Valgeir Thorvaldsson, MSc, of Goteberg University in Sweden, who conducted the study, said that these terminal changes in cognitive abilities are different from those that occur due to ageing.
The scientists found rapid changes in metal skills that start years prior to death. Various mental functions start declining at different stages.
According to the results of the study, perceptual speed, an ability to match figures rapidly, worsens around 15 years prior to death. Spatial functioning, which is associated with the ability to comprehend and interpret information starts declining about 8 years before death. The start of decline in verbal skills was found to be nearly 6, 6 years before death.
The research involved 288 people without dementia, followed from the age 70 until death. The cognitive abilities of the participants were measured 12 times during a 30 years period. These measurements were evaluated to ensure the participants did not develop dementia.
Thorvaldsson explained that these rapid changes may occur due to several factors such as cardiovascular diseases that are too early to be identified. Other health conditions and physical weakness in older age often result in inactivity and lack of metal stimulation, and this may speed up the decline in mental skills.
The author added that verbal skills decline sharply before death and this fact is not connected to age only. This means that people's verbal functioning is quite stable unless they have a disease and this increases the risk of mortality. Thus this factor may indicate the critical point for degeneration in older people.
The study has been published in the August issue of Neurology, the medical journal of the American Academy of Neurology.