Mind's eye in the Alzheimer's disease spectrum continuum.

Background: Visual mental imagery (VMI) is the ability to represent stimuli in the mind without sensory visual input. Previous studies have shown alterations in VMI in Alzheimer's disease (AD). However, VMI has not been investigated in the AD prodromal stage, mild cognitive impairment (MCI).

Objective: We investigated VMI ability in mild AD and MCI patients, hypothesizing that VMI ability could be compromised since early disease stage.

Methods: We enrolled 14 patients with mild AD, 19 amnestic MCI (aMCI), and 23 healthy control subjects (HC), matched for sex, age, and education. VMI assessment included: 1) the O'clock test that allows disentangling the possible role of visuo-perceptual difficulties in the VMI task's performance; 2) a modified version of The Complete Visual Mental Imagery Battery (CVMIB), including tasks evaluating the different VMI processes (generation, maintenance, inspection and transformation).

Results: Results indicated that AD patients performed worse than HC in both perceptual and imaginal tasks of the O'clock test and in all CVMIB's tasks but maintenance. On the contrary, aMCI patients showed difficulties in the generation process and in the imaginal task of the O'clock test.

Conclusions: Visual images generation, inspection and transformation processes are impaired in mild AD. Moreover, the generation process is selectively impaired in aMCI patients, suggesting that VMI deficits are already present in the prodromal stage of AD.