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Arousal and Attention
Overview
• Arousal – Mechanisms and Deficits
• Automatic (‘Attention’) vs. Controlled
(‘Concentration’) Processes
– Spatial Attention
– Working Memory
• Neuropsychological Assessment of Attention
and Concentration
• Syndromes featuring A/C deficits
Arousal
• Normal, waking state
– Active process influenced by
reticular activating system (brain
stem), hypothalamus, NBM and
thalamus (mid-brain)
– provides activation to cortex
(cortical ‘tone’)
– thalamus
• gates sensory input
• modulates normal sleepwake cycle
Deficits in Arousal
• Normal Arousal
– awake and oriented to person, place and time
• Disoriented/Confused
– responsive & conversant, but easily distracted
– disconnected thoughts, purposeless behavior
• Delirium
– disoriented/confused
– hyperactive, autonomic hyperactivity, hallucinations/delusions
• Stupor
– arousable only to vigorous simulation
– responses when aroused are minimal, very slow
• Coma
– unresponsive to external stimuli
– basic functions (e.g. reflexes) may be absent
Common Causes of Arousal Deficits
(Encephalopathies)
• Acute neurologic insult
– stroke, traumatic brain injury, CNS infection
• Metabolic dysfunction
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hypoxia (heart attack, drowning)
hypo/hyperglycemia (diabetes)
hypo/hyperthyroidism (thyroid disease)
hyperammonemia (liver failure)
uremia (kidney failure)
acute intoxication
• sedatives (alcohol, opiates, benzodiazepines)
• heavy metals (manganese, arsenic, lead)
Attention
“Everyone knows what attention is. It is the
taking possession by the mind, in clear and vivid
form, of one out of what seem several
simultaneously possible objects or trains of
thought…It implies withdrawal from some things
in order to deal with others.”
William James, 1890
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Attention
• Necessary because of the limited processing power of
the brain
• Requires effort
– The mental process of concentrating effort on a stimulus or a mental
event.
• Involuntary or voluntary
– Bottom-up (“sensory, “stimulus-driven”, “implicit”, “exogenous”,
“automatic”)
– Top-down (“executive”, “goal-driven”, “explicit”, “endogenous”,
“controlled”
Feature search
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Conjunction search
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Response Time
Conjunction Search
Feature search
Number of Stimuli in Display
Attention in Visual Search
• Feature search
– Fast, ‘bottom-up’
– Based on one dimension
– Pop-out
• Conjunction search
– Slow, ‘top down’
– Multiple dimensions
– Serial
Degree of
Control
Automatic vs. Controlled
Attentional Processes
Controlled
‘Top-down’
Processing Association
Features
Areas
Tertiary
Central
Executive
Phonological
Loop
Episodic
Buffer
VisuoSpatial
Sketchpad
LimitedCapacity
Slow
Decay
Secondary
‘Filter’
Automatic
‘Bottom-up’
Auditory
Input
Baddeley, 2000
Visual
Input
HighCapacity
Rapid
Decay
Primary
‘Top-Down’ Attentional Effects
Stimulus-Specific
Neurons in Secondary Cortex
(Area V4)
Selective
Firing by
Neurons A & B
+/- = A not B
-/+ = B not A
-/- = Neither
-/+
+/-
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Field where response is rewarded
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Visual Fixation Point
Moran & Disimone, 1985
‘Top-Down’ Attentional Effects
Stimulus- and Field-Specific
Neurons in Secondary Cortex
(Area V4)
Selective
Firing by
Neurons A & B
+/- = A not B
-/+ = B not A
-/- = Neither
-/+
+/-
+
-/-/-
Field where response is rewarded
+
Visual Fixation Point
Moran & Disimone, 1985
Attentional Network
Sensory
Representation
Posterior
Parietal
Cortex
Frontal
Cortex
Motor-Exploratory
Representation
Thalamus
Striatum
Cingulate
Cortex
Motivational
Representation
Reticular
Structures
(Adapted from Mesulam, 1981
Arousal
Attentional Processes, Behaviors
and Tests
• Selective attention
– Process: capacity to capture one source, ignore or filter distractions
– Behavior: conversing at loud party, finding friend in crowd, answer phone
while watching TV
– Tests: Trail a & b, Cancellation, Stroop
Trail A
Trail B
CANCELLATION TASK
Stroop Effect
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GREEN
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GREEN
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Stroop Effect
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Stroop Effect
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RED
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GREEN
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GREEN
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BLUE
Attentional Processes, Behaviors
and Tests
• Selective attention
– Process: capacity to capture one source, ignore or filter distractions
– Behavior: conversing at loud party, finding friend in crowd, answer phone
watching TV
– Tests: Stroop, Trails A, Cancellation, Trails B
• Divided attention (‘working memory’)
– Process: Capacity to attend to multiple tasks/stimuli simultaneously
– Behavior: Driving and texting, typing and listening to phone message
– Tests: Digit Span, Letter-Number Sequencing, dichotic listening
Letter-Number Sequencing
Response - ‘4 6 F L”
Letter-Number Sequencing
Response - ‘2 4 7 9 E K P M’
Attentional Processes, Behaviors
and Tests
• Selective attention
– Process: capacity to capture one source, ignore or filter distractions
– Behavior: conversing at loud party, finding friend in crowd, hear phone while
watching TV
– Tests: Stroop, Trails A, Cancellation, Trails B
• Divided attention (‘working memory’)
– Process: Capacity to attend to multiple tasks/stimuli simultaneously
– Behavior: Driving and texting, typing and listening to phone message
– Tests: Digit Span, Letter-Number Sequencing, dichotic listening
• Sustained attention
– Process: maintain attention over time, aka vigilance
– Behavior: highway driving, radar monitoring
– Tests: Continuous performance task
Test of Variable of Attention
(TOVA)
Respond
Don’t Respond
Attention Deficits are Typically Associated
with Frontal Lobe or Diffuse Dysfunction
• Attention Deficit Hyperactivity Disorder
– Hypoactivity of frontal lobes (delayed maturation?)
• Traumatic Brain Injury
– Focal frontal lesions
– Diffuse effects due to hypoxia
– Diffuse axonal injury
• Multiple Sclerosis
– Loss of axonal myelin slows transmission, impairs smooth
integration of attention network
Visual Neglect
Spatial
ObjectCentered
Visual Neglect is Ego-Centric
Facing East
Facing West
Line Bisection
Normal
Line Bisection
Left Neglect
Balint’s Syndrome
• Optic ataxia
– deficit in visually guided reaching – coordination of visual
information with motor response
• Gaze apraxia
– deficit in shifting visual attention intentionally
• Impaired distance estimation
• Narrowed Attentional Field (Simultanagnosia)
– can only attend to one stimulus at a time
• Absence of other deficits
• Associated with bilateral parietal lesions – more
severe when frontal lobes are involved
Simultanagnosia
• Attention to spatial ‘field’ is normal
• Attention to object ‘field’ is impaired