The genesis of closing-in in Alzheimer disease and vascular dementia: A comparative clinical and experimental study.

Abstract

Closing-in (CI) in visuo-constructional tasks occurs when a drawing is reproduced close to or superimposed on the original model. CI has been often observed in Alzheimer disease (AD) patients and only rarely investigated in patients with vascular dementia (VD). Recent studies suggested that CI in AD patients represents a default behavior released by frontal-executive impairments, but the cognitive mechanisms behind this phenomenon in VD patients have not been clarified. We aimed to ascertain whether the same mechanisms could determine CI in VD and in AD patients. For this purpose we explored whether CI is related to frontal-executive or visuospatial impairments in a prospective sample of AD and VD patients, and investigated whether CI can be induced by a secondary task in patients with either disease. Sixty-three VD patients and 70 AD patients underwent a neuropsychological assessment of frontal-executive and visuospatial skills, and a copying drawings task for CI. Moreover, VD and AD patients without CI also performed a drawing copying task combined with a simple or a demanding verbal task. In both VD and AD patients CI was related to frontal-executive impairments, with more severe forms of CI related to greater frontal-executive defects. In AD patients the tendency to deviate toward a salient model was significantly enhanced by reduction of cognitive resources, whereas VD could compensate for this tendency. CI is related to the tendency to deviate toward a salient model and can be released by frontal-executive impairments in demented patients, independently from clinical diagnosis.