How is your lifestyle affecting your brain?
Oxford’s neuroscientists answer some questions from The Big Brain Competition
Over the last year, neuroscientists at Oxford University have been taking over busy streets by day and haunting the magnificent halls of our museums by night to share their latest research through exhibitions, games, plays and fun fairs. One of these ‘Brain Diaries’ events is ‘The Big Brain Competition’ which offers entrants the chance to suggest an experiment to investigate the human brain. The lucky winner will get to watch their idea come to life and see the human brain in action using state-of-the-art brain scanners. We’ve received hundreds of brilliant ideas along with heaps of burning questions about how the brain works, which we will tackle in a series of blogs.
With the Christmas holidays fast approaching, I was drawn to the many queries about how sleeping and leisure activities affect our brain. Equipped with questions from the public, I went to Oxford-based researchers Christopher-James Harvey, Naiara Demnitz and Melis Anatürk for their expertise on these topics. What followed was a fascinating discussion on the neuroscience of dreams, what differentiates night owls from early birds, and what we can do to keep our brain healthy.
3Rs of brain health: reserve, restore, and regenerate
Most of us probably feel energized after a good night’s sleep, a walk or a social gathering, but what does the science say about the long-term effects of these activities? Neuroscientists generally agree that regular exercise, sleep, and leisure activities are linked to better brain health and memory, although the specific mechanisms for these relationships are still being explored.
“Frequent involvement in a number of leisure activities over our lifetime helps to build cognitive reserve, which is the brain’s ability to cope with changes that happen to it as a result of ageing”, Melis explains. “So cognitive reserve, in effect, may potentially delay cognitive decline caused by ageing”. Her doctoral research examines whether socially and mentally engaging activities like visiting friends and family or reading a book promote brain health in older ages.
Sleep, too, is critical for a well-functioning brain and some sleep disorders are even linked to the later development of dementia and Parkinson’s disease. When we are awake, our nervous system produces waste products that need to be regularly cleared from the brain to prevent them from building up. “The most compelling explanation for the restorative effects of sleep comes from rodent studies that find that the brain sort of washes itself while we sleep,” says Chris, describing a study in rats showing how proteins called beta amyloids are removed from the brain during sleep. “If these beta amyloids build up, they can accumulate to form toxic plaques that we know are linked to neurodegenerative diseases.”
Indeed, neuroscientists often turn to rodents to unravel the biological mysteries of the relationship between the brain and our behaviour. Naiara recalls a milestone study which found that young mice who had regularly run on an exercise wheel were faster learners and had better memory than mice that remained sedentary. “The researchers also found that physical activity promoted neurogenesis, or the regeneration of brain cells, in an area called the hippocampus, which is important for memory,” she says. “We’re now exploring whether similarly beneficial effects of exercise can be observed in humans.”
The devil is in the experimental detail
Neuroscientists can measure brain health in humans using neuroimaging such as magnetic resonance imaging (MRI) or electroencephalography (EEG) to record brain activity. But mimicking real-world environments in an experimental setting can be challenging, particularly for sleep studies, which require participants to be hooked up to several wires while in a sleep lab.
“As well as the many EEG electrodes to the head, we also attach electrodes around the eyes to study eye movement, on the chin to assess muscle tone, on the chest to measure heart rate, on the legs to observe limb movements,” Chris explains, checking off the wires on his fingers. “And we may also place a cannula on the nose to record breathing rate and a clip on the finger to monitor oxygen saturation.”
It’s hard to imagine falling asleep with this paraphernalia and so sleep experiments are preferably conducted over two nights: an adaptation night when participants can get accustomed to the set-up and a test night, when scientists can assess experimental manipulations of sleep.
“Another challenge in lifestyle experiments is designing an appropriate control condition,” says Naiara. This is especially important in randomized controlled trials, where people are randomly assigned to different groups, one that does and one that does not receive an intervention. “For example, think of two groups of participants in an exercise study, one which visits the lab twice a week to do an exercise task, and a control group which doesn’t come in at all. The exercise group may end up going to tea after their session, socializing and making friends as a result of this study. And suddenly we have an uncontrolled experiment, where we can no longer tell if our observed effects are related to an increase in social or physical activity. So we must be careful to make sure that we have a well-matched control group that also comes in to the lab twice a week, but does not exercise.”
Carefully designed neuroimaging studies offer a valuable window into the living brain and have shaped our understanding of the inner workings of sleep and exercise.
Body clocks and wake-up calls
“Every cell in our body has a clock, and the best time for us to sleep is predicted by our internal circadian (daily cycle) clock,” Chris explains. In the morning, the sunlight entering the cells in our eye resets this clock and signals the body to increase its heart rate and blood pressure to prepare for the day. When it becomes dark, our eyes signal the hypothalamus in the brain to initiate feelings of tiredness and the body prepares to sleep.
Our internal clock works best when we match our sleep-wake cycle to the light-dark cycle, but there are also individual variations in how fast our internal clock ticks. “For instance, teenagers are more like night owls; they have a later-running clock, which makes them physiologically ready for sleep later in the evening than adults. But because they still have to wake up early for school, they may be studying at a time when their bodies are not optimally prepared to engage. This can also make them groggy and more sleep deprived,” he describes, highlighting the need for studies that examine whether a delay in school start times would improve mental health and academic performance in teens.
Chris supervises the “Teensleep” project; the largest ever study to investigate this delay in adolescent circadian clocks. This on-going project is delivering sleep education interventions in 10 UK schools, teaching year 10 students about the neuroscience of sleep, the importance of good bedtime routines, and how to maintain sleep during high stress periods. If this intervention is effective in improving students’ quality of sleep and physical and psychological wellbeing, it could even be scaled to introduce sleep education programmes across the UK school system.
Few people enjoy the luxury of waking up naturally, sans alarms or animated toddlers, but waking up in the wrong stage of sleep can disrupt important processes that prepare our body for the next day.
We have four main stages of sleep, Chris tells me, going from the transition into sleep, light sleep, deep sleep, and rapid eye movement (REM) sleep. “One of the reasons we recommend naps for 20 or 90 minutes is so that we either wake up during the lighter stages of sleep, or while we’re in REM sleep, which allow for the easiest transitions to waking,” he says. “If we’re woken up in stage 3 [deep sleep], we often experience sleep inertia, where we feel tired and disoriented, sometimes taking quite a while to get back into the real world.” This is because during deep sleep, brain activity slows down to allow cells to rest and our muscles to refresh from the stresses of the day.
During REM sleep on the other hand, brain activity is surprisingly similar to recordings from a fully awake brain. This is when scientists believe our most vivid dreams occur. During this time, activity within a brain area called the amygdala is heightened, whereas activity in the prefrontal cortex of the brain is reduced. The amygdala is associated with our emotional responses and the prefrontal cortex is involved in logical reasoning and impulse control, so these activation patterns are consistent with the uninhibited and disorganised nature of dreams. “These studies certainly don’t explain our bizarre or illogical dreams, but they give us an appreciation of the biological underpinnings of dream states,” he concludes.
Running or Tai Chi?
Unfortunately, there haven’t been many studies that directly compare different forms of social and physical activities. “The field is relatively new”, Melis explains. “There are only a handful of neuroimaging studies that have examined the relationship between different types of leisure activities and the brain. We can’t yet say whether there’s one that is particularly beneficial for brain health”. However, her recent analysis of the existing literature suggests that socially and cognitively engaging activities, when combined, are associated with a bigger hippocampus and healthier brain white matter, the ‘cables’ that connect different brain regions.
“One randomized trial found that older adults who regularly practised Tai Chi or met in a community centre for the course of 40 weeks had higher brain volumes and better cognitive function than adults who received neither intervention,” she says, citing support for the beneficial effects of non-aerobic exercise and social interaction while also stressing the need for replicating this finding.
The same goes for more strenuous physical activities, Naiara says. “Studies on exercise have typically looked at two main categories: aerobic training like running and cycling that affect our cardiovascular health, and resistance training like weights which affect our balance and strength,” she explains. “There is some preliminary research that suggests that combining both forms of exercise may show the greatest improvements in cognition, but we we’re still investigating if and how they have distinct effects on the brain.”
Naiara is part of a research team working on the REACT or ‘REtirement in ACTion’ study, which assesses whether exercise can reduce mobility-related disability in older adults. “Mobility is the ability to move around safely and independently and unfortunately this decreases as we age. Lower mobility is linked to a higher risk of falls and hospitalizations so we are looking at whether physical activity can improve mobility and if that has knock on effects on cognition.”
While we can’t yet say which form of exercise is best, we do know that we as a society are not doing nearly enough. The WHO recommends that adults who are 19 to 64 years old should do at least 2 days of resistance training along with either 150 minutes of moderate intensity exercise (cycling, brisk walks) or 75 minutes of high intensity exercise (jogging, swimming) per week. Less than two-thirds of UK adults currently adhere to these guidelines, with the number falling to lower than 15% for older adults. But it’s never too late to start, Naiara assures me, and I walk away with a renewed resolve to stay active in between the many holiday meals that lie ahead.
Written by
Dr Sana Suri, Postdoctoral researcher in the Oxford Centre for Human Brain Activity, Wellcome Centre for Integrative Neuroimaging. Follow Sana.
Interviews with
Ms Melis Anatürk, DPhil candidate in the Department of Psychiatry
Ms Naiara Demnitz, DPhil candidate in the Department of Psychiatry
Dr Christopher-James Harvey, Associate Director of the Online Programme in Sleep Medicine, Nuffield Department of Clinical Neurosciences
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