When the phenomenon of "mirror neurons" that fire both when a specific action is perceived and when it is intended was first reported, I was impressed by the research but skeptical about its significance. Specifically, I doubted, and continue to doubt, that these circuits are specific adaptations for purposes of various higher mental functions. I saw mirror neurons as simple units in circuits that represent specific actions, oblivious as to whether they had been viewed when performed by someone else, or represented as the goal of one's own intended action (so-called reafference copy). Why have two separate representations of the same thing when one will do? Activity elsewhere in the brain represents who the agent is, self or another. I still think that this is the most economical interpretation. But from a broader perspective I have come to realize that mirror neurons are not only less than meets the eye but also more. Instead of being a specific specialization, they play their role as part of a fundamental design characteristic of the brain; that is, when percepts are activated, relevant intentions, memories and feelings automatically fall into place.
External event are "represented" by the patterns of neuronal activity that they engender in sensory cortex. These representations also incorporate the actions that the percepts potentially afford. This "enactive coding" or "common coding" of input implies a propensity in the observer's brain to imitate the actions of others (consciously or unconsciously). This propensity need not result in overt imitation. Prefrontal cortex is thought to hold these impulses to imitate in check. Nonetheless, the fact that these action circuits have been activated, lowers their threshold by subtle increments as the experience in question is repeated over and over again, and the relative loading of synaptic weights in brain circuitry become correspondingly adjusted. Mirror neurons exemplify this type of functioning, which extends far beyond individual circuits to all cell assemblies that can form representations,
That an individual is likely to act in the same ways that others act is seen in the documented benefit for sports training of watching experts perform. "Emotional contagion" occurs when someone witnesses the emotional expressions of another person and therefore experiences that mood state oneself. People's viewpoints can subtly and unconsciously converge when their patterns of neural activation match, in the total absence of argument or attempts at persuasion. When people entrain with each other in gatherings, crowds, assemblies and mobs, diverse individual views reduce into a unified group viewpoint. An extreme example of gradual convergence might be the "Stockholm Syndrome"; captives gradually adopt the worldview of their captors. In general, interacting with others makes one converge to their point of view (and vice versa). Much ink has been spilled on the topic of the lamentable limitations of human rationality. Here is one reason why.
People's views are surreptitiously shaped by their experiences, and rationality comes limping after, downgraded to rationalization. Once opinions are established, they engender corresponding anticipations. People actively seek those experiences that corroborate their own self-serving expectations. This may be why as we grow older, we become ever more like ourselves. Insights become consolidated and biases reinforced when one only pays attention to confirming evidence. Diverse mutually contradictory "firm convictions" are the result. Science does take account of the negative instance as well as the positive instance. It therefore has the potential to help us understand ourselves, and each other.
If I am correct in my changed views as to what mirror neurons stand for and how representation routinely merges perception, action, memory and affect into dynamic reciprocal interaction, these views would have a bearing on currently disputed issues. Whether an effect is due to the brain or the environment would be moot if environmental causes indeed become brain causes, as the impressionable brain resonates with changing circumstances. What we experience contributes mightily to what we are and what we become. An act of kindness has consequences for the beneficiary far beyond the immediate benefit. Acts of violence inculcate violence and contaminate the minds of those who stand by and watch. Not only our private experiences, but also the experiences that are imposed on us by the media, transform our predispositions, whether we want them to or not. The implications for child rearing are obvious, but the same implications apply beyond childhood to the end of personal time.
What people experience indeed changes their brain, for better and for worse. In turn, the changed brain changes what is experienced. Regardless of its apparent stability over time, the brain is in constant flux, and constantly remodels. Heraclitus was right: "You shall not go down twice to the same river". The river will not be the same, but for that matter, neither will you. We are never the same person twice. The past is etched into the neural network, biasing what the brain is and does in the present. William Faulkner recognized this: "The past is never dead. In fact, it's not even past".