Focus on Fatigue

Sleeping to Remember

By May 10, 2019 No Comments

Welcome to Focus on Fatigue!

There are a lot of things we struggle to remember. People’s names, the title of that book someone recommended, where we put our car keys. Then there are all those events we’d like to forget, like that embarrassing thing we did in high school (we ALL have at least a few of those memories). Thankfully, for most of us, the not-so-great memories are far outweighed by the many happy moments that are scattered throughout a life. Wedding days, the births of children, the time we performed perfectly at a piano recital or recalled every fact needed to get an A on an important exam.

In this month’s Focus on Fatigue, we’ll be looking at the different types of memory, how memories are formed, and how to ensure the memories we want to hold onto last a lifetime. Unsurprisingly, it’s all a matter of a good night’s sleep.

Best wishes,
The FRMS Team



InterDynamics Pty Ltd
320 Adelaide Street Brisbane Qld 4000
Tel +61 7 3229 8300

Views expressed in articles and links provided are those of the individual authors, and do not necessarily represent the views of InterDynamics (except where directly attributed).


Sleeping to Remember

In the past, sleep has often been viewed as wasted time. But as more and more research is done on sleep, we’ve begun to realise just how active our brains are during those hours of slumber. Just because we’re not conscious of what our brain is doing during sleep, doesn’t mean there is nothing going on. One of the many ways in which our brain is helping us while we sleep is in the consolidation and regulation of memories.

There are different types of memory, including short-term memory (remembering a new phone number long enough to write it down) and long-term memory. Within long-term memory are explicit memory (conscious) and implicit memory (unconscious). Explicit memory can then be broken down into episodic memory (memories of events that have happened to you) and semantic memory (your general knowledge about the world). Finally, implicit memory can be broken down in priming (the word ‘bread’ is likely to make you think of the word ‘butter’ but not the word ‘doctor’) and procedural memory (learned motor skills such as how to drive a car). That’s a lot of different types of memory for the brain to keep track of!

How do memories form?

When you drift off to sleep at night the neurons in your hippocampus come alive, performing a replay of the memories from that day. The hippocampus and the neocortex spend time sifting through these memories, deciding what needs to be stored and what can be forgotten. Important memories are then stored in the neocortex so they can be recalled in the future. This replay only happens during sleep. Which means, if you don’t get enough sleep, those memory you’re making won’t be consolidated and you’re less likely to retain them.


When you recall a memory (either consciously or unconsciously) you are reactivating the neurons where that memory is stored. These neurons are connected through synapses, which can be strengthened or weakened depending on how often you recall the memory (the ability of the brain to make these ongoing changes is called synaptic plasticity). This is why you can remember events from long ago, such as the birth of a child or the first time you were stung by a bee. Because the memories are important to you, or caused a strong emotional reaction. By remembering them many times, you’ve created strong connections between the neurons where the memories are stored.


What did you have for breakfast on the second Tuesday of last month? You probably knew the answer to that question the next day, maybe even the day after. But as time passed you’ve probably forgotten. What happened to those memories?

This is another way in which sleep helps us to regulate memories. Not only does it help us retain important memories, but it helps us forget memories that aren’t important. This is done through a process called ‘synaptic homeostasis’ (it’s still a hypothesis currently, but the evidence is mounting). The theory suggests that during sleep there is an overall weakening of the synaptic connections throughout the brain. Memories that had weak connections in the first place will be forgotten, while those with strong connections will continue to be retained. This effectively ‘cleans the slate’ so that we’re able to learn new information and make new memories upon waking.

Sleep stages and memory type

Studies have found evidence that different stages of sleep are important for different types of memory. For example, REM (Rapid Eye Movement) sleep is thought to be important for emotional memories (the painful sting of that bee) and for procedural memories (driving a car, playing the piano). Meanwhile, slow-wave sleep (deep, restorative sleep) is important for episodic memories. Motor learning has also been linked to the lighter stages of sleep.

The research is still in its early stages here, but the implication is clear: if you want good consolidation of all memory types, you need to be cycling through all the various stages of sleep.

Learning new information

The learning of new information is often described as having three parts: the acquisition of new information, the consolidation of this information through memory formation (occurs during sleep) and recall of the information. While we’ve already discussed how a lack of sleep effects the consolidation of new information, there are a number of other ways in which sleep deprivation interferes with learning. For example:

  • Lack of focus, attention and vigilance
  • Over-worked neurons no longer able to coordinate information properly
  • Reduced ability to access previously learned information
  • Judgement becomes impaired
  • Negatively impacts mood, making learning more difficult

While we may not have all the answers on how sleep and memory work, the evidence is clear. If you want to lay down good memories, clear out unimportant memories, and have access to the information you’ve taken the time to learn – get a good night’s sleep.


  • Blanco, W., Pereira, C. M., Cota, V. R., Souza, A. C., Rennó-Costa, C. and Santos, S. (2015) Synaptic Homeostasis and Restructuring across the Sleep- Wake Cycle. PLoS Computational Biology, 11(5): e1004241.
  • Kirszenblat, L. (2017, October 19) Sleep deprivation: Why your brain needs to go to sleep. Queensland Brain Institute. Retrieved from
  • Harvard Medical School (2007) Sleep, learning, and memory. Retrieved from
  • Squire, L. R., Genzel, L., Wixted, J. T. and Morris, R. G. (2019) Memory consolidation. Cold Spring Habor Perspectives in Biology, 7, a021766.


InterDynamics News

FAID Quantum Utilised in Research on U.S. Police Rosters

A research team at Washington State University recently published a paper in which FAID Quantum was used in an investigation of the association between police fatigue and complaints made by members of the public. The details are given below:

Riedy, S. M., Dawson, D., and Vila, B. (2019) U.S. police rosters: Fatigue and public complaints. Sleep, 42(3), 1-10.


Study Objectives: Recent experimental research indicates a substantial impact of shift work related fatigue on police officers’ encounters with the public. In recent years, biomathematical models of fatigue have provided a new way to identify potential relationships between working time arrangements and job performance. This study focused on public complaints against police officers and determined whether the odds of a public complaint were associated with work schedules and/or a biomathematical model’s predictions of fatigue and sleepiness.

Methods: N = 144 police officers from two municipal police departments in the United States reported shift start times, shift hours, court hours, and public complaints each duty day during study participation. A biomathematical model of fatigue (FAID Quantum) predicted sleep duration and sleep timing and inferred fatigue and sleepiness for 15 744 shifts. Fatigue, sleepiness, 24 hr sleep estimates, and work schedule were tested as predictors of public complaints.

Results: Greater fatigue, greater sleepiness, and less sleep in the 24 hr prior to a shift increased the odds of a public complaint (F ≥ 9.14, p < 0.01). Working back-to-back night shifts increased the odds of a public complaint (OR = 4.27, p < 0.01), particularly when off-duty court hours were worked between the night shifts (OR = 4.73, p < 0.01).

Conclusions: On-duty fatigue and sleepiness, sleep obtained prior to a shift, and working night shifts were strongly associated with public complaints. Off-duty court appearances reduced sleep between night shifts and further increased the odds of a public complaint. The results suggest that off-duty court hours should be limited between night shifts and duty schedules should be considered when scheduling court appearances.


In the News

Provided below are a selection of articles from around the web on the issues associated with fatigue. We hope you find them useful and interesting.

Video: The benefits of a good night’s sleep
Shai Marcu, TED-Ed (5 January 2015)
It’s 4am, and the big test is in 8 hours. You’ve been studying for days, but you still don’t feel ready. Should you drink another cup of coffee and spend the next few hours cramming? Or should you go to sleep? Shai Marcu defends the latter option, showing how sleep restructures your brain in a way that’s crucial for how our memory works.

Article: Memory ‘brainwaves’ look the same in sleep and wakefulness
University of Birmingham (9 October 2018)
Identical brain mechanisms are responsible for triggering memory in both sleep and wakefulness, new research at the University of Birmingham has shown. The study sheds new light on the processes used by the brain to ‘reactivate’ memories during sleep, consolidating them so they can be retrieved later.

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