WCN 2013 No: 900 Topic: 5 — Dementia Are practice effects an important confounder of longitudinal studies of HIV-associated neurocognitive disorders? A.-C. Meyer, K. Robertson, E.A. Bukusi, G.L. Birbeck, C.R. Cohen, P. Oyaro, R.W. Price. Neurology, SFGH/University of California, San Francisco, CA, USA; Family AIDS Care and Education Services, Kenya Medical Research Institute, Nairobi, Kenya; Neurology, University of North Carolina, Chapel Hill, NC, USA; Neurology, Michigan State University, East Lansing, MI, USA; Obstetrics and Gynecology, University of California, San Francisco, CA, USA Background: The diagnosis of HIV-associated neurocognitive disorders (HAND) is based on neuropsychological testing. Scores on neuropsychological tests tend to improve with repeated administrations—the practice effect. Longitudinal studies of HANDmay be confounded by the practice effect. We determined the magnitude of the practice effect among HIV-uninfected individuals in Kenya. Methods: A comprehensive battery of seventeen neuropsychological tests designed to diagnose HAND was administered to 100 HIV-uninfected individuals in 2009. We traced these individuals, performed HIV-antibody testing, and re-administered the neuropsychological tests. Raw scores were converted to Z-scores, and practice effect was defined as the difference between the Z-scores at initial and repeat administrations. A clinically significant change was defined using the Reliable Change Index (standardized Z-score difference≥|1.64|). Results: Of 100 individuals initially studied, we located 69 of whom 47 participated. The median interval between testing was 98 weeks [Range: 83–130]. Mean age was 30 years, 26% were female, 26% had less than primary school education, and 24% had more than secondary school education. One individual was found to be HIVinfected and was excluded. Overall, practice effects ranged from −0.29 to 0.75 and, among the 33 individuals without neurologic or psychiatric co-morbidities, ranged from −0.26 to 0.72. Practice effects were significantly different from the null for Color Trails, Grooved Pegboard and WAIS-3 Digit Symbol. Between 3 and 9% of HIV-uninfected individuals had clinically significant improvements or declines. Conclusions: Practice effects may be an important confounder of longitudinal studies. Further research in larger andmore representative populations in sub-Saharan Africa is essential. doi:10.1016/j.jns.2013.07.1161 Abstract — WCN 2013 No: 663 Topic: 5 — Dementia Aerobic physical activity stabilizes cognitive status in patients with dementia WCN 2013 No: 663 Topic: 5 — Dementia Aerobic physical activity stabilizes cognitive status in patients with dementia M. Seijo-Martinez, J.M. Cancela, C. Ayan, S. Varela. Neurology, Xestion Integrada Pontevedra-Hospital do Salnes, Spain; Facultad de Ciencias de la Educacion y el Deporte, Universidad de Vigo,