From an enlightening piece in the New York Times:

Brain scans are revealing what happens in our heads when we read a detailed description, an evocative metaphor or an emotional exchange between characters. Stories, this research is showing, stimulate the brain and even change how we act in life.

Researchers have long known that the “classical” language regions, like Broca’s area and Wernicke’s area, are involved in how the brain interprets written words. What scientists have come to realize in the last few years is that narratives activate many other parts of our brains as well, suggesting why the experience of reading can feel so alive. Words like “lavender,” “cinnamon” and “soap,” for example, elicit a response not only from the language-processing areas of our brains, but also those devoted to dealing with smells.

Stanislavsky famously defined acting as “the life of the human soul receiving its birth through technique.” More basically, acting is bringing a kind of life into a being, it is coming alive. The above excerpt from the Times article is highly suggestive of the profound importance for acting. The actor wants to come fully alive, and reading provides a way of coming alive not only to actualities, but to fictional things as well, to a land of make-believe. We tend to think of acting as a physical activity, as something that we “do”: speak, move, gesture, grimace, etc. But all of those things are of interest largely because they illuminate inner movements: movements of thought and feeling.

In some sense, the actor works to allow these mental activities to manifest themselves physically, in movement, in speech, in expressiveness. However, if there are no mental activities to manifest, nothing much is going to happen in the physiognomy of the actor. Receptiveness and sensitivity to the power of words (scripts are written in words, after all) is an absolutely critical skill for any actor, and there is no better way to develop this receptiveness and sensitivity than reading.

We are prone to think of acting as a fundamentally extroverted activity: actors express things, we are told. And there is truth to this: acting is nothing if not manifesting some inner life. But much depends on the richness of that inner life, and that points to the “introverted” side of acting. Actors must possess a kind of practical psychological insight, in order to get at what “makes someone tick”, they must possess richly the sensitivity to language that I previously described, and they must be comfortable in trafficing with the unreal, with the imaginary. In that it depends on both extroversion and introversion, acting is a very special, if not totally unique practice.