IPSILESIONAL VERSUS CONTRALESIONAL NEGLECT DEPENDS ON ATTENTIONAL DEMANDS Duk L. Na 1 , John C. Adair 2 , Seong Hye Choi 3 , Dae Won Seo 1 , Yeonwook Kang 1 and Kenneth M. Heilman 4 ( 1 Department of Neurology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea; 2 Department of Neurology, University of New Mexico, Albuquerque, New Mexico; 3 Department of Neurology, College of Medicine, Inha University, Incheon, Korea; 4 Department of Neurology, University of Florida, and Veterans Affairs Medical Center, Gainesville, Florida ABSTRACT Right hemisphere injuries often produce contralesional hemispatial neglect (CN). In contrast to CN, some patients with right hemisphere damage can also show so-called ipsilesional neglect (IN). Previous reports found that patients tend to show IN on line bisection tasks but CN on other tasks such as target cancellation. To learn why these two tasks induce different spatial biases in patients with right hemisphere injury, conventional (i.e. solid) line bisection was compared with two novel bisection tasks consisting of horizontally aligned strings of characters. The subjects’ task was to mark a target character that was at or closest to the true midpoint of the simulated line. Four of the 5 patients showed a dissociation whereby IN occurred for solid lines while CN was observed on character lines. The two patients assessed with an antisaccade paradigm showed a “visual grasp” for leftward stimuli. The present results suggest that neglect on line bisection may reflect two opposing forces, an approach behavior or “visual grasp” toward left hemispace and an attentional bias toward right hemispace. Key words: hemispatial neglect, contralesional, ipsilesional, attentional, visual grasp INTRODUCTION The neglect syndrome refers to a patient’s failure to report, respond, or orient to stimuli presented in the space opposite a brain lesion despite intact elementary sensory and motor function (Heilman, Watson and Valenstein, 1979). Right hemisphere injury is often associated with left hemispatial neglect in which patients tend to place the subjective midpoint of horizontal lines to the right of true center, omit targets from the left side of a stimulus array, and fail to draw or copy features from the left side of a figure. In contrast to neglect of contralesional space (i.e. contralesional neglect, CN), recent studies also report patients who demonstrated neglect of ipsilesional space (i.e. ipsilesional neglect, IN) (Kwon and Heilman, 1991; Robertson, Halligan, Bergego et al., 1994; Kim, Na, Kim et al., 1999; Halligan and Marshall, 1998). Heterogeneity exists in the few available descriptions of IN. Albert (1973) and Weintraub and Mesulam (1987) asked patients with right hemisphere lesions to perform target cancellation tasks and found both profound CN as well as more subtle evidence of inattention for the ipsilateral items. Weintraub and Mesulam (1987) interpreted their findings in terms of right hemisphere Cortex, (2000) 36, 455-467