Mirror neurons are specialized brain cells that become active both when an individual performs a particular action and when they observe someone else performing that same action. These neurons essentially “mirror” the behavior of another. The story of how these remarkable neurons were first identified is a tale of scientific inquiry and accidental observation.
The Research Environment
The discovery of mirror neurons began in the early 1990s at the University of Parma in Italy. Neurophysiologist Giacomo Rizzolatti led a team of researchers, including Giuseppe Di Pellegrino, Luciano Fadiga, Leonardo Fogassi, and Vittorio Gallese. Their primary research focused on motor control and planning, specifically studying hand and mouth actions in macaque monkeys. The team aimed to understand how the brain’s ventral premotor cortex, particularly an area known as F5, controlled these movements.
The experimental setup involved implanting tiny electrodes into the F5 area of the monkeys’ brains to record the activity of individual neurons. Researchers observed the monkeys performing various tasks, such as grasping objects. The objective was to map which neurons fired during specific motor actions. The team sought neurons active when the monkeys themselves performed an action.
The Unexpected Discovery
During these experiments, an unexpected moment occurred that shifted the team’s understanding. While a monkey was hooked up to neural recording equipment, a human researcher entered the laboratory. The monkey was observing. As the researcher reached for and grasped an object, the monitoring equipment registered a burst of activity in the monkey’s brain.
The neurons that fired were precisely the same ones that would have been active if the monkey itself had performed the grasping action. This observation was unexpected and perplexing, as the prevailing scientific view at the time held that distinct neural pathways governed action and perception. The Parma investigators were unprepared for a motor neuron to also exhibit properties of a perception neuron. This accidental observation, where the monkey’s brain mirrored the human’s action without physical movement, opened a new avenue of neurological inquiry.
Identifying and Naming Mirror Neurons
Following this initial unexpected observation, Rizzolatti’s team embarked on systematic testing to confirm and characterize these novel neurons. They conducted further experiments, observing the monkeys while researchers performed various actions like grasping a peanut or bringing it to the mouth. Consistently, the same neurons that fired when the monkey executed these actions also became active when the monkey observed the researcher performing them.
This careful verification process demonstrated that these were distinct from purely sensory neurons, which respond only to visual input, or purely motor neurons, which fire only during self-initiated movement. The unique property of these neurons, firing for both action execution and observation, led the researchers to coin the term “mirror neurons.” The team’s initial findings were published in 1992 in the journal Experimental Brain Research.