Download Attention

Neuroscience: Exploring the Brain, 4e
Chapter 21: The Resting Brain, Attention, and
Consciousness
Chapter 1: Applying Research to
Everyday Exercise and Sport
Copyright © 2015 Wolters Kluwer Health | Lippincott Williams & Wilkins
Introduction
• Attention: ability to focus on one aspect of sensory input
• Preferentially process some information and ignore the
rest
• Attention has significant effects on perception.
• Corresponding changes in sensitivity of neurons at many
brain locations
• Consciousness: awareness of something
• Neural basis of the conscious brain?
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Resting State Brain Activity
• Generally, neurons become more active in cortical areas
processing ongoing perceptual or motor information.
• Resting state activity
– Some regions are fairly quiet.
– Others surprisingly active
– Revealed by PET and fMRI imaging of whole brain
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The Brain’s Default Mode Network
• Engaging in task  decreases in activity of some brain
areas, whereas task-relevant areas become more active.
• Resting brain activity: fundamental and significant
• Patterns in brain activity changes consistent across
human subjects
• Brain areas active in resting state
– Medial prefrontal cortex, posterior cingulate cortex,
posterior parietal cortex, hippocampus, lateral
temporal
– Together, the default mode network
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The Default Mode Network
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Functions of the Default Mode Network
• Two hypotheses
– The sentinel hypothesis
• Broadly monitoring the environment
• Rare disorder: simultagnosia
– The internal mentation hypothesis
• Supports thinking and remembering, like
daydreaming
• Imaging: state like remembering
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Attention
• Selective attention—directed, filers out input
• Limited capacity of attention
– Attention-deficit hyperactivity disorder
• Exogenous attention—bottom–up attention
– Like animal detecting predator
• Endogenous attention—top–down attention
– Deliberately directed by the brain
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Behavioral Consequences of Attention
• Attention enhances
visual sensitivity.
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Effect of Cueing on Target Detection
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Attention Speeds Reaction Times
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Shifting Attention
• What happens to neural activity?
• What brain areas are involved?
– Effects of attention observed in high-level cognitive
and numerous sensory areas
• Consequences of allocating attention revealed
– Imaging studies in humans
– Individual neuron changes in animal studies
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Functional MRI Imaging of Attention to
Location
• Subjects view stimulus
• Location of cued sector
changes
• Brain activity shifts
retinotopically.
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PET Imaging of Attention to Visual
Features
• Same–different discrimination task:
color, shape, speed
• (A) Selective attention experiment
• (B) Divided attention experiment
• Subtract B from A shows brain
activity associated with attention to
one feature.
• V4, IT, and other visual areas in
temporal lobe color and shape
• Area MT speed of motion
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Feature-Specific Effects of Visual
Attention
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Enhanced Neuronal Responses in Parietal
Cortex
• Attention: experimental versus normal conditions
• What happens to attention under normal conditions?
• Assumption: Attention changes location prior to eye
movement.
• Experiments of Wurtz, Goldberg, and Robinson
– Recorded neural activity from several brain regions
– Response enhancement in posterior parietal cortex
• May speed visual processing and reaction times
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Enhanced Neuronal Responses in Parietal
Cortex
• Effect of attention
on the response
of a neuron in
posterior parietal
cortex
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Effect of Attention in Visual Cortical Area V4
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Brain Circuits for the Control of Attention
• Cortical, subcortical areas
– Guide attention
– Saccadic eye movements
• The pulvinar nucleus
– Projects to many areas of
cortex
– Regulates visual
information flow
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Attention and Eye Movements
• Frontal eye fields (FEF)
– Cortical area in
frontal lobe
– FEF neurons—
motor fields
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Attention and Eye Movements—(cont.)
• Experiment of Moore and colleagues
– Train monkeys to look at display of small light spots
– Place electrode in FEF and determine motor field of
neurons at its tip
– Small electrical stimulation  enhancement?
• Results
– FEF is involved in directing attention, enhances visual
performance.
– FEF stimulation mimics physiological and behavioral
effects of attention.
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Effect of FEF Stimulation on Neuron
Activity in Area V4 in Monkey Brain
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Directing Attention with Salience and
Priority Maps
• Hypothesis of how certain visual features grab attention
– Bottom–up attention
– Salience map shows locations of conspicuous
features.
• Top–down attentional modulation from cognitive input
– Priority map shows locations where attention should
be directed.
• Based on stimulus salience and cognitive input
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A Priority Map in the Parietal Lobe
• Lateral intraparietal cortex
(area LIP)—priority map
based on bottom–up and
top–down inputs
– Guides eye
movements and
attention
• Lesions in parietal cortex
associated with neglect
syndrome
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Hemispatial Neglect Syndrome as
Attentional Disorder
• Person ignores objects, people, and their own body to
one side of the center of the gaze.
• Associated with right-sided lesions in posterior parietal
cortex
• Neglect syndrome might be a disruption of ability to
shift attention.
• Hypothesis: Left hemisphere attends to right hemifield,
whereas right hemisphere attends to both right and
left hemifields.
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Frontoparietal Attention Network
• Bottom–up attention
– Input from visual areas in the occipital lobe reaches
area LIP.
– Construction of salience map
– Visual processing is enhanced; eyes may move.
• Top–down attention
– Attention effects occur first in frontal and parietal
areas.
– Priority map in LIP and FEF
– Visual processing is enhanced; eyes may move.
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Frontoparietal Attention Network in
Macaque Brain
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Consciousness
• Materialist perspective
– Consciousness arises from physical processes
– Based on structure and function of nervous system
• Alternative: dualism
– Mind and body are different things.
– One cannot be fully explained by the other.
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What Is Consciousness?
• Nature of human consciousness problematic
– Even defining consciousness is controversial.
• The easy problems of consciousness
– Phenomena answerable by scientific methodology
– Example: sleep–awake difference
• The hard problem of consciousness
– The experience itself
– Why the experience is the way it is
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Neural Correlates of Consciousness
• The minimal neuronal
events sufficient for a
specific conscious percept
• Experimental approach
with bistable visual
images—changes in
neural activity?
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Neuronal Correlates of Alternating
Perception in Binocular Rivalry
• Different images seen by the two eyes.
– Perceptual awareness alternates
• Experimentally demonstrated
– Neural recordings in monkey area IT show changes
correlated with perceptions.
– Neural activity in IT may be neural correlate of this
awareness.
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Visual Awareness and Human Brain
Activity
• Rivalry experiments in humans using fMRI to record brain
activity
– Using rival images of a face and a house
– Recording in FFA (faces) and PPA (places)
– Produced alternating patterns of brain activity in FFA
and PPA
• Imagining imagery activates same visual processes
– Similar results with neuronal probe recording in
human subject
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Challenges in the Study of Consciousness
• Small steps succeeding in studying neural correlates of
consciousness (NCC)
• Challenges of interpreting NCC study data
– What is “minimal” brain activity sufficient for
conscious experience?
– Is the neural activity a prerequisite for conscious
experience or consequence of the experience but not
NCC?
– Can attention be confounded with awareness?
• The “hard problem” of consciousness remains.
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Concluding Remarks
• Resting state activities likely include monitoring
environment and daydreaming.
• Attention confers behavioral flexibility.
– We use attention to focus mental resources.
– Network of brain areas, priority maps
– Allocation of attention followed by selective enhanced
processing in sensory cortex
• Many mysteries remain about consciousness of
information we attend to.
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