© Don Bartletti/August 29, 2002
What makes us dream? A new study suggests the impulse to dream during sleep may come from signals in the brainstem, not from the brain's higher-order regions.
It's a question that has long fascinated and flummoxed those who study human behavior: From whence comes the impulse to dream? Are dreams generated from the brain's "top" -- the high-flying cortical structures that allow us to reason, perceive, act and remember? Or do they come from the brain's "bottom" -- the unheralded brainstem, which quietly oversees such basic bodily functions as respiration, heart rate, salivation and temperature control?
At stake is what to make of the funny, sexual, scary and just plain bizarre mental scenarios that play themselves out in our heads while we sleep. Are our subconsious fantasies coming up for a breath of air, as Sigmund Freud believed?
Is our brain consolidating lessons learned and pitching out unneeded data, as neuroscientists suggest? Or are dreams no more meaningful than a spontaneous run of erratic heartbeats, a hot flash, or the frisson we feel at the sight of an attractive passer-by?
A study published this week in the journal Brain
suggests that the impulse to dream may be little more than a tickle sent up from the brainstem to the brain's sensory cortex.
The full dream experience -- the complex scenarios, the feelings of fear, delight or longing -- may require the further input of the brain's higher-order cortical areas, the new research suggests. But even people with grievous injury to the brain's prime motivational machinery are capable of dreams, the study found.
The latest research looked for sleep-time "mentation" -- thoughts, essentially -- in a small group of very unusual patients. These patients -- 13 in all -- had suffered damage within their brains' limbic system, the seat of our basic desires and motivations -- for sex, for food, for pleasurable sensations brought on by drugs and friendship and whatever else turns us on.