Neuroscientists are beginning to understand what is happening in our brains while we slumber. What they discover could profoundly change how we view sleep and dreaming.
By Francois Badenhorst
In Hans Christian Andersen’s famous fairy tale, Ole-Luk-Oie – or, the Sandman as we Anglophones would call him – appears to a boy named Hjalmar. “Now pay attention,” says Ole-Luk-Oie to Hjalmar, “and I will decorate the room.” Ole-Luk-Oie transforms the child’s room into a greenhouse, pot plants become trees with their branches covered in flowers.
Sleep, and dreams for that matter, has always been excellent fodder for storytelling: Everyone – knight or knave, pope or peasant – needs it. It is a universally relatable phenomenon. But Stories like Ole-Luk-Oie also exhibit that we have always had a very limited understanding of an act we spend one-third of our life engaging in.
What is sleep? Or, more specifically, what exactly is going on when we sleep? That’s actually a tricky question. What Scientists are absolutely sure of is that we need it and if we don’t get it, we experience a variety of consequences.
“Sleep deprivation does have visible, physical consequences,” says Dr Henk Badenhorst, a Cape Town based neurologist, “but the main symptom is we see that people enter an almost psychotic condition: They hallucinate and become confused and, extreme cases, can die.”
But before you can even attempt to unravel the mystery of sleep, it’s pertinent to distinguish between the two stages of sleep we experience. There are two varieties: Slow Wave Sleep (SWS) and Rapid Eye Movement (REM) sleep. And they are rather different.
“There are a ton of differences: Firstly, there is a general decrease in overall brain utilization of oxygen and glucose during SWS,” says Dr Robert Stickgold, director of Harvard University’s Centre for Sleep and Cognition. “In REM some regions associated with emotional processing ramp back up, while others involved in logical reasoning and executive function become even less active.”
Electroencephalography (EEG) patterns, which measures brain activity, look fairly normal during REM. But during Slow Wave Sleep they show a dramatic slowing, showing a more meandering wave pattern – hence, “slow wave” sleep, or, “deep sleep” as it is popularly known.
But it is how the brain seems to interact with information during the different stages which is the most interesting. “Information appears to flow from the cortex into the hippocampus, the seat of episodic memory, during REM, and in the opposite direction during SWS.”
Episodic memory is the memory of autobiographical events – times, places, and the associated emotions. This opposite flow of information point to the critical role sleep plays in memory formation and storage. We can begin to understand why a lack of sleep causes such confusion.
“It seems to us that conscious experience of the here and now has to be interrupted for the brain to gain the chance to integrate new and old memories; sleep provides that respite,” wrote Dr Giulio Tononi, a psychiatrist at the University of Wisconsin, in a recent article for Scientific American.
“The brain works with electricity but at the points where brain cells communicate with each other, at the connection points,” says Badenhorst. “The electrical impulse gets put over into chemical impulse by a synapse.”
It is around these synapses – our brain’s telegraph poles that permit our brain cells, or neurons, to communicate with one another – where an exciting debate is taking place.
“It is thought that dreams, and sleep more generally, act through synaptic strengthening, improving the connections between nerve cells,” says Stickgold. Neuroscientists are able to detect the molecular processes that facilitate synaptic strengthening.
But the issue with arguing for just synaptic strengthening comes down to a problem of energy. The brain is not a perpetual motion machine; it uses external energy – lots of energy. The brain consumes almost 20 percent of our energy budget. The problem with the theory of synaptic strengthening is that stronger synapses consume more energy. But if the body has only finite energy stores, and synapses are strengthened ad infinitum, how are we achieving this?
“There is likely to be both strengthening and weakening of synapses during different sleep phases,” says Professor Terry Sejnowski, head of neurobiology at the Salk Institute for Biological Studies. “But there are no direct measurements yet to confirm this,” he adds carefully.
It seems clear, however, that this strain on resources is unsustainable. As Tononi writes, “The brain cannot go on strengthening and maintaining revved-up synapses both day and night for the whole of an individual’s lifetime.” This implies that during sleep, synapses are strengthened and weakened.
And how this occurs seems to be encoded into our dreams.
Sigmund Freud had very particular ideas about dreams. For Freud, dreams were wish fulfilment. More importantly, things in the dream had a totemic significance: An elongated object would be symbolic of the penis, or a box was the womb.
Dreams altered memories – that is, the penis became an elongated object – to cater for decreased ability of the pre-conscious, our neural policeman, to supress them during sleep. “There’s no evidence that dreams develop to keep memories from coming into our awareness during sleep, disguising and censoring their most ‘objectionable’ content,” says Stickgold.
“David Lynch was in a war with Hitler, and he handed over the plan to enter the city with tanks to me – and I was thinking should I hand it over or should I keep it because it was a painting by David Lynch.” Rickie Klingler is lying on her bed as she relates her dream. Her starkly blue eyes stare at the ceiling as she tries to tease the details from her mind.
“In the end, I did not hand it over and I went driving with you,” she suddenly looks at me, “and we we’re driving in my hometown and we wanted to go to the harbour and at a fork in the road but you just drove straight and we crashed. And then I was floating in space looking down on Earth.”
While Rickie’s dream sounds like a Freudian wonderland of neuroses. The Freudian notion of dreams communicate a hidden meaning disguised in symbolic language has become entrenched in popular psychology, and as Stickgold says, “there is scant empirical evidence to support this view.”
Freudian dream theory’s coup de grâce came in 1977, when Harvard University psychiatrists John Allan Hobson and Robert McCarley presented the activation-synthesis hypothesis.
“The key tenet of Hobson’s distinctly anti-Freudian theory was that dreams originate from neural signals in the brainstem generated during REM sleep,” wrote Stickgold in an article entitled Dreaming and offline memory processing. “Dreaming is experienced when the sleeping brain attempts to make some sense of this chaotic input into its higher-level cortical circuitry.”
Neuroscience has come along leaps and bounds since 1977, specifically in regards to memory. “There is now substantial empirical evidence to suggest that, during sleep, the neural level ‘replay’ of recent experience plays a critical role in the consolidation and evolution of memory,” writes Stickgold, “helping us to process our past experiences and prepare for future events.” Basically, our brain processes our short term memories during slumber and tries to discern which need to be transferred to long term memory to form schemas for future use.
In light of this, Ricky’s dream suddenly doesn’t seem so bizarre (or, at least, less bizarre). Her dream contains David Lynch, a filmmaker she has met and admires; her hometown of Karlsruhe, Germany; and me, a person she has gotten to know recently.
“Dreams seem to take elements of recent memories and blend them with a large collection of older, weakly associated memories,” says Stickgold. “I presume that this serves to both strengthen the individual memories and to also establish, or strengthen, the associations among them.”
And tests seem to show the value dreams, and not only sleep, have for the consolidation of memory. A test at the Centre for Sleep and Cognition at Harvard University let students navigate a 3-D virtual maze in the morning. Some subjects were permitted a 90 minute nap – the length of one full sleep cycle.
Sleeping subjects were awoken twice during their naps to collect dream reports. Critically, the napping subjects that dreamt exhibited a sudden uptick in performance of one minute when they completed the task in the late afternoon.
“Just 33 years or so after Hobson and McCarley’s speculation, firm scientific evidence confirms that, for at least this one memory task, sleep enhances subjects’ memories of what they recently learned,” says Stickgold, “but only if they dream about it.”
The science does not demean the psychological or emotional value of sleep. Critically, dreaming does not only process and strengthen memories but, as Stickgold says, “also aid in extracting their meaning”.
Their essentiality in forming new memories actually makes them more meaningful. Your dreams aren’t just Freudian totems, the embodiments of some hidden guilty pleasure. Instead, they are your brains attempt to understand our vast existence.
Meaningful experiences create dreams and dreams create meaning.