My youngest son, Alex, who is also a neurointensivist like me, recently lost one of the treasures of his life, his dog Milo (whose middle name was Rafa, after Rafael Nadal). As Milo’s health was fading over his last months, Alex and his wife Reem rescued a puppy. I’m sure it was only partly intentional, but the resemblance of the new puppy to Milo was striking.
Which brings up a fascinating phenomenon in the brain: that of “mirror neurons.” Mirror neurons fire not only when we perform a motor act, but also when we merely observe someone else performing that action. They also fire when we experience an emotion such as love or disgust, and when we observe someone else expressing the same emotion.
The first published description of mirror neurons was in 1992 when a class of cells in the monkey brain discharged both when the animal performed a goal-directed action (grabbing a food morsel) and when the animal observed an experimenter, or another monkey, performing the same action (di Pellegrino et al., 1992).
Mirror Neurons and the Science of Empathy
Just as it’s hard not to yawn when we see another person yawn, our mirror neurons are irresistibly connected to their mates… even in another person’s brain.
Mirror neurons are also felt to explain empathy—the human capacity to understand another’s emotional state, to put yourself in their visceral shoes…to mirror their happiness or pain.
A poignant example of the complexity of human empathy came to me recently as I read of Dolly Parton’s death. In her song “Jolene,” instead of expressing vengefulness alongside her honest jealousy of the beautiful bank teller who had flirted with her husband, Dolly Parton made the song a vulnerable admission of her own insecurity. No matter our self-confidence, our own beauty, intellect or success, we all are still vulnerable to being uncertain.
Just like bodily movement, emotional states are observable by our brain, and when viewed by another, are associated in the viewer with subjective arousal and specific feelings. This arousal can support and augment the observed emotional state, or, on the flip side, can counter it. For example, when confronting a child who is agitated or angry, parents respond by decreasing their own arousal, in effect, defusing the highly charged affective state, and calming the child.
The ability to register and reproduce facial expressions begins in infancy, as any parent of a newborn can attest: their child readily smiles in response to a close grinning face in front of them.
Social Behavior and Mirror Neurons Before Birth
Remarkably, this ability to interact with another human begins even before birth, in the fetus. A twin pregnancy study investigated the kinematic profiles of movements in five pairs of twin fetuses, finding that by the 14th week of gestation these fetuses displayed movements specifically aimed at the co-twin, and that these directed movements reached 29% of all observed movements at 18 weeks. [Reference below]
It’s fascinating that humans even before birth show social behavior with actions directed at their co-twin that exceed in number both self-directed and random movements. At this markedly early stage of human development, we get an inkling of the near-telepathic intuition that twins, and close siblings, have, of each other’s emotions. They will share this intuition—which may begin in the womb—through childhood and beyond.
Neuroscientists aren’t sure about the ontogenetic origin of mirror neurons—that is, whether these nerve cells are innate or have been developed by learning experiences. These prenatal twin studies seem to suggest their being innate, but we don’t know for sure.
Mirror Neurons in Animals Beyond Humans
Monkeys and humans are not the only hosts of these intriguing mirror neurons. Songbirds’ brains contain an anatomic area homologous to primate cortico-striatal cells that provide song learning by imitation, likely an evolutionary benefit.
I truly believe our own pets also have this capacity for imitative rapport and empathy. If you’ve ever spent an afternoon with TikTok’s “Guilty Dog” collection, you know what I mean.
Mirror Neurons Essential Reads
I pulled my hamstring awkwardly while waterskiing this summer, and my dog Chief didn’t leave my bedside for two days before I could limp around. I think Chief’s own mirror neurons were firing; intertwined with my own. So remarkable!
