What is spatial neglect?
- Failure to report, respond or orient to novel or meaningful stimuli on the side opposite of the lesion
- persists when blindfolded
- Patients unaware of deficit
- Can be temporary or permanent
- results in poor working memory for space
When does spatial neglect occur?
In 33% of patients with right hemisphere stroke and also can occur in response to Alzheimers Disease
What can spatial neglect resemble?
Hemianopia - damage to the visual system, however patients are aware of deficit and orient themselves accordingly
How can spatial neglect be diferentially diagnosed?
Assessing whether motor and visual functions are adequate
What are the standardised tests for spatial attention?
- Cancellation task, gives CoC score
- Line bisection
- Replication of a figure
- Measure accuracy and reaction time responding to letters on the left and right
Where is the critical lesion for spatial neglect?
- Depends on assesment method eg line bisection very different to personal neglect
- Idea that a network of brain areas support spatial attention and therefore lesion results in a faulty system (critical network hypothesis)
What is the function of attention?
Bottleneck by which the brain selects what is important in terms of goals and events
What is the attention hypothesis for spatial neglect?
That spatial neglect is an inability to allocate attention in space
What is the transformation hypothesis for spatial neglect?
- Neglect is an error in transforming sensory input into a supra-modal frame of reference
- Ipselional shift of the subjective egocentre (body midline)
- This is as different modalities perceive space differently
What is the premotor hypothesis?
That there is a witheld eye movement and so the deficit is with movement planning
What is the representational hypothesis?
There is a deficit in memory representations, patients recalling places only describe one side but can do the other when asked to
What are the 3 theories of the causes of the attention hypothesis?
- Interhemispheric competition - hemispheres fight for resources and attention is allocated to ‘winning’ hemisphere
- Left neglect more frequent than right as hypothesised that right controls attention on both sides and the left controls the right visual field only
- A general decrease in attentional resources aggrevates the deficits
Why is the hypothesis that the right brain controls attention on both sides likely false?
fMRI data
- Orienting attention to left shows right activated activity in occipatal, visual, parietal and frontal cortex
- Symmetrical pattern when directed to the right
- Attention is symmetrically represented in the brain
What support is there for the hemispheric competition hypothesis?
transcranial magnetic stimulation - temporary ‘lesion’/inhibition
- Applied to left and right parietal cortex, participants asked to report whether stimulus was on left or right
- Bilateral stimulation significant
- Unilateral stimulation did not induce neglect, but enhanced other side response
What is the support for the transformation hypothesis?
Number of somatosensory interventions can improve symptoms
- Neck muscle vibration which acts on neck proprioception can create sense of elongation
- Caloric vestibular stimulation can change head tilting sensation
What is the transformation hypothesis?
Faulty perception of spatial alignment
- People with spatial neglect who must stop LED on their nose percieve it 10 degrees to the right
- Corrected with neck stimulation
What is the problem with the transformation hypothesis?
- Can have deviations in body egocentre without neglect
- Lack of correlation of egocentre deviation with severity
What rehabilitation strategy has been proposed for spatial neglect?
- Decrease activity of healthy hemisphere to induce balance
- Prism adaptation - optical shift in the visual field may correct the midline and improve the neglect (only for a couple of hours)
- Meta-analysis of cognitive interventions however shows no significant effect
- Attemps at pharmalogical interventions involving nodadrenaline and dopamine (same as ADHD), so far quality of evidence very low as there have been very few studies
How is the CoC score measured?
Mean horizontal location of cancelled items, provides direct measure of neglect severity
