Neuroscientists in Italy listened in on monkeys’ brains cells that they say may lie at the root of empathy, the ability to discern others’ thoughts and intentions.
Nerve cells located in premotor tissue toward the back of the brain assist in discerning the goals of specific actions, Leonardo Fogassi of the University of Parma and his colleagues propose in the April 29 Science. Some of these neurons discharge strong electrical impulses as a monkey grasps a food pellet with the intention of eating it as well as when the monkey sees a person pick up a food pellet and start to raise it to his mouth. Other premotor cells become especially active as a monkey clutches a food pellet to place it in a container and also when the animal sees a person do the same thing.
These neurons “may be responsible for understanding the intention of action in other people,” Kiyoshi Nakahara and Yasushi Miyashita, both of the University of Tokyo School of Medicine, write in a commentary that accompanies the study.
Scientists recently found that in monkeys, certain premotor neurons get fired up both when the animals perform an action, such as grasping or manipulating an object, and when they watch an experimenter do the same (SN: 5/24/03, p. 330: Repeat After Me). These neurons and another group located elsewhere in the premotor cortex have been dubbed mirror cells.
Fogassi’s group built on the earlier work by examining how certain mirror cells respond to the intention behind the actions. The researchers trained two monkeys to respond to cues either for picking up a food pellet to eat or for picking up an object—sometimes a food pellet, sometimes an inedible item—to place in a container.
Electrodes implanted in the creatures’ brains measured the activity of 165 premotor neurons. Of that number, 77 cells were intensely active as the monkeys grasped pellets before eating them; another 29 displayed activity surges at the start of pluck-and-place operations. No goal-related activity appeared in the remaining 59 neurons. Each monkey had cells of all three types.
The monkeys then watched an experimenter pick up a food pellet and bring it toward his mouth or toward a container. Many of the eating- or placing-oriented neurons fired with an intensity similar to that observed when the monkeys had performed the same action.
Nakahara and Miyashita caution that these findings leave much unanswered about how mirror neurons work. For example, no study yet shows that damage to these brain cells leaves monkeys unable to understand another’s actions and intentions. Whether people have the same kinds of mirror neurons as monkeys do also remains unknown.