So does listening to enjoyable music or viewing an impressive art gallery. I assume you're talking about glutamergic activity in populations in the shell of the nucleus accumbens. (edit: after reading the paper, https://www.nature.com/articles/tp2016256 , I was correct).

And that's funny because in the incentive salience theory of addiction, which they cite at the start of their paper, the nucleus accumbens populations don't encode for wanting, those populations encode for liking. The actual voxels of the brain this study should have been watching would be the ventral pallidum and ventral tegmental area. Those are necessary and sufficient for wanting(craving). The nucleus accumbens is not.

You'd think the director of the National Problem Gambling Clinic who cites the incentive salience theory in his first paragraph would actually take the time to understand the neurological correlates of the theory he's citing (but then again, "It is difficult to get a man to understand something when his salary depends on his not understanding it."). This lack should make you question the other aspects of this study.

Like how a 19 person MRI studies might as well not be studies at all in the neuroscience sense. They're for getting more funding to do a study with actual statistical power to make inferences. And note that in the actual paper they don't call it addiction, it's gambling disorder.