MARCO IACOBONI, a neuroscientist, is the director of the Transcranial Magnetic Stimulation Laboratory at the David Geffen School of Medicine at UCLA.
Media violence induces imitative violence. If true, this idea is dangerous for at least two reasons: first, because its implications relate to the issue of freedom of speech; second, because it suggests that our rational autonomy is much more limited than we like to think.
The idea is especially dangerous now, because we have discovered a plausible neural mechanism that can explain why observing violence induces imitation. 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 (“speech” in the broad sense, including movies and video games) has typically been that the effects of speech are always subject to the mental intermediation of the listener/viewer. If there is a plausible neurobiological mechanism that suggests that such an intermediate step can be bypassed, this argument is no longer valid.
For more than fifty 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 subsequent violent behavior. The lab data have been criticized as not having enough ecological validity; the correlational data have been criticized as having no explanatory power. As a neuroscientist studying the human mirror neuron system and its relations to imitation, I want to focus on a recent neuroscientific 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, 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 his or her own actions reflected in a mirror while watching somebody else’s actions. My group has shown, in several studies, that human mirror neuron areas are also critical to imitation. There is evidence that the activation of this neural system is fairly automatic, thus suggesting that it may bypass conscious mediation. Moreover, mirror neurons also code the intention associated with the 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 the system can indeed code sequences of action (that is, 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 just starting to investigate 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 now have 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—the one that might explain why we imitate violent behavior, which requires a fairly complex sequence of motor acts—is mirroring of sequences of motor actions. Super-mirror mechanisms may provide a fairly detailed explanation for imitative violence that arises after exposure to media violence.