Chapter Six

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Chapter Six

• The Neuroscience Approach Mind As Brain

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Neuroscience

• 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?

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Neuroscience methods

• In brain damage techniques investigators study
  the effects of accidental or deliberate nervous-
  system 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.
• 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

• The brains 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.

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Brain recording techniques

• 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 event-related potential.

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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

• 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.

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Electrical stimulation

• 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.

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Anatomy of a neuron
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Anatomy of a synapse
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The cortex
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Visual pathways
(motion location)
(color form)
See also, Image 722 from Grays Anatomy
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Visual agnosias

• 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.
• 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

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Prosopagnosia

• 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.
• (Based on fMRI studies.)

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Alternative Theoryof the Two Visual Pathways

• The ventral pathway is
• For object recognition
• Vision for perception
• Leads to consciousness awareness of object
• The dorsal pathway is
• For visuomotor control
• Vision for action
• Nonconscious, only here and now
• Consider blindsight.
• See Milner Goodale, The Visual Brain in Action

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Neural models of attention

• 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.

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Neural models of attention

• 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.

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Attentional Structures (p. 183-4)

• Reticular Activating System (RAS)
• In midbrain
• Controls overall arousal and alertness level
• Superior Colliculus
• In midbrain
• Shifting of visual attention
• Thalamus
• Relay center and filter for further processing

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Attentional Structures (cont)

• Parietal Lobe
• Binding of visual features
• Allocation of attentional resources
• Cingulate Cortex
• Response selection to competing inputs
• See Stroop Effect
• Frontal Lobe
• Goal-directed action
• Executive and problem solving

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Stroop Effect

• Read the word

RED
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Neuroscience of memory

• 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.

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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
Sensory information
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Neural substrates of working memory

• 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.

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Neural substrates of long-term memory

• 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.

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Neuroscience of problem solving

• 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.

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The Tower of London problem

• Left anterior frontal lobe damage seems to
  underlie planning and sequencing in this task
  (Shallice, 1982).

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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

• Stuss and Benson (1986) propose an alternate
  model with three levels
• Lowest level governs automatic responses.
  Location posterior brain areas.
• Intermediate supervisory level runs executive
  processes and solves problems. Location frontal
  lobe.
• Highest level is metacognitive. It monitors and
  regulates any aspect of cognition. Location
  prefrontal cortex.