Lifetime experiences and their effect on cognitive reserve in Parkinson's disease

Parkinson’s disease (PD) is a chronic, progressive neurological condition of largely unknown aetiology. It is the second most common neurological disorder after Alzheimer’s Disease, affecting 1-2% of the population aged sixty and above (de Lau and Breteler, 2006). The condition is characterised by bradykinesia, resting tremor, rigidity and postural instability.

As many as 90% of PD patients experience some cognitive impairment (Dubois et al., 1991 in Montel & Bungener, 2008).

Dementia is usually viewed as cortical dementia. In contrast, PD patients often experience sub-cortical changes, with a less recognisable pattern of symptoms. These typically include deficits in executive function, memory and visuo-spatial skills (Vingerhoets et al., 2003).

As these dysfunctions differ to what is classically expected in those who have dementia, Parkinson’s Disease Dementia (PDD) can be difficult to diagnose. As a result, it is believed that the prevalence of those individuals who have PDD is significantly underestimated (Marinus, 2003).

Reserve theories explain that the extent of damage to a brain and the level of impairment produced are not consistent; two individuals with similar amounts of brain damage, through trauma or disease, can show very different levels of cognitive deficit, even if their deficits are in the same function(s). The theory of reserve is that there is some protective factor in the brain that protects against cognitive deficits as a result of damage (Stern, 2002).

Cognitive reserve can be measured in a number of ways. Valenzuela (2008) proposes three types of measurement as being of interest in determining cognitive reserve; pre-morbid IQ, cognitive efficiency, and behavioural or environmental measures.

Behavioural and environmental factors with implications for the development of dementia have been identified in a number of studies including Qiu et al (2007) who identified education, social networks, physical activity and mentally stimulating leisure activities as preventative in the development of dementia. These same factors were identified by Stern (2003) and Valenzuela (2008). If these factors are protective against dementia, they may reflect an individual’s cognitive reserve. Valenzuela and Sachdev (2007) consolidated these factors into the Lifetime of Experiences Questionnaire (LEQ) which measures these factors and could be used as a measure of cognitive reserve. Valenzuela (2008) has shown that a relationship exists between LEQ scores and cognitive decline in dementia populations.