http://www.weizmann.ac.il/home/masag
i/MIB/
Neuroscience: Exploring the
Brain, 3e
http://youtu.be/vJG698U2Mvo
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins
Introduction
• Attention:
• State of selectively processing simultaneous sources of
information
• Benefits performance of behavioral tasks
• Importance emphasized by attention-deficit hyperactivity
disorder
• Brain Imaging – changes in cortical activity
• Study attention by examining behavioral manifestations, e.g.,
visual attention
• http://youtu.be/vJG698U2Mvo
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Behavioral Consequences
of Attention
• Attention enhances visual
detection
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Behavioral Consequences of Attention
• Attention Decreases Reaction Times
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i/MIB/
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Physiological Effects of Attention
• Shifting Attention
– What happens to neural activity?
– What brain areas are involved?
• Observed in high-level cognitive and numerous
sensory areas
• e.g., Area V1 to visual cortical areas in the
parietal and temporal lobes
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Physiological Effects of Attention
• Functional MRI Imaging of
Attention to Location
– Subjects view stimulus
– Change location of
attended sector
– Brain activity shifts
retinotopically
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Physiological Effects of Attention
• PET Imaging Attention to Features
– Same-different discrimination task:
Color, shape, speed
– (A) Selective attention: one feature
– (B) Divided attention: all features
– Subtract B from A shows brain
activity associated with attention to
one feature V4, IT and other visual
areas in temporal lobe Color &
shape
– Area MT Speed of motion
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Physiological Effects of Attention
• PET Imaging of Attention to Features (Cont’d)
Color
Shape
Motion
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Physiological Effects of Attention
• Enhanced Neuronal Responses in Parietal Cortex
– Attention: Experimental vs. Normal conditions
– What happens to attention under normal conditions?
– Assumption: Attention changes location prior to eye
movement
– Wurtz, Goldberg, and Robinson
• Record neural activity from several brain regions
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Physiological Effects of
Attention
• Enhanced Neuronal Responses in
Parietal Cortex
–
Wurtz, Goldberg, and
Robinson
• Implications of Superior
Colliculus work for explaining
these findings
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Physiological Effects of Attention
• Enhanced Neuronal Responses in Parietal Cortex (Cont’d)
– Posterior parietal cortex neurons
– Directing eye movements
– Response significantly enhanced neuronal response
when eyes went to target
• Spatially selective effect – not a general increase
in excitability
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Physiological Effects of Attention
• Receptive Field Changes in Area V4
(Response to effective stim.
But attention directed at
location of ineffective stim.)
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How is Attention Directed?
• Cortical, subcortical areas
– Modulate the activity of neurons in sensory cortex
areas
• The Pulvinar Nucleus
– Guiding attention
– Muscimol
• GABA agonist
• Neuron activity
suppressed
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How is Attention Directed?
• Attention and Eye Movements
– Eye moves to attended object
– Eye movements & attention closely related
– Recent experiments
• Brain circuitry: Directing eyes to objects of
interest
– Frontal Eye Fields (FEF)
• Cortical area
• FEF neurons
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How is Attention Directed?
• Attention and Eye Movements (Cont’d)
– Experiment
• Train monkeys to look at display of small light spots
• Place electrode in FEF and determine motor field of
neurons at the tip
• Small electrical stimulation enhancement?
– Results
• FEF involved in directing attention; Enhancing visual
performance
• V4 activity increased
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How is Attention Directed?
• Attention and Eye Movements
– Results (Cont’d)
• FEF stimulation mimics physiological and
behavioral effects of attention
• Electrical stimulation of superior colliculus
– Conclusion
• Guidance of attention
• Integrated with system to move eyes
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Physiological Effects
of Attention
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Physiological Effects
of Attention:
LIP Neurons
Respond best if
Star is flashed on
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Physiological Effects
of Attention:
LIP Neurons: Is
Increased activity
For ‘cued’ star
Attention related?
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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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Visual Awareness and Human Brain
Activity
Entorhinal cortex neuron in
human: Selective response
to seen or imagined
dolphins.
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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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Concluding Remarks
• Studies of attention point to flexibility of the human brain
• More mental energy to one location
– Enhanced sensitivity & reaction time
– Ignore competing stimuli
– Can be seen in brain imaging studies
– Effects receptive field properties
• Why do we need attention?
– Cannot process all information simultaneously
– Selects what information should access the limited
processing resources
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End of Presentation
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Behavioral Consequences of Attention
• Neglect Syndrome as an Attentional
Disorder
–
Person ignores objects, people,
and their own body to one side of
the center of the gaze
–
Associated with right-sided lesions
–
Hypothesis: Left hemisphere
attends to right hemifield whereas
right hemisphere attends to both
right and left hemifields
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins