Neglect - week 5 (Chris) Flashcards
(24 cards)
Lesion
Area of brain damage
Contralesional stimuli
Things occurring on the opposite side to the lesion
Ipsilesional stimuli
Things occurring on the same side as the lesion
Extinction
A milder form of neglect only apparent when stimuli occur on both sides of space.
Middle Cerebral Artery (MCA)
Largest branch of the internal carotid.
Supplies lateral and inferior frontal lobe, and the lateral surface of the temporal and parietal lobes, including the primary motor and sensory areas of the face, throat, hand and arm, and in the dominant hemisphere, Broca’s area.
Anterior Cerebral Artery (ACA)
Supplies the medial frontal lobes, basal ganglia, primary motor cortex
Posterior Cerebral Artery (PCA)
Supplies temporal and occipital lobes
Clinical presentation of MCA stroke
contralesional hemiparesis (weakness/inability to move opposite side of body/face)
contralesional hemisensory loss (e.g. inability to feel touch on opposite side of body/face)
Hemianopia (loss of vision on opposite side of space)
Aphasia (if stroke affects the dominant hemisphere for language – usually left)
Hemispatial neglect
Cancellation tests
This is a standard test for hemispatial neglect, requiring the patient (who has a right hemisphere lesion) to cross out all of the lines on the page. As you can see, the patient only crosses out lines on the right, ignoring all those on the left.
Copying tests
Another test simply requires patients to copy what they see. Here, you can see they ignore all the numbers on the left and the left side of the house.
How do we know patient is not blind on one side?
Hemispatial neglect is not specific to any sense
A patient with neglect will have difficulty identifying contralesional visual, auditory and tactile stimuli
Extinction
Often patients can detect contralesional stimuli, just not when they occur simultaneously with ipsilesional stimuli
So what is ‘broken’ in neglect?
Consensus is that neglect/extinction is a disorder 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 from ipsilesional to contralesional, rather than a clear divide.
Hemispheric asymmetry of neglect
Neglect more common (and persistent) in right hemisphere stroke patients (38%) than in left hemisphere stroke patients (18%)
May reflect a right hemisphere dominant system for spatial attention
Could also be due to presence of additional (nonspatial) deficits in right hemisphere stroke patients (e.g. alertness, sustained attention) that interact with and exacerbate spatial deficits (Husain & Rorden, 2003)
Neuroanatomy of neglect
Anatomy of neglect – Temporoparietal junction (TPJ) is the most common area but neglect can occur after damage to all of these regions.
Neglect has revealed several interesting properties of 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 a late stage of processing – severity of extinction can be modulated by higher-level properties of stimuli
- Attention is a competitive process
- Attention may not be a unitary system
Evidence from hemispatial neglect for object-based attention
Here, the patient is asked to copy the pictures. In the picture of the two flowers, the patient copies the right half of each flower, rather than only the flower on the right.
Demonstrates that attention operates in an object, rather than spatial, frame of reference.
Attention operates on internal representations as well as external stimuli (Bisiach & Luzatti, 1978)
Bisiach and Luzatti asked Italian patients with neglect to recall a famous landmark in Florence and asked them what they could see in their minds eye.
The patients mostly reported seeing the buildings, cafes, shops on the side of space ipsilateral to their lesion (their ‘good’ side). It was as if they had lost the representation of things on the left side of space, even those that only existed in their memory or imagination, not simply in the external world.
The researchers also asked the patients to imagine they were standing at the opposite end of the square and to recall what they could. This time, they recalled all of the previously neglected information and again couldn’t report all of the contralesional information (the information they had previously recalled correctly!)
This finding suggests that attention operates also on ‘internal’ representations (e.g. memory, imagination) as well as ‘external’ representations (perception)
Mattingley, Davis & Driver (1997)
In this study Mattingley and colleagues wanted to test whether attention operates at a late stage in processing, i.e. after low level visual processing
They presented subjects with Kanizsa figures, in which removing a segment of each circle produces the illusion of an object in the centre.
These figures rely on substantial low level visual processing – edges, brightness combine to form a single illusory surface.
They found that extinction of left sided circles was substantially reduced when an illusory surface was formed.
Suggests attention operates after the low level visual processing has occurred – even after stimuli in the environment have been interpreted as objects.
Vuilleumier and Schwartz (2001)
Further evidence for substantial processing of items in the contralesional side of space comes from this study.
They tested patients with extinction on a task where they were asked simply to identify what they could see.
Patients were presented with two pictures at a time, which could either be fearful (e.g. spiders) or neutral (e.g. a ring).
They found that extinction was highest in all patients when the stimulus on the left was neutral but that extinction was reduced when the stimulus on the left was fearful.
This suggests that despite the patient not being aware of information on the left side of space, if the information is sufficiently meaningful, or important, the stimulus can ‘break through’ the attentional filter
Vuilleumier & Rafal, 2000
More evidence for preattentive processing – this time up to the semantic level.
Here subjects were shown two words, either the same (e.g one one) or different (e.g. one two)
The first thing to note is that extinction was higher when the words were the same demonstrating that the meaning of the word is processed preattentively.
However a potential confound is that the words also look visually the same – same features etc – so could be just visual features that are processed.
So next they showed subjects words that looked different but with either the same semantic meaning (e.g. one 1) or a different meaning (e.g. one 2).
Found that neglect was still lower for words that had the same meaning, even if they looked different, than words that had different meaning
This shows that it is not the low level visual features of the words that drives the difference, but the semantic meaning of the words.
How much information is processed ‘preattentively’ (prior to attention and awareness)?
Task-relevance of stimuli (response related information)
Integration of features into whole objects/shapes
Emotional significance of stimuli
Semantic information
Evidence that neglect involves a deficit disengaging from ipsilesional stimuli
(Posner et al., 1984)
Reflexive attention has also been studied using the Posner cueing paradigm, but in this version subjects are cued exogenously.
This means that a flash of light or something attention grabbing occurs in a peripheral location, and then a target appears either in the location of the flash (called a cued trial) or in the other location (uncued trial).
RTs are much higher for the uncued contra condition indicating a problem disengaging attention from cues on the ipsilesional side.
Posner et al. (1984)
Suggests patients have trouble disengaging from stimuli on the ipsilesional side to focus on contralesional stimuli
Spatial attention is a competitive process
Reflexive attention has also been studied using the Posner cueing paradigm, but in this version subjects are cued exogenously.
This means that a flash of light or something attention grabbing occurs in a peripheral location, and then a target appears either in the location of the flash (called a cued trial) or in the other location (uncued trial).
Anatomical voxel-based lesion-symptom mapping analysis
Inferior parietal
Perceptive/visuospatial
E.g. bias in line bisection
Temporal lobe
object-centred
Missing left side of objects
Dorsolateral prefrontal cortex
exploratory/visuomotor
Missing left side of space in cancellation tasks
