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Six amnesia

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					    Chapter Six
The Neuroscience Approach:
      Mind As Brain
               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?
        Neuroscience methods
In brain damage techniques investigators study the
    effects of accidental or deliberate nervous-
    system damage. There are two types:

1. 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.
      Brain recording techniques
•   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
•   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.
              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).
                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.
           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.
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
•     A visual agnosia is an inability to recognize a
      visual object. There are two categories:
1.    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.”
2.    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
•   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.)
             Alternative Theory
        of 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
       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.
       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.
            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
            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
             Stroop Effect
Read the word:


                 RED
        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.
         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.
            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.
Hippocampal structure and
        function
     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.
    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.
    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.
    The Tower of London problem
   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.
    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.
    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.
    Theories of executive function
•   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.

				
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