1) From a Psychological stand point the minimum number of participants required in an experiment where so many possible participants can be found is 25, which both discredits the study and the researcher because they would have known that to begin with it they are really qualified to do such an experiment. Also 22 is an extremely small sample size when the population it is taken from is in the millions.
2) Indiana U school of medicine isn't even in the top 50 schools in the US for research let alone worldwide, so it isn't exactly the most valid source of information.
3)Due to the small size of the condition, it's entirely possible that gaming just aggravated the two week cycle which every man goes through, pushing more testosterone through their bodies and causing these effects, which would disappear after a while as ones body gets used to it.
4) it doesn't say whether the non gaming group were retested as well after the week or the results of those tests so it's entirely possible that the changes happened in non gamer's as well.
5) A larger number of studies with larger sample sizes have shown that gamer's generally do better in life as the reward centre of the brain is much larger than non-gamers so they are much more driven to complete rewarding tasks.
6) It even says in the article that this may be due to brain function restructuring (which would likely have positive effects during such a short period of study, negative effects generally happen over a longer time) rather than using less of certain parts of the brain.
7) The tests used could cause problems with the results, if they were the same tests then the participants will succumb to order effects as they have had practice, so won't need to use as much of their brain. If they were different tests then one could have been more difficult than the other which would produce similar results.
8) As the participants were assigned the conditions randomly, individual differences aren't accounted for and so the gamer group could have had more people who are predisposed to changes in brain activity such as this.