Closing-in in Parkinson's disease individuals with dementia: An experimental study

INTRODUCTION The tendency to reproduce figures close to or superimposed on the model in copying tasks, the so-called Closing-in (CI) phenomenon, has been rarely reported in individuals affected by Parkinson's disease and associated dementia (PD-D). We aimed to comprehend the genesis of CI in PD-D individuals by assessing whether reduction of attention/executive resources can increase the tendency to deviate toward the model. METHOD: Thirty PD-D individuals underwent a neuropsychological evaluation exploring visuo-spatial, visuo-constructional, executive and memory abilities. An experimental copying task was employed in single and in two dual task conditions to assess whether a (verbal) cognitive load can increase CI in these individuals, compared with a matched sample of healthy adults. RESULTS: CI occurred in 19/30 (63.3%) PD-D individuals: 4 of them produced copies close to the model (near-CI), whereas 15 individuals also superimposed their copies on the model (adherent-CI) besides showing near-CI. Presence of CI in PD-D individuals was significantly correlated with executive dysfunction but not with general cognitive impairment. In the experimental copying task the tendency to deviate toward the model was strongly correlated with executive dysfunction, and significantly increased when PD-D individuals were engaged in dual-task compared with single task conditions. Some individuals attempted to counteract CI, but this trend significantly decreased in dual-task compared with the single task conditions. In healthy adults the drift toward the model was significantly smaller than in PD-D individuals; in dual-task conditions healthy adults only showed a significant decrease in their ability to compensate for this drift. CONCLUSIONS: In PD-D individuals the tendency to deviate toward a salient model is strongly enhanced by a concurrent cognitive load. Such preliminary findings would suggest a relationship between reduction of executive attentional resources and the genesis of CI in PD-D individuals.