t he functional role of the inferior parietal lobe in the dorsal and ventral stream dichotomy...
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THE FUNCTIONAL ROLE OF THE INFERIOR PARIETAL LOBE IN THE DORSAL AND VENTRAL STREAM DICHOTOMYVictoria Singh-Curry & Masud Husain, 2009
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POSTERIOR PARIETAL CORTEX
Bisley J.W. & Goldberg M.E. (2010). Attention, Intention, and Priority in the Parietal Lobe. Annual Review of Neuroscience. 33:1–21
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OVERVIEW
Critical appraisal of the proposed functions of the (right) IPL in existing models of dorsal-ventral stream dichotomy.
Review evidence that shows the right IPL plays an important role in two different, but broadly complementary, aspects of attention: 1. Maintaining attentive control on current task
goals2. Responding to salient new information or
alerting stimuli in the environment. Singh-Curry & Husain’s proposal of IPL
function
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DORSAL–VENTRAL VISUAL STREAM DICHOTOMY MILNER & GOODALE (1995)
“Vision for action”
“Vision for
perception”
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THE POSITION OF THE IPL IN MILNER & GOODALE’S DORSAL–VENTRAL
DICHOTOMY
In humans, the D-S terminates in the SPL & IPS. The IPL isn’t part of the dorsal stream!
High-level spatial representational system that subserves perceptual awareness?
Explains object-centered neglect (rare!), but not impairments of egocentric spatial representation, directing attention or planning movements.
Non-spatial cognitive process in neglect?
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RIZZOLATTI & MATELLI’S TWO DORSAL STREAM MODEL (2003)
D-S is formed by 2 sub-systems: o Dorso-Dorsal stream
(≈ Milner & Goodale D-S, includes SPL)o Ventro-Dorsal stream
Right IPL - spatial perception & action
Left IPL - action recognition, grasping & manipulation
Hemi-neglect
Limb apraxia
Direct homologies between all parts of macaque and human parietal cortex? hemispheric asymmetry, expanded IPS and IPL…
Addresses apraxia and neglectx non-spatial components of neglect
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CORBETTA AND SHULMAN’S GOAL-DIRECTED AND STIMULUS-DRIVEN STREAMS (2002)
Dorsal fronto-parietal network
Top-Down, goal-directed Includes SPL, IPS,
Dorsal frontal cortex
Ventral fronto-parietal network
Bottom-Up, stimulus-driven
Includes TPJ, IPL, ventral frontal cortex
lateralised to the RH
But – the IPL is implicated in sustained attention!!
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ROLE OF RIGHT IPL IN VIGILANCE &SUSTAINING ATTENTION
Vigilance
Sustained
Attention
Intensity continuum
Both require Top-down processes!
Converging evidence comes from both functional imaging studies in healthy subjects as well lesion studies with RH patients.
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11 studies Healthy
subjects Detection of
rare events at single locations/ CPT
Various sensory modalities
VIGILANCE & SUSTAINED ATTENTION: META-ANALYSIS OF PET & FUNCTIONAL
MRI STUDIES
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VIGILANCE & SUSTAINED ATTENTION: LESION STUDY
44 RH stroke patients, with or without neglect A non-spatial task of auditory sustained
attention.
Robertson, I. H. et al., Neuropsychologia,1997
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SALIENCE DETECTION & PHASIC ALERTING
Salience: stimulus properties which make it stand out from the background. Novelty Behavioral or Target-related salience Phasic alerting – a warning of an event of a
behavioral significance
Not only bottom up! (as Corbetta & Shuman claims)
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TARGET RELATED SALIENCE: META-ANALYSIS
10 studies, oddball paradigm at single location, various sensory modalities
Activation foci: RH IPL, IPS, TPJ & frontal regions
Reduced P3 in Neglect patientsDetection of target-related salience requires both ‘top-down’ (discriminating targets from non-targets) as well as ‘bottom-up’ processes!
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NOVELTY: META-ANALYSIS 5 studies, oddball
paradigm Healthy subjects various sensory
modalities More posterior
activation; involves IPL, TPJ, ventral frontal lobe
Detection of novel events requires both ‘top-down’ (memory of target/previously seen stimuli is necessary) as well as ‘bottom-up’ processes!
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PHASIC ALERTING: META ANALYSIS Readiness to detect/ respond to
environmental changes occurring as a result of an exogenous warning stimulus
2 studies RH IPL, TPJ
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THE PROCESS OF RECONFIGURATION Task switching (rule shift, motor response) Study paradigms vary in processes required as
well as working memory load. A variety of bilateral frontal & parietal foci of
activation are found in such studies. What are the critical regions underlying
reconfiguration?
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RECONFIGURATION: META-ANALYSIS
In conjunction analysis only the RH IPL & ventral frontal cortex were activated.
Buchsbaum, B. R. et al., Human Brain Mapping, 2005
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RECONFIGURATION & LC NA SYSTEM
P300 is associated with task switching & with phasic activity of LC NA system
LC phasic activity: facilitates focused selective responding, goal-focused state
LC tonic activity: distractibility, exploration, responses to novel environment stimuli
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IPL & LC
PPC receives sensory, motor, goal-related and reward information.
Different types of information may compete LC Signals biasing the outcome
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SINGH-CURRY & HUSAIN’ PROPOSAL: ROLE OF RIGHT IPL IN CONTROLLING BEHAVIOR
Right IPL: Detection of salient stimuli in the
environment Sustaining attention on task goalsFlexibly switching between these modes via NA system
Lesions may exacerbate spatial biases
Left IPL: Functions underpinning limb praxis
IPL is a crucial node in the fronto-parietal system of allocating resources optimally.
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