Environmental cues like light and noise are just two of many factors that can impact the duration and quality of your slumber, but did you know that even a single night of bad sleep can alter your brain chemistry?

Sleep is an important pillar of our physical and mental health, and inadequate rest can negatively impact our day-to-day cognitive functioning in a multitude of ways.

“As we sleep, our brain moves through different stages of sleep called NREM (non-rapid eye movement) and REM (rapid eye movement) on a cycle of roughly 90-110 minutes in adults, with NREM split into lighter and deeper stages,” explains Dr Lizzie Hill, clinical physiologist and senior lecturer in sleep physiology at University of the West of England (UWE). “REM and NREM have different functions and it’s important for us to get sufficient amounts of both for optimum daytime performance and brain health.”

Here are six key effects insufficient sleep can have on our brains…

1. Impairs memory

“Sleep plays a vital role in consolidating memories – the process of transferring information from short-term to long-term storage,” says Dr Steven Allder, consultant neurologist at Re:Cognition Health. “During deep sleep, particularly in slow-wave and REM stages, the brain replays and organises the day’s experiences, strengthening important connections between neurons.

“When sleep is cut short, this process is disrupted, making it harder to retain new information and recall details later. Over time, chronic sleep deprivation can impair both learning and memory accuracy, leaving the brain less efficient at storing and retrieving knowledge.”

**2. Leads to attention and focus difficulties **

“A lack of sleep reduces activity in the prefrontal cortex which is the part of the brain responsible for concentration, reasoning and decision-making,” says Allder. “This makes it harder to stay alert, sustain attention and filter out distractions. Fatigue also slows the brain’s reaction times, so tasks that require mental effort feel more demanding.

“Even a single night of poor sleep can affect focus levels similar to mild intoxication, while ongoing deprivation leads to lapses in attention and errors in everyday tasks, from driving to workplace performance.”

3. Impacts emotional regulation

“REM sleep is linked to emotional processing, and vivid or unpleasant dreams are a natural response to stressful situations – our brain’s way of trying to process the emotional content of our day,” explains Hill.

Therefore, sleep is essential for emotional balance.

“When we don’t get enough rest, the amygdala (the brain’s emotional centre) becomes overactive, while communication with the prefrontal cortex weakens,” highlights Allder. “This means we’re more likely to react impulsively and struggle to manage stress or frustration.

“Essentially, the brain loses its ability to regulate emotions effectively, making us more irritable, anxious, or prone to overreacting to small challenges. Adequate sleep restores this neural balance, helping us remain calm and resilient in the face of daily pressures.”

4. Worsens mood

“Insufficient rest can lower levels of serotonin and dopamine, neurotransmitters that help stabilise mood and motivation, while increasing stress hormones like cortisol,” explains Allder. “This chemical imbalance can lead to irritability, low mood, and, over time, increase the risk of anxiety and depression.”

This relationship can work both ways.

“Poor sleep worsens mood, and low mood further disrupts sleep patterns, creating a difficult cycle that can significantly affect mental wellbeing,” notes Allder.

5. Affects information processing

“During sleep, the brain organises and integrates new information, linking it to existing knowledge,” explains Allder. “Without enough rest, this process is incomplete, leaving neural connections weaker and thinking less efficient. The result is slower comprehension, poorer recall, and reduced ability to absorb or apply new information.

“Sleep deprivation also affects the brain’s speed of communication between cells, meaning that even simple tasks can feel mentally sluggish or confusing the next day.”

6. Impacts decision making and problem solving skills

“The prefrontal cortex, which governs reasoning and judgement, is highly sensitive to sleep loss,” notes Allder. “When under-rested, this area struggles to evaluate risks, consider consequences, or plan effectively. At the same time, emotional centres of the brain become more reactive, leading to impulsive or poorly thought-out decisions.

“Sleep deprivation also dulls creative thinking and the ability to see problems from different perspectives, making complex decision-making far more challenging than when the brain is well rested.”

What amount of sleep per night would you recommend to maximise cognitive performance?

“The National Sleep Foundation in the United States recommends seven to nine hours sleep as optimum in adults, but this varies from person to person and with age,” says Hill. “Everyone’s optimum sleep need is different. Think about how much sleep you need to really feel refreshed (for example, if you are off work for a few days and don’t need to set an alarm), and be guided by this.”

Good sleep hygiene habits and regular sleep patterns are key.

“Creating a calming bedtime routine, limiting screen time and ensuring a cool, dark environment all contribute to optimal rest and peak cognitive performance,” explains Allder.

However, if something feels wrong and isn’t helped by lifestyle adjustments, get in touch with a professional.

“If you constantly feel unrefreshed after sleep, even on your days off, you could have an underlying sleep disorder, so speak to your GP,” advises Hill.