Drugs are available which enhance the ability of some one with dementia to better complete the interaction between the neurons that are being damaged by their specific dementia disease. 
Although the available drugs currently do not halt the disease or reverse existing brain damage, they may improve symptoms and may slow the progression of the disease.  
Many of  these drugs may improve an individual’s quality of  life, ease the burden on caregivers, or possibly delay admission to a nursing home for a short period of time.

Much of the current research is showing some promising results in finding a way to stop many of the dementia's.
However currently none of these treatments are available for use except in research test groups.

Many people with dementia, particularly those in the early stages, may benefit from practicing tasks designed to improve performance in specific aspects of cognitive functioning.
For example, people can sometimes be taught to use memory aids, such as mnemonics, computerized recall devices, or note taking.

There is hope on the horizon in finding and end to these devastating diseases. 

Studies in using viruses for a cure, as well as many drugs, are showing very promising results towards a possible cure.

However for those who have dementia when the cure does finally come, the one problem will be that these cures will not return the functions one once had. 
Once the damage has been done to the brain, currently, that damage is irreversible.