[1] Trinity Coll Dublin, Irish Longitudinal Study Ageing, Dublin 2, Ireland
[2] Univ E Anglia, Sch Nursing Sci, Norwich NR4 7TJ, Norfolk, England
[3] St James Hosp, Dept Med Phys & Bioengn, Dublin 8, Ireland
[4] St James Hosp, Mercers Inst Res Ageing, Dublin 8, Ireland
[5] Trinity Coll Dublin, Trinity Coll Inst Neurosci, Dublin 2, Ireland