For the first study, 20 people were shown a video of a hand being poked with a pin and then asked to imitate photographs of faces displaying a range of emotions. Meanwhile, the researchers scanned participants’ brains with functional magnetic resonance imaging, paying close attention to activity in several areas of the brain. One brain cluster they analyzed — the amygdala, somatosensory cortex and anterior insula — is associated with experiencing pain and emotion and with imitating others. Two other areas are in the prefrontal cortex, which is responsible for regulating behavior and controlling impulses.
In a separate activity, participants played a version of the “dictator game.” They were given $10 per round for 24 rounds to either keep for themselves or to share with a stranger. The recipients’ names were changed, but their actual ages and incomes were used. After each participant had completed the game, researchers compared their payouts with brain scans.
Participants with the most activity in the prefrontal cortex proved to be the stingiest, giving away an average of $1-to-$3 per round. But one-third of the participants who had the strongest responses in the areas of the brain associated with perceiving pain and emotion and imitating others were the most generous. On average, subjects in that group gave away about 75 percent of their bounty. Researchers referred to this tendency as “prosocial resonance,” or mirroring impulse, which they believe to be a driving force behind altruism.
“It’s almost like these areas of the brain behave according to a neural Golden Rule,” says Leonardo Christov-Moore, a postdoctoral fellow in the Semel Institute. “The more we tend to vicariously experience the states of others, the more we appear to be inclined to treat them as we would ourselves.”
In the second study, the researchers explored whether or not the same portions of the prefrontal cortex might be blocking the altruistic mirroring impulse. Fifty-eight participants were subjected to 40 seconds of a noninvasive procedure called theta-burst transcranial magnetic stimulation, which temporarily dampens activity in specific regions of the brain. In the 20 participants assigned to the control group, a portion of the brain that had to do with sight was weakened on the theory it would have no effect on generosity. But in the others, the researchers dampened either the dorsolateral prefrontal cortex or the dorsomedial prefrontal cortex, which combine to block all impulses.
Surprisingly, study participants with disrupted activity in the brain’s impulse-control center were 50 percent more generous than members of the control group. The researchers also found that whom people chose to give their money to changed depending on which part of the prefrontal cortex was dampened.
“Increasing Generosity by Disrupting Prefrontal Cortex,” Social Neuroscience, March 21, 2016
“Self-other Resonance, Its Control and Prosocial Inclinations: Brain-behavior Relationships,” Human Brain Mapping, February 1, 2016