Troubles with normal dreaming could be an early warning sign for ailments such as Parkinson's disease, researchers said.
The brain stem has been known since the 1960s to be involved in controlling dreaming during rapid eye movement sleep (REM), when vivid dreams occur.
Dr John Peever of the University of Toronto, Canada, has since found the cells responsible for the dream state - called REM-active neurons - and his team have learned how to control the cells in rodents, and in the process, dreaming.
They can "switch on" the cells to cause a rapid transition into REM sleep, he said.
The team have used the knowledge to examine dreaming dysfunctions such as REM sleep behaviour disorder in humans, in which sleepers act out their dreams with sometimes violent physical movements.
Their research found a link between the dreaming condition and development of a group of neurodegenerative diseases later in life.
More than 80% of people who suffer from REM sleep disorder eventually develop conditions such as Parkinson's disease and dementia with Lewy bodies, Dr Peever said.
"Our research suggests sleep disorders may be an early warning sign for diseases that may appear some 15 years later in life."
Dr Peever, who presented his results at the 2017 Canadian Neuroscience Meeting, the annual meeting of the Canadian Association for Neuroscience - Association Canadienne des Neurosciences (CAN-ACN), hopes it will eventually allow for the development of protective strategies for people who may go on to develop the conditions.
"Much like we see in people prone to cancer, diagnosing REM disorders may allow us to provide individuals with preventative actions to keep them healthy long before they develop these more serious neurological conditions," he said.