The Neurological Effects of Sleep Deprivation

It’s common nowadays to delay our bedtime—whether to watch just “one more episode” of a series or to start studying for tomorrow’s exam. But what happens inside our head when we follow these kinds of routines?

This article explores, from a neurological perspective, how new social demands and work overload—or simply the habit of procrastination—contribute to new routines, whose implementation may lead to sleep deprivation and result in negative consequences. Sleep deprivation, increasingly common due to adaptation needs, has been the subject of study because of its major impacts, especially in the neurological field.

What Is Sleep?

Sleep is a cyclical activity regulated by biochemical substances, primarily from hypothalamic and mesopontine structures, which modulate the cerebral cortex and thalamus, and can be affected by both intracorporeal and extracorporeal stimuli.

Image of brain parts.

Intracorporeal stimuli:

Adenosine, the neurotransmitter responsible for reducing neuronal activity and inducing sleep.
Circadian rhythms, regulated by the suprachiasmatic nucleus (SCN), synchronize the sleep-wake cycle with the environment.
Neurotransmitters such as GABA and serotonin are essential for initiating sleep, while orexins promote wakefulness; a deficiency is associated with narcolepsy (a disorder of constant drowsiness).

Extracorporeal stimuli:

Environmental factors, like light, which inhibits melatonin and delays sleep.
Temperature, which affects thermoregulation and sleep continuity.

Stages of Sleep

Non-REM Sleep (NREM)

During the NREM phase, neuronal restoration, memory consolidation, and metabolic regulation take place.

Stage 1 – Light sleep

During this stage, the activity of the ascending reticular activating system (ARAS) decreases, as does the release of acetylcholine and norepinephrine, leading to the transition into sleep. It is marked by reduced cortical activity and neuronal excitability.

Stage 2 – Relaxation and drop in temperature

The thalamus actively inhibits external sensory stimuli. The autonomic system is also regulated, decreasing energy expenditure and heart rate.

Stage 3 – Deep and restorative sleep

Synchronized neuronal activity is observed in the cerebral cortex, with a predominance of delta waves, the lowest frequency waves, associated with the activation of the glymphatic system, responsible for eliminating toxins from the brain. There is a reduction in sympathetic activity and an increase in parasympathetic tone, promoting cardiovascular and metabolic stability.

REM Sleep (Rapid Eye Movement)

This phase is characterized by intense cortical activity, similar to wakefulness, with a predominance of beta and theta waves. There is also an increase in cholinergic system activity, using acetylcholine (ACh) as the main neurotransmitter, which facilitates the formation of neural connections and the consolidation of emotional and procedural memory.

Studies have shown that REM sleep deprivation affects emotional balance, intensifying amygdala activation—a key structure of the limbic system—which plays a major role in emotional processing and increases responses to stress and anxiety.

The Importance of Sleep for the Brain

Based on the above, it is clear that sleep, in its different stages, carries out vital processes for proper brain function. These include:

Consolidation of declarative memory (facts and concepts).
Strengthening of procedural memory and emotional processing.
Transfer of information to long-term memory through the prefrontal cortex, hippocampus, and thalamus.
Activation of emotional circuits, helping regulate fear and anxiety.
Amygdala activation, increasing emotional responses and the risk of anxiety and depression.
Contraction of brain cells facilitates cleansing via cerebrospinal fluid (CSF).
Elimination of neurotoxic proteins (e.g., beta-amyloid) → prevention of Alzheimer’s disease.

What Happens in the Brain When We Don’t Sleep Enough?

Cognitive Impact

Lack of sleep affects the ability to store and retrieve memories due to altered functioning of the hippocampus, a brain structure crucial for memory consolidation. It also slows down stimulus processing and problem-solving, as mental fatigue weakens synaptic connections, reducing our capacity to respond to new situations.

Studies show that sleep-deprived people have more difficulty learning new tasks and making informed decisions due to decreased activity in the prefrontal cortex, which is responsible for cognitive processes like planning, decision-making, problem-solving, impulse control, and adapting to changing situations.

Changes in Brain Neurochemistry

Sleep deprivation alters neurotransmitters by modifying levels of dopamine, serotonin, and glutamate, directly affecting motivation, mood, and synaptic plasticity (the ability of neural connections to change), impairing learning and emotional regulation.

It is also known that insufficient sleep leads to excessive production of cortisol, the stress hormone, which increases inflammation and oxidative stress. This cellular-level damage can cause neuronal degeneration and affect memory and cognition.

Long-Term Damage and Risk of Neurological Diseases

Insufficient or disrupted sleep over time is associated with a higher risk of developing neurodegenerative diseases, such as Alzheimer’s, due to impaired neural cleansing processes. Specifically, the accumulation of β-amyloid, a protein that builds up during the day and should be drained by the glymphatic system during sleep, increases due to the dysfunction of this waste-clearing mechanism.

Chronic sleep deprivation is also linked to disorders such as depression and psychosis, as a result of changes in neurotransmitter activity and dysfunction of the hypothalamic-pituitary-adrenal (HPA) axis.

In Conclusion…

Lack of sleep is a global epidemic, and the extent to which it is normalized is concerning. Given the consequences of sleep deprivation on the brain—both cognitive and emotional, in the short and long term—it is essential to change how we perceive sleep. We should not treat it as secondary, because it is the foundation that allows the proper functioning of the body. If we don’t allow the brain to recover and renew its functional capacity during sleep, how can we expect the interdependent systems of the body to perform adequately?

Bonus Point

If you’ve read this article and want to dig deeper into the topic, I recommend watching the presentation by Nora Volkow, a neuroscientist best known for her research on dopamine and its role in addiction, where she links her specialty to sleep.

The Sleep-Deprived Human Brain | Nora Volkow || Radcliffe Institute