) observed 150 babies during the first 2 days after birth and found that 2/3 of
       them preferred to lie with their heads turned to the right.
      When restudied at 5 mos. Almost all of the ―head right‖ babies reached for things with their right hand
       and almost all of the ―head left‖ babies responded by reaching for things with their left hands.
 Studies have failed to show direct genetic linkages to handedness. In studies of twins, from 459
   families,
       if neither parent is left handed, or if only the father is left handed, the children have a 1:10 chance of
        being left handed.
       If only the mother is lefthanded, the ratio is 2:10
       If both parents are left handed the chance rises to 4:10
       The chance of being right handed is still greater, no matter what the parents handedness.
       There appears to be no differences in school achievement between left and right handers and no
        physical or mental defects associated with left-handedness.
       These twin studies also provided further complications to the genetically inherited theory. Identical
        twins have identical genes and if one is left handed the other should be too. Only 76% of the
        expected 100% of the twins are both left handed.


                                         Why the Brain Switch?
 Fluctuations in the chemical environment in the womb may be responsible.
 There are more male left handers than female. If we accept that this is true, then it seems that the
  chemical which causes the shift to right brain dominance is male-linked.
 Stress during pregnancy can cause fetal testosterone levels to rise in rats.
 In the womb both males and females share the same maternal and placental hormones. Once the testes
  develop, testosterone rises to high levels.
 An increase in testosterone in the womb at the same time can slow development in the left hemisphere.
  This would explain why there are slightly more lefthanded males.

 When a weeks-old fetus sucks its thumb, hand preference may in the making.

   Scientists who studied ultrasound scans of 1,000 fetuses and followed the progress of some of these
   babies after birth, found that if a fetus preferred to suck its right thumb more than its left at just 10 to 12
   weeks gestational age, the child tended to be right-handed after birth, reports New Scientist magazine of
   research at Queen's University in Belfast, Northern Ireland.

   In other words the hand you favored as a 10-week-old fetus is likely the hand you have favored all your
   life. And that's not all. Lead study author Peter Hepper and his team also looked at hand movement in
   the womb, which begins at about 10 weeks. They found a similar association between the preference to
   move one hand over the other in the womb and handedness after birth.


                                 When Babies First Prefer Left or Right Hands

 Interestingly, there is no evidence the brain controls the choice of hand preference at his early fetal age
     since nervous system connections to the body from the brain don't even begin to develop until about
      20 weeks of gestation.
 Instead, it appears to be a local reflex arc of the spinal cord. Hepper speculates that the fetus may prefer
  one side of its body just because that side develops slightly faster, notes New Scientist.

   This is news--and in some circles controversial news--because scientists have always thought hand
   preference developed at age 3 or 4 years.

   Hepper has other ideas that turn conventional wisdom upside-down. He thinks the fetus's body
   movements may somehow lead to the development of an asymmetrical brain. Why?
     The sensory connections from the body to the brain develop before the connections that allow the
      brain to control the body's movement, he explained to New Scientist.
      Not everyone agrees with this theory. Stephen W ilson, a developmental biologist at University
      College London, told the magazine, "The movements you see in a fetus don't have to be influencing
      brain asymmetries." He thinks it's more likely that in the early fetus there is already a difference in
      gene activation between the right and left sides of the brain and that this leads to hand preference
                                    Advantages of Left-Handedness
    There may actually be some advantages….
     In history a notable number of artists have been lefties . Leonardo da Vinci, and Michelangelo, Pablo
      Picasso. Paul McCartney and the last two US presidents are all left handed. Ideally since the right
      hemisphere is superior at imagery and visual abilities, there is some advantage to using the left hand
      for drawing or painting.
     The left-handed do seem to be better at putting together verbal and pictorial symbols or ideas which
      is why there are many left handed architects.
       Lefties are less lateralized than the right handed. There is less distinct specialization in the two sides
        of their brains. Even the physical size of their two hemispheres are more alike. Left handers appear
        to be more symmetrical in almost everything including eye dominance, fingerprints even foot size.
       The real advantage is for those who are only moderately left handed or ambidextrous, they seem to
        have better pitch memory which is a basic musical skill.
       Students who more fully use the right hemisphere are extremely gifted in math and much more likely
        to be left handed.
       The clearest advantage shows up when there is brain injury. Because of their mild lateralization, left
        handed individuals typically experience less language loss after damage to either brain hemisphere
        and they recover more easily.

                                      Disadvantages of Left-Handedness
 Disadvantage - more people with reading disabilities, allergies, and migraine headaches are lefties.
Obstacles for left handers:
 intrinsic bias – a tool or a system has an inherent or built-in bias for one hand over the other. The
  majority of tools in any technological society are designed for the right handed. The following tools all
  require left to right wrist turning movements that are more comfortable for right handers:
     corkscrew
     rotary dial phone
     clock setting and winding
     screws
     Lightbulbs


                                           Obstacles for Lefties
   These items are designed specifically for right handers
     scissors
     can openers
     coffee makers
     computer keyboards (number keyboard on right)
     golf clubs
     most hand held power tools
     cars built in right lane countries
     many workplace items such as; industrial meat slicers, drill presses, hand saws, production line s
      and heavy equipment
     calculators and pushbutton phones ( left to right array)
 This means that the risk to left handers is greater than that of right handers and this may explain the
  complaint that left handers are clumsy and will live shorter lives.