Line bisection judgments implicate right parietal cortex and cerebellum asassessed by fMRI

Objective: To use functional MRI (fMRI) to determine which brain regions ar e implicated when normal volunteers judge whether pretransected horizontal Lines are correctly bisected (the Landmark test). Background: Manual line b isection and a variant thereof involving perceptual judgments of pretransec ted lines (the Landmark test) are widely used to assess unilateral visuospa tial neglect in patients with neurologic disease. Although unilateral (left ) neglect most often results from lesions to right temporoparietal cortex, the normal functional anatomy of the Landmark test has not been convincingl y demonstrated. Methods: fMRI was carried out in 12 healthy right-handed ma le volunteers who judged whether horizontal lines were correctly prebisecte d. In the control task, subjects detected whether the horizontal lines cont ained a transection mark irrespective of the position of that mark. Respons e was by two-choice key press: on half the trials, subjects used the right, and on half, the left hand. Statistical analysis of evoked blood oxygenati on level-dependent responses, measured with echoplanar imaging, employed st atistical parametric mapping. Results: Performing the Landmark task: showed neural activity (p < 0.05, corrected) in the right superior posterior and right inferior parietal lobe, early visual processing areas bilaterally, th e cerebellar vermis, and the left cerebellar hemisphere. Only the latter ar ea showed a significant interaction with hand used. Conclusions: The right hemispheric dominance observed in inferior parietal cortex is consistent wi th the results of lesion studies. Right superior parietal cortex, vermis, a nd left cerebellar hemisphere have not been implicated in neglect, but all appear to play a cognitive role in the Landmark task.