Biomedical Research Unit: Acute and Chronic effects of transcranial Direct Current stimulation in Lewy body dementia patients

INTERVENTION: Transcranial Direct Current Stimulation (tDCS). This involves the application of a weak electrical current (<2mA) between two scalp surface electrodes. Participants will either receive active or sham (placebo) tDCS treatment on the basis of prior randomisation (1:1 allocation to active treatment:sham/placebo) and electrodes will be applied to the scalp overlying the parietal cortex and visual cortex. The treatment (2 x 20 minute sessions with a 30 minute break) will be delivered over four consecutive days. CONDITION: Topic: Dementias and Neurodegenerative Diseases Research Network; Subtopic: Dementia; Disease: Lewy Body Dementias ; Nervous System Diseases ; Lewy body(ies)(dementia)(disease) PRIMARY OUTCOME: 1. The acute benefits of tDCS treatment on visual hallucinations at Day 5 ; 2. The chronic benefits of tDCS as assessed at one and three months. ; The measure used for the severity and frequency of visual hallucinations will be the composite score derived from question 2 of the neuropsychiatric inventory (NPI). This measure normally assesses hallucination occurrence over the previous month, so the question will be modified for the acute assessment (Day 5) to ask about hallucination frequency and severity over the 4 days of treatment. SECONDARY OUTCOME: 1. The Neuropsychiatric Inventory (NPI) hallucinations subscale will be used to assess maintenance of any benefit at 3 months follow‐up. Two other visual hallucination scales (NEVI‐H and the Neuropsychiatric Inventory ? Clinician (NPI‐C) hallucination severity score) will be used as secondary measures of visual hallucinations at each of the assessment time points (Day 5, 1 month and 3 months). ; 2. Other secondary measures will include changes in visuo‐perceptual function (following treatment), global measures of neuropsychiatric symptom severity (NPI), as well as cognitive and quality of life indexes. The clinician global impression of scale change will also be used as a general marker of improvement or deterioration at 1 month and 3 months. As a biomarker measure of response, the repeat phosphene excitability measure at Day 5 will be compared to the baseline and against any improvements in visual hallucinations. INCLUSION CRITERIA: 1. Age > 60, either sex 2. Provision of written informed consent or, if lacking capacity, consent provided by legal or other appropriate representative in accordance with provisions of the 2005 Mental Capacity Act 3. Absence of concurrent major psychiatric illness (e.g. major depression) 4. Absence of severe physical illness or comorbidity that may limit ability to fully participate in study 5. Sufficient English to allow assessment scales and cognitive testing For Lewy body dementia participants: 1. MMSE>12 2. Meet criteria for probable DLB or probably PDD 3. If taking anticholinesterase drugs, memantine, antipsychotic medication and/or antiparkinsonian medication ? need to be stable on these agents for at least 1 month 4. Presence of reliable informant sufficient to provide information for informant rated scales 5. Evidence of persistent and recurrent visual hallucinations of a moderate to severe nature occurring in the month prio