Teensleep: The Neuroscience of Sleep and Circadian Rhythms in Adolescent Learning

By Dr. Christopher-James Harvey

 

At its simplest, sleep is driven by two broad systems working symbiotically: sleep/wake homeostasis and biological circadian rhythms. Sleep/wake homeostasis tells us that the need for sleep is accumulating as we progress throughout the day, and helps us to maintain sleep throughout the night to make sure that the ‘sleep debt’ we have built up throughout the day is repaid.

 

If this homeostatic system existed alone then we would all start the day feeling fresh and progressively get drowsier as the day went on. This is not the case: we have peaks and troughs in our tiredness/alertness throughout the day. This rhythm is driven by our internal circadian biology: our biological clock. In adults we naturally feel more tired between 13:00-15:00 and our strongest sleep-drive is at around 02:00-04:00. The intensity of tiredness during the circadian-lows will vary depending on how much sleep we have had the night before, as will the intensity of the alertness: if we are sleep deprived we will feel more tired during the natural dips and less alert during the natural highs. In this way sleep homeostasis informs circadian rhythms. Of course, as with anything in nature, there is natural variation in these rhythms from person to person but as a general rule these patterns are pretty consistent.

 

The circadian rhythm is driven by the suprachiasmatic nuclei (SCN), a part of our brains, which receives light signals from the optic nerve. In the morning, when it begins to get light, the SCN tells us it is time to be awake. The SCN then signals the onset of various processes, such as increasing body temperature and the production of certain hormones, such as cortisol which, amongst other functions, increases blood sugar, to provide an increase in energy levels. Other hormones, such as melatonin, are suppressed. Melatonin is involved in the onset of sleep and sleep maintenance. Melatonin levels typically remain low during the day and high during the night, increasing as we approach sleep.

During adolescence our circadian rhythm begins to change. From the age of about 10, our circadian rhythms begin to delay, and continue to do so until around 21 years old. This means that as we go through adolescence and into early adulthood we are naturally more inclined to go to bed later and also to get up later. The biological underpinnings of this pattern are well mapped out.

 

In adolescence melatonin levels naturally rise later, making it difficult to go to sleep early, and likewise difficult to get up early. Therefore, asking an adolescent to get up at 07:00 to start school at 09:00 is akin to asking a 55-year-old to get up at 05:00: this leads adolescence to accumulate a significant amount of sleep deprivation. This sleep deprivation (which informs the sleep homeostasis mechanism) interacts with the circadian mechanism. Adolescents generally have a natural circadian dip between 03:00-07:00. The interaction between the circadian rhythm and sleep deprivation elongates this dip, extending it until around 10:00.

 

This means that adolescent sleep is particularly vulnerable. Maintaining good sleep is essential for optimal development, and we know that sleep has a key role to play in memory formation, mood regulation, and physical well-being. The delay in the circadian drive for sleep means that adolescents are typically 2 hours sleep deprived a day.  This situation may be further exacerbated by behavioural and societal factors. For example the use of electronic devices to communicate or for entertainment may also impact sleep. TV screens, tablets and phones emit light at a level which may interfere with sleep onset, compounding the effects of the naturally occurring circadian delay. Students are also dealing with the stress of exams and the pressure to perform well, as well as the use of stimulants to overcome the sleep deprivation.

 

The Teensleep study (funded by the Wellcome Trust and Education Endowment Foundation as part of the Education and Neuroscience initiative) will look at the effect of sleep education on sleep quality, mood and well-being. Eventually we want to investigate the impact of this on educational achievement. This educational intervention will teach pupils about good bed-time routines, the science behind good sleep related behaviours and also about stress-management techniques and how to maintain good sleep during periods of stress. 

 

We will also be monitoring sleep patterns in a sub-sample of pupils in each school. This will be done via telemetric devices worn on this wrist. These ‘watches’ give a pseudo-objective measure of sleep, allowing us to investigate if sleep length improves as a result of the intervention. Alongside this we will be carrying out surveys across all the schools involved to assess physical and psychological well-being. This will provide insight into and well-being benefits of the intervention as it is well established that sleep has a crucial role to play in mood regulation, physical health and perceived quality of life.

 

This important study is designed to tell us the extent to which understanding about the importance of sleep and how to get enough of it affects the lives of adolescents. It is vital that we do this testing so that schools can make well informed decisions based on rigorous evidence generated from classroom based studies.

 

 

For more information on the Teensleep project please contact:

Christopher-james.harvey@ndcn.ox.ac.uk

 

For more information about the wider ‘Education and Neuroscience Initiative’ please visit:www.wellcome.ac.uk/edneuroscience