By Victoria Gill
Science reporter, BBC News
Humans bet for money, whereas rats gamble for food
Rats are able to play the odds in a "gambling task" designed by scientists to test the biology of addiction.
In the journal Neuropsychopharmacology, researchers describe how the rodents developed a "strategy" in a timed task where they make choices to earn treats.
The rodents avoided high-reward options because these carried high risks of punishment - their sugar pellet supply being cut off for a period.
This decision-making task provides an animal model to study neuropsychiatry.
During the task, which lasted for 30 minutes, rats were given four choices - in the form of holes to investigate.
Nosing each of these holes triggered either the delivery of tasty sugar pellets or a "punishing time-out period" during which rewards could not be earned.
But high-reward holes - those that delivered more pellets at once - also carried the bigger risk of triggering longer periods of punishment.
And rats quickly learned an "optimal strategy" - earning more pellets over the duration of the task by choosing the holes with smaller gains and smaller penalties.
Weigh the odds
The task is based on a card game used to test human decision-making
One of the authors of the study, Trevor Robbins from the University of Cambridge, explained that the rat task was based on an existing clinical experiment called the "Iowa gambling test".
"This is a game designed to test decision-making in patients who have suffered damage to the frontal lobes of their brains," he explained.
"This type of injury is unusual - it doesn't really affect intellect, but patients become extremely compulsive, making disastrous decisions that can have serious impacts on their lives."
In the Iowa gambling test, participants choose cards from four decks. With each card they draw, they either win or lose money, and the object of the game is to win as much as possible.
Some of the decks are associated with small gains and small losses, and will earn a player more money over time.
Certain "bad decks" carry higher rewards, but also incur larger penalties, and will lose money over time.
Like the rat in its quest for sugary rewards, if the player adopts an "optimal strategy", they will make a profit.
"But patients with frontal lobe damage just don't learn from their experiences", said Professor Robbins. They continue to choose from the "bad decks".
To further test their model, the team looked at how the rats' performance was affected by drugs that altered levels of two neurotransmitters, dopamine and serotonin.
These are signalling chemicals in the brain that are both thought to play an important role in addiction.
Researchers hope to develop treatments for "pathological gambling"
The rats were given a drug that reduced the amount of serotonin circulating in their brains. This impaired their ability to make good decisions, and to successfully play the odds.
"Not only have we seen that our rats will gamble, but we've also been able to modulate that behaviour," lead author Catharine Winstanley from the University of British Columbia told BBC News.
"This coincides with data we've seen from pathological gamblers, who have been shown to have lower levels of serotonin in their brains," she added.
"We also found that we could make our rats better gamblers by giving them a dopamine receptor antagonist - a drug that reduces the effects of the neurotransmitter dopamine."
This also ties in neatly with clinical findings in humans. "Treatments for Parkinson's disease [which increase dopamine to aid movement] have been seen to induce pathological gambling," said Dr Winstanley.
"The hope is that this will stimulate interest in studying gambling."
Marc Potenza, a psychiatrist from Yale University who specialises in addiction and problem gambling, described the new test as a "significant step forward" that could eventually lead to new therapies to treat gambling behaviour.
"This is truly translational. It's a rat model that is mimicking human behaviour," said Professor Potenza.
"There are currently no approved treatments for pathological gambling or any of the other formal impulse control disorders. Having good animal models is vital in their development."