Socially artful responses emerge largely in the neural chatter between the orbitofrontal cortex and emotional centers like the amygdala that generate impulsivity. But the cortex needs social information — a change in tone of voice, say — to know how to select and channel our impulses. And in e-mail there are no channels for voice, facial expression or other cues from the person who will receive what we say.

True, there are those cute, if somewhat lame, emoticons that cleverly arrange punctuation marks to signify an emotion. The e-mail equivalent of a mood ring, they surely lack the neural impact of an actual smile or frown. Without the raised eyebrow that signals irony, say, or the tone of voice that signals delight, the orbitofrontal cortex has little to go on. Lacking real-time cues, we can easily misread the printed words in an e-mail message, taking them the wrong way.

And if we are typing while agitated, the absence of information on how the other person is responding makes the prefrontal circuitry for discretion more likely to fail. Our emotional impulses disinhibited, we type some infelicitous message and hit “send” before a more sober second thought leads us to hit “discard.” We flame.

Flaming can be induced in some people with alarming ease. Consider an experiment, reported in 2002 in The Journal of Language and Social Psychology, in which pairs of college students — strangers — were put in separate booths to get to know each other better by exchanging messages in a simulated online chat room.

While coming and going into the lab, the students were well behaved. But the experimenter was stunned to see the messages many of the students sent. About 20 percent of the e-mail conversations immediately became outrageously lewd or simply rude.

And now, the online equivalent of road rage has joined the list of Internet dangers. Last October, in what The Times of London described as “Britain’s first ‘Web rage’ attack,” a 47-year-old Londoner was convicted of assault on a man with whom he had traded insults in a chat room. He and a friend tracked down the man and attacked him with a pickax handle and a knife.