Serious gamblers demonstrate a similar pattern of brain activity to people who are addicted to drugs, a new study has suggested.
Players won if they chose a red card
The researchers from Hamburg, Germany, said this showed gambling was also a form of addiction.
They said the parts of the brain which are active when people feel rewarded, curbing activity, are less so in those who take drugs or gamble to excess.
The research is published in the journal Nature Neuroscience.
In the study, the brains of 12 compulsive gamblers and 12 non-gamblers were monitored using functional magnetic resonance imaging (fMRI) while they played a simple card guessing game.
Players had to choose one of two face-down cards. If the card came up red, they won one euro.
It was found that the ventral striatum, a part of the brain that signals reward, was less active in the pathological gamblers even though both groups won and lost the same amount of money.
Reduced activity in the area is recognised as a hallmark of drug addiction.
The researchers suggest the explanation could be that people with such addictions cannot maintain the amount of the brain chemical dopamine - which produces feelings of satisfaction and pleasure - which they need in the ventral striatum, through everyday life.
Instead, they need stronger triggers - such as drugs or excessive gambling - to compensate.
Writing in Nature Neuroscience, the researchers from the Universitaets-Krankenhaus Eppendorf, led by Dr Christian Buchel, said their findings "favour the view that pathological gambling is a non-substance related addiction".
But Mark Griffiths, professor of gambling studies at the International Gaming Research Unit at Nottingham Trent University, said differences in brain activity were too simplistic an explanation for why some people gambled and others did not.
"The explanation for why people gamble is more holistic than that. It's not just about the gambler, it's about other factors such as their social environment."
He added that the design of gambling activities was also a factor in prompting people to become addicted.
"There are differences. For example, a slot machine is more problematic than buying a weekly lottery ticket.
"This study is one more piece of the jigsaw that helps give gambling legitimacy as a bona-fide addiction."