1. Figure 1 – Accuracy for control and LBD patients on attentional tasks
Visual hallucinations, attention and visuo-perceptual function in Lewy body dementia
@LewyBodyLab
Steven P Errington1, Greg J Elder1, Michael Firbank1, Daniel Collerton2 & John-Paul Taylor1
Institute of Neuroscience & Institute for Ageing, Newcastle University, Newcastle-upon-Tyne, UK.
2. Northumberland, Tyne and Wear NHS Foundation Trust, Bensham Hospital, Gateshead.
Introduction
Methodology
Participants
Seven patients (Mage=73.27; SD=6.92), with a Lewy body disease (LBD) were recruited from a community-dwelling population. Twelve healthy control participants (Mage=71.50; SD=8.27) were also recruited.
Lewy body dementias (LBD) are considered to be the second most common dementia [1].
Complex visual hallucinations (CVH; images of people, animals or objects which are perceived to be real within a waking state but have no objective reality) are reported in an estimated 80% of patients with DLB and 20-46% of patients with PDD and can significantly impair patient quality of life [2,3].
Several models have been proposed for CVH including the perception-attention deficit (PAD) model [2]; however , little is known about what specific aspects of attention and visuo-perceptual function may play in the active manifestation of CVH.
Recent research has suggested that there may potential meaningful surrogates for visual hallucinations; these include the pareidolia task [4] and the mirror gazing task (also known as Caputo’s illusion) [5].
Using these methods, hallucinations can then be assessed in a quasi-objective manner and then correlated against performance on visuo-perceptual and attentional tasks.
Neuropsychological measures
General Cognition: Addenbrooke’s Cognitive Examination - Revised (ACE-R), incorporating the MMSE.
Parkinsonian Motor Features: Unified Parkinson’s Rating Scale (UPDRS III).
Visual Hallucination Ratings: North East Visual Hallucinations Inventory (NEVHI) and the Neuropsychiatric Inventory (NPI).
Visual acuity: Freiburg Visual Acuity test.
Computerised cognitive tasks
Visuo-perceptual tasks: Angle-discrimination, motion discrimination & visuo-spatial memory.
Attentional tasks: Simple reaction time (SRT), choice reaction time (CRT), digit vigilance (DVT), symbol vigilance (DVT), & visual attention.
Illusion tasks
Noise pareidolia: participants were required to state whether or not they see a face (a) or not (b) in the noise. Faces were actually present in 8/40 trials (20%)
Mirror-gazing: In a darkened room participants looked at their reflection in a large mirror centred at eye level for a period of 10 minutes (c). They were then asked about these experiences upon completion of the task c)
Statistical analysis
Mann-Whitney U-test for group comparisons & Spearman’s rank for correlational analysis.
Results
Participants matched in measures of age & education.
Significant differences were found in overall ACE-R score, with healthy controls (M=94.08) scoring higher than LBD patients (M=82.88) [p=.017].
Significant differences in were found in the following sub-sections: Verbal fluency: Controls (M=12.08) > LBD (M=8.86) [p=.017]; Visuo-spatial ability: Controls (M= 15.58) > LBD (M=12.29) [p=.004].
Significant differences between groups were also noted for visual acuity, with greater impaired vision in LBD patients (M=0.16) than in healthy controls (M=-0.09) [p=.027]
Attentional tasks
Significantly greater reaction times for LBD patients compared to controls on the SRT, CRT, DVT, SVT and motion attention task [all p-values <.05]
Significantly greater accuracy (% correct) on the DVT , SVT, and visual attention tasks [all p-values <.05]. (Figure 1)
Visuo-perceptual tasks
Significantly greater accuracy in controls (92.50%) than LBD patients (50.00%) on a visuo-spatial memory task [p<.001]
Control participants (0.16) also had a lower motion discrimination threshold between controls in comparison to LBD patients (0.57) [p<.001].
Figure 1 – Accuracy for control and LBD patients on attentional tasks
Pareidolia task
There were significant differences between groups for number of correctly identified faces (C=37.92 v LBD=29.86; p=.013) and number of pareidolic responses (C=2.08 v LBD=9.00; p=.013; Figure 2).
In patients, pareidolic responses were significantly correlated with motion discrimination threshold (rs=1.00, p<.001)
Mirror-gazing task
No significant differences were noted between controls & LBD patients on any measures of the mirror-gazing task. However, qualitatively greater hallucination-like experiences tended to occur in healthy controls than LBD.
Figure 2 – Number of correct and pareidolic responses by controls and LBD patients
Conclusions
References
McKeith, I.G., et al., Consensus guidelines for the clinical and pathologic diagnosis of dementia with Lewy bodies (DLB): report of the consortium on DLB international workshop. Neurology, (5): p
Collerton, D., E. Perry, and I. McKeith, Why people see things that are not there: a novel Perception and Attention Deficit model for recurrent complex visual hallucinations. Behav Brain Sci, (6): p
Bostrom, F., et al., Patients with dementia with lewy bodies have more impaired quality of life than patients with Alzheimer disease. Alzheimer Dis Assoc Disord, (2): p
Uchiyama, M., et al., Pareidolias: complex visual illusions in dementia with Lewy bodies. Brain, (Pt 8): p
Caputo, G.B., et al., Visual perception during mirror gazing at one's own face in schizophrenia. Schizophr Res, (1-3): p
Taylor, J.P., et al., Visual hallucinations in dementia with Lewy bodies transcranial magnetic stimulation study. British Journal of Psychiatry, (6): p
Deficits in measures of visuo-perception and attention between LBD patients and healthy, age-matched controls are specific to motion discrimination, motion attention, visuo-spatial memory, and vigilance - this is in line with previous research and in-fitting with the PAD model of CVH. [2]
In addition to this, motion discrimination was associated with the identification of meaningful stimuli (faces) in non-meaningful noise for DLB patients.
This may be indicative of deficits in the dorsal visual attention pathway – previously implicated in neuroimaging studies. Indeed it may be the interplay between a failing occipito-parietal pathway and the ventral pathway that leads to the manifestation of CVH. [6]
Surprisingly there was absence of hallucinatory experiences on the mirror gazing task in LBD patients. This may point toward the concept that hallucinations in the waking state may only occur in the context of adequate visual input and context in LBD. Therefore this may suggest that bottom up input is pre-requisite in the manifestation of CVH.
This Research was supported by the National Institute for Health Research Newcastle Biomedical Research Unit based at Newcastle Hospitals NHS Foundation Trust and Newcastle University. The views expressed are those of the authors and not necessarily those of the NHS, the NIHR or the Department of Health