Fundamentals of NeuroscienceUnilateral Neglect (Lec 01)

James Danckert PAS 4040 jdancker@watarts.ca

Web page for slides http://www.arts.uwaterloo.ca/~jdancker/Fundamentals_2003/fund_index.htm

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

Critical lesion

• Vallar – inferior parietal lobe (based on CT scans)

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

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

Anton Raederscheidt

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

Clinical tests of neglect – cancellation tasks.

Albert’s lines

Star cancellation

Clinical tests of neglect – line bisection.

patient’s midline

Clinical tests of neglect – line bisection.

Schenkenberg et al. 1980

left centre right

Clinical Tests of Neglect – figure copying

Clinical Tests of Neglect – free drawing

Show video?

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

Neglect and Imagery• Map of France test.

Spatial vs. Object based neglect.

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?

Spatial vs. Object based neglect.

• Axis-based neglect

Spatial vs. Object based neglect.• Figure – Ground Segregation

Spatial vs. Object based neglect.

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

Neglect and Extinction• Double simultaneous stimulation (DSS) – two stimuli

(targets) presented simultaneously to the left and right of the patient’s midline – left target typically “extinguished”

single left single right DSS trial

Object based effects on extinction.

• Gestalt Principles – visual occlusion

Temporal components of Neglect• Temporal Order Judgement (TOJ) task

Which came first?

Temporal components of Neglect• Phasic Alerting – arousal levels important in neglect too!

Temporal components of Neglect• Attentional Blink task – Hussain et al. Nature, 1997

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M7

H TARGET 1

TARGET 2

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Temporal components of Neglect• Attentional Blink task – Hussain et al. Nature, 1997

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Break 1

What happens to neglected information?

The Burning House example.

Which house would you prefer to live in?

A. The top one.

Why?

A. Roomier, especially in the attic.

Implicit Processing in Neglect – illusions.

• Line bisection in the Judd and Muller-Lyer illusions

Illusions and extinction• improvement of extinction for illusory figures

illusory square no illusory square

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

Neglect and Extinction• Double simultaneous stimulation (DSS) – two stimuli

(targets) presented simultaneously to the left and right of the patient’s midline – left target typically “extinguished”

single left single right DSS trial

Object specific extinction

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

Unconscious activation in extinction• right striate and extrastriate

regions activated for extinguished stimuli

Rees et al. 2000 Brain

What happens to neglected information?

The Burning House.

What would happen if a different question was asked?

Which house is warmer?

Implicit processing in neglect using the Flanker Task

Colour flanker

EO

Letter flanker

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Unidimensional Stimuli.

Colour and form processing in blindsight Colour and form processing in blindsight using the flanker task.using the flanker task.

flankers in sighted fieldflankers in sighted field flankers in blind fieldflankers in blind field

O O E O EOOO

congruent incongruent congruent incongruent

Colour flankersColour flankers Letter flankersLetter flankers

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sighted blindC IC I

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Blindsight patient AG – occipital lesion.

L R

Implicit Processing in Neglect – flanker task.

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

JS

star star cancellationcancellation(LVF/RVF)(LVF/RVF)

letter letter cancellationcancellation(LVF/RVF)(LVF/RVF)

line line bisectionbisection

simplesimpledetection detection

(LVF/RVF)(LVF/RVF)

4 / 254 / 25 0 / 140 / 14 + 43.3+ 43.3 0 / 1000 / 100

Patient JS - Unidimensional flanker performance.Patient JS - Unidimensional flanker performance.

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RT (

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cong incong

73 msec

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neglected flankers perceived flankers

The Flanker Task: Bidimensional Stimuli.

EE EEdouble congruence(CD)

EO EEsingle congruence

(CS)

EE EOsingle incongruence(IS)

EO EOdouble incongruence

(ID)

identify colour identify letter

EE EO EE EO

goal driven

data driven

Goal-driven selection is dominant.

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Patient JS - Bidimensional flanker performance.Patient JS - Bidimensional flanker performance.

name colourname colour

name lettername letter

perceived flankers neglected flankers

EE EO EE EO EE EOEE EO

What happens to neglected information?

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

All of this is despite a lack of awareness!

Top-down – goals can influence how the information is processed

Motor control in Neglect• Line bisection in different regions of space

• Pointing to targets

• TOJ pointing

• Motor imagery

Clinical hints• cancellation tasks

Line bisection in near and far space

• Altitudinal neglect

neglect of lower visual fieldneglect of near space

Line bisection in near and far space

• PET in normals – line bisection in near and far space

IntraparietalVentral frontal

NEAR SPACE

Ventral occipital

FAR SPACE

Weis et al. Brain, 2000

Pointing to targets

• Pointing and bisecting LEDS

Goodale et al. Can J Psych, 1990

Pointing to targets

• Pointing and bisecting LEDS

Goodale et al. Can J Psych, 1990

bisection errorsbisection errors

Pointing to targets

Goodale et al. Can J Psych, 1990

Temporal order pointing in patient PB (neglect).

• Point to which target appeared first.

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Patient PB - left target (incorrect first response)

Speed accuracy trade offs.

left to right near to far

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 LR LR LR L R L

time (sec)0 2 4 6 8 10 12

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Motor Imagery

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Movement duration for the VGPTMovement duration for the VGPT

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Patient LR – Contralesional hand (L)Patient LR – Contralesional hand (L)

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real movements

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imagined movements

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Patient LR – Ipsilesional hand (R)Patient LR – Ipsilesional hand (R)

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view target for 2 sec

perform movements while imagining the previously viewed target

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?

t i m e

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imagined movements

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Control subject MRControl subject MR

Patient LRPatient LRImagining the target vs. imagining the whole movement.Imagining the target vs. imagining the whole movement.

target width (mm)

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Pointing without vision of the Pointing without vision of the hand.hand.

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real movements (without vision of 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)

Spatial re-mapping – retinal co-ordinates

Spatial re-mapping – updated representation.

Saccadic Dysmetria• Patient with a fronto-parietal lesion can’t do the double-

step saccade task when first saccade is contralesional

Saccadic Dysmetria• No problem with visually guided saccades (targets

presented for 500 msec)

contra move first contra move second

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

Break 2

Rehabilitation of Neglect

• Caloric stimulation• Neck muscle vibration• Restriction of the ipsilateral

limb• Prism Adaptation

Prism Adaptation – Rossetti and colleagues

• prisms shift world further to the right (into the patient’s ‘good’ field)

• patient’s movements compensate for the prismatic shift – in the opposite direction

• after effects lead to better processing of previously neglected stimuli

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

Prism adaptation – is neglect really ameliorated?

• patient LR showed classic neglect bias on chimaeric faces test

• eye movement pattern also showed neglect

Patient LR – chimaeric faces.Patient LR – chimaeric faces.

Which one is happier? Top or bottom?

Controls – bias towards left smiling face

Neglect – bias towards right smiling face

Perceptual task.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.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

Prism adaptation for LR.Prism adaptation for LR.

Subjective judgment of straight ahead.

Eye movements to chimaeric faces - Eye movements to chimaeric faces - controls.controls.

LR’s eye movements pre and post.LR’s eye movements pre and post.

PRE POST

Eye movements pre and post.Eye movements pre and post.

PRE POST

Ferber, Danckert, Joanisse, Goltz & Goodale 2002 Neurology (in press)

Perception pre and post.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 LR’s awareness of the chimaeric faces!

Prism adaptation – is neglect really ameliorated?

• after prism adaptation LR’s 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

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!

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!

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• Bisiach’s pulley system

A E

congruent movementcongruent movement

incongruent movementincongruent movement

Other factors to consider• Spatial working memory

– our neglect patient showed a SWM deficit for vertically arranged stimuli

– if it doesn’t get into SWM (or processes of SWM are deficient – more limited than usual) then it won’t 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?

Introducing the Neglect Syndromes

motor neglectmotor neglect(fronto-parietal lesions)(fronto-parietal lesions)

pure neglectpure neglect(inferior parietal or (inferior parietal or

STG for the true connoisseur!)STG for the true connoisseur!)

extinctionextinction(superior parietal – (superior parietal –

but what about simultanagnosia but what about simultanagnosia and optic ataxia?)and optic ataxia?)

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”

Neglect and consciousness

• What does neglect tell us about the neural correlates of consciousness?

• Does the brain really represent objects in halves?

• Can’t simply be an exploration deficit.• Some complex interaction between

working memory, temporal processing, body schemas, actions/intentions, etc.?

AcknowledgementsFlanker tasks in neglect and

blindsight

Paul MaruffGlynda KinsellaSteven de GraaffJon CurrieMurat YucelCarly Ymer

Motor imagery in neglect

Susanne FerberMel GoodaleTimothy Doherty

Prisms in neglect

Susanne FerberHerb GoltzMarc JoanisseMel GoodaleYves Rossetti

Motor control in neglect

Susanne FerberMel GoodaleHaitao Yang

End of Lecture