Assessing visual extinction in right-hemisphere stroke patients with and without neglect

Introduction: Visual neglect and extinction are two common neurological syndromes in patients with right-hemispheric brain damage. The question of how these two syndromes are associated is still a matter of debate. Since – contrary to the diagnosis of neglect – no standardized tests exist for the assessment of visual extinction, we aimed to investigate the relationship between the two syndromes in right-hemispheric stroke patients by using a novel standardized experimental task.

Methods: Sixty patients with right-hemispheric stroke (including 18 patients with spatial neglect) and 18 healthy controls performed a computerized extinction test in which left and right target stimuli had to be detected in uni- and bilateral stimulation conditions. An extinction index was determined and a cluster-analytic approach was employed to classify different patient subgroups. For patients showing neglect and/or extinction (n=24), lesion analyses were performed.

Results: The cluster analysis identified a subgroup of 13 patients showing visual extinction, i.e., a selective decrease in detection probability for left targets that were simultaneously presented with a right non-target stimulus. Although there was a significant statistical relationship between the presence of extinction and neglect (Χ²=4.49, p<0.05), the two syndromes also were observed independently from each other in some of the tested patients. While patients with neglect suffered from lesions within the right frontal and parietal cortex, the lesion overlap in patients with extinction was located in the right temporo-parietal cortex. Moreover, lesions within the right temporo-parietal cortex were related to the degree of visual extinction.

Conclusion: The findings show that visual extinction can be quantitatively assessed and that extinction and neglect are dissociable syndromes in patients with right-hemispheric stroke. The data moreover suggest that the right temporo-parietal cortex is critically involved in the ability to detect a left target in the presence of a right distractor.