London: Scientists have used light to
program the memories of fruit flies, according to an Oxford
University-led study published in the journal Cell.
The research team genetically engineered the fruit flies
so that a small set of nerve cells in the brains would 'fire'
in response to a flash of laser light.
This showed which cells are involved in how a fruit fly
learns and remembers what to avoid, and offers an exciting new
opportunity to investigate how memories are formed.
"Remote-controlling these cells and turning them on using
light creates an illusion in the brain of the fly that it is
experiencing something bad. The fly learns from the 'mistake'
it never really made and improves its actions the next time,"
explains Professor Gero Miesenböck of the Department of
Physiology, Anatomy and Genetics at Oxford University, who
led the work.
The Oxford scientists, with colleagues at the University
of Virginia, Charlottesville, demonstrated that they could use
flashes of laser light to train flies to dislike a certain
odour.
"We tracked the flies using a video camera as they moved
around a small chamber while two different odours were fed
into the chamber from either end. We found that we could
implant a lasting preference for one odour over the other by
remotely activating a specific set of brain cells each
time a fly strayed into a particular odour," says Dr Adam
Claridge-Chang, who is now at the Wellcome Trust Centre for
Human Genetics at Oxford University.
Using this method, the researchers were able to pinpoint
the precise nerve cells that are responsible for telling the
flies that they've done wrong, narrowing down the search from
the 1,00,000 cells in the brain of a fruit fly to a set of
just 12 neurons.
"Surprisingly, the source of these signals is in a
limited number of cells – just twelve," says Professor
Miesenböck.
"These cells send the signals that train the fly to
associate the odour with something bad, so wherever their
signals go must be the seat of memory. We can now follow this
up and start to characterise the process by which memories are
formed and organised."
While this work has been done in fruit flies, general
lessons about how actions are learned and memories are stored
should hold true for humans.
"Biology teaches us that fundamental mechanisms tend to
be conserved. Learning about the storage of memories from
brain cells in flies should tell us a lot about how they are
stored in humans," says Professor Miesenböck.
Professor Miesenböck has pioneered this method of genetic
engineering to remote control the action of specific cells
within tissues, or whole organisms like worms, fruit flies,
fish and mice, using light from the outside. These efforts
have given rise to a new field sometimes called
'optogenetics', to indicate that sensitivity to light is
encoded genetically.
A separate paper by Professor Miesenböck summarising the
status of this new field is to be published in Science the
same day. As the ability to write memories directly to the
brains of fruit flies demonstrates, optogenetic techniques
have particular power in neuroscience.
"The great advantage is that we are no longer just
passive observers of processes in the brain. In the past,
neuroscientists had to be content with recording the chatter
of brain cells and trying to infer what it all meant. The
ability to talk back and influence behaviour directly is
proving quite valuable," Professor Miesenböck added.
Bureau Report