Transcript Brain

Brain Function
How We Investigate
and What We Know
Basic Structure
The Left Cortical Hemisphere
Anterior
Posterior
(front)
(back)
http://www.driesen.com/cortical_illustrations.htm
Cortical Surface
http://www.driesen.com/cortical_illustrations.htm
Main Parts of the Brain:
Midsagittal view
http://www.driesen.com/cortical_illustrations.htm
Main Parts of the Brain:
Midsagittal view—MRI Scan
http://www.driesen.com/cortical_illustrations.htm
Main Parts of the Brain:
Midsagittal view—More detail
http://www.driesen.com/cortical_illustrations.htm
Studying Brain Function
 What brains:
► Animals
and humans
► Individuals with damaged brains
► Individuals with intact brains
► Individuals with split brains.
 Electroencephalography (EEG) and
Magentoelectroencephalography (MEG)studies
► Brain
mapping using its electrical activity
 Imaging techniques
► CAT
scans
► PET scans
► fMRI scans
► Ultrasound
Techniques
Studies of Brain Damaged Individuals
► How
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do brains get damaged?
Strokes
Aneurysms
Traumatic brain injury (TBI)
Surgery
Illness (e.g., encephalitis, meningitis)
Tumors
Techniques
Studies of Brain Damaged Individuals
► How
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do brains get damaged?
Strokes
Aneurysms
Traumatic brain injury (TBI)
Surgery
Illness (e.g., encephalitis, meningitis)
Tumors
Techniques
What Does Brain Damage Tell Us?
► Damage
to the brain produces changes and
deficits in behaviour.
 For example, individual may lose ability to
handle one or more aspect of language, may
have memory loss of various kinds, may have
paralysis or sensory loss, or personality change.
► Location
of damage is linked to its effect on
behaviour.
Cortical Surface
Right Hemisphere
Central fissure
Sensory strip
Lateral fissure
Motor
strip
Right Hemisphere Damage
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Damage to the right motor cortex can lead to paralysis
on the left side of the body.
Damage to the right sensory cortex can lead to loss of
sensation on the left side of the body.
Damage to other areas of the right hemisphere can lead
to difficulty with:
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Attention and multi-tasking. May have left-side neglect.
Facial and pattern recognition.
Organization, reasoning, problem solving.
Orientation
Integrating information.
Depth perception
Social Interaction
Non-musicians who have lost most of their spoken
language may still be able to sing both the words and
the music to songs.
Cortical Surface
Left Hemisphere
Lateral fissure
1.
2.
3.
4.
5.
6.
7.
http://www.ohiou.edu/~linguist/soemarmo/
L270/Notes/neurolingvid.htm
Broca's area—larger in left hemisphere
Visual cortex
Wernicke's area—larger in left hemisphere.
Motor cortex
Cerebral cortex
Auditory cortex
Angular Gyrus (reading)
Motor Cortex as Homunculus
Broca’s area contains
the lower motor cortex
that controls the
articulatory muscles.
http://www.socsci.uci.edu/psych9a/lectures/lec2notes.html
Copyright /Mary-Louise Kean 1995/
Left Hemisphere Damage
► Damage
to the left motor cortex can lead to
paralysis on the right side of the body.
► Damage to the left sensory cortex can lead to
loss of sensation on the right side of the body.
► Damage to Broca’s area relates to laboured,
slow speech with impaired articulation.
► Damage to Wernicke’s area relates to speech
that is phonetically and grammatically correct
but has lost its meaning—word salad.
► Damage in these and other areas can lead to
both expressive and receptive language deficits
as well as body image problems.
Two Hemispheres
Working Together
Association Cortex
► The
association areas are all those areas that
connect the various primary areas (motor,
sensory, visual, auditory) that we have
identified.
► The association areas make up the major part of
the cortex and are where the real action is.
► The main functions of the brain take place
here—organizing, planning, recognizing
patterns, carrying out arithmetic, rational
thinking, intuitive thinking, and so on.
Techniques
Studies of Split Brain Individuals
http://www.driesen.com/cortical_illustrations.htm
Techniques
Studies of Split Brain Individuals
► What
is a ‘split brain’?
Commisures: several
different bands of fibers
joining right and left
hemispheres, viewed from
below.
Left Hemisphere
Corpus callosum: main
commissure
Right Hemisphere
Commisurotomy: Surgical
technique that severs the
corpus callosum
From Virtual Hospital: The Human Brain: Chapter 5: The Cerebral
Hemispheres, Authors: Terence H. Williams, M.D., Ph.D., D.Sc.,
Nedzad Gluhbegovic, M.D., Ph.D., Jean Y. Jew, M.D. Copied from
http://www.vh.org/adult/provider/anatomy/BrainAnatomy/Ch5Tex
t/Section21.html on July 10, 2003
Techniques
Studies of Split Brain Individuals
► Neurological
connections are such that
sensory input from the right side of the
body reaches the left hemisphere first,
input from the left reaches the right
hemisphere first.
► For vision, input from the left half of the
visual field reaches the right hemisphere
first, and vice versa. The input from the
two half visual fields is integrated at the
primary visual cortex.
Left Visual Field
X
Nasal
hemiretinas
Right Visual Field
Right
Temporal
Hemiretina
Optic Chiasm
Left Visual Cortex
Right Visual Cortex
Techniques
Studies of Split Brain Individuals
Left & right visual field as person looks straight ahead.
Light from an object to the side reaches a different
half of each retina .
Eyes. The two hemiretinas are marked for each eye.
The temporal hemiretina is dark for the left eye and
light for the right eye. The shading for the nasal
hemiretina is reversed. The neural pathway for each
hemiretina continues the same shading.
Neural pathways from the nasal hemiretinas cross at
the optic chiasm. Temporal hemiretinas go straight
back
Primary visual receiving area in each half of the
occipital lobe. Information from the left visual field
ends up in the right visual cortex and from the right
visual field in the left visual cortex. It is here that the
information from the two halves of the visual field is
integrated via the corpus callosum.
Left Visual Field
X
KEY
Right Visual Field
RING
Nasal
hemiretinas
Right
Temporal
Hemiretina
Optic Chiasm
Left Visual Cortex
Right Visual Cortex
Techniques
Studies of Split Brain Individuals
► Recall
also:
 Motor control is also contralateral. The left
hemisphere controls the right side of the body and
vice versa.
► As
long as the corpus callosum is intact,
information flows freely and rapidly between the
two hemispheres, no matter which hemisphere
receives it first.
 Either side of the body can be directed to respond
and either hand can point to or pick up an object
based on input to either hemisphere.
Techniques
Studies of Split Brain Individuals
Right
hemisphere
LVF
Intact brain: A picture of a key ring is flashed
the left visual field. The neural message is then
received by the right hemisphere. It is
immediately passed to the left hemisphere,
which directs the right hand to pick up the key
ring.
Split brain: Right hemisphere receives the
information that the object was a key ring.
However, it cannot pass it to the left hemisphere.
Only the left hand can pick out the key ring
because the hemisphere that controls that hand
has the information. The left hemisphere does
not know what the image was and cannot direct
the right hand to pick it up.
Techniques
Studies of Split Brain Individuals
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Typically, the left hemisphere directs speech.
If there can be no communication between hemispheres, what the
right hemisphere sees it cannot talk about because it cannot send
that message to the left, and speaking, hemisphere. However,
because the right hemisphere controls the opposite hand, the left
hand could point to, or pick up, what the right hemisphere has seen.
If two words, such as key and ring, are flashed simultaneously from
the left & right visual fields respectively, the split brain individual will
only be able to say he saw the word ‘ring’ because that is what the
left hemisphere received.
If the patient is asked to use the right hand to point to what she
saw, she will point to the ring, because that is what the left
hemisphere (controlling the right hand) received.
If asked to use the left hand, he will point to the key, because that
is what the right hemisphere (controlling the left hand) received.
Techniques
Studies of Intact Brain Individuals
► Visual
half-field presentation, using
pictures, letters, numbers, dots, shapes,
etc.
 If individual gets more correct, or is faster,
from one visual field than the other, we
assume that the opposite hemisphere is
specialized for that particular kind of
information.
► Dichotic
listening presentation.
Techniques
Studies of Intact Brain Individuals
► Electroencephalography
(EEG),
Magentoelectroencephalography (MEG)
 Uses external electrodes to map brain activity.
 Useful to track timing of electrical signals
(temporal resolution).
 Difficult to determine the source of the signals
(spatial resolution).
Techniques
Computer Assisted/Coaxial Tomography
► X-rays
are focused at a certain level as the CAT/CT
scanner is rotated around the body.
► As X-rays pass through the body they are
absorbed and weakened, creating a profile of Xray beams of different strengths.
► All the various images are read onto a film.
► A computer is then used to backward construct a
two-dimensional image of the ‘slice’ of the brain
that was scanned by the X-rays, blocking out the
images from above or below that level.
Techniques
CAT/CT Scans
Outside view of modern CT
system showing the patient
table and CT scanning patient
aperture
Inside view of modern CT system, the x-ray tube is
on the top at the 1 o'clock position and the arcshaped CT detector is on the bottom at the 7
o'clock position. The frame holding the x-ray tube
and detector rotate around the patient as the data
is gathered.
Techniques
CAT/CT Scans
Techniques
CAT/CT Scans
3D CT Scan of Chest
CT Scan of Brain
Techniques
Positron Emission Tomography (PET)
Radionuclide, which emits positrons, combined with a
sugar, is injected into individual.
► Certain types of tissue will pick up more of the sugar, and
therefore, the radionuclide, than others.
► Scanner picks up the radiation--the positron emissions.
► Areas with increased blood flow will release greater
radiation and be seen as more dense.
► Computer creates images as slices of the brain as a
difference between the activity for task under consideration
and a control task.
►
Imaging Techniques
Positron Emission Tomography
PET Scan
Four horizontal PET slices from a
resting brain.
Same 4 slices, subject is now listening to
music. Note greater activity in right
temporal region of upper right picture.
Four horizontal PET slices from a
resting brain.
Subject is now exposed to a visual
stimulus with pattern and colour. Note
greater activity occipital region—primary
visual receiving area..
Four horizontal PET slices from a
resting brain.
Subject has been given a thinking task.
Four horizontal PET slices from a
resting brain.
Subject has now been asked to remember an
image for later recall. The arrows point to
activity in the region of the hippocampus in
both hemispheres. Note also the primary
visual receiving area is activated.
Four horizontal PET slices from a
resting brain.
Subject is hopping up and down on his right
foot. Note the activity in the left hemisphere.
The arrows point to the left motor cortex.
Photos by Michael E. Phelps, Ph.D. & John Mazziotta, M.D., Ph.D.
Dept. of Molecular and Medical Pharmacology andDept. of Neurology, UCLA School of Medicine. Found
at http://www.crump.ucla.edu/software/lpp/clinpetneuro/function.html
Magnetic Resonance Imaging
MRI
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Based on magnetic properties of protons (hydrogen nuclei)
that make up most of water and fat.
Scanner passes a powerful magnet over body—protons
briefly all line up in the same direction.
Protons are then misaligned using radio waves and their
varying rates of return to alignment with the magnet are
tracked. Produces map of the brain tissue.
Images are of high quality.
fMRI is functional MRI—MRI scans done during various
cognitive activity.
Techniques – fMRI Studies
A normal volunteer prepares
for an fMRI study of face
recognition. She will have to
match one of the faces at
the bottom of the display
with the face at the top.
James Haxby, chief of the
section on functional brain
imaging at the National
Institute of Mental Health in
Bethesda, Maryland, adjusts
the mirror that will allow her
to see the display from
inside the magnet.
Photo: Kay Chernush.
Found at http://www.hhmi.org/senses/e110.html
Techniques – fMRI Studies
This is an fMRI scan from
the study of face recognition.
The volunteer's brain is
particularly active in an area
of her right hemisphere
called the fusiform gyrus
(arrow) as she matches one
of the two faces at the
bottom of the display with
the face at the top. This
"slice" of her brain is seen as
though looking through her
face.
Photo: Vincent Clark and James Haxby,
Section on Functional Brain Imaging, Laboratory of Psychology and Psychopathology,
NIMH, NIH.
Found at http://www.hhmi.org/senses/e110.html
Brainstem
http://www.driesen.com/cortical_illustrations.htm
Brainstem
► The
lower extension of the brain where it connects
to the spinal cord.
► Oldest part of brain.
► Neurological functions located in the brainstem
include those necessary for survival (breathing,
digestion, heart rate, blood pressure) and for
arousal (being awake and alert).
► Most of the cranial nerves come from the
brainstem. The brainstem is the pathway for all
fiber tracts passing up and down from peripheral
nerves and spinal cord to the highest parts of the
brain.
Brainstem: Medulla
► Functions
primarily as a relay station for the
crossing of motor tracts between the spinal cord
and the brain.
► Also contains the respiratory, vasomotor and
cardiac centers, as well as many mechanisms for
controlling reflex activities such as coughing,
gagging, swallowing and vomiting.
► Controls orientation of the head, affecting balance.
Brainstem: Pons
►A
bridge-like structure which links different
parts of the brain and serves as a relay
station from the medulla to the higher
cortical structures of the brain. It contains
the respiratory center.
► Responsible for integrating facial sensations
and movements.
► Regulates attentiveness.
Brainstem:
Midbrain & Tectum
► The
midbrain serves as the nerve pathway of the
cerebral hemispheres and contains auditory and
visual reflex centers.
 Integrates information from eyes and ears.
 Controls eye movements.
 Involved in regulating body temperature and pain
perception.
 Works with pons in controlling sleep-wake schedules.
► The
tectum is on top of the midbrain and acts as
an orienting centre. It serves to direct our body
movements toward that to which we are
attending.
Brainstem:
Reticular Formation
► Network
of neurons in brain stem that are
responsible for arousal and sleep.
► Controls the different stages of sleep.
Cerebellum
► The
portion of the brain behind the pons that
helps coordinate movement (balance and muscle
coordination), especially rapid, well-timed
movement.
► Integrates motor and sensory input from the body.
► Damage may result in ataxia which is a problem of
muscle coordination. This can interfere with a
person's ability to walk, talk, eat, and to perform
other self care tasks.
Brainstem & Cerebellum
Damage
Problems with breathing, which can also affect speech.
► Difficulty swallowing food and water (dysphagia).
► Difficulty with organization/perception of the environment.
May not be able to reach out and grasp objects.
► Problems with balance and movement. May be unable to
walk or make rapid movements. May have tremors if
cerebellum is involved.
► Vertigo—dizziness and nausea.
► Sleeping difficulties (e.g., insomnia, sleep apnea),
particularly if the damage is in the reticular formation.
► If severe, there may be no purposeful behaviour, or can
result in coma or death.
►
Forebrain
Forebrain
► Two
cerebral hemispheres, each including:
 Subcortical structures such as hypothalamus,
thalamus, hippocampus, amygdala, basal
ganglia.
 Cerebral cortices
Hypothalamus
Hypothalamus
► Main
function is homeostasis, or maintaining the
body's status quo. Blood pressure, body
temperature, fluid and electrolyte balance, and
body weight are held to a precise value called the
set-point.
► Receives inputs about the state of the body, and
must be able to initiate compensatory changes if
anything drifts out of whack.
► Regulates:
 Heart rate, vasoconstriction, digestion, sweating, etc.
through the ANS.
 Every endocrine gland in the body, regulating blood
pressure, body temperature, metabolism and adrenaline
levels through the pituitary gland and the rest of the
endocrine system.
Other Subcortical Structures
Thalamus
► Just
above the midbrain.
► Consists of nuclei/ganglia (grey matter) and
therefore is a relay centre.
► Passes on visual and auditory information to
the primary cortical receiving areas.
► May be involved in attention.
Hippocampus
► Essential
in learning and memory.
► Recently been found to actually create new
neurons.
► Every new experience creates new
interconnections in the hippocampus.
Amygdala
► Regulates
emotional behaviour.
► Processes feelings of fear as well as anxiety and is
involved in the experience of post-traumatic stress
disorder.
► Plays a role in regulating the changes in heart
rate as a result of emotional stimulation.
► Seems to be important in linking emotional
experience to events and in establishing emotional
memories.
Basal Ganglia
► System
of structures on
either side of the thalamus.
► Relay motor information
between the cortex and
motor centres of the brain
stem.
► Involved in planned motor
control of slow movement
and posture.
► Area involved in Parkinson’s
disease.
Neuroplasticity
► Refers
to the property of the brain that allows it to
change as the result of experience, drugs, or
injury.
► Includes several different processes that take
place throughout a lifetime and involves several
different kinds of cells.
► Occurs under two conditions:
 Part of normal brain development.
 Following injury as an adaptive mechanism and to
maximize remaining functions.
► The
environment is an important influence on
brain plasticity.
Use It or Lose It!
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As each neuron matures, it
sends out multiple branches
increasing the number of
synaptic contacts and laying the
specific connections from, from
neuron to neuron.
As we grow older synaptic
pruning eliminates weaker
synaptic connections and
strengthens others. Unused
neurons weaken and die.
This is how the brain adapts to
its environment and how we
learn.
Neuroplasticity
► Experience
literally changes
the amount of
neural tissue
devoted to a
structure—the
cortical map is
changed.
Neuroplasticity
► When
the brain is
injured, surrounding
tissue can take over
the function of the
damaged area.
► Touch on the man’s
cheek feels as if his
missing hand was
touched—brain has
rewired itself.