Mr Phillip Tan Fong Lip asked a very pertinent question in his letter (Should a doctor be practising at 93?, Feb 15).

The more important question is how one's cognitive ability changes with ageing.

A commonly held misconception is that ageing results in an inevitable loss of cognitive abilities and that nothing or little can be done to halt this decline.

Researchers from Emory University's Alzheimer's Disease Research Centre, however, offered another perspective.

They said knowledge and experience accumulated over time remain stable with age, but abilities not based on experience or education tend to decline.

Verbal abilities, including vocabulary, are preserved.

The researchers also found that when it comes to problem-solving, traditional ways of approaching solutions are maintained in older people.

Prospective memory, like whether one has taken medication after breakfast, declines with age.

But procedural memories, such as remembering how to play the piano or ride a bike, are preserved with age.

To keep dementia at bay, senior citizens should indulge in light physical exercises and keep the mind active by reading a book, magazines and newspapers.

Heng Cho Choon