A new study on dementia has found how damage spreads through the brain by "jumping" between cells.
Scientists used new technology to discover key chemicals disrupting brain cells in a common type of the condition.
Tissue from people with Dementia with Lewy Bodies (DLB) showed protein builds up in vital parts of neurons that link cells.
Researchers believe these may jump from one cell to another through these connections.
Professor Tara Spires-Jones, who co-led the study, said: "DLB is a devastating condition and our findings suggest that it is at least partly driven by damage to synapses.
"These discoveries should invigorate the search for therapies aimed at reducing synaptic damage and open the possibility of targeting the spread of alpha-synuclein through the brain, which could stop disease progression in its tracks."
The study focused on synapses, which are shared connection points between brain cells allowing chemical and electrical signals to flow.
These are vital for forming memories and are key to brain health, experts say.
Researchers showed synapses in five people who had died with DLB contained clumps of the damaging protein which could contribute to dementia symptoms.
The toxic substance, known as alpha-synuclein, was spotted in both sides of the synapses, suggesting that it may jump between cells.
Similar findings were not seen in brain tissue from people who had died with Alzheimer's disease or those without dementia.
The discovery was made with extremely powerful technology which allowed scientists to view detailed images of over one million single synapses.
Although the protein clumps had been previously identified in DLB, their effects on synapses were unknown because of difficulties in studying them due to their tiny size.
Dr Rosa Sancho, head of research at Alzheimer's Research UK, said: "This exciting research using cutting-edge technology sheds new light on the progression of DLB in the brain.
"The results provide convincing, measurable and visual evidence that toxic alpha-synuclein is disrupting synapses that could potentially contribute to the devastating symptoms of the disease."
DLB is the third most common form of dementia after Alzheimer's and vascular dementias, affecting around 100,000 people in the UK.
The study was carried out by the University of Edinburgh, Hospital de Sant Pau and Universitat Autonoma de Barcelona and is published in the journal Brain.
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