Did you know that a single night of poor sleep can actually change your brain chemistry? While light and noise are just a couple of the many environmental factors that can affect both the quality and duration of your sleep, sleep itself is a critical pillar for our mental and physical health. Lack of adequate rest can significantly impair our cognitive abilities throughout the day.

Dr. Lizzie Hill, a clinical physiologist and senior lecturer in sleep physiology at the University of the West of England (UWE), provides insight into the sleep process. “As we sleep, our brain cycles through various stages known as NREM (non-rapid eye movement) and REM (rapid eye movement). In adults, these cycles last approximately 90-110 minutes. NREM is further divided into lighter and deeper sleep stages,” she explains. “Both REM and NREM serve different purposes, and it is vital to receive enough of both for optimal brain health and daytime performance.”

Six effects insufficient sleep can have on our brains

Memory Impairment

Dr. Steven Allder, a consultant neurologist at Re:Cognition Health, highlights the importance of sleep in memory consolidation. “Sleep plays a crucial part in solidifying memories, which involves transferring information from short-term to long-term memory storage,” he states. “During deep sleep, especially during slow-wave and REM stages, the brain revisits and organizes the day’s experiences, reinforcing key neural connections.”

When sleep is insufficient, this consolidation process is interrupted, making it more challenging to retain new information and recall details in the future. Over time, chronic sleep deprivation can significantly hinder learning and memory accuracy, making the brain less efficient in storing and retrieving knowledge.

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.”

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, adequate rest is crucial for maintaining emotional equilibrium.

“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.”

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.

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.”

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 is recommended for maximising 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.”

Maintaining good sleep hygiene habits alongside consistent sleep patterns remains essential.

“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.

Nevertheless, if something feels amiss and lifestyle changes don’t help, seek professional advice. “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.