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Attentional distractibility by optokinetic stimulation in Alzheimer disease

From the Department of Neurology (E.J.K., B.H.L., S.W.S., D.L.N.), Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Republic of Korea; Department of Neurology (S.Y.M.), School of Medicine, Ajou University, Suwon, Republic of Korea; Department of Neurology (D.S.J., K.H.P.), Pusan National University School of Medicine, Busan, Republic of Korea; Department of Neurology (K.M.H.), University of Florida College of Medicine, and the Veterans Affairs Medical Center, Gainesville, FL.

Address correspondence and reprint requests to Dr. Duk L. Na, Department of Neurology, Samsung Medical Center, Sungkyunkwan University School of Medicine, 50 Ilwon-dong, Kangnam-gu, Seoul 135-710, Korea dukna{at}smc.samsung.co.kr

Objective: Unilateral temporoparietal injury may result in an attentional deficit for stimuli presented in contralesional space. Thus, bilateral temporoparietal degeneration associated with Alzheimer disease (AD) might result in a bilateral attentional disturbance. Tests for hemispatial neglect, however, primarily assess spatial attentional asymmetries, and a bilateral attentional disorder might not be detected with these tests. The goal of this study was to learn whether optokinetic stimulation (OKS) would perturb the balanced attentional deficits of AD patients and alter their spatial allocation of attention.

Methods: In Experiment I, 10 AD patients with bilateral temporoparietal glucose hypometabolism on PET and 10 controls bisected lines in two conditions: stationary solid lines superimposed on a moving background and "striped lines" where the whole line was stationary but the stripes within the line moved. The background OKS or the stripes within the line moved leftward or rightward or were stationary. In Experiment II, to investigate whether the influence of background movements would increase with AD severity, we conducted a similar experiment in 56 patients with various stages of AD.

Results: In Experiment I, the line bisection errors (LBEs) of AD subjects, but not of the controls, were markedly influenced by both background and within line stripe motions, deviations occurring in the same direction of movement. In Experiment II, LBEs also occurred in the same direction as background movement and increased with dementia severity.

Conclusions: These results demonstrate that patients with Alzheimer disease are spatially distracted by moving stimuli.

Abbreviations: AD = Alzheimer disease; ANOVA = analysis of variance; CDR = Clinical Dementia Rating; LBEs = line bisection errors; MMSE = Mini-Mental State Examination; NC = normal control; OKS = optokinetic stimulation.

Supported by a grant of the Korea Health 21 R&D Project, Ministry of Health and Welfare, Republic of Korea (A050079), the Samsung Medical Center Clinical Research Development Program grant, #CRS-104-04-2, the U.S. Department of Veteran's Affairs Research Service, and the Byrd Alzheimer Institute.

Disclosure: The authors report no conflicts of interest.

Received January 2, 2007. Accepted in final form April 13, 2007.