Preparation Lecture 9
Danckert (2006). Revisiting unilateral neglect.
Unilateral neglect is traditionally defined as a failure to report, respond to or orient towards stimuli in
contralesional space. A more appropriate description is that the patient behaves as if one half – the
contralesional half – of their world has simply ceased to exist. This loss of awareness is often evidence
even in the face of orienting behaviors directed towards the same region of space. Despite moving their
eyes or hand towards contralesional space or the contralesional side of a centrally presented object, the
patient may nevertheless be unaware of what they have just explored.
The classic case of neglect
Neglect is often seen after right hemisphere lesions, leading the patient to behave as if the left half of
their world does not exist. The tasks used to examine neglect typically require perception of and
responses towards both ipsilesional and contralesional stimuli (e.g., cancellation tasks, line bisection
task, and the figure copying of free drawing tasks). Typically, the patient fails to cancel targets on
the left of the page, places their midline mark to the ipsilesional side of the true center of lines in the
bisection task and omits or distorts aspects of drawings on the contralesional side of space.
Sorts of neglect -> patients can demonstrate personal neglect, deficits on tasks of extrapersonal neglect,
or neglect their location in space or alternatively, may neglect the left half of objects irrespective of
their location in space. ‘Sub-syndromes’ of neglect symptoms, such as neglect dyslexia in which the
patient fails to read the left half of words, are present in some but not all, neglect patients. Finally, the
related disorder of extinction to double simultaneous stimulation in which patients can detect single
targets presented in left or right space but ‘extinguish’ left targets when presented simultaneously with
right targets, is often but not always evident in neglect patients.
Distinction of disorders of neglect and distinction -> there are two reasons why this should be done:
1. The lesion locus for extinction in the parietal cortex tends to be more superior than the focus for
neglect.
2. Extinction has been demonstrated to be equally common following left and right hemisphere
lesions, while neglect is far more common following right hemisphere lesions.
Exploratory and goal-directed motor behavior in neglect
One aspects of some patients with severe neglect concerns their posture. Wheelchair bound patients
tend to slump towards the ipsilesional side of their chair and direct their gaze towards ipsilesional
space. If a neglect patient is asked to determine where they think straight-ahead of their body is in the
absence of any external reference frame, they typically demonstrate a deviation towards the right of an
objective midline position. Patients seem to anchor their motor behavior around this shifted straight
ahead position.
Subtle motor control impairment -> the initiation and execution of leftward movements can be
impaired in left neglect patients even in the absence of any overt spatial distortions of the movement
trajectory. When required to make a goal-directed pointing movement towards a single target in left
hemispace, the patient is generally able to acquire that target.
1
, Exploring space -> the region of space to which patients direct their eye (or hand) is dramatically
shifted and constricted relative to controls. Typically, the patient explores a region of space largely to
the right of an objective midline.
Disengaging attention in neglect
While people typically explore their surround with over movements of eyes or hands, they can also
redirect their attention covertly toward a location in space. Damage to the parietal lobe leads to a
deficit in disengaging attention from the ipsilesional side. This disengage deficit was present in study
patients with either left or right parietal lesions, although larger for right.
Study -> found that search times for contralesional targets increased with increasing numbers of
ipsilesional distractors, indicative of a difficulty in disengaging attention from ipsilesional stimuli in
order to reorient attention to contralesional space. However, although less dramatic than their
impairment for contralesional space, neglect patients commonly fail to detect targets in ipsilesional
space. This can be due to observed deficits in temporal aspects of attention in neglect patients.
TOJ and attentional blink -> the performance of neglect patients on both the temporal order
judgement task (TOJ) and attentional blink tasks, suggest that there are severe limits on their ability to
allocate attention over time and to disengage attention regardless of location in space. This can be
potentially explained by the impairment involving decreased levels of arousal commonly observed in
neglect patients.
Lost in space – spatial working memory impairments and the neglect syndrome
When completing cancellation tasks, many neglect patients cancel the same target multiple times. This
suggests that they have a deficit in spatial working memory. Findings suggest that neglect patients
suffer from a spatial working memory deficit - a failure to mentally maintain visited locations.
However, there are several alternate interpretations:
- When patients revisit ‘old’ or previously marked locations it is unclear whether or not this is due
to a working memory problem per se or a problem related to the programming of successive eye
movements. It is thought that there is a remapping deficit. This has several key components:
o The spatial remapping deficit inherent to neglect can occur for both overt and covert shifts
of attention.
o For neglect patients, directing attention to contralesional field leads to a problem in
remapping the entire visual space, while directing attention ipsilesionally leads only to a
problem in remapping contralesional space.
Findings could suggest that patients with neglect suffer from a spatial working memory deficit – a
failure to mentally maintain visited locations. However, it is possible that when patients revisit “old”
or previously marked locations, it is unclear whether or not this is due to a working memory problem
or a problem related to the programming of successive eye movements. It is possible that patients suffer
from an impairment in the ability to “remap” space as a consequence of previously executed saccades.
Proposal -> a spatial (not simply saccadic) remapping impairment is at the heart of the disorder. It is
suggested that neglect is a combination of a pathological gradient of attention, such that patients direct
their attention more towards the ipsilesional side of space, coupled with a deficit in spatial remapping.
There are several key components to the remapping deficit:
2
Danckert (2006). Revisiting unilateral neglect.
Unilateral neglect is traditionally defined as a failure to report, respond to or orient towards stimuli in
contralesional space. A more appropriate description is that the patient behaves as if one half – the
contralesional half – of their world has simply ceased to exist. This loss of awareness is often evidence
even in the face of orienting behaviors directed towards the same region of space. Despite moving their
eyes or hand towards contralesional space or the contralesional side of a centrally presented object, the
patient may nevertheless be unaware of what they have just explored.
The classic case of neglect
Neglect is often seen after right hemisphere lesions, leading the patient to behave as if the left half of
their world does not exist. The tasks used to examine neglect typically require perception of and
responses towards both ipsilesional and contralesional stimuli (e.g., cancellation tasks, line bisection
task, and the figure copying of free drawing tasks). Typically, the patient fails to cancel targets on
the left of the page, places their midline mark to the ipsilesional side of the true center of lines in the
bisection task and omits or distorts aspects of drawings on the contralesional side of space.
Sorts of neglect -> patients can demonstrate personal neglect, deficits on tasks of extrapersonal neglect,
or neglect their location in space or alternatively, may neglect the left half of objects irrespective of
their location in space. ‘Sub-syndromes’ of neglect symptoms, such as neglect dyslexia in which the
patient fails to read the left half of words, are present in some but not all, neglect patients. Finally, the
related disorder of extinction to double simultaneous stimulation in which patients can detect single
targets presented in left or right space but ‘extinguish’ left targets when presented simultaneously with
right targets, is often but not always evident in neglect patients.
Distinction of disorders of neglect and distinction -> there are two reasons why this should be done:
1. The lesion locus for extinction in the parietal cortex tends to be more superior than the focus for
neglect.
2. Extinction has been demonstrated to be equally common following left and right hemisphere
lesions, while neglect is far more common following right hemisphere lesions.
Exploratory and goal-directed motor behavior in neglect
One aspects of some patients with severe neglect concerns their posture. Wheelchair bound patients
tend to slump towards the ipsilesional side of their chair and direct their gaze towards ipsilesional
space. If a neglect patient is asked to determine where they think straight-ahead of their body is in the
absence of any external reference frame, they typically demonstrate a deviation towards the right of an
objective midline position. Patients seem to anchor their motor behavior around this shifted straight
ahead position.
Subtle motor control impairment -> the initiation and execution of leftward movements can be
impaired in left neglect patients even in the absence of any overt spatial distortions of the movement
trajectory. When required to make a goal-directed pointing movement towards a single target in left
hemispace, the patient is generally able to acquire that target.
1
, Exploring space -> the region of space to which patients direct their eye (or hand) is dramatically
shifted and constricted relative to controls. Typically, the patient explores a region of space largely to
the right of an objective midline.
Disengaging attention in neglect
While people typically explore their surround with over movements of eyes or hands, they can also
redirect their attention covertly toward a location in space. Damage to the parietal lobe leads to a
deficit in disengaging attention from the ipsilesional side. This disengage deficit was present in study
patients with either left or right parietal lesions, although larger for right.
Study -> found that search times for contralesional targets increased with increasing numbers of
ipsilesional distractors, indicative of a difficulty in disengaging attention from ipsilesional stimuli in
order to reorient attention to contralesional space. However, although less dramatic than their
impairment for contralesional space, neglect patients commonly fail to detect targets in ipsilesional
space. This can be due to observed deficits in temporal aspects of attention in neglect patients.
TOJ and attentional blink -> the performance of neglect patients on both the temporal order
judgement task (TOJ) and attentional blink tasks, suggest that there are severe limits on their ability to
allocate attention over time and to disengage attention regardless of location in space. This can be
potentially explained by the impairment involving decreased levels of arousal commonly observed in
neglect patients.
Lost in space – spatial working memory impairments and the neglect syndrome
When completing cancellation tasks, many neglect patients cancel the same target multiple times. This
suggests that they have a deficit in spatial working memory. Findings suggest that neglect patients
suffer from a spatial working memory deficit - a failure to mentally maintain visited locations.
However, there are several alternate interpretations:
- When patients revisit ‘old’ or previously marked locations it is unclear whether or not this is due
to a working memory problem per se or a problem related to the programming of successive eye
movements. It is thought that there is a remapping deficit. This has several key components:
o The spatial remapping deficit inherent to neglect can occur for both overt and covert shifts
of attention.
o For neglect patients, directing attention to contralesional field leads to a problem in
remapping the entire visual space, while directing attention ipsilesionally leads only to a
problem in remapping contralesional space.
Findings could suggest that patients with neglect suffer from a spatial working memory deficit – a
failure to mentally maintain visited locations. However, it is possible that when patients revisit “old”
or previously marked locations, it is unclear whether or not this is due to a working memory problem
or a problem related to the programming of successive eye movements. It is possible that patients suffer
from an impairment in the ability to “remap” space as a consequence of previously executed saccades.
Proposal -> a spatial (not simply saccadic) remapping impairment is at the heart of the disorder. It is
suggested that neglect is a combination of a pathological gradient of attention, such that patients direct
their attention more towards the ipsilesional side of space, coupled with a deficit in spatial remapping.
There are several key components to the remapping deficit:
2
