Executive function (EF) abilities tend to decline with age, and disproportionately so for people with neurodegenerative disorders such as Parkinson’s Disease (PD), where EF deficits are commonly seen in the early stages of the disease. Due to their nature, EF are essential for performing tasks of daily life, particularly for the more complex instrumental activities of daily living (IADL), and deficits can impair the ability to execute IADL in PD participants. The aim of this study was to examine how EF impairments relate to IADL deficits in both healthy elderly controls and PD participants.

Seventy-four participants with idiopathic PD and 66 elderly controls were recruited. All participants were non-demented. A comprehensive neuropsychological assessment was administered including the following measures of EF: Hayling Sentence Completion, Brixton Spatial Anticipation, Trail Making Test A and B, Stroop Color-Word Test, Symbol Span (Wechsler Memory Scale-III), Digit Span (Wechsler Adult Intelligence Scale-III), F-A-S test, and Semantic Fluency (Animals and Actions). Z scores were calculated from respective test manuals. Independence was measured using the 8-item Lawton IADL Scale where items are coded from 0 (dependent) to 1 (independent) and the total score ranges from 0 to 8. Motor impairments were assessed using Part III of the Movement Disorder Society Unified Parkinson’s Disease Rating Scale. Regression models were run with each cognitive measure as the dependent variable, with group (control vs. PD), age, sex, education, and motor severity as predictors, to examine the effect of group on each cognitive variable. Correlations were then run between the total IADL score, demographic variables, and cognitive variables for each participant group separately to identify the relationship between IADL and EF measures.

PD participants were predominantly males (n=51, 68.9%), with an average age of 70.64±6.03 and 15.22±2.78 education years. Controls were predominantly female (n=34, 51.5%) and had an average age of 71.19±7.75 and 15.85±2.82 education years. Regarding IADL function, all participants were relatively independent in their IADLs (PD: 7.72±0.69, range 4-8, Controls: 7.98±0.13, range 7-8). The most difficult IADL items for PD participants were shopping (8.2% dependent) and food preparation (12.2% dependent). When correcting for age, education, sex, and motor severity, only the Stroop Interference z-score was significant for participant group (b=0.44, t=2.14, p=0.034), where controls had slightly lower scores (-0.33±0.77) than PD participants (-0.31±0.91). Correlations in controls were significant between IADL total score and Hayling trials 1 (r=0.35, p=0.005) and 2 (r=0.33, p=0.008), and semantic fluency actions trial (r=0.34, p=0.006). In PD participants, IADL total score was only correlated with semantic fluency (animals trial, r=0.26, p=0.028).

There were only weak associations between EF abilities and IADL in both healthy controls and PD participants, suggesting that impairments in EF do not necessarily translate into worse ability to execute IADL in PD. More correlations were found in the control group, which may be confounded by the inclusion (in both groups) of participants who already had cognitive impairment. This highlights a further need to examine whether EF impairments in people with PD influence IADL functioning above and beyond normal aging and whether specific deficits have more real-life consequences not attainable through IADL questionnaires.