Why do we dream?
—Christina Zuniga, via e-mail
Psychologists Gerhard Kloesch of the Medical University of Vienna and John P. Dittami of the University of Vienna explain:
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PUT SIMPLY, dreams are the by-products of neurological processes associated with sleep. But is that the end of the story, or does dreaming serve a purpose? Scientists have not yet discovered whether dreaming has a vital biological function, but we have many theories about where dreams originate in the brain and how we can use them in daily life.
Dreams are tightly linked to phases of sleep that have defined roles in neural maintenance and restructuring, physiological regulation of functions such as metabolism, and information processing associated with cognition. Shorter dreams also occur in the daytime. Most dreaming at night occurs during rapid eye movement (REM) sleep, which is governed by the pons—a region in the brain stem responsible for relaying messages in the brain. Excessive activity in the pons generates random images and information based on memory stores. In addition, some research indicates that newly learned information is consolidated into our memory during REM sleep, which could explain why we often dream about our recent experiences. A related theory maintains that the function of dreams is to clear the brain of its excess baggage—for example, by deleting unnecessary memories. And some experts believe that dreams are a primitive form of thinking and representation associated with subconscious or even psychotic thought.
Dreams linger as our brains make the transition from one state to another (unconscious to conscious). They maintain emotional salience and hence can be used as a positive or negative reinforcement. People can train themselves to recall dreams more frequently and to use them as a conditioning process to become, for instance, braver or more creative.
Dreams are an expression of our physiological, cognitive and emotional underpinnings—with effects that are dependent on each unique situation and individual.
I heard that the chimpanzee brain is evolving more quickly than the human brain. If humans are evolving at a slow rate, are we in trouble?
—Carlos Navarro, via e-mail
Genetics researcher Michael Oldham of the University of California, Los Angeles, responds:
EVEN THOUGH our understanding of humankind’s closest living relative has increased considerably in recent years, evolution remains a tricky subject to study in the lab. As a result, the premise of your question—though interesting and certainly possible—has not been established.
The human brain is about three times larger than that of the chimpanzee. This size difference is primarily the result of the massive expansion of the human cerebral cortex that has occurred over the past 2.5 million years. In this time frame, the human brain has certainly experienced more obvious changes than the chimp’s has (suggesting that our brains are evolving faster).
Recently, however, completion of the human and chimpanzee genome sequences has ushered in a new wave of comparisons between the species based on DNA sequence and patterns of gene expression—how and when a gene’s coded instructions are carried out. Genes are expressed in different tissues at different times, so scientists have begun coupling comparisons of human and chimp DNA sequences with comparisons of gene expression in each species’ brain. Some researchers have found evidence that mutations in human genes are accumulating faster than in chimp genes, but one recent study found just the opposite (likely forming the basis for your question).
Such findings are provocative and exciting, but it is important to note that there are different ways of estimating evolutionary rates based on these molecular changes. Only when they all start pointing to the same conclusion can we feel confident in our inferences about the evolution of the brain.
With all these caveats in mind, let me answer the question posed. Are we in trouble? Although we cannot completely discount the possibility that chimpanzee overlords may one day wreak terrible vengeance on us for our crimes, another scenario is far more likely: it is the chimps who will disappear—and soon. Wild populations of chimps are predicted to vanish from Africa within the next 50 years as a result of human activities. So, no, we are not in trouble. It is the chimps that are in trouble.
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