Letters Onset of cognitive decline

Intellectual functions may be slower but no worse with age

BMJ 2012; 344 doi: http://dx.doi.org/10.1136/bmj.e1044 (Published 14 February 2012) Cite this as: BMJ 2012;344:e1044
  1. Rosaleen A McCarthy, consultant neuropsychologist1
  1. 1Southampton University Hospital Trust, Department of Neuropsychology, Wessex Neurological Centre, Southampton General Hospital, Southampton SO16 6YD, UK
  1. rosaleen.mccarthy{at}mac.com

The research article by Singh-Manoux and colleagues has widely been reported as providing evidence for rapid decline in cognitive ability from age 45 years.1 However, all tasks were administered with very tight time limits (and often required writing responses), except for the vocabulary test, which showed no evidence of deterioration with age. People may fare worse on these measures of reasoning and memory because they get slower as they age rather than because their thinking skills or memory are worse.

Abundant evidence exists that as people age they are less able or less willing to work at speed. This reduction in processing speed can be seen on tasks such as pressing a button in response to a light and on more complex challenges such as recall of a word list or spatial thinking. Slowed performance does not necessarily imply declining ability. Older people may be more cautious and less willing to take risks than younger ones.2 The extent to which slowed performance reflects biological constraints is unclear,3 and we need to ascertain where and why the effects arise. Disentangling the contributions of strategy, biology, and cognition requires studies in which speed of information processing is not confounded with cognitive performance. The variables are tangled in this study and cannot be differentiated.

The interpretation of this study’s findings may not be as straightforward as has been suggested.


Cite this as: BMJ 2012;344:e1044


  • Competing interests: None declared.