Transcript The Structures of the Brain

THE STRUCTURES OF
THE BRAIN
Mod 4 Part 1
The Tools of Discovery
• How do neuroscientists explore the connection among brain, mind,
and behavior?
• Lesions (cutting)
• Can remove damaged tissue without disturbing surrounding tissue.
• Can selectively cut tissue and gauge response
• Measurement of electrical impulses
• Color Representations of Brain injury
• Clinical observations
• Injury
• Disease
• Manipulating the Brain
• Electrical, chemical, or magnetic stimulation
• Legion in a rat’s hypothalamus causes itself to starv to death (will not eat)
• Electroencephalogram (EEG)
• Measures surface electrical activity
• Filtering out background allows scientist to see response to stimulus.
Brain imaging
• Computed Tomography Scan
• X-ray photographs of cross sections
• Can indicate damage
• Positron Emission Tomography
• Consumption of glucose
• Radioactive glucose lights up on scan
• Different area lights up when someone says the name of an animal vs. when
someone says the name of a tool (Martin et al 1996)
• Magnetic Resonance Imaging
• Strong magnetic field depolarizes atoms briefly
• Detailed picture of soft tissues
• Functional MRI (fMRI)
• Tracks oxygen
• Findings
• Similar brain areas involved in reading and remembering words (Posner and Raichle 1998)
• Larger than average neural area of the left brain in musicians with perfect pitch (Schlaug et al
1995)
• If second language is learned simultaneously with first, it is stored in the same area. If it is learned
later, it is stored in a different area. (Kim et al 1997)
• Men use only left side of brain for rhyming tasks, women use both sides (Shaywitz et al 1995)
Lower-Level Brain Structures
• What are the lower level brain structures and what are their
functions?
• Size to body weight matters (some)
• Wrinkles matter more
• The Brainstem
• Medulla
• Controls the heartbeat and breathing
• Cat can live with only a medulla (Klemm 1990)
• Autonomic nervous system hub
• Reticular formation
• Finger shaped network that connects spinal chord to thalamus
• Electronically stimulating reticular formation of cat makes the cat wide awake and alert
(Magoun and Moruzzi 1949)
• Severing cat’s reticular formation causes irreversible coma (Magoun)
• Thalamus
• Sensory hub
• Receives sensory information and sends to appropriate brain part
• Controls occillations (Llinas and Ribary 2001)
The
Cerebellum
and
Limbic
System
• Cerebellum
•
•
•
•
•
Little brain
Processes things outside of our awareness
Balance
Refined motor skills
Manages life-sustaining functions
• Limbic system
• Border between cerebrum and lower structures
• Hippocampus: essential to memory processing
• Links to emotions and drives
• Amygdala
•
•
•
•
Almond shaped neural clusters influence aggression and fear
Can make ill-tempered monkey meek (Kluver 1939)
Role in rage, fear, and perception of anger (Anderson and Phelps 2000, Poremba and Gabriel 2001)
Lesioning amygdala shows varied response in humans (Mark and Ervin 1970, Valenstein 1986)
• Hypothalamus
• Hunger, thirst, body temperature, sexual behavior
• Controls pituitary gland
• Reward centers (Olds and Milner 1954, Olds 1975)
• Rat experiments with reward centers (Olds 1958)
• Can train rats using reward systems (Talwar et al 2002)
• Human experiments with electrical stimulation show mixed results (Deutsch 1972, Hooper and Teresi
1986)
• Addictions linked to reward deficiency system (Blum et al 1996)
The Cerebral Cortex
• How do the neural networks within the cerebral cortex enable
perceiving, thinking, and speaking?
• Intricate covering of interconnected cells
• Ability to adapt based on large cerebral cortex
• Wrinkled
• Two hemispheres
• Thin surface layer if hemispheres= cerebral cortex
• Glial cells- glue cells that guide neural connections
• Lobes
• On each hemisphere
• Frontal lobes: behind the forehead
• Parietal lobes: at the top and to the rear
• Occiptal lobes: back of the head
• Temporal lobes: above the ears
Cortex Functions
• Errors based on autopsy information of brain damaged patients
• Many activities involve multiple parts of the brain
• Damage in one area might appear to cause global problems
• Vocal music involves speech and music processing (Besson et al
1998)
• Motor Functions
• Stimulation of the arch shaped region at the back of the frontal lobe
caused specific movements in dogs (Fritsch and Hitzig 1870)
• Each hemisphere controls the opposite hemisphere
• Scientists can stimulate different movements by stimulating different
parts of the motor cortex
• Can elicit smile or fist, despite will (Degado 1969)
• Can predict motor activity (Gibbs 1996)
• Monkeys can move joystick just by thinking about it if recording
devices implanted in motor cortex
More cortex functions
• Sensory Functions in Sensory Cortex
• Receives information
• Located parallel to the motor cortex, but behind it, in front of the
parietal lobe
• Stimulation causes sensation of being touched
• The more sensitive the body region, the greater the area of the
sensory cortex
• When limbs are lost, neighboring areas become more sensitive (Fox
1984)
• Pianists have larger than average auditory cortex (Bavelier et al 2001)
• Deaf people have enhanced visual cortex (Pantev et al 1998)
• Visual cortex in occipital lobe receives visual stimulus
• Auditory areas in temporal lobe
• Active during auditory hallucinations in schizophrenics
• Phantom ringing sound activates auditory cortex
Even More Cortex Functions
• Association Areas
• Integration of information (interpret, integrate, and act)
• Stimulation does nothing
• False belief that we only use 10% of our brains (McBurney 1996)
• Judge, plan, and process new memories
• Frontal lobe damage causes lack of ability to plan (Kimberg et al
1998)
• Phineas Gage
• Two children with frontal lobe damage grew up without moral
compass (Dolan 1999)
• Parietal lobe associational areas involvedd in mathmatical and
spatial reasoning (Witelson et al 1999)
• Underside of right temporal lobe allows facial recognition
Even
Even
More
Cortex
Functions
• Language
• Damage to any area can cause aphasia (impaired use of language)
• Some with aphasia can speak but not read, read but not speak, sing but not speak,
read but not write, etc.
• Clues
• Broca’s area: damage to this area (part of frontal lobe) causes someone to struggle to form
words.
• Wernicke’s area (left temporal lobe): damage to this area causes people to speak in
meaningless words.
• Reading aloud involves angular gyruswhich takes words from visual cortex and moves it to
auditory cortex while Wernicke’s area gives meaning
• Nerve fibers connect the areas
• Geschwind assembled clues into process of reading aloud
• Register in visual area
• Relayed to angular gyrus, transformed to auditory code
• Received and understood by Wernicke’s area
• Sent to Broca’s area
• Controls motor cortex to pronounce words
• Brain computes word form, sound and meaning in different areas (Posner and Carr
1992)
• Jokes that are puns are processed differently than jokes that are based on
language sounds (Goel and Dolan 2001)
• Function is localized but processes are globalized
Brain reorganization
• Neurons will not regenerate, but they can reorganize
• Neuroplasticity
• Neurons that receive sensory information from one area can adapt to receive it from a
•
•
•
•
•
•
•
•
•
•
•
•
different area. (Pons et al 1991)
Cats’ brains can switch sensory information from visual to auditory
Newborn ferrets can be reorganized to see with their auditory cortex (von Melcher et al
2000)
For blind people who read braille with one finger, the sensory cortex area devoted to that
finger expands (Barinaga 1992)
PET scans show that visual cortex responds to braille reading (Sadato et al 1996)
People feel sensations related to other areas in their phantom amputated limbs
(Ramachadran and Blakeslee 1998)
Brain can rewire itself or choose new uses for old pathways (Gazzaniga 1992, Kolb and
Whitshaw 1998)
Adult mice and humans can generate new brain cells (Kempermann and Gage 1999, Van
Praag et al 2002)
Monkey brains create thousands of neurons per day (Gould et al 1999)
Greater plasticity when young (Kolb 1989)
Young people can reassign hemispheres
Person with half brain removed at age 5 scored high on IQ tests and finished grad school.
(Smith and Sugar 1975, A. Smith 1987)
Children retain memory, personality, and humor after hemispherectomy (Vining et al 1997)
Exit Ticket/Homework/Advice
• Exit Ticket
• 1. Identify three regions of the brain
• 2. Describe two functional areas of the cerebral cortex.
• 3. Explain how the brain repairs or restructures itself after brain
damage.
• Homework
• Read Mod 4
• Complete “Test Yourself” on page 95
• Advice
• Be prepared for a Mod 4 Part 1 Quiz
• Begin to study mods 3 and 4 for Unit 3 Test