Media violence induces imitative violence. If true, this idea is dangerous for at least two main reasons. First, because its implications are highly relevant to the issue of freedom of speech. Second, because it suggests that our rational autonomy is much more limited than we like to think. This idea is especially dangerous now, because we have discovered a plausible neural mechanism that can explain why observing violence induces imitative violence. Moreover, the properties of this neural mechanism — the human mirror neuron system — suggest that imitative violence may not always be a consciously mediated process. The argument for protecting even harmful speech (intended in a broad sense, including movies and videogames) has typically been that the effects of speech are always under the mental intermediation of the listener/viewer. If there is a plausible neurobiological mechanism that suggests that such intermediate step can be by-passed, this argument is no longer valid.
For more than 50 years behavioral data have suggested that media violence induces violent behavior in the observers. Meta-data show that the effect size of media violence is much larger than the effect size of calcium intake on bone mass, or of asbestos exposure to cancer. Still, the behavioral data have been criticized. How is that possible? Two main types of data have been invoked. Controlled laboratory experiments and correlational studies assessing types of media consumed and violent behavior. The lab data have been criticized on the account of not having enough ecological validity, whereas the correlational data have been criticized on the account that they have no explanatory power. Here, as a neuroscientist who is studying the human mirror neuron system and its relations to imitation, I want to focus on a recent neuroscience discovery that may explain why the strong imitative tendencies that humans have may lead them to imitative violence when exposed to media violence.
Mirror neurons are cells located in the premotor cortex, the part of the brain relevant to the planning, selection and execution of actions. In the ventral sector of the premotor cortex there are cells that fire in relation to specific goal-related motor acts, such as grasping, holding, tearing, and bringing to the mouth. Surprisingly, a subset of these cells — what we call mirror neurons — also fire when we observe somebody else performing the same action. The behavior of these cells seems to suggest that the observer is looking at her/his own actions reflected by a mirror, while watching somebody else's actions. My group has also shown in several studies that human mirror neuron areas are critical to imitation. There is also evidence that the activation of this neural system is fairly automatic, thus suggesting that it may by-pass conscious mediation. Moreover, mirror neurons also code the intention associated with observed actions, even though there is not a one-to-one mapping between actions and intentions (I can grasp a cup because I want to drink or because I want to put it in the dishwasher). This suggests that this system can indeed code sequences of action (i.e., what happens after I grasp the cup), even though only one action in the sequence has been observed.
Some years ago, when we still were a very small group of neuroscientists studying mirror neurons and we were just starting investigating the role of mirror neurons in intention understanding, we discussed the possibility of super mirror neurons. After all, if you have such a powerful neural system in your brain, you also want to have some control or modulatory neural mechanisms. We have now preliminary evidence suggesting that some prefrontal areas have super mirrors. I think super mirrors come in at least two flavors. One is inhibition of overt mirroring, and the other one — the one that might explain why we imitate violent behavior, which require a fairly complex sequence of motor acts — is mirroring of sequences of motor actions. Super mirror mechanisms may provide a fairly detailed explanation of imitative violence after being exposed to media violence.