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Early Bottom-Up Visual Information Processing in Hallucinating Patients with Parkinson’s Disease with Dementia: A Preliminary Visual Evoked Potential Study

Lookup NU author(s): Nik Murphy, Dr Alison Killen, Dr Sara Graziadio, Dr Luis Peraza RodriguezORCiD, Dr Michael FirbankORCiD, Professor Mark BakerORCiD, Dr Greg Elder, Professor Alan ThomasORCiD, Professor Ian McKeith, Professor Lynn RochesterORCiD, Professor John-Paul TaylorORCiD


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Background: A number of reports suggest that bottom-up visual processing is relatively intact inParkinson's disease with dementia (PDD). However, previous studies have implicated bottom-updeficits in the aetiology of visual hallucinations (VH). The visual evoked potential (VEP) can beused as a marker of bottom-up visual information transfer, but the findings in PDD are mixed.Therefore, in this study we sought to characterise the VEP in PDD patients with a range of VHseverity. Methods: PDD patients with a range of VH severity (n = 14), and age matched controls(n = 17) underwent electroencephalography, where a checkerboard pattern was used to elicit theVEP response. Occipital P100 component latencies and amplitudes were compared betweengroups using a one-way analysis of covariance test, controlling for age. The relationship betweenVEP latencies and amplitudes, and VH severity, was tested using Pearson correlations.Secondary correlations were performed between measures of medication (levodopa dose andnumber of medications) and disease duration. Results: There were no significant differences inP100 latency and amplitude between groups. However, VH severity was negatively associatedwith P100 latency (p < .001) but not amplitude. VH severity was also associated with greaterdisease duration (p < .001). Finally, as expected, disease duration was further associated with anincreased levodopa dose (p < .05) and a higher number of PD medications (p < .001).Conclusions: The inverse relationship between VH severity and VEP P100 latency wasunexpected but may reflect that an intact bottom-up system is a necessary prerequisite for themanifestation of visual hallucinations. Further studies examining the relevance of top-downfunction and its relationship with bottom-up processing are warranted to help understand theobserved relationship between VEP P100 latency and VH severity.

Publication metadata

Author(s): Murphy N, Killen A, Graziadio S, Peraza LR, Firbank M, Baker M, Elder G, Thomas A, McKeith I, Rochester L, Taylor J-P

Publication type: Conference Proceedings (inc. Abstract)

Publication status: Published

Conference Name: International Dementia with Lewy Bodies Conference 2015

Year of Conference: 2015

Pages: 158-158

Acceptance date: 01/11/2015

ISSN: 2165-591X

Publisher: American Journal of Neurodegenerative Disease