An Accidental Discovery
In the late 1980s and early 1990s, a team of neurophysiologists at the University of Parma was studying the motor cortex of macaque monkeys. The group, led by Giacomo Rizzolatti, included researchers Leonardo Fogassi, Vittorio Gallese, and Giuseppe di Pellegrino. Their goal was to understand how the brain's motor command neurons controlled specific actions, like grasping or bringing food to the mouth. To do this, they implanted microelectrodes into a region of the monkeys' ventral premotor cortex known as area F5 to record the activity of single neurons.
The discovery was entirely serendipitous. The story goes that one day a researcher reached for a piece of fruit, and the equipment monitoring a monkey's brain activity registered a response. A neuron in the monkey's motor cortex fired, but the monkey hadn't moved at all. It was the same neuron that fired when the monkey itself performed the action of grasping. The team had stumbled upon a cell that activated both when the monkey acted and when it simply observed the same action performed by another. This unexpected finding was initially met with skepticism; the team's first paper was famously rejected by the journal Nature for a "lack of general interest" before being published in Experimental Brain Research in 1992.