Visual mental imagery in Lewy Body Dementia patients with visual hallucinations: preliminary results

Background Lewy body dementia (LBD) is characterized by the presence of visual hallucinations (VH), however mechanisms underpinning these phenomena are still unknown. Visual mental imagery (VMI) is defined as the ability to see with the mind’s eye, in the absence of adequate sensory input (Kosslyn, 1987). Hallucinations are defined as percepts in the absence of an appropriate stimulus from the external world. Both visual mental images and VH consist of a “stimulus‐independent” image production, however the association between VH and VMI has not yet been investigated in LBD. The aim of the study was to investigate VMI processes in patients LBD with VH. Method Nineteen LBD patients (mean age = 75.4, SD = 6.9; mean education = 10.2, SD = 4) attending the “Sapienza” University Hospital in Rome and 13 Healthy controls (HC) (mean age = 71.9,DS = 7.9; mean education = 12.8, SD = 4.9) matched for age and education were enrolled. VMI was assessed in patients and HC by means of an adapted version of The Complete Visual Mental Imagery Battery (CVMIB; Palermo et al., 2016), including tasks probing the generation of different visual mental images (i.e. object; building and face), maintenance, inspection and transformation processes, and through the O’Clock test (Grossi et al.,1994) including a perceptual and imaginative tasks. Result Non‐parametric analyses revealed that LBD performed worse than HC in all CVMIB tasks. Furthermore LBD performed worse than HC in both O’clock tests, imaginative and perceptual ones, suggesting a role of the visuoperceptual deficits in VMI alterations. It is worth noting LBD and HC did not differ in response time. Conclusion LBD patients with VH show alterations of VMI compared to HC. Alterations of VMI process might influence VH occurrence. Thus, it is possible that VH and VMI share neural mechanisms and are placed on a continuum along the perceptual processes. Future studies are needed to disentangle the possible role of perceptual difficulties in VMI alterations in LBD and to clarify how VMI alterations are related to VH occurrence. Furthermore, investigating VMI and its relationship with visuoperceptual skills in LBD patients could help to better characterize their neuropsychological profile.