Download Functional Neural Anatomy

Functional
Neural Anatomy
Honors Psychology
Linking
Structure & Function
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Three Types of Evidence
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Association of function: “If brain area A controls behavior
X, then those with deficient behavior X will have a deficient
area A, and individuals with a better behavior X will have a
better area A.”
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Single dissociation of function: “If brain area A controls
behavior X, then those with a deficient area A will have a
deficient behavior X but not Y ….”
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Double dissociation of function: “If brain area A controls
behavior X, then those with a deficient area A will have a
deficient behavior X but not Y, and those with a deficient area B
will have a deficient behavior Y but not X ….”
Tools of
Functional Anatomy
Situation #1: When you can kill the animal
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Analysis of structure
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Ablations: the removal of a brain area
Lesions: the destruction of brain areas, e.g., accidental lesions, or as
a result of the deliberate application of electrodes, chemicals, or
gene-knockouts.
Analysis of activity
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Microdialysis: a method for measuring concentrations of
neurotransmitters
Tools of
Functional Anatomy
Situation #2: When you can’t
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Analysis of structure
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CAT scans provide a high-contrast x-ray of the brain with excellent
spatial resolution, but provide no temporal resolution
MRIs provide higher resolution images of the brain and use no
radiation, but provide no temporal resolution.
Analysis of activity
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EEGs record electrical activity of the brain through electrodes
attached to the scalp, thereby providing excellent temporal records
of neural processes but poor spatial resolution.
PET scans provide a high-resolution image of brain activity with
moderate temporal and spatial resolution.
fMRIs have excellent spatial resolution and near-excellent temporal
resolution.
The Basics of the Nervous
System
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Three basic functions:
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To receive sensory information
To organize and integrate that information with past information
To enact the muscles and glands to produce organized
movements and adaptive secretions
Three basic structures:
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Sensory neurons
Interneurons
Motor neurons
Nervous System Hierarchy
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Animal evolution involved moving from
simple reflexes to intentional control
of movement.
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This evolution is (roughly) manifest in
the hierarchical organization of motor
control.
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At the simplest level, motor neurons
work alone to control muscles.
At higher levels, muscles are controlled
by motor neurons, which are
controlled by the brainstem, which is
controlled by the primary motor
cortex, which is controlled by the....
Central vs. Peripheral
Central Nervous System:
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Brain
Cortical Structures
Subcortical Structures
Spinal Cord
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Peripheral Nervous System:
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Nerves connecting the CNS with
organs and muscles
Autonomic Nervous System
Sympathetic ganglia
Parasympathetic ganglia
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Central Nervous System
Peripheral Nervous System
Autonomic Nervous System
Sympathetic Division--the
war-maker preparing for “fight or
flight”
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Primarily, the function of these
neural cell bodies (or ganglia) is
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to accelerate breathing and heart
rate and
to decrease digestive activity to
preserve energy for the muscles
Activated secondarily (or “in
sympathy”) are
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the sweat glands,
adrenal glands,
the muscles that constrict blood
vessels, and
the muscles that make your hair
stand on end.
Autonomic Nervous System
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Parasympathetic
Division--the peace-keeper
that heals, promotes growth,
conserves energy
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Parasympathetic ganglia are not
linked to one another as tightly
as the sympathetic
Consequently, they
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increase the digestive rate,
decrease the heart rate,
increase the flow of sinus fluids
independently
Spinal Cord
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Sends and receives input from the
sense organs and muscles below
the level of the head
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Bell-Magendie Law: entering dorsal
roots carry sensory information
to the brainstem and exiting
ventral roots carry motor
information to the muscles and
glands.
Contains networks of neurons,
pattern generators, that stimulate
one another cyclically to generate
rhythmic sequences of motor
movements, such as flying, walking,
running, etc. The brain inhibits
these movements.
Subserves some reflexes, such as
the flexion reflex, which removes a
limb from a potentially damaging
reflex even without the perception
of pain.
Subcortical Structures/Brainstem
Subcortical Structures/Brainstem
Subcortical Structures/Brainstem
Subcortical Structures/Brainstem
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The Brainstem
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Medulla controls vital reflexes such as
breathing, heart rate, and vomiting, and
exerts control over the spinal cord.
During REM sleep, for example, the
medulla is activated and suppresses
movement.
Pons receives input from facial skin,
nose, mouth, eye muscles, and part of the
tongue. It also controls chewing and
swallowing, eye movements, and facial
expressions.
Midbrain controls the speed of
locomotion and with the pons controls
levels of arousal. In birds, reptiles,
amphibians, and fish the midbrain is
proportionately larger than in mammals.
When a mammal’s midbrain is cut, it can
react to stimuli (such as to climb a pole
whether or not it has food at the top)
but it cannot selectively react to stimuli
(such as to climb a pole that has food at
the top rather than a pole that does not).
Subcortical Structures/Thalamus
Subcortical Structures/Thalamus
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The thalamus is a sort of relay station.
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Non-olfactory sensory information goes
first to the thalamus, which then
processes it and relays the output to the
cerberal cortex.
Relays information in modality-specific
ways.
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Many nuclei in the thalamus receive their
input primarily from the visual system, then
relays the information to a single area of
the cerebral cortex, while receiving
feedback information from the same
cortical area.
The thalamus also relays information from
higher parts of the brain to movementcontrol centers in the brainstem.
Lesions placed in some thalamic nuclei can
temporarily relieve the deep, chronic pain
caused by chemotherapy without
abolishing the patient’s physical sensations.
Subcortical Structures/Cerebellum
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The cerebellum responds to
sensory information that guides
movements that require the rapid
integration of sensory information, such
as flying and tree hopping.
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Birds and monkeys, for example, have
particularly large cerebella.
Cerebellar lesions in sloths had no
detectable effect.
People with damage to the
cerebellum look drunk, and
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have trouble moving their eyes to a
particular point
have trouble shifting their attention
from visual to auditory information
have trouble tapping a rhythm,
pointing at a moving object, and
adapting to prisms that distort vision
Subcortical Structures/Limbic System
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The limbic
system forms a
border around
the thalamus and
basal ganglia.
The limbic
system includes
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hypothalamus,
hippocampus,
amygdala.
Subcortical Structures/Limbic System
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In rabbits, cats, and monkeys, it takes up a large proportion of
the brain.
Subcortical Structures/Limbic System
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The primary tasks of the
hypothalamus:
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to influence the activity of the
autonomic nervous system,
control the release of certain
hormones,
influence hunger and thirst.
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When the amygdala is removed or
diseased, people are not startled by
loud sounds, experience fear very
weakly, and have difficulty recognizing
fear in others.
The amygdala seems to be responsible
for emotional learning.
The hippocampus serves spatial
memory in non-humans, and serves to
convert short-term to long-term
memories in humans.
Subcortical Structures/Basal Ganglia
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The basal ganglia exchanges information
with the cerebral cortex, itself, and the
thalamus.
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The function of the basal ganglia seems to
be to organize movement plans from the
cerebral cortex by inhibiting unwanted
movements. As a result, it is important for
slow, deliberate movements, such as a
reaching for an object.
One study of very clumsy children found
that those with cerebellar impairment were
inaccurate with the timing of their
movements, whereas those with basal
ganglia impairments were inaccurate in their
control of muscle force (Lundy-Ekman, et
al., 1991).
The basal ganglia may also be important for
inhibiting unwanted thoughts.
Psychotherapy and drug-treatments of
obsessive-compulsive disorder seem to
work by lowering the metabolic rate of the
basal ganglia.
Nervous System: Phylogeny
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Species-differences involve differences in “smoothness” and differences in the amount of
cortex relative to the body, which is related to species-typical diets (e.g., fruit-eating bats
have relatively bigger brains than insect-eating bats; carnivores have relatively bigger brains
than herbivores) and basal metabolic rate.
Primates devote more energy to brain development than any other species.
Other species-differences relate to specific areas of the brain, such as the olfactory lobe
(smell), hippocampus (spatial abilities),
Nervous System: Ontogeny
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The development of the
cortex shows a roughly
similar pattern as the
phylogenetic differences:
relatively small and
smooth cortex early in
development.
This observation was
expressed by 19th
century biologists as
“ontogeny recapitualates
phylogeny.”
Cortex Evolution: Does size matter?
Cortex Evolution: Does size matter?
Cortex Evolution: Does size matter?
Cortex Evolution: Apes vs. Humans
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Motor and visual areas are proportionately smaller in
humans (77% & 60%), whereas the prefrontal area is 202%
larger.
Cortex Evolution: Apes vs. Humans
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The human brain has more axons between cortical areas and
between the basal ganglia.
Humans control their vocalizations primarily from the cortex rather
than the limbic system.
Some neurotransmitters are proportionately more widespread in
humans than in apes.
The Truth about Cortex
• The Truth about the brain
– What is true: People get sensory information, think about it, and act.
– What is not: “Sensory area” gets sensory information; “association area”
thinks about it; “motor area” acts on it.
• Why?
– Association cortex processes information more elaborately than the
primary sensory areas do, but they do not link one kind of sensory
information with another. Only visual info goes to associative visual
cortex; only auditory info goes to associative auditory cortex, etc.
– The brain has no single site at which all information funnels into a
hidden observer. There is no “little person in the brain.”
– Thinking depends on separate, simultaneous processes throughout the
brain. How they produce a unified consciousness remains a mystery.
• Consequently, we divide the brain into lobes named for the
skull bones which cover them.
Cerebral Cortex
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The occipital lobe primarily receives information about
objects that we see.
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Destruction of the top layer causes cortical blindness: normal
eyes, normal pupillary reflexes, some eye movements, but no
pattern perception.
Cerebral Cortex
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The parietal lobe primarily receives information from the
pressure that we feel by touch.
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Destruction of parietal cortex does not lead to total loss of the sense of
touch, but rather difficulties in using such information. For example, blind
people lose the ability to read Braille. Other symptoms include: clumsiness on
the side of the body opposite the damage, the inability to draw and follow
maps, and the inability to say what something might look like when viewed
from a different angle.
Cerebral Cortex
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The temporal lobe primarily receives information from the
tones that we hear.
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Damage to the temporal lobe affects the ability to understand
both spoken and signed language.
Cerebral Cortex
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The frontal lobe contains the motor and prefrontal cortex.
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The primary motor cortex is necessary for making delicate hand
movements, such as lifting a small piece of food out of a narrow
hole.
The supplementary motor cortex is necessary for visualizing
motor sequences such as visualizing a basketball shot you’re
about to make. More complex tasks require greater activation
of this area.
The amazing prefrontal cortex
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The prefrontal cortex is the only cortical
area that receives information from all
the sensory systems, including the
interior of the body.
The prefrontal cortex is important for
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working memory, the ability to remember
recent events, such as how many people
ran in vs. out of a building
delayed response tasks, in which a
stimulus appears, then disappears, and
after a delay, the person must respond to
the remembered stimulus
monitoring recent events, calculating
possible actions, ascertaining the results
of those actions, and determining the
emotional value of each of those
outcomes. Damage to your PFC may
result in showering with your clothes on,
shaking salt into your drink instead of
your food, or pouring water on the tube
of toothpaste rather than your
toothbrush.