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The What and Where Pathways

• William W. Crissman
• 02/08/13

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Study Question Overview

1. How have the two cortical pathways historically
   been modeled by the like of Ungerleider, Mishkin,
   Goodale, and Milner?
2. How does the de Haan and Cowey (2011) differ from
   the previous model?
3. What evidence is there to support a more
   patchwork-like model of cortical info-processing?
4. What does heading disorientation (HD) a
   characteristically unique form of topographical
   disorientation?
5. What area of the brain has been heavily
   implicated in the integration of information
   about objects in space based on your own frame of
   reference and changes you make in body direction?

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Historical Perspectives

• Lissauer (19th century)
• Electrophysiological studies with animals and
  neuroimaging studies with humans (20th century)
• Ungerleider and Mishkin
• 1st to suggest organization of 2 major paths from
  V1
• Ventral and dorsal paths

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Historical Perspectives con.t

• The Dual-Pathway paradigm (Goodale and Milner,
  1995)
• Reconceptualized framework in terms of WHAT the
  visual info is USED for, rather the KIND of
  information is relayed
• Thus, the same info is being used differently,
  rather than different info going to different
  directions
• Ventral info terminating in the MTL, hippocampus,
  and amygdala used for visual recognition, memory,
  and emotional content
• Dorsal info feeds into motor cortex of frontal
  lobe and uses visual information for action

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The Patchwork Model

• Challenges previous model in terms of
• Whether a pathway model is more parsimonious than
  a patchwork model?
• Latter fails to account for the an organizational
  structure that consists of many interrelations
  b/t different visual maps
• Whether there is sufficient evidence to support a
  model that suggests strict hierarchical
  processing of visual information?

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Evolution and Innate Design

• Visual architecture and gross organization of
  visual maps
• Both very well-defined
• little variability in humans (total extent of
  striate cortex)
• HOW did the architecture and organization develop
  in terms of evolution and natural selection?
• In one sweep, or more independently, haphazard
  manner?
• Evolution supports a patchwork model
• Previous model assumes too elaborate of a
  Darwinistic step

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Neural Wiring

• Issue on white matter tracts
• Very little systematic evidence, but overall
  picture does not support linear path model
• If no internal organization, then connections
  should be equally strong b/t all possible nodes
• If organized into hierarchical pathways,
• Then connections within a path would be stronger
  than connections between the paths,
• And shorter connections would be stronger than
  more long-range connections
• V1 and V2 gt V1 and V3?
• Very little systematic evidence concerning this
  issue

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Two Streams (Or are there?)

• Hierarchical model works well to conceptualize
  ventral what stream
• Color, orientation, and brightness enable
  perceptions of objects, places, and faces
• Not so much with dorsal where/how stream
• In space, what qualifies are basic or advanced
  features?
• Position feed into depth, or vice versa?
• At present, three paths have been postulated in
  parietal lobe
• Parieto-prefrontal path top-down eye movements,
  spatial WM
• Parieto-premotor path visually-guided actions
• Parieto-medial temporal path visuo-spatial
  navigation info, spatial LT memory
• Four, if we add path from LGN to area MT
• Five, if we add path for processing temporal
  order (when path)

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Two Streams (Or are there?)
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Too much Cross-talk

• How can two paths with fundamentally content
  communicate?
• Why even have two paths given the continuous and
  meaningful cross-talk?
• How is the strict division in terms of conscious
  perception continually maintained, given the
  extensive cross-talk?
• How can we explain certain aspects of dorsal
  processing that can reach conscious awareness?

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Integration of Features

• If hierarchical organization, then basic features
  processed during early stages are integrated in
  subsequent stages
• Maybe at the local, micro-circuit level, in a
  single area
• End-stopped cells in V2 integrate orientation
  and position/length info
• Is this really integration? Or an implicit
  assumption?
• Theoretically, face recognition, a higher-order
  process, would call for important visual features
  that are processed in more posterior visual areas
• Role of various visual parameters in face
  recognition have shown modest effects at best

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Complexity

• Hierarchical model also assumes that the
  complexity of information increases progressively
  and systematically as it is processed further
  down stream (cascade specification)
• Is color processing really more basic, in terms
  of complexity and processing characteristics,
  than reading or face recognition?

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Color Perception and Recognition

• Involves numerous separate stages (maps)
• Concerns a stimulus-specific perception system
• Involves categorical perception
• Leads to conscious perception
• Part of processing occurs subconsciously
• Heredity does influence ontological development

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Authors Concluding Remarks

• Prevailing view makes more elaborate assumptions
  about evolution of visual system than evidence
  currently warrants
• Pathway model are not supported by physiological
  neural wiring between different visual maps
• It is not clear why there should only be two
  paths
• In new model, there are no functional highways,
  nor presupposed hierarchy between different
  visual abilities
• Allows more flexibility in the role of the visual
  system and visual information from different
  visual areas
• Not advocating to throw the baby out with the
  bath water, rather reserve hierarchical
  processing for the columnar and microcircuit
  level

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• Hasimoto, R., Tanaka, Y., Nakano, I. (2010).
  Heading disorientation A new test and possible
  underlying mechanism. European Neurology, 63, 87
  93.
• http//www.youtube.com/watch?vuF7-AxleI_0feature
  endscreen

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Topographical Disorientation

• Inability to orient ones self within
  large-scale, locomotor environments
• Oftentimes the result of diffuse brain damage via
  stroke, dementia, Alzheimers disease, etc.
• Also, implicated in focal brain damage as
  suggested here
• Four unique varieties

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Types of TD

• Egocentric Disorientation
• Implicated in damage to posterior parietal lobe
• Marked inability to represent the location of
  objects with respect to ones self
• Unable to reach out and grab objects, point to
  locations of objects, or state the spatial
  relationship between objects (above, below, left,
  right, near, far),
• Pt. GW would turn the wrong way when greeted by
  someone she was not facing towards

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Types of TD cont.

• Landmark Agnosia
• Implicated in damage to bilateral lingual gyrus
• Inability to recognize salient environmental
  stimuli for purposes of orientation
• Anterograde disorientation
• Implicated in damage to parahippocampal gyrus
• Inability to orient in novel environments
• Pt.s often able to recall spatial layout of
  known places before becoming amnestic
• Findings suggest the MTL is not necessary for
  forming LT declarative memories, such as spatial
  maps, learned prior to injury

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Types of TD cont.

• Anterograde disorientation
• Implicated in damage to parahippocampal gyrus
• Inability to orient in new environments
• Pt.s often able to recall spatial layout of
  known places before becoming amnestic, but
  nothing about new places after injury
• Findings suggest the MTL is not necessary for
  forming LT declarative memories, such as spatial
  maps, learned prior to injury
• More ab the hippocampus and its surrounding areas

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Heading Disorientation (HD)

• Inability to represent direction of orientation
  with respect to external environment
• No visuo-spatial agnosia, nor landmark agnosia,
  but still unable to derive orienting info based
  on salient environmental cues
• Unable to draw maps or describe routes b/t
  familiar places

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Review of Cases Reports

• Patient 1
• 67 yr old man that became lost while driving his
  usual route home
• Patient 2
• 72 yr old man that became lost while riding his
  bicycle
• Patient 3
• 67 yr old man that kept forgetting where his
  hospital room was

L
R
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Card-Placing Test (CPT)

• Two-part performance-based test designed to
  examine individuals ability to represent spatial
  locations of surrounding objects placed on the
  floor
• DEMO

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Card-Placing Test (CPT)
Age SD CPT part A (mean SD) full scores correct/30 trials CPT part B (mean SD) full scores correct/30 trials
Controls (n 9) 65.4 4.8 27.6 3.0 25.0 4.3
Pt. 1 67 28 4
Pt. 2 72 26 12
Pt. 3 67 26 17
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Discussion

• Common damage
• 3 cases, same localized damage to right
  retrospenial area
• Damage to left retrospenial reportedly associated
  with impaired episodic memory, rather HD

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Discussion con.t

• Common symptoms
• Inability to derive directional info from
  environmental cues
• TD in novel AND familiar environments
• Mild to moderate visual memory impairment
• Absence of prominent visuospatial disorientation
• Preserved tapping span
• Absence of hemispatial neglect
• Intact constructional abilities
• Fairly well-preserved general intellectual
  functioning
• Underlying mechanism of HD?
• Anterograde visual memory impairment?
• Poor egocentric frame of reference?
• Integration of information on changes in body
  direction?

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Discussion con.t

• Converging sources of evidence
• Rat studies
• Excision of retrospenial cortex shows impairment
  of spatial navigation
• Human research via PET and MRI
• Retrospenial area active during large-scale
  navigation tasks
• Head direction cells
• Excited when rats maintain a certain heading or
  orientation in the environment
• Found in retrospenial cortex and many other
  structures that may be implicated in the
  functional circuit of directional information to
  the self

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Study Questions Revisit

• How have the two cortical pathways historically
  been modeled by the like of Ungerleider, Mishkin,
  Goodale, and Milner?
• As hierarchically organized paths the ventral
  what path which is involved in object
  recognition and memory, and the dorsal where
  path which is involved in action
• How does the de Haan and Cowey (2011) model
  differ from previous ones?
• Their patchwork model that does not assume an
  internal organizing structure consisting of 2
  independent paths, rather a network of
  connections within the visual maps.
• What evidence is there to support a more
  patchwork-like model of cortical info-processing?
• More than 2 streams, too much cross-talk,
  integration, shared complexity, etc.

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Study Questions Revisit

• What makes heading disorientation (HD) a
  characteristically unique form of topographical
  disorientation?
• The inability to navigate both novel and familiar
  environments through the derivation of
  directional info from landmarks and changes in
  body direction, despite normal visuospatial
  functioning and the absence of landmark agnosia
• What area of the brain has been heavily
  implicated in the integration of information
  about objects in space based on your own frame of
  reference and changes you make in body direction?
  
• Right retrospenial cortex