Hemispatial Neglect

Question 1

LESION

Answer 1

• area of brain damage
• site of lesion depends on which blood vessel is occluded

Question 2

CONTRALESIONAL STIMULI

Answer 2

• things occurring on opposite side as lesion

Question 3

IPSILESIONAL STIMULI

Answer 3

• things occurring on same side as lesion

Question 4

EXTINCTION

Answer 4

• milder form of neglect only apparent when stimuli occur on both sides of space

Question 5

STROKE

Answer 5

• when a blood clot breaks off & travels up the artery until it gets caught & blocks blood flow to 1 side of the brain
• blood flow restricted to 1 half of brain -> neuronal death & eventual fluid-filled cavity (shown in white on MRI scans)

Question 6

BLOOD VESSELS

Answer 6

MIDDLE CEREBRAL ARTERY (MCA)
ANTERIOR CEREBRAL ARTERY (ACA)
POSTERIOR CEREBRAL ARTERY (PCA)

Question 7

MIDDLE CEREBRAL ARTERY (MCA)

Answer 7

• largest branch of internal carotid
• supplies:
  1) lateral/inferior frontal lobe
  2) lateral surface of temporal/parietal lobes (incl. primary motor & sensory face/throat/hand/arm areas) & dominant hemisphere (Broca’s area)
  STEIN ET AL. (2007)
• 51% stroke victims suffer this region

Question 8

ANTERIOR CEREBRAL ARTERY (ACA)

Answer 8

• supplies:
  1) medial frontal lobes
  2) basal ganglia
  3) primary motor cortex

Question 9

POSTERIOR CEREBRAL ARTERY (PCA)

Answer 9

• supplies:
  1) temporal lobes
  2) occipital lobes

Question 10

MCA: CLINICAL STROKE

Answer 10

• contra-lesional hemiparesis (weakness/inability to move opposite side of body/face)
• contra-lesional hemisensory loss (inability to feel touch on opposite side of face/body)
• hemianopia (loss of vision on opposite side of space)
• aphasia (if stroke affects dominant hemisphere for language (left))
• hemi-spatial neglect

Question 11

CANCELLATION TESTS

Answer 11

• right hemisphere lesion affects left side of space (vice versa) due to crossed nature of human sensory system
• aka. patients w/right hemisphere lesions have weakness on left body half & issues noticing things on left side of space
• cancellation tests = standard for hemispatial neglect; require patient w/right hemisphere lesion to cross out all lines on a page
• patient will only cross out right-hand side lines

Question 12

COPYING TESTS

Answer 12

• simply requires patients to copy what they see
• patients w/hemispatial neglect will ignore all features on left-hand side of picture

Question 13

RECOGNISING BLINDNESS

Answer 13

• hemispatial neglect isn’t specific to any sense; a patient w/it will have difficulty identifying contra-lesional visual/auditory/tactile stimuli
  EXTINCTION
• patients can oft detect contra-lesional stimuli BUT not when they occur simultaneously w/ipsilesional stimuli

Question 14

ACQUIRED BRAIN INJURY: EXTINCTION

Answer 14

• neglect oft resolves into extinction during patient recovery
• extinction = patient perceives individual touches on left/right side
• BUT can only perceive right side when presented w/simultaneous touch on both sides
• same w/visual stimuli; patients can see on either side individually BUT will miss things on contra-lesional side (opposite lesion) when presented together w/things on ipsilesional side (same side)

Question 15

“BROKEN” NEGLECT

Answer 15

• neglect x extinction = disorder of attention & spatial representation
• inability to consciously detect/respond to stimuli in contra-lesional side of space
• manifests as gradient of awareness from ipsilesional -> contralesional > clear divide

Question 16

NEGLECT: HEMISPHERIC ASYMMETRY

Answer 16

• neglect = more common/persistent in right hemisphere stroke patients (38%) > left hemisphere stoke patients (18%)
• may reflect right hemisphere dominant system for spatial attention
  HUSAIN & RORDEN (2003)
• could also be due to presence of additional nonspatial deficits in right hemisphere stroke patients (ie. alertness/sustained attention) that interact w/& exacerbate spatial deficits

Question 17

NEGLECT: NEUROANATOMY

Answer 17

• temporaparietal junction (TPJ) = most common
• BUT neglect can occur post damage to several regions

Question 18

NEGLECT: ATTENTION SYSTEM PROPERTIES

Answer 18

• revealed several interesting features:
  1) attention can operate in object-centred reference frame
  2) attention can operate on internal representations as well as external stimuli
  3) attention can operate at a late processing stage (extinction severity can be modulated by higher lvl stimuli properties)
  4) attention = competitive process
  5) attention may NOT be a unitary system

Question 19

ATTENTION: OBJECT-BASED

Answer 19

MARSHALL & HALLIGAN (1993)
- patient asked to copy flower pics
- 2 flower pic = patient copies right half of each flower > only the flower on the right
- demonstrates that attention operates in object > spatial/frame of reference

Question 20

ATTENTION: INTERNAL REPRESENTATIONS (BISIACH & LUZATTI (1978) EXP I)

Answer 20

• Italian patients w/neglect asked to recall famous landmark in Florence; asked what they can see in minds eye
  RESULTS
• mostly reported seeing landmarks on good/ipsilateral side to lesion; like they’d lost representation of things on left side both externally/internally

Question 21

ATTENTION: INTERNAL REPRESENTATIONS (BISIACH & LUZATTI (1978) EXP II)

Answer 21

• Italian patients asked to imagine they were standing at opposite square end of Florence
  RESULTS
• recalled all of previously neglected info; again couldn’t report all contralesional info (though previously recalled correctly)
• suggests that attention also operates on internal representations (ie. memory/imagination) & external (perception)

Question 22

ATTENTION: LATER PROCESSING (MATTINGLEY ET AL. (1997))

Answer 22

• tested whether attention operates at later processing stage (ie. post low lvl visual processing)
• presented subjects w/Kaniza figures (removing segment of each circle produces illusion of object in centre); rely on substantial low lvl visual processing (edges/brightness combine -> single illusion)
  RESULTS
• extinction of left-sided circles = substantially reduced when illusory surface was formed
• suggests attention operates post low lvl visual processing (even post environmental stimuli being interpreted as objects)

Question 23

ATTENTION: LATER PROCESSING (VUILLEUMIER & SCHWARTZ (2001))

Answer 23

• further evidence for substantial processing of items in contralesional side of space
• tests pps w/extinction on task; asked simply to identify what they could see from pic set
• pps presented w/2 pics at a time; either fearful (ie. spiders) OR neutral (ie. ring)
  RESULTS
• extinction highest in all patients when left stimulus = neutral
• BUT extinction reduced when left stimulus = fearful
• suggests that stimulus can break attentional filter despite patient not being aware of info on left side (if info = sufficiently meaningful/important)

Question 24

ATTENTION: LATER PROCESSING (VUILLEIMUER & RAFAL (2000) EXP I)

Answer 24

• evidence that unattended items = processed up to semantic lvl in extinction
• pps shown 2 same/dif words (ie. one/one or one/two)
  RESULTS
• higher extinction when words = same aka. meaning of words = processed pre-attentively
• BUT potential confound = words look similar visually (ie. features); could just be visuals being processed

Question 25

ATTENTION: LATER PROCESSING (VUILLEIMUER & RAFAL (2000) EXP II)

Answer 25

• showed pps words that looked dif BUT w/either same semantic meaning (ie. one/1) or dif meaning (ie. one/2)
  RESULTS
• neglect = still lower for words w/same meaning even if they looked dif > words w/dif meanings
• aka. NOT low lvl visual features of words that drive dif but semantic meaning

Question 26

ATTENTION: LATER PROCESSING

Answer 26

• info processed pre-attentively (prior to attention/awareness) includes:
  1) task-relevance of stimuli (response related info)
  2) integration of features into whole objects/shapes
  3) emotional stimuli significance
  4) semantic info

Question 27

ATTENTION: COMPETITION (POSNER ET AL. (2014))

Answer 27

• evidence that neglect involves deficit disengaging from ipsilesional stimuli
• reflexive attention = also studies w/Posner cueing paradigm BUT pps = cued exogenously here
• aka. light flash/something attention grabbing occurs in peripheral location
• target appears in flash location (cued trial)/ other (uncued trial)
  RESULTS
• RTs = ^ for uncued contra condition
• indicates issue disengaging attention from cues on ipsilesional side

Question 28

ATTENTION: NOT A UNITARY SYSTEM (VERDON ET AL. (2010) PROCEDURE)

Answer 28

• neuroanatomy of hemispatial neglect & functional components using voxel-based lesion-symptom mapping
• attempted to map specific symptoms onto lesion locations; 80 patients w/left neglect due to right hemisphere lesions tested on range of standard neuropsychological tests
• factor analysis used to break down symptoms into coherent profiles of co-varying deficits

Question 29

ATTENTION: NOT A UNITARY SYSTEM (VERDON ET AL. (2010) RESULTS)

Answer 29

• 3 distinct components identified:
  INFERIOR PARIETAL
  1) perceptive/visuo-spatial neglect
• left side omissions on word/text reading
• bias on line bisection
  DORSOLATEAL PREFRONTAL CORTEX
  2) exploratory/visuo-motor performance
• missing left space side in cancellation tasks
  TEMPORAL LOBE
  3) object-centred neglect
• missing left word side in compound reading
• missing left object side in Ota search task

Question 30

SUMMARY

Answer 30

• neglect may be a syndrome/condition characterised by set of associated symptoms (some dissociable) rather than unitary attention disorder
• attention may be collection of associated functions mediated by connected by anatomically separate brain regions; may be system for resolving competition at dif brain lvls:
  1) sensory input
  2) simple visual features/objects/semantics/emotion
  3) sensory inputs for awareness/response