3: Disease Mechanisms Flashcards
Briefly describe some neglect symptoms.
Unaware of issue, normal visual fields but cannot represent some space, poor working memory, reduced vigilance, ignorance of objects on one side, manually explore only one side, normal motor function but lack of recognition of one side.
Define neglect.
A failure to report, response, or orient to novel or meaningful stimuli presenter to the side opposite to the brain lesion, when this failure cannot be attributed to either sensory or motor deficits.
What do differential diagnostics investigate?
Adequacy of visual and motor functions, and potential visual field deficits or extinction.
What do standardised tests for spatial attention investigate?
Whether there is a lateral bias.
What do neuroanatomical assessments investigate?
If there is a brain lesion in the critical area.
Describe a popular view on the critical lesion in spatial neglect.
There is a critical, interconnected network of areas that can be anatomically remote, but share the same function, and a lesion to any part can cause neglect.
Broadly, where is the critical lesion in spatial neglect?
The hemisphere contralateral to the neglected side, around the perisylvian (lateral) sulcus.
Why is it hard to identify a critical lesion in spatial neglect?
The exact location identified depends on the assessment method, and each one may have different specificity, tap into different symptoms, etc.
What do attention hypotheses predict?
Bias in attention in favour of the ipsilesional hemispace.
What do transformation hypotheses predict?
Error in transforming sensory input into a supra-modal frame of reference so there is an ipsilesional shift of the subjective egocenter.
What fMRI evidence is compatible with the opponent model of spatial neglect?
Shifting and attending to the left visual field yields activation in the right hemisphere, and vice versa.
What TMS evidence is compatible with the opponent model of spatial neglect?
Inhibitory TMS caused enhanced task performance with ipsilesional stimuli.
What 4 observations cannot be explained by attentional hypotheses?
Alleviation of spatial neglect by neck muscle vibration, caloric vestibular stimulation, prism adaptation and somatosensory cortex lesion.
What evidence from neck muscle vibration and caloric vestibular stimulation supports the transformation hypotheses?
They can improve the subjective visual straight ahead in neglect.
Give 4 problems with he transformation hypotheses of spatial neglect.
Not all neglect patients experience a deviation of the egocenter, not all people who experience a deviation have neglect (so it’s not causal), restoration of the egocenter does not always improve neglect symptoms, and an experimental deviation in healthy does not cause neglect.
