WEDNESDAY, 16 JULY 2014
Short nights and hitting the snooze button for an additional ten minutes of sleep are all too familiar in today’s society. Be it the threat of a looming deadline or last minute cramming for exams, skimping on sleep is too frequent for most of us. And it is not just students. In today’s ‘24/7’ society sleeping less to meet the pressures of work-life seems to have become the rule. The market is filled with countless remedies for lost sleep: coffee, super-foods and vitamin pills are all touted as energisers to help combat fatigue. Recent years have even seen an increasing number of people turning to ‘smart drugs’ like Ritalin and modafinil to stay alert and increase productivity.
Our society’s trend to devalue sleep is worrying, particularly as reams of evidence suggests that sleep deprivation reduces wellbeing. Indeed, chronic sleep deprivation has been linked with the onset of conditions such as obesity and diabetes, as well as several psychiatric disorders. Neurological disorders like Alzheimer’s disease are also frequently associated with sleep disturbances. It is thus concerning that in modern societies very few adults are getting the recommended 7-8 hours of sleep per night. According to a 2013 International Bedroom Poll the average time slept on work nights is approximately 6.5 hours in the US and 6.8 hours in the UK.
It has recently been established that sleep is crucial for a number of physiological processes, such as the regulation of the immune system and metabolism. In particular, sleep is vital for memory consolidation, the process by which memories become more stable. For instance, declarative verbal memories-‘homework’ type facts that are important for exam revision-are better consolidated with enough sleep. Although staying up all night to cram in that extra bit of information might seem like the obvious choice, hard-pressed students revising for exams are probably better off getting a good night’s sleep.
Staying up for extended hours can make the brain swing between emotional extremes. Aside from making us feel moody, a less-known side effect of pulling an all-nighter is actually increased euphoria. After finding that sleep deprivation has antidepressant effects in patients with major depressive disorder, researchers at UC Berkeley and Harvard Medical School decided to further investigate the effects of sleep on emotional regulation. Using functional magnetic resonance imaging the researchers scanned the brains of sleep-deprived and well-rested participants, whilst showing them positive and neutral images. The sleep deprived group rated more images as emotionally pleasant and showed increased activity in reward regions of the brain. Other studies also showed that acute sleep loss is associated with increases in dopamine, a brain chemical that regulates reward, motivation and decision-making, amongst other things.
Exaggerated responses to positive stimuli associated with sleep loss could lead to deficits in judgment and more impulsive decision-making. This can have strong implications for people making high-stakes decisions, such as doctors and air traffic controllers, who need to perform at their best at all times. Recent studies have suggested that smart drugs like modafinil could be used to reverse the effects of fatigue in sleep-deprived doctors. However, getting enough sleep might actually be the better option for those making important decisions about our health and safety.
This is not to say that cognition-enhancer drugs are not useful. Not only do drugs like modafinil and Ritalin help people with sleep disorders, they are also crucial in cases of obligatory sleep restriction as happens to soldiers in combat or shift-workers. Studies on rats have demonstrated that caffeine, which is consumed on a daily basis worldwide, can help counteract the effects of sleep deprivation. As well as improving alertness and concentration, a cup of coffee can even enhance memory consolidation. This is useful when we are not performing optimally, either because of sleep deprivation, jet lag or other stressors. It is when we turn to these drugs as a crutch to cope with less sleep that it becomes a problem.
But it’s not just mood and cognition that are affected; not sleeping enough could actually be damaging your brain. A study conducted by researchers at Uppsala University found that a single night of sleep loss increases morning blood levels of neuron-specific enolase and S-100 calcium binding protein B, molecules which mark neuronal damage and typically rise in the blood after brain damage. Earlier this year, researchers showed for the first time that sleep loss leads to a loss of neurons. Mice kept awake for extended periods of time lost neurons in the locus coerulus, a region of the brain associated with alertness and cognitive function.
Yet, despite the fact that we devote roughly a third of our lives to sleep, researchers have long struggled to understand why sleep is restorative and a lack of sleep impairs brain function. Not obtaining enough sleep makes it harder to pay attention and learn new information, and also affects reasoning and decision-making abilities. A recent study by Maiken Nedergaard and colleagues, which has identified a new role for sleep, could help explain why. It turns out that getting adequate shut-eye time allows the brain to clean itself.
In a first study, Nedergaard and colleagues identified a ‘plumbing’ system responsible for removing metabolic waste products from the brain. During waking hours, molecules linked to neurodegenerative diseases, including beta-amyloid, alpha-synuclein and tau, accumulate in the fluid that surrounds brain cells (known as the interstitial space). Cerebrospinal fluid (CSF) flows through the interstitial space and flushes away these potentially toxic metabolites. Sleep, it turns out, speeds up this process. The researchers injected a dye into the CSF of mice and observed that the dye flowed much faster when the mice were asleep compared to when they were awake. When the researchers measured the space between cells, they found a 60% increase in the interstitial space during sleep.
This heretofore unknown function of sleep could finally yield insights into how certain neurological disorders develop. For instance, Alzheimer’s disease is often accompanied by sleep disturbances and older adults with fewer sleeping hours show increased levels of beta-amyloid, a protein associated with Alzheimer’s disease. The enhanced flow of CSF during sleep also leads to a more effective clearance of molecules such as beta-amyloid. Nedergaard and her team observed that radio-labeled beta-amyloid injected into the brains of mice disappeared faster when the mice were asleep than when they were awake.
Most people have probably forgotten what it feels like to be well rested. Maybe if they tried it, they would realise it is a pretty good cognitive enhancer.
Camilla d'Angelo is a 3rd year PhD student at the Department of Psychology