Hemispatial Neglect (5b) Flashcards
(17 cards)
Key Terminology: define
1. Lesion
2. Contra-lesional
3. Ipsilesional
4. Extinction
- Lesion - area of brain damage
- Contra-lesional: things occuring on OPPOSITE SIDE to lesion
- Ipsilesional: things occurring on SAME SIDE as the lesion
- Extinction: a MILDER form of neglect only apparent when stimuli occur on BOTH sides of space
Common Lesion example - what is a stroke? (outline briefly the mechanism)
A stroke occurs when blood flow to part of the brain is blocked or reduced, causing brain cells to be deprived of oxygen and nutrients.
–> In an ischemic stroke, a THROMBUS (a blood clot) forms and lodges in a cerebral artery (because arteries become narrower), blocking blood flow.
Without blood supply, the affected brain tissue begins to die. Over time, the dead brain tissue can be cleared away and replaced by a fluid-filled cavity (called a cystic cavity or encephalomalacia), which is a space where brain tissue was lost.
What is the Middle Cerebral Artery (MCA) and the Posterior Cerebral Artery (PCA)
Middle:
- largest branch of the internal carotid
- supplies a lot of areas
- supplied lateral and inferior frontal lobe, surface of temporal and parietal lobes, including primary motor and sensory areas, Broca’s area
Posterior
- supplies temporal and occipital lobes
What is the clinical presentation of a MCA stroke
Contra-Lesional hemiparesis: weakness to move opposite side of body/face
Contra-Lesional hemisensory loss (inability to feel touch on opposite side of body/face)
Hemianopia: loss of vision on opposite side of face
Aphasia: if stroke affects the dominant hemisphere for language (usually when the stroke affects the left)
Hemispatial neglect (usually when stroke affects right side)
What is hemispatial neglect
- cancellation tests
- copying tests
- line bisection tests
Hemispatial neglect: loss of awareness of things happening in the contralesional side of space
Cancellation
- give patient paper full of lines, will neglect some/most (depending on severity)
- eg. lesion on right, ignore most on left
Copying:
- asked to copy images
- will miss out detail on contralesional side
Line Bisection
- asked to cross a line in half
- right lesions: will cross line leaning more on the right (ignores the left)
How do we know the patient is not blind (so what is ‘broken’ in neglect)
Hemispatial neglect is not specific to a certain sense!
Extinction: a milder form of attentional difficulty
- patients can detect contralesional
- difficulty is when stimuli is presented on both sides
What is BROKEN:
- consensus: neglect/extinction are disorders of attention and/or spatial representation
- inability to consciously detect or respond to stimuli in the contralesional side of space
- manifests as a gradient of awareness
Hemispheric Asymmetry:
- neglect more common in RIGHT HEMISPHERE STROKE PATIENTS (38% v 18%)
- may reflect a right hemisphere dominant system for spatial attention
- could also be due to presence of additional (nonspatial) deficits in right hemisphere that interact with spatial deficits
Neuroanatomy of neglect: briefly, what is the damage often like?
Damage includes:
- junction of temporal and parietal lobes
- inferior parietal lobe
- intraparietal sulcus
- superior temporal gyrus
- middle frontal gyrus
damage can be EXTENSIVE
What five interesting things has neglect showed us about the attention system
- Attention can operate in an object-centred frame of reference
- Attention can operate on INTERNAL REPRESENTATIONS as well as external stimuli
- Attention can operate at LATE STAGE (extinction severity can be modulated by higher-level properties of stimuli)
- Attention is a competitive process
- Attention may not be a unitary system
Further evidence: looking at emotionally significant stimuli (Vuilleumier and Schwartz, 2001)
To see whether emotionally significant stimuli can modulate attention
Key condition is SPIDER on left side, ring on right
- patients with right hemisphere lesion have problem seeing on left
- so stimuli is extinguished on left side
- when spider appeared on poor side, it appears to INTRUDE (there must be some pre-attentive stimuli occuring)
Unattended items - how much processing goes on?
In tests of word pairing
- extinction much higher when two words the same
- degree of similarity appears to modulate severity of extinction (points to an attentional deficit)
- when they are similar: appears to be increased competition
all points to idea of attention occuring LATE
- Object-centred frame of reference
Object-centred attention means you focus on parts of an object itself, no matter where the object is or how it’s turned.
Shows attending to certain sides of objects
- there is substantial pre-attention awareness
- Internal representations and external stimuli
Can happen to our IMAGINATION
- famous work by Bisiach and Luatti
- asked patients to imagine themselves in famous landmark
- patients with right hemisphere lesion (left side neglect) could only recall landmarks on right side
- ability to attend in imagination changed
- Late stage of processing
Kanizsa Figures
- When patients see an illusory Kanizsa square, they miss fewer items on their affected side.
- This shows their brain uses the overall shape to help attention, not just individual parts. It means attention works at a later stage, after the brain organizes the scene.
- Because of this, extinction can be reduced by how the stimulus is grouped or interpreted, not just by basic sensory input.
- Competitive (Posner et al. 1984)
Took patients with lesions, showed them cue on either right or left side, followed by target either in same or opposite location
–> In healthy: faster attention on same side cue/target
–> FOUND: striking pattern:
- evidence that neglect involves a deficit disengaging from ipsilesional stimuli
- when cued contralesional and target: performed a lot better
SUGGESTS: patients have trouble disengaging from stimuli on ipsilesional side to focus on contralesional stimuli
–> Spatial attention is COMPETITIVE (we have limited resources)
- May not be unitary (Verdon et al. 2010)
Large study attempting to map specific symptoms onto lesion locations
- 80 patients with left neglect (right lesions)
- distinct components identified:
- perceptive/visuo-spatial neglect (left side omissions on text reading and line bisection)
- exploratory performance (missing left side of space in cancellation tasks)
- object-centered neglect (missing left side of words and objects in search tasks)
Showed: rather than being a unitary disorder, neglect might best be viewed as a syndrome (characterised by a set of associated symptoms)
–> One way to characterise attention might be as a system for resolving competition at multiple levels in the brain
* Many brain areas are activated by sensory input, and within most of these systems activations for different objects compete.
* Competition can occur at different levels including simple visual features, objects, semantics and emotion.
Attention can be seen as a global system for resolving the competition among sensory inputs for awareness and response
Summarise the key points about neglect as a concept
common consequence of stroke
more common after right hemisphere lesion
can occur after lesions to a broad range of areas
extinction is a milder form of neglect (only apparent under bilateral stimulation)
evidence from patients with neglect highlights the fragmentation of the attention system
How much information is processed ‘preattentively’ (prior to attention and awareness?)
- Task relevance of stimuli
- Integration of features into whole shapes
- Emotional significance of stimuli
- Semantic info
