Monkeys are natural risk-takers, but when scientists implanted chips into their brains, they became much more careful, according to a new study.

A team of researchers at Kyoto University in Japan used flashes of light from implanted chips to activate two different sections of the macaque monkeys’ brains. 

Switching one on encouraged them to take bigger risks with the hope of a bigger payoff, while switching the other section on led the animals to settle for a smaller but more certain reward.

This research offers insight into the neural roots of gambling addiction, said the researchers behind the study. 

The specially designed electrode array measures brain activity and shines a light to activate gene-edited neurons

But before digging into the brain, scientists began by figuring out whether their six monkeys liked to gamble.

They trained the macaques to look at different colored spots on a screen to receive a water reward.

Some spots would give the monkey a small reward 90 percent of the time – low risk, low reward. 

Others gave a reward that was 10 times larger, but it only paid out 10 percent of the time – high risk, high reward. 

Overwhelmingly, the monkeys went for the high-risk, high-reward spots. Like a gambler at a slot machine, even though they may lose more often than they win, they gambled with their eye on a big payout.

Next the team tried to figure out which brain areas were in control of this risk-reward calculation. 

Activating one part of the monkey frontal lobe encouraged the animal to go for a big reward that had a low likelihood of success. Activating another region caused the monkey to stick to an option with better odds of winning a smaller reward

Japanese macaques, famous for lounging in mountain hot springs, also tend to be risk-takers, scientists have found. In a video game task, they opt for the high-risk, high-reward scenario almost every time

They chose several candidate areas, brain regions known to be involved in decision-making, and injected each one with a chemical that keeps neurons from sending signals.

When they inactivated one specific region, the monkeys stopped making risky choices. 

No other areas had a similar effect, even areas that have been shown to play a role in monkey decision-making.

The region researchers identified is part of the Brodmann area in the monkey frontal lobe, which has dozens of smaller parts that are associated with all sorts of brain activities including speech, hearing, and movement.

The electrode array shines red light to activate neurons and also records their electrical activity

Specifically, it was Brodmann area 6, which is involved in planning complex and coordinated movement.

In people, the frontal lobe is involved in personality, planning, organizing, and goal-oriented behavior. 

The macaque frontal lobe plays a similar role in the animal’s behavior, past research has suggested.

The new study, published today in the journal Science, supports this idea.

Scientists next tested whether they could target this brain area to switch the gambling tendency on and off.

Local gene editing in Brodmann area 6 made the neurons light-sensitive, activating in response to red light. 

The team implanted a special electrode array over the altered brain region. This device not only recorded electrical activity of the brain, but also shone red lights onto its surface to turn on the neurons.

Then they introduced the monkeys to a new video game, one that recreated the same idea as the first one but which added some new elements.

It was a simple game where monkeys either took a safe path to collect a single banana or a dangerous path to get a whole bunch of bananas. Monkeys controlled the game by looking around the screen. 

When the bottom part of Brodmann area 6 was illuminated and activated, the monkeys ramped up the riskiness, opting even more often for the dangerous path to greater reward.

But when the top part of the same region was activated, they became more cautious, choosing the safer path with a smaller payoff.  

The video game gave monkeys a risky path to receive a large reward or a safe path to get a smaller reward

‘This unexpected finding implies that two neighboring regions in the frontal cortex together regulate risk attitude in a competitive push-pull–like fashion and can both increase and decrease risk seeking,’ wrote Veit Stuphorn, associate professor of neuroscience at Johns Hopkins University, in an accompanying commentary. 

‘This is important because it opens up the possibility to identify the neuronal mechanisms in the circuit underlying this ability,’ added Stuphorn, who was not involved in the new work.

Dopamine, the chemical messenger that we associate with reward and positive feelings, seems to play a role in balancing risk and reward, too, the researchers found.

The neurons that extend from the Brodmann area carry dopamine to the ventral tegmental area, an area that has been linked to addictive behaviors in people.

Plus, cell staining of the monkey’s brains revealed that most of the neurons that became light-sensitive were dopamine-producing neurons.

All together, the results led the researchers to speculate that the two parts of the Brodmann area 6 ‘might separately encode for different risk-return computations.’

In other words, different parts of the same brain region may be working in totally different ways to calculate risk many times every day.

Future research is necessary to determine whether this experiment is illuminating the same areas as people with gambling addictions, but these results show early promise.

An important connection, they noted, is the dopamine-promoting Parkinson’s disease drug pramipexol that has been shown to promote gambling disorders.

Because of this connection, they wrote, ‘our findings not only have broad implications for answering such clinically relevant questions but also provide opportunities to better understand the underlying neural mechanism of gambling disorder in humans.’