Brain scans taken while Patient X guessed the feelings revealed an alternative to the usual pathways for seeing that flow from the eyes to the thalamus, where all the senses first enter the brain, and then to the visual cortex. The second route sends information straight from the thalamus to the amygdala (the brain has a pair, right and left). The amygdala then extracts emotional meaning from the nonverbal message, whether it be a scowl, a sudden change of posture, or a shift in tone of voice–even microseconds before we yet know what we are looking at.
Though the amygdala has an exquisite sensitivity for such messages, its wiring provides no direct access to the centers for speech; in this sense the amygdala is, literally, speechless. When we register a feeling, signals from our brain circuits, instead of alerting the verbal areas, where words can express what we know, mimic that emotion in our own bodies. So Patient X was not seeing the emotions on the faces so much as feeling them, a condition called "affective blindsight."
In intact brains, the amygdala uses this same pathway to read the emotional aspect of whatever we perceive–elation in someone's tone of voice, a hint of anger around the eyes, a posture of glum defeat–and then processes that information subliminally, beneath the reach of conscious awareness. This reflexive, unconscious awareness signals that emotion by priming the same feeling (or a reaction to it, such as fear on seeing anger) in us–a key mechanism for "catching" a feeling from someone else.
The fact that we can trigger any emotion at all in someone else–or they in us–testifies to the powerful mechanism by which one person's feelings spread to another. Such contagions are the central transaction in the emotional economy, the give-and-take of feeling that accompanies every human encounter we have, no matter what the ostensible business at hand may be.
Take, for example, the cashier at a local supermarket whose upbeat patter infects each of his customers in turn. He's always getting people to laugh–even the most doleful folks leave smiling. People like that cashier act as the emotional equivalent of zeitgebers, those forces in nature that entrain our biological rhythms to their own pace.
Such a contagion can occur with many people at one time, as visibly as when an audience mists up at a tragic movie scene, or as subtly as the tone of a meeting turning a bit testy. Though we may perceive the visible consequences of this contagion, we are largely oblivious to exactly how emotions spread.
Emotional contagion exemplifies what can be called the brain's "low road" at work. The low road is circuitry that operates beneath our awareness, automatically and effortlessly, with immense speed. Most of what we do seems to be piloted by massive neural networks operating via the low road–particularly in our emotional life. When we are captivated by an attractive face, or sense the sarcasm in a remark, we have the low road to thank.
The "high road," in contrast, runs through neural systems that work more methodically and step by step, with deliberate effort. We are aware of the high road, and it gives us at least some control over our inner life, which the low road denies us. As we ponder ways to approach that attractive person, or search for an artful riposte to sarcasm, we take the high road.