How is empathy manifested physiologically?
In the 90s, scientists conducting an experiment involving primates noticed an interesting phenomenon, later defined as a result of mirror neuron activity.
Quick description: Monkey is wired to a device. Scientists are observing the firing of certain neurons in its brain while the monkey grabs a banana. At lunchtime, a hungry scientist grabs a banana in sight of the monkey. The device shows that same neurons that fired when the monkey was reaching for the banana fire when the monkey observes the experimenter reaching for the banana.