Progress on new research and treatments for dementia has been 'achingly slow', an expert has said.
Dr Dennis Gillings, the recently appointed global dementia envoy, said the pledge by G8 countries to develop a cure or treatment by 2025 was 'impossible' without better incentives for investment.
He also called for faster and cheaper clinical trials for drugs.
Around 800,000 people in the UK - and 44 million globally - have dementia.
'Special case'
Six months since the UK hosted a G8 summit on dementia, the prime minister is speaking at a follow-up event in central London where he will commit to accelerating progress on dementia drugs.
Experts and health officials from other G8 countries are expected to attend.
'Just as the world came together in the fight against HIV/AIDS, we need to free up regulation so that we can test ground-breaking new drugs', said Dr Gillings, who was appointed by Prime Minister David Cameron to be the global leader on dementia.
Cancer v dementia research
UK government funded £52m of research into dementia in 2012/13 It has pledged to increase this to £66m by 2015 Around £600m is spent on cancer research each year For every one dementia scientist in the UK, at least six work in cancer
Source: Alzheimer's Research
'The amount of scrutiny by regulators is considerable, but there probably needs to be a special case made for dementia by regulators so they can help move things through more quickly... Simplify the clinical trials process or simplify the sort of data being demanded. This happened with HIV in the mid-80s.'
Dr Gillings added that a major barrier to research was the 'ratio of risk to reward' facing pharmaceutical companies investing in dementia.
Only three out of 104 dementia drugs assessed in clinical trials since 1998 have received regulatory approval.
Globally, research and development losses in dementia since then have reached around $50bn (£29bn).
'Massive Challenge'
A key reason for the lack of movement in this area, along with limited funding, is simply that research is extremely difficult.
'The brain is our most inaccessible organ,' said Tim Parry from Alzheimer's Research UK.
'We're looking to find the fault in the world's biggest supercomputer (our brains) but we're doing it in the dark. It's an absolutely massive challenge.'
The charity is announcing a £100m research campaign as part of the summit.
Its chief executive, Jeremy Hughes, said: 'We have seen the huge progress that has been delivered for cancer research because of a sustained boost in funding and now we need the same for people with dementia.'
The government will also announce the Medical Research Council's new UK Dementias Research Platform (UKDP) which it hopes will 'speed up' research into dementia.
The £16m public-private partnership aims to enable earlier detection of dementia, improved treatment and - ultimately - prevention of the disease.
The key project will be the world's biggest study into dementia involving two million people in the UK who scientists have already been tracking as part of other studies.
Mr Hughes said: 'Today's announcements mean the UK is leading the fight in dementia research but our global partners will be crucial to fulfilling the promise of the G8.'
Dr John Gallacher, from Cardiff University and director of the UKDP, said neurodegeneration could be linked with changes in parts of the body 'seemingly unrelated' to the brain.
He said it was 'imperative' to look at the different stages of developing the disease.
'By looking at the links between development of the disease and other factors - such as diet or illness - we hope to unearth targets for new drugs or new uses for existing drugs,' he added.
