However, the ruling wasn't unanimous. Justice Stephen Breyer filed a dissenting opinion. Unfortunately, it contains a whopping misuse of neuroscience. The ruling is here. Thanks to the Law & Neuroscience Blog for noticing this.
Breyer says (on page 13 of his bit)
Cutting-edge neuroscience has shown that “virtual violence in video game playing results in those neural patterns that are considered characteristic for aggressive cognition and behavior.”He then cites this fMRI study from 2006. It's from the same group as this one I wrote about recently.
Breyer quotes this study as part of a discussion of the evidence linking violent video game use to violence. I have nothing to say about this, but I will point out than the fact that violent crime fell heavily in America after 1990, which is when the Super Nintendo and Sega Megadrive were invented.
Anyway, does this study show that playing violent games causes aggressive brain activity? Not exactly. By which I mean "no".
They scanned 13 young men playing a shooter game. The main finding was that during "violent" moments of the game, activity in the rostral ACC and the amygdala activity falls. At least this is the interpretation the authors give.
OK, but even if this neural response is "characteristic for aggressive cognition and behavior", it only lasted a few seconds. There's no evidence at all that this causes any lasting effects on brain function, or behaviour.
The real problem though is that the whole thing is based on the theory that violence is associated with reduced amygdala (and rACC) activity.
The authors cite various studies to this effect, but they don't distinguish between reduced activity as an immediate neural response to violence, as in this study, and reduced activity in people with high exposure to violent media, in response to non-violent stimuli.
This is rather like saying that because having a haircut reduces your total hair, and because bald people have no hair, haircuts cause baldness. Short-term doesn't automatically become long-term.
Besides, the whole idea that amygdala deactivation = violence is a bit weird because they used to destroy people's amydalas to reduce violent aggression in severe mental and neurological illness:
Different surgical approaches have involved various stereotactic devices and modalities for amygdaloid nucleus destruction, such as the injection of alcohol, oil, kaolin, or wax; cryoprobe lesioning; mechanical destruction; diathermy loop; and radiofrequency lesioning...Lovely. It even worked sometimes, apparantly. Although it killed 4% of people. You can't reduce the activity of a region much more than by destroying it, yet destroying the amygdala reduced violence, or at the very least, didn't make it worse.
The truth is that aggression isn't a single thing. Everyone knows that there are two main kinds, "in cold blood" and "in the heat of the moment". Killing someone in a spontaneous bar brawl is one thing, but carefully planning to sneak up behind them and stab them is quite another.
Just based on what we know about the rare cases of amygdala-less people, I would imagine that destroying the amygdala would reduce violence "in the heat of the moment", which is motivated by anger and fear. The kind of patients who got this surgery seem to have been that kind of violent person, not the cold calculating kind.
So, even if violent video games reduced amygdala activity long term, that would probably reduce some kinds of violence.
Weber, R., Ritterfeld, U., & Mathiak, K. (2006). Does Playing Violent Video Games Induce Aggression? Empirical Evidence of a Functional Magnetic Resonance Imaging Study Media Psychology, 8 (1), 39-60 DOI: 10.1207/S1532785XMEP0801_4