Sleep and dreaming: Where do our minds go at night?
Baku, February 7 (AZERTAC). Mary Shelley's involved a pale student kneeling beside a corpse that was jerking back to life. Paul McCartney's contained the melody of Yesterday, while James Cameron's feverish visions inspired the Terminator films. My dreams often feature a shrinking rabbit, which then turns into an insect that leaps across the lawn and under the neighbour's fence.
With their eerie mixture of the familiar and the bizarre, it is easy to look for meaning in these nightly wanderings. Why do our brains take these journeys and why do they contain such outlandish twists and turns? Unfortunately for armchair psychoanalysts, Sigmund Freud's attempts to interpret our dreams remain hotly disputed. Nevertheless, neuroscientists and psychologists have recently made big strides in understanding the way the brain builds our dreams, and the factors that shape their curious stories. Along the way, they have found startling hints that our use of technology may be permanently changing the very nature of this fundamental human experience.
Anyone who has ever awoken feeling amazed by their night's dream only to forget its contents by the time they reach the shower will understand the difficulties of studying such an ephemeral state of mind. Some of the best attempts to catalogue dream features either asked participants to jot them down as soon as they woke up every morning or, better still, invited volunteers to sleep in a lab, where they were awoken and immediately questioned at intervals in the night. Such experiments have shown that our dreams tend to be silent movies - with just half containing traces of sounds. It is even more unusual to enjoy a meal or feel damp grass beneath your feet - taste, smell and touch appearing only very rarely.
Similar studies have tried to pin down some of the factors that might influence what we dream about, though they have struggled to find anything reliable. You might expect your dreams to reveal something about your personality, but traits such as extroversion or creativity do not seem to predict features of someone's journeys through the land of nod. Shelley and McCartney's dreams aren't that unlike ours.
"People's dreams seem to be more similar than different," says Mark Blagrove at Swansea University in the UK. That suggests common symbols in dreams might represent shared anxieties and desires, but attempts to find these have also been disappointing - something like a surreal shrinking rabbit, for instance, probably reveals nothing "that you didn't already know", says Blagrove, gnomically.
A more fruitful approach has been to look at the brain's activity during sleep for clues to the making of our dreams. Of particular interest is the idea that sleep helps to cement our memories for future recall (see "What is the point of sleep?"). After first recording an event in the hippocampus - which can be thought of as the human memory's printing press - the brain then transfers its contents to the cortex, where it files the recollection for long-term storage.
This has led some psychologists, including Blagrove, to suspect that certain elements of the memory may surface in our dreams as the different pieces of information are passed across the brain. Studying participants' diaries of real-life events and comparing them with their dream records, his team has found that memories enter our dreams in two separate stages. They first float into our consciousness on the night after the event itself, which might reflect the initial recording of the memory, and then they reappear between five and seven days later, which may be a sign of consolidation.
Even so, it is quite rare for a single event to appear in a dream in its entirety - instead, our memories emerge piecemeal. "What usually happens is that small fragments are recombined into the ongoing story of the dream," says Patrick McNamara at Northcentral University in Prescott Valley, Arizona. And the order in which the different elements appear might reflect the way a memory is broken down and then repackaged during consolidation.
One of McNamara's studies, which compared one individual's dream and real-life diaries over a two-month period, found that a sense of place - a recognisable room, for instance - was the first fragment of a memory to burst onto the subject's dreamscape, followed by characters, actions and finally physical objects.
While it may cement a memory into our synapses during consolidation, the sleeping brain also forges links to other parts of your mental autobiography, allowing you to see associations between different events. This might dredge up old memories and plant them in our dreams, which in turn might explain why we often dream of people and places that we haven't seen or visited for months or even years. It could also lie behind those bizarre cases of mistaken identity while dreaming, when objects or people can appear to be one thing, but assume another shape or character - such as the shape-shifting rabbit that haunts my dreams. "It's a by-product of the way the brain blends different elements," says McNamara.
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