Mirror neurons are neurons in the brain that fire when another person is observed doing a certain action. The neurons fire in imitation of the action being observed, causing the same muscles to act minutely in the observer as are acting grossly in the person actually performing the action. Research on mirror neurons, since their discovery in 1996,  suggests that they may have a role to play not only in action understanding, but also in emotion sharing empathy . Cognitive neuro-scientist Jean Decety thinks that the ability to recognize and vicariously experience what another individual is undergoing was a key step forward in the evolution of social behavior, and ultimately, morality.  The inability to feel empathy is one of the defining characteristics of psychopathy , and this would appear to lend support to Decety's view.  
For our purposes, perhaps the most important point is that both positions highlight a series of factors important to responsibility and mutual accountability. These factors include: general responsiveness to others (for instance, via moral reasoning or feelings such as sympathy); a sense of responsibility for our actions (for instance, so that we may offer reasons for our actions or feel emotions of shame or guilt); and tendencies to regard others as responsible (for instance, to respect persons as the authors of their deeds and to feel resentful or grateful to them). In each case, note that the first example in brackets has a typically Kantian (reason-based) cast, the second a Humean (feeling/emotion-related) cast.
After I had eaten the small portion which sufficed to fill my stomach halfway, Brother David casually mentioned his belief that it was an offense against God to leave food uneaten on the table. This was particularly the case when such a great restaurant had so clearly been placed in our path as a special grace. David was a slim man and a monk, so I found it hardly credible that he followed this precept generally. But he continued to eat so much that I felt good manners, if not actual spiritual guidance, required me to imitate his example. I filled my belly for the first time in a year.