1. Inhibition and processing speed impaired in MCI and AD groups • Standardised tests detect cognitive changes in impaired groups, and more so in inhibition than processing speed 2. WM fibre density (FD) in SLF differed between groups, but not FC, and little for FDC • Density, rather than volume of the fibre, steadily decreased between groups • While C and SCD groups had similar cognitive performance, the SLF FD differed. The C group had greater SLF FD, while the SCD group’s SLF FD was more similar to the MCI and AD groups 3. Inhibition, and not processing speed significantly correlated with FD in the left SLF 2 and 3 • The SLF plays a critical role in inhibition processes in AD risk cohorts Funding from Brain Research New Zealand (BRNZ) We thank the participants and DPRC staff for giving their time for this study. SCD n = 60 C n = 35 mMCI n = 52 AD n = 27 aMCI n = 55 Lenore T Tahara-Eckl1,2, Reece Roberts1,2, Catherine Morgan1,2, Flavio Dell’Acqua3, Ian Kirk1,2, Tracy R Melzer4,6, John C Dalrymple-Alford4,5, Tim J Anderson4,6, Nicholas J Cutfield7, Lynette Tippett1,2 1School of Psychology, University of Auckland, New Zealand; 2Centre for Brain Research, University of Auckland, New Zealand; 3Forensic and Neurodevelopmental Sciences, King’s College, London, England; 4NZ Brain Research Institute, Christchurch, New Zealand; 5School of Psychology, Speech and Hearing, University of Canterbury, Christchurch, New Zealand; 6Department of Medicine, University of Otago, Christchurch, New Zealand; 7Department of Medicine, University of Otago, Dunedin, New Zealand Participants. n = 229 (122 F, 69.75 ± 8.25 years), recruited from the Dementia Prevention Research Clinic (DPRC) over three sites: Auckland, Christchurch, Dunedin Neuropsychological assessment. Normal Fibre Bundle Reduced FD Reduced FC Reduced FDC Fixel-based analysis (FBA) for FD, FC, and FDC5 1. Rabin, L. A., Smart, C. M., and Amariglio, R. E. 2017. Annual Review of Clinical Psychology, 13(1), 369–396. 2. Lockhart, S. N., & DeCarli, C. 2014. Neuropsychology Review, 24(3), 271–289. 3. Perry, R. J., & Hodges, J. R. 1999. Brain, 122(3), 383–404. 4. Bennett, I. J., & Madden, D. J. 2014. Neuroscience, 12(276), 187–205. 5. Sasson, E., Doniger, G. M., Pasternak, O., Tarrasch, R., and Assaf, Y. 2013. Frontiers in Neuroscience, 7(7 MAR), 1–13. 6. Cremers, L. G. M., de Groot, M., Hofman, A., Krestin, G. P., van der Lugt, A., Niessen, W. J., Vernooij, M. W., and Ikram, M. A. 2016. Neurobiology of Aging, 39, 108–117. 7. Raffelt, D. A., Tournier, J. D., Smith, R. E., Vaughan, D. N., Jackson, G., Ridgway, G. R., and Connelly, A. 2017. NeuroImage, 144, 58–73. 8. Tournier, J. D., Smith, R., Raffelt, D., Tabbara, R., Dhollander, T., Pietsch, M., Christiaens, D., Jeurissen, B., Yeh, C. H., and Connelly, A. 2019. NeuroImage, 202(August), 116137. Five participant groups (total n = 229) Poorer executive function is associated with lower white matter fibre density in the superior longitudinal fasciculus in groups at risk of Alzheimer’s disease Diffusion FOD Image acquisition and preprocessing. Diffusion-weighted MRI (100 directions, b = 1000, 2000 s/mm2). FOD estimation with multi-tissue constrained spherical deconvolution and FBA processed with MRtrix38 Six SLF tracts of interest. Left: SLF tracts coloured by direction (red = right-left, blue = superior-inferior, green = anterior- posterior). Right: SLF tracts segmented by number (SLF1, SLF2, SLF3) In groups at different levels of risk of AD… 1. Do measures of processing speed and inhibition differ? 2. Do SLF fibre properties differ? 3. Do the SLF tracts correlate with processing speed and inhibition measures? Research Questions Background Methods Processing Speed Hayling’s Congruent Sentence Set 1 Stroop Colour Naming Stroop Word Reading Trail Making Test A Inhibition Hayling’s Incongruent Sentence Set 2 Hayling Category A Error Hayling Category B Error Stroop Inhibition Category Switching Trail Making Test B Our findings suggest that specific mi