Transcript Chapter Six

Chapter Six
The Neuroscience Approach:
Mind As Brain
Neuroscience
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The study of nervous system anatomy and
physiology in man and other species.
Cognitive neuroscience studies the
structures and processes underlying
cognitive function.
What are the neural mechanisms for pattern
recognition, attention, memory, and problem
solving?
Neuroscience methods
In brain damage techniques investigators study the
effects of accidental or deliberate nervoussystem damage. There are two types:
The case study method looks at the effects of
brain damage due to stroke, head trauma, or
other injury in humans.
2. In lesion studies, an electrode is used to
selectively destroy a specific brain area of an
animal. The resulting behavioral deficits are then
examined.
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Brain recording techniques
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The brain’s electrical activity can be
measured in a variety of ways.
In single-cell recording an electrode is
inserted into or adjacent to a neuron.
In multiple-unit recording, a larger electrode
is used to measure the activity of a group of
neurons.
Brain recording techniques
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An electroencephalogram (EEG) provides
an even broader view of brain action.
Electrodes placed on the scalp measure the
gross electrical activity of the entire brain.
An EEG recording in response to the
presentation of a stimulus is an eventrelated potential.
Brain imaging
Recent years have seen the introduction of more
sophisticated devices.
• Computer Axial Tomography (CAT). X-rays passed
through the brain from different perspectives are
used to construct 2-D and 3-D images.
• Positron Emission Tomography (PET).
Radioactively tagged glucose molecules (in the
blood stream) used to measure which brain areas
are most active (and get most blood supply).
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Brain imaging
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In magnetic resonance imaging (MRI) soft
tissue structure is measured by the
alignment of protons within a powerful
magnet.
Functional magnetic resonance imaging
(fMRI) is a version that shows changes in
brain activity (blood flow and oxygen level)
over time. Current method of choice for
investigating brain function.
Electrical stimulation
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In this procedure neurons are electrically
stimulated and the resulting behavior is
studied.
Involves activation of brain areas rather than
their destruction or passive measurement.
Anatomy of a neuron
Anatomy of a synapse
The cortex
Visual pathways
(motion & location)
(color & form)
See also, Image 722 from Gray’s Anatomy
Visual agnosias
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A visual agnosia is an inability to recognize a
visual object. There are two categories:
Apperceptive agnosia. Difficulty in assembling
the pieces or features of an object together into a
meaningful whole.
“General damage to the occipital lobes and nearby areas.”
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Associative agnosia. Can perceive a whole
object but have difficulty naming or assigning a
label to it.
“Damage to the connections that enable the formation of
object representations”
Prosopagnosia
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Prosopagnosia is another type of agnosia in
which patients have difficulty recognizing
faces.
In humans, cells that respond to faces are
found in the fusiform face area (FFA)
located in the temporal lobe.
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Alternative Theory
of the Two Visual Pathways
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The ventral pathway is
 For object recognition
 “Vision for perception”
 Leads to consciousness & awareness of object
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The dorsal pathway is
 For visuomotor control
 “Vision for action”
 Nonconscious, only “here and now”
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Consider blindsight.
 See Milner & Goodale, The Visual Brain in Action
Neural models of attention
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In this component process model of
attention, different brain areas perform
distinct functions (Posner, et. al., 1987).
Parietal lobe disengages attention from a
fixed position.
Superior colliculus moves attention to a new
location.
Thalamus engages attention at the new
position.
Neural models of attention
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In this distributed network model (Mesulam, 1981)
the brain areas subsuming attention are redundant
and can perform multiple functions.
Posterior parietal cortex provides a sensory map
of space to which attention is directed.
Cingulate cortex determines what is important to
pay attention to and what can be ignored.
Frontal cortex coordinates motor programs.
Reticular structures generate arousal and
vigilance levels.
Attentional Structures
(p. 183-4)
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Reticular Activating System (RAS)
 In midbrain
 Controls overall arousal and alertness level
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Superior Colliculus
 In midbrain
 Shifting of visual attention
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Thalamus
 Relay center and filter for further processing
Attentional Structures
(cont)
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Parietal Lobe
 Binding of visual features
 Allocation of attentional resources
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Cingulate Cortex
 Response selection to competing inputs
 See Stroop Effect
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Frontal Lobe
 Goal-directed action
 Executive and problem solving
Stroop Effect
Read the word:
RED
Neuroscience of memory
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Karl Lashley (1950) searched for the
engram, the physical location of a memory.
He destroyed progressively larger areas of
monkey brain tissue after training them on a
task.
The monkeys retained the memory,
suggesting it was distributed to many parts
of the brain, a principle known as
equipotentiality.
Learning and memory
Learning is a change in the nervous system
caused by some event that in turn causes a
change in behavior.
• Learning in a nervous system requires a change in
the structure or biochemistry of a synapse, what is
called synaptic plasticity.
• If a group of neurons is repeatedly activated, the
synaptic connections between them will be
strengthened. This circuit will then contain the new
information.
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The hippocampus
This brain structure is responsible for
consolidation, the transfer of information from STM
to LTM.
• Damage to the hippocampus results in
anterograde amnesia, an inability to retain new
information subsequent to the damage. Example:
The tragic case of H.M.
• This should be distinguished from retrograde
amnesia, in which it is difficult to remember
information learned prior to a traumatic incident.
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Hippocampal structure and
function
Neural substrates of working
memory
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Storage of verbal material: posterior parietal
cortex in left hemisphere.
Rehearsal of verbal material: prefrontal
cortex.
Storage of spatial information: posterior
parietal cortex in right hemisphere.
Maintenance of spatial information:
dorsolateral prefrontal cortex.
Neural substrates of long-term
memory
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Semantic memory linked to the limbic
cortex.
Consolidation of episodic memory mediated
by the hippocampus.
Procedural memory function associated with
basal ganglia and motor cortex.
Neuroscience of problem solving
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Patients with executive dysfunction have
difficulty starting and stopping behaviors and
in problem solving. They suffer frontal lobe
damage.
They may also be impelled to engage in a
behavior triggered by a stimulus. This is
called environmental dependency
syndrome. Example: seeing a pen causes
them to pick it up and start writing.
The Tower of London problem
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Left anterior frontal lobe damage seems to
underlie planning and sequencing in this task
(Shallice, 1982).
Theories of executive function
Executive function refers to the cognitive
operations used in problem solving. They include
planning, sequencing of behavior, and goal
attainment.
• Automatic attentional processes do not require
conscious control. They are triggered by
environmental stimuli.
• Controlled attentional processes require conscious
control. Made in response to novel or difficult
situations.
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Theories of executive function
In the Norman-Shallice (1980) model, action
schemas are activated by stimuli or other schemas
and produce a behavior.
• Action schemas are like scripts in that they specify
what to do in a specific situation. They control
automatic attentional processes.
• Action schemas inhibit one another so that
multiple actions are not executed simultaneously.
Called contention scheduling.
• This system works well for routine familiar tasks.
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Theories of executive function
But for new or difficult problem solving situations
for which there is no known solution, another
system is needed.
• The Supervisory Attentional System (SAS) has
more general flexible strategies that can be
applied to any problem situation.
• The SAS monitors schemas and can suppress or
turn off inappropriate ones.
• Probable neural location is the left anterior frontal
lobe.
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Theories of executive function
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Stuss and Benson (1986) propose an
alternate model with three levels:
1. Lowest level governs automatic responses.
Location: posterior brain areas.
2. Intermediate supervisory level runs executive
processes and solves problems. Location:
frontal lobe.
3. Highest level is metacognitive. It monitors and
regulates any aspect of cognition. Location:
prefrontal cortex.