Transcript Ch_06x - Computer Science

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 nervous- system
damage. There are two types:
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The case study method looks at the effects of brain
damage due to stroke, head trauma, or other
injury in humans.
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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
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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 event-related potential (ERP).
Brain Imaging Methods
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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 used to measure which
brain areas are most active.
Brain Imaging Methods
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In magnetic resonance imaging (MRI) soft tissue
structure is measured by the alignment of protons
within a powerful magnet. A “snapshot”.
Functional magnetic resonance imaging (fMRI) is a
version that shows changes in brain activity over
time. A “movie”.
Brain Imaging Methods
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Magnetoencephalography (MEG) measures changes in
small magnetic fields that occur when neurons fire.
Better spatial and temporal resolution than fMRI.
Knife-edge scanning microscope (KESM) takes pictures
of slices of tissue and reconstructs a 3-D image.
A complete 3-D cellular-level recording of the human
brain is now possible.
Electrical Stimulation Techniques
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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.
In transcranial magnetic stimulation (TMS) an electrical
current is passed through a part of the brain causing
neurons to fire.
Repetitive applications can be used to treat
psychological disorders.
Anatomy of a Neuron
Anatomy of a Synapse
Neurotransmitters
Directions in the Nervous System
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Dorsal – “Top”.
Ventral – “Bottom”.
Anterior – “Front”.
Posterior – “Back”.
Medial – “Middle”.
Lateral – “Side”.
Major Cortical Features
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Two cerebral hemispheres on each side, one on the
left, the other on the right.
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Corpus callosum connects each hemisphere.
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A gyrus is a fold of cortical tissue.
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A fissure is a cleft or separation between gyri.
The Cortex
Left-Brain Functions
Analytic thought
Logic
Language
Science and
Math
Right-Brain Functions
Holistic thought
Intuition
Creativity
Art and
Music
The Split Brain
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Information from one side of the environment or
body is mapped onto the contralateral side.
In split brain patients, the corpus callosum is severed
It is now possible to present information to only one
side or the other – with interesting results.
Visual Pathways
Visual Agnosias
A visual agnosia is an inability to recognize a
visual object. There are two categories:
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Apperceptive agnosia. Difficulty in assembling the
pieces or features of an object together into a
meaningful whole.
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Associative agnosia. Can perceive a whole object but
have difficulty naming or assigning a label to it.
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.
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.
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Superior colliculus moves attention to a new location.
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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.
Disorders of Attention
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Damage to the right superior temporal gyrus
causes hemispatial neglect, an inability to attend to
the left side of the body and the environment.
These patients can only perceive the right side of
objects and will leave out the left sides when asked
to draw them.
Disorders of Attention
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Attention deficit hyperactive disorder (ADHD) is
characterized by distractibility, impulsivity, getting
easily upset, and difficulty in planning or carrying
out plans.
The gene for one type of dopamine receptor is
more common in some patients who also have
smaller brains.
Treated pharmacologically with Ritalin
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
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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, a process called long-term potentiation
(LTP). This circuit will then “contain” the new
information or mediate the learned behavior.
The Hippocampus
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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.
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. The inability to stop an action once started
is called psychological inertia. 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.
Theories of Executive Function
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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
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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
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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
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Stuss and Benson (1986) propose an alternate
model with three levels:
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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.
Interdisciplinary Crossroads: Neural
Synchrony
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Each object is made up of many different features
like shape, color, motion, etc.
Different parts of the brain process each of these
features.
How do all of these features get combined together
so that we can recognize them? This is the perceptual
binding problem.
The neurons in each of the different areas start to
fire at the same time.