Does napping after a meal affect memory formation?

—Yadhu Kumar, Konstanz, Germany

Neuroendocrinologists Manfred Hallschmid and Susanne Diekelmann of the University of Lbeck in Germany reply:

THE PAST two decades have yielded considerable evidence for sleep’s pivotal role in memory consolidation. The lion’s share of research has focused on the relevance of longer periods of nocturnal rest. For that reason, the duration that is actually needed for sleep’s effects on memory to become behaviorally relevant has not yet been exhaustively investigated. We have reason to assume, however, that even short periods of rest can indeed improve memory formation.

There are only a handful of studies investigating the effect of a short nap on the consolidation of declarative memories, which involve facts and events. Most of these studies have reported better memory performance after sleep as compared with wakefulness, revealing improvements of 4 to 46 percent in word-pair memory after a nap and a 3 percent loss to a 28 percent improvement after wakefulness. Even an ultrashort catnap of about six minutes resulted in better memory retention than staying awake did, but a longer doze of 35 minutes was clearly superior. Interestingly, a number of experiments have indicated that sleep improves memory regardless of whether it occurs during the night or the day, which further highlights the cognitive potential of a postprandial nap.

Research on procedural memory, which comprises perceptual and motor skills (such as learning to play an instrument), has found that a short siesta of 60 to 90 minutes improves visual perception only if the nap includes both slow-wave and rapid-eye-movement sleep, the two phases that the brain cycles through while we doze. In studies focusing on motor skills, such as those in which subjects were asked to repetitively type certain keyboard sequences, a posttraining nap of 60 to 90 minutes likewise improved finger-tapping performance. Even so, the study participants did not show as much improvement after the nap as they did after the following full night of sleep.

In sum, these observations suggest that napping may indeed help you remember what you have just learned but that you need longer periods of shut-eye to tap the full potential of sleep.

Why do we find it funny when someone falls down?

—William B. Keith, Houston

William F. Fry, a psychiatrist and laughter researcher at Stanford University, explains:

EVERY HUMAN develops a sense of humor, and everyone’s taste is slightly different. But certain fundamental aspects of humor help explain why a misstep may elicit laughter.

The first requirement is the “play frame,” which puts a real-life event in a nonserious context and allows for an atypical psychological reaction. Play frames explain why most people will not find it comical if someone falls from a 10-story building and dies: in this instance, the falling person’s distress hinders the establishment of the nonserious context. But if a woman casually walking down the street trips and flails hopelessly as she stumbles to the ground, the play frame may be established, and an observer may find the event amusing.

Another crucial characteristic is incongruity, which can be seen in the improbable or inconsistent relation between the “punch line” and the “body” of a joke or experience. Falls are incongruent in the normal course of life in that they are unexpected. So despite our innate empathetic reaction—you poor fellow!—our incongruity instinct may be more powerful. Provided that the fall event establishes a play frame, mirth will likely ensue.

Play frames and incongruity are psychological concepts; only recently has neurobiology caught up with them. In the early 1990s the discovery of mirror neurons led to a new way to understand the incongruity aspect of humor. When we fall down, we thrash about as we reach out to catch ourselves. Neurons in our brain control these movements. But when we observe another person stumbling, some of our own neurons fire as if we were the person doing the flailing—these mirror neurons are duplicating the patterns of activity in the falling person’s brain. My hypothesis regarding the relevance of this mechanism for humor behavior is that the observer’s brain is “tickled” by that neurological “ghost.” The observer experiences an unconscious stimulation from that ghost, reinforcing the incongruity perception.

Note: This story was originally published with the title, "Ask the Brains".