Fundamentals of Neuroscience Unilateral Neglect (Lec 01)

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Fundamentals of NeuroscienceUnilateral Neglect
(Lec 01)
James Danckert PAS 4040 jdancker_at_watarts.ca Web
page for slides http//www.arts.uwaterloo.ca/jda
ncker/Fundamentals_2003/fund_index.htm
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Unilateral Neglect

• failure to respond to or attend to contralesional
  stimuli
• usually a result of right parietal lesions
• current controversy whether the inferior parietal
  lobe or the superior temporal gyrus is the
  critical lesion site for neglect

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Critical lesion

• Vallar inferior parietal lobe (based on CT
  scans)

• Karnath, et al. superior temporal gyrus (based
  on MRI)

Regardless of who is right the lesion is in
tertiary association cortex integration of
multiple sensory signals and extensive
connections with frontal areas.
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Anton Raederscheidt
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Unilateral Neglect

• most commonly observed for the visual modality
  (so often called visual neglect)
• can have multimodal neglect auditory and
  tactile neglect most common
• can occur following left parietal lesions
  usually less severe and recovers more frequently

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Clinical tests of neglect cancellation tasks.
Star cancellation
Alberts lines
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Clinical tests of neglect line bisection.
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Clinical tests of neglect line bisection.
Schenkenberg et al. 1980
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Clinical Tests of Neglect figure copying
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Clinical Tests of Neglect free drawing
Show video?
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Neglect

• Neglect is not a disorder of vision or memory per
  se even when asked to imagine scenes the
  patient neglects the left and this is viewpoint
  dependent

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Neglect and Imagery

• Map of France test.

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Spatial vs. Object based neglect.
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Chimaeric Faces

• Healthy controls prefer faces smiling on left (Q
  reading bias?)
• Neglect patients prefer faces smiling on right
  even though they see the whole face

Which one is happier?
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Spatial vs. Object based neglect.

• Axis-based neglect

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Spatial vs. Object based neglect.

• Figure Ground Segregation

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Spatial vs. Object based neglect.

• Behrman and Tipper, 1994 strongest evidence for
  object based neglect.

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Neglect and Extinction

• Double simultaneous stimulation (DSS) two
  stimuli (targets) presented simultaneously to the
  left and right of the patients midline left
  target typically extinguished

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Object based effects on extinction.

• Gestalt Principles visual occlusion

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Temporal components of Neglect

• Temporal Order Judgement (TOJ) task

Which came first?
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Temporal components of Neglect

• Phasic Alerting arousal levels important in
  neglect too!

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Temporal components of Neglect

• Attentional Blink task Hussain et al. Nature,
  1997

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Temporal components of Neglect

• Attentional Blink task Hussain et al. Nature,
  1997

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Break 1
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What happens to neglected information?

• The Burning House example.
• Which house would you prefer to live in?
• The top one.
• Why?
• Roomier, especially in the attic.

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Implicit Processing in Neglect illusions.

• Line bisection in the Judd and Muller-Lyer
  illusions

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Illusions and extinction

• improvement of extinction for illusory figures

• when asked how many objects did you see? less
  extinction was observed for illusory figures

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Neglect and Extinction

• Double simultaneous stimulation (DSS) two
  stimuli (targets) presented simultaneously to the
  left and right of the patients midline left
  target typically extinguished

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Object specific extinction

• Target specific two forks lead to greater
  extinction than a fork and a key (Rafal, 1996).

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Unconscious activation in extinction

• right striate and extrastriate regions activated
  for extinguished stimuli

Rees et al. 2000 Brain
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What happens to neglected information?

• The Burning House.
• What would happen if a different question was
  asked?
• Which house is warmer?

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Implicit processing in neglect using the Flanker
Task
Unidimensional Stimuli.
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Colour and form processing in blindsight using
the flanker task.
flankers in sighted field
flankers in blind field
congruent
incongruent
congruent
incongruent
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Blindsight patient AG occipital lesion.
L
R
Colour flankers
Letter flankers
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Implicit Processing in Neglect flanker task.

• Neglected flankers are nevertheless processed
  (Danckert et al. 1999)

star cancellation (LVF/RVF)
letter cancellation (LVF/RVF)
simple detection (LVF/RVF)
line bisection
4 / 25
0 / 14
43.3
0 / 100
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Patient JS - Unidimensional flanker performance.
800
750
mean VRT (msec)
700
650
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The Flanker Task Bidimensional Stimuli.
identify colour
identify letter
double congruence (CD)
single congruence (CS)
single incongruence (IS)
double incongruence (ID)
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Goal-driven selection is dominant.
480
n.s.
COLOUR
470
LETTER
460
n.s.
REACTION TIME (msecs)
450
440
430
420
E
E
O
O
E
E
E
E
E
O
E
O
E
E
E
E
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Patient JS - Bidimensional flanker performance.
name letter
name colour
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What happens to neglected information?

• Bottom-up information is still processed in
  extrastriate visual cortex

All of this is despite a lack of awareness!
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Motor control in Neglect

• Line bisection in different regions of space
• Pointing to targets
• TOJ pointing
• Motor imagery

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Clinical hints

• cancellation tasks

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Line bisection in near and far space

• Altitudinal neglect

neglect of near space
neglect of lower visual field
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Line bisection in near and far space

• PET in normals line bisection in near and far
  space

Intraparietal Ventral frontal NEAR SPACE
Ventral occipital FAR SPACE
Weis et al. Brain, 2000
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Pointing to targets

• Pointing and bisecting LEDS

Goodale et al. Can J Psych, 1990
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Pointing to targets

• Pointing and bisecting LEDS

bisection errors
Goodale et al. Can J Psych, 1990
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Pointing to targets
Goodale et al. Can J Psych, 1990
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Temporal order pointing in patient PB (neglect).

• Point to which target appeared first.

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Speed accuracy trade offs.
left to right
near to far
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Velocity profiles in Patient LR (neglect).

• Higher peak velocity for rightward movements of
  either hand
• Longer deceleration periods for leftward and near
  movements of either hand.

R
L
R
L
R
L
R
L
R
L
200
velocity (cm/sec)
100
velocity (cm/sec)
0
0
2
4
6
8
10
12
time (sec)
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Motor Imagery
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Was the poor relationship between real and
imagined movements for LR due to a loss of
visual and/or proprioceptive feedback of the
moving hand?
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Motor control in Neglect

• Path curvature is controversial difficulty
  replicating
• Role in spatial components of movements
  relatively uncontroversial
• Probably controls the spatial component of
  movements of both limbs
• TMS and fMRI data suggesting right FEF important
  for saccades to both contralateral and
  ipsilateral space
• PET and fMRI suggests right parietal important
  for covert attention (in all regions of space?)
• Fronto-parietal patient with a specific remapping
  deficit (Colby et al. 1992)

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Spatial re-mapping retinal co-ordinates
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Spatial re-mapping updated representation.
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Saccadic Dysmetria

• Patient with a fronto-parietal lesion cant do
  the double-step saccade task when first saccade
  is contralesional

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Saccadic Dysmetria

• No problem with visually guided saccades (targets
  presented for 500 msec)

contra move first
contra move second
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Saccadic Dysmetria

• Errors come when both targets are presented
  before the first eye movement begins (targets
  presented in less than 180 msec)

contra move first
contra move second
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Break 2
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Rehabilitation of Neglect

• Caloric stimulation
• Neck muscle vibration
• Restriction of the ipsilateral limb
• Prism Adaptation

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Prism Adaptation Rossetti and colleagues

• prisms shift world further to the right (into the
  patients good field)
• patients movements compensate for the prismatic
  shift in the opposite direction
• after effects lead to better processing of
  previously neglected stimuli

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Prism Adaptation Rossetti and colleagues

• effects of prism adaptation not restricted to
  adapted hand or eye
• visual imagery, postural balance also affected
• after effects most prominent 2 hours after
  adaptation and can last for weeks not so for
  controls for whom effects are absent after only a
  few trials

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Prism adaptation is neglect really ameliorated?

• patient LR showed classic neglect bias on
  chimaeric faces test
• eye movement pattern also showed neglect

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Patient LR chimaeric faces.
Which one is happier? Top or bottom? Controls
bias towards left smiling face Neglect bias
towards right smiling face
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Perceptual task.

• 6 different pairs of faces
• top and bottom smiling faces and left and right
  sided smiling
• faces randomised across trials
• 3 different durations of stimulus 500, 1000
  and 1500 msec

Eye movement task.

• 18 different faces presented individually
• simply explore the full extent of the faces
• 6 of the 18 faces were chimaeric probes
• durations of stimuli 10 sec

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Prism adaptation for LR.
Subjective judgment of straight ahead.
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Eye movements to chimaeric faces - controls.
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LRs eye movements pre and post.
PRE
POST
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Eye movements pre and post.
PRE
POST
Ferber, Danckert, Joanisse, Goltz Goodale 2002
Neurology (in press)
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Perception pre and post.

• On 96 of trials LR chose the right-smiling
  face to be the happier one.
• When asked if he noticed anything unusual about
  the faces stimuli he said he thought one of them
  needed a shave!
• Even at the longest durations (and even for the
  10 sec duration for chimaeric faces in the eye
  movement task) LR was unaware that the faces were
  chimaeric.

Prism adaptation did not alter LRs awareness of
the chimaeric faces!
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Prism adaptation is neglect really ameliorated?

• after prism adaptation LRs eye movements now
  fully explored the faces
• despite a dramatic change in the pattern of eye
  movements he still chose the right sided happy
  faces on 92 or trials
• more importantly, he was unaware that the
  chimaeric faces were unusual in any way his
  only comment regarding the faces was that one of
  them needs a shave!

Ferber, Danckert, Joanisse, Goltz, Goodale, in
press, Neurology
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Mechanisms of Neglect

• Why is neglect more common after right parietal
  lesions?
• Kinsbourne attentional asymmetry (global vs.
  local)
• Ferber spatial working memory
• Goldberg novelty seeking?
• Danckert some combination of all three?

Object-based neglect is still puzzling!
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Attentional Hypotheses

• inattention
• unaware of left stimuli (cuing can correct this)
• ipsilesional bias
• each hemisphere orients contralaterally and
  inhibits orienting of the opposite hemisphere
• hyper vs. hypo orienting why is neglect more
  common from right parietal lesions?
• ipsilesional bias vs. reduced contralesional
  capacity?
• disengage deficit
• ipsilesional cues led to longer RTs to
  contralesional targets (contra cues with ipsi
  targets were not affected as much)
• reduced sequential attentional capacity
• neglect of centre!

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Motor Intention

• patients may be aware of stimuli but may fail to
  act
• reduced capacity vs. ipsilesional bias
• exploration deficits searching by touch or eyes
• Bisiachs pulley system

congruent movement
incongruent movement
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Other factors to consider

• Spatial working memory
• our neglect patient showed a SWM deficit for
  vertically arranged stimuli
• if it doesnt get into SWM (or processes of SWM
  are deficient more limited than usual) then it
  wont make it into awareness
• Novelty vs. familiarity
• if the right hemisphere is dedicated to novelty
  seeking behaviours (exploratory eye movements are
  one good example) then a deficit in this capacity
  would lead to poor allocation of attention across
  the whole visual field (does left hemispehere
  cover the RVF deficit in neglect?)
• Mutual Exclusivity who needs it?

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Introducing the Neglect Syndromes
extinction (superior parietal but what about
simultanagnosia and optic ataxia?)
motor neglect (fronto-parietal lesions)
pure neglect (inferior parietal or STG for the
true connoisseur!)
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Neglect and anosagnosia

• anosagnosia denial or unawareness of impairment
  (even extends to inanimate objects!)
• caloric stimulation ameliorates anosagnosia
  temporarily
• difference between insight and anosagnosia
• knowing what (or that something is so) vs.
  knowing how or why

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Neglect and consciousness

• What does neglect tell us about the neural
  correlates of consciousness?
• Does the brain really represent objects in
  halves?
• Cant simply be an exploration deficit.
• Some complex interaction between working memory,
  temporal processing, body schemas,
  actions/intentions, etc.?

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Acknowledgements

• Flanker tasks in neglect and blindsight
• Paul Maruff
• Glynda Kinsella
• Steven de Graaff
• Jon Currie
• Murat Yucel
• Carly Ymer

Motor imagery in neglect Susanne Ferber Mel
Goodale Timothy Doherty
Prisms in neglect Susanne Ferber Herb Goltz Marc
Joanisse Mel Goodale Yves Rossetti
Motor control in neglect Susanne Ferber Mel
Goodale Haitao Yang
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End of Lecture