Wakefulness & Sleep (Week 8)

Definition (#f7aeae)

Important (#edcae9)

Extra (#fffe9d)

Circadian Rhythm:

Endogenous circannual rhythm:

• These are internal body rhythms that follow a yearly pattern.

• Found in some animals. Happen even without outside cues like weather or daylight.

Endogenous circadian rhythm:

• Internal rhythms that follow a 24-hour cycle.

• Found in all animals, including humans.

• Help regulate daily activities and body functions.

• Ex: Sleep & wake cycles, when we feel hungry/thirsty or hormone release.

What is the Circadian Rhythm?

• The body’s internal clock that helps keep daily activities in sync with the world.

• Without outside cues, the body naturally runs on a rhythm that’s a bit longer than 24 hours.

• We need to reset this rhythm, especially after travel or work.

• Zeitgeber: German word meaning “time giver.” Refers to anything that helps reset the biological clock.

• If the body relied on weak cues, it can lead to: depression, easy irritation & trouble focusing.

Jet Lag:

• Jet lag happens when your body’s internal clock (circadian rhythm) doesn’t match the local time after traveling across time zones.

• Causes:

  • Feeling sleepy during the day.

  • Trouble sleeping at night.

  • Difficulty concentrating or thinking clearly

• Travelling west: Body clock is delayed → day feels longer. Easier to adjust as you can stay up later and sleep in.

• Travelling east: Body clock is advanced → day feels shorter. Harder to adjust as you need to sleep earlier.

Shift Work & Your Body Clock:

• The amount of sleep you get depends on what time you go to bed.

• Working at night doesn’t automatically reset your body’s internal clock (circadian rhythm).

• Your body thinks it should be awake during the day and asleep at night. Hard for the body to adapt to night work.

Morning vs Evening people:

• Age influences sleep patterns.

• Young children tend to be morning people, they wake up early & feel energetic.

• Teenagers often become night owls, they stay up late and struggle to wake up early.

• Adults vary, either morning or evening types.

• Your sleep pattern as an adult is partly influenced by your genes.

Gender Differences in Circadian Rhythms:

• Sleep timing & body clock:

  • Women’s circadian rhythms often run slightly earlier than men’s.

  • Men’s rhythms are usually later, prone to being night owls.

• Sleep quality:

  • Women rate their sleep quality lower than men.

  • Report more fluctuations in sleep, especially during different phases of the menstrual cycle.

• Hormonal influence:

  • Hormones like estrogen and progesterone affect sleep patterns and sensitivity to light.

• Mental health connection:

  • Poor sleep quality in women is linked to higher risks of anxiety and depression, which are more common in women than men.

Mechanisms of the Circadian Rhythms:

1. The suprachiasmatic nucleus (SCN)

2. Genes that produce certain proteins (PER & TIM)

3. Melatonin levels

SCN:

• Brains internal clock.

• The SCN is the main control center for your body’s circadian rhythms.

• Located in the hypothalamus, above where the optic nerves cross (optic chiasm).

• If damaged:

  • Your body rhythms become inconsistent.

  • You may no longer follow a regular sleep-wake cycle or respond properly to light and dark.

SCN Research:

• Scientists injected rats with a chemical that shows which brain cells are active.

• Rats injected during the day showed more SCN activity than those injected at night.

• Proving that SCN is more active when it’s light, regulating the body clock.

Light, the SCN, and the Retinohypothalamic Path:

How light resets the body clock:

• Your SCN keeps your body on a 24-hour rhythm.

• Light helps reset this clock every day so it stays in sync with the outside world.

The retinohypothalamic path: Light shortcut to the brain

• Special pathway from your eyes to the SCN called the retinohypothalamic path.

• Direct route from the retina to the SCN.

Special light sensing cells:

• This path uses unique ganglion cells in the retina.

• These cells have their own light-sensitive chemical called melanopsin.

• They can detect light on their own, don’t need help from rods or cones.

Biochemistry of the Circadian Rhythm:

Key genes:

2 important genes help control your body’s daily rhythm:

1. Period gene → makes PER protein

2. Timeless gene → makes TIM protein

PER and TIM proteins:

• These proteins build up during the day and break down at night.

• They activate neurons in the SCN to help regulate:

  • When you feel sleepy.

  • When you feel alert.

If the gene is mutated:

A mutation in the PER gene can mess up your sleep rhythm.

You might:

• Feel sleepy at odd times.

• Struggle to stay alert if you didn’t sleep well.

mRNA’s role:

• mRNA carries instructions from the Period and Timeless genes to make PER and TIM proteins.

• These proteins then interact to keep your circadian rhythm running smoothly.

Melatonin:

HOW YOUR BRAIN CONTROLS SLEEP?

• The SCN sends signals to the pineal gland.

• The pineal gland releases melatonin, a hormone that makes you feel sleepy.

Pineal gland: Small gland near the center of the brain.

When melatonin is released:

• Melatonin levels start rising about 2–3 hours before bedtime.

• Helps the body prepare for sleep by lowering alertness and body temperature.

Helps reset the clock:

• Melatonin sends signals back to the SCN to help adjust your internal clock.

• This feedback keeps your sleep-wake cycle in sync with the day-night cycle.

Melatonin as a sleeping aid:

• Taking melatonin in the afternoon or early evening can help shift your sleep schedule earlier.

• This is called a phase advance; useful for jet lag or night owls trying to sleep earlier.

• Often used to treat sleep problems or adjust to new time zones.

Stages of Sleep:

Sleep:

• A special state that your brain actively creates.

• Serves important functions like:

  • Restoring energy

  • Strengthening memory

  • Supporting immune and brain health

How it works:

• During sleep, your brain:

  • Slows down activity → Responds less to sounds, light, and touch.

  • Brain uses specific mechanisms to control when and how you fall asleep.

Not forms of sleep:

1. Coma: Caused by brain injury, no awareness or control.

2. Vegetative state: Awake but not aware.

3. Minimally conscious state: Limited awareness, may respond to stimuli.

4. Brain death: no brain activity at all.

EEg to study the brain:

• EEG (Electroencephalograph) is a tool that records electrical activity in the brain.

• Helps see how brain waves change during sleep.

Discovered:

• Sleep isn’t just one state: it has different stages (light sleep, deep sleep & REM).

• EEG shows how brain activity changes in each stage.

Polysomnograph:

A sleep study tool that combines:

EEG (brain waves) and eye movement tracking.

Helps researchers understand:

• When someone enters REM sleep (when eyes move quickly).

• How deep or light their sleep is.

Stage 1 of sleep:

• Light sleep, when you’re just starting to fall asleep.

• Your brain shows alpha waves, appears when you're relaxed but still awake.

• EEG shows irregular, jagged, low-voltage waves and brain activity starts to slow down.

Stage 2 of sleep:

• Deep sleep starts, fully asleep but not deep sleep.

• EEG shows two special features:

  • Sleep spindles: Quick bursts of brain activity lasting about half a second.

  • K-complexes: sharp waves that help block out distractions and keep you asleep.

Stage 3 & 4 of sleep:

• Deepest stages of sleep.

• EEG shows slow, large waves, brain activity is very low.

• Heart rate, breathing and brain activity slow down.

• Neurons fire in a highly synchronized way.

REM sleep:

• Rapid Eye Movement, eyes move quickly under your eyelids during this stage.

• Called paradoxical sleep as it’s:

  • Deep sleep (your body is very relaxed).

  • Also light sleep (your brain is active, like when you're awake).

What happens in the brain:

• EEG shows fast, irregular, low-voltage waves.

• Meaning the brain is busy and active, even though you're asleep.

In the body:

• Postural muscles (back and legs) are very relaxed, almost paralyzed.

• This prevents you from acting out your dreams.

REM & nREM sleep:
Types of sleep:

1. NREM: Includes Stages 1, 2, 3, and 4.

2. REM: Stage where most vivid dreaming happens.

Cycle:

• When you fall asleep, your brain goes through: Stage 1 → Stage 2 → Stage 3 → Stage 4.

• After about 1 hour, it reverses: Stage 4 → Stage 3 → Stage 2 → REM

• Repeats every 90 minutes.

In the night:

• Early in the night: Spend more time in deep sleep (Stages 3 & 4). The body repairs and restores itself.

• Later in the night: Spend more time in REM sleep Dreaming becomes more frequent and intense.

Brain Mechanisms of Wakefulness & Arousal:

Reticular formation:

• Located in the midbrain, stretching from the medulla to the forebrain.

• Acts like a wake-up switch, keep you alert and awake.

Pontomesencephalon:

• Part of the midbrain.

• Sends signals to the hypothalamus, thalamus, and basal forebrain.

• Releases acetylcholine and glutamate, chemicals that excite the brain.

• Can wake someone or boost alertness when already awake.

Locus coeruleus:

• A tiny structure in the pons.

• Releases norepinephrine, activating the cortex and helps you stay awake.

• Inactive during sleep, but fires up when you wake.

Hypothalamus:

• Releases histamine, which stimulates the brain and keeps you alert.

• Antihistamines block this and make you feel sleepy.

Orexin (Hypocretin):

• Activates cells in the basal forebrain to release acetylcholine.

• Keeps you awake and alert, important for staying awake over time.

Gaba & acetylcholine in basal forebrain:

• Gaba: A calming chemical that slows down brain activity, essential for sleep.

• Acetylcholine: An excitatory chemical that boosts arousal and alertness.

• These two work like opposites, one helps you sleep, the other helps you wake.

Summary:

Morning:

• Reticular formation activates → sends alert signals.

• Pontomesencephalon and locus coeruleus fire → boost brain activity.

• Hypothalamus releases histamine → keeps you awake. Orexin helps you stay alert through the day.

Night:

• GABA from the basal forebrain increases → brain slows down.

• You fall asleep.

Sleep Phenomena:

1. Sleep walking:

   • Some brain areas are asleep, but motor areas are still awake.

   • The person can walk or do simple actions — but they’re not fully conscious.

2. Lucid dreaming:

   • You’re dreaming, but a part of your brain is aware that you’re dreaming.

   • You might even be able to control the dream.

3. REM paralysis (Pons Still in REM):

   • The pons (part of the brainstem) stays in REM sleep, keeping your body muscles relaxed.

   • But other brain areas wake up, so you become aware but can’t move.

Brain Activity During REM Sleep:

Increased activity in:

• Pons (controls REM and sends signals to the body)

• Limbic system (handles emotions and memory)

Decreased activity in:

• Primary visual cortex (less real visual processing)

• Motor cortex (less movement planning)

• Dorsolateral prefrontal cortex (less logical thinking and decision making).

PGO waves (dream signals):

• REM sleep shows special brain waves called PGO waves:

  • Starts in the pons.

  • Moves to the lateral geniculate nucleus (part of the thalamus).

  • Ends in the occipital cortex (vision center).

• These waves are linked to dreaming and visual imagery.

• If deprived of REM sleep, they’ll have more PGO waves when they sleep.

Brain activity in REM sleep:

Why you can’t move in REM:

• The pons sends signals to the spinal cord to turn off motor neurons.

• This paralyzes large muscles so you don’t act out your dreams.

Chemical control of REM:

• Acetylcholine: Boosts REM sleep.

• Drugs that activate acetylcholine receptors can trigger REM quickly.

• Serotonin: Interrupts REM sleep. Too much serotonin can reduce REM.

Sleep Disorders:

It’s when someone can’t get enough good-quality sleep.

This can lead to tiredness, poor focus, and mood problems during the day.

Causes:

Common:

1. Environmental factors: Noise, light, or uncomfortable temperature.

2. Stress and emotional issues: Worry, anxiety or sadness can keep your brain too active to sleep.

3. Physical discomfort: Pain or illness can make it hard to relax.

4. Diet and medication: Caffeine, alcohol or drugs can interfere with sleep.

Medical conditions:

• Disorders like: Epilepsy, parkinson’s disease, depression or anxiety.

• These can disrupt sleep patterns or make it harder to fall asleep.

Sleep aids and circadian rhythm disruptions:

• Relying too much on sleeping pills or alcohol can make sleep worse over time.

• Circadian rhythm shifts can cause insomnia.

Sleep Apnea:

• A sleep disorder where a person stops breathing for short periods while asleep.

• These pauses can last several seconds and happen many times a night.

• Causes cognitive problems like memory issues or slower thinking.

• Consequences:

  • Daytime sleepiness even after a full night’s sleep.

  • Trouble focusing or paying attention.

  • Mood issues like depression or irritability.

  • Heart problems in serious cases.

Causes:

• Genetics: Runs in families.

• Hormonal changes: Can affect breathing control.

• Aging: Muscles that keep airways open may weaken.

• Obesity: Extra tissue can block the airway.

• Brain issues: Parts that control breathing may not work properly.

Treatment:

• CPAP machine (Continuous Positive Airway Pressure): A mask worn during sleep that keeps airways open using gentle air pressure.

• Weight loss: Losing weight can reduce pressure on the airway.

• Surgery: In some cases, surgery can remove blockages in the nose or throat.

• Dental devices: Special mouthpieces that keep the airway open by adjusting jaw or tongue position.

• Avoiding alcohol/sedatives: These relax throat muscles and make apnea worse.

Narcolepsy:

• A sleep disorder where a person feels very sleepy during the day, even after a full night’s sleep.

• Can cause sudden or gradual “sleep attacks”, the person may fall asleep unexpectedly.

Key symptoms:

• Sudden Sleepiness: Can happen anytime, in the middle of a conversation or activity.

• Cataplexy: Sudden muscle weakness, often triggered by strong emotions like laughter or surprise.

• Sleep Paralysis: Temporary inability to move when falling asleep or waking up.

• Hypnagogic Hallucinations: Dream-like images or sounds that happen just before falling asleep.

Causes:

• May run in families, but no specific gene has been found.

• Caused by a lack of orexin, made in the hypothalamus.

Treatment:

• Treated with stimulant medications like Ritalin.

• These drugs boost dopamine and norepinephrine, which help increase alertness.

Periodic Limb Movement:

• A sleep disorder where the legs or arms move without control during sleep.

• Movements are repetitive and involuntary.

• Legs may kick or twitch every 20 to 30 seconds.

• These movements can last for minutes or even hours.

• Usually happens during NREM sleep.

Night Terror:

• A person suddenly wakes up in fear, often screaming or panicking.

• Happens during NREM sleep (not dreaming stage).

• Person usually doesn’t remember the episode.

Sleepwalking:

• A person gets up, walks or does simple actions while still asleep.

• Happens during deep sleep (stage 3 or 4 of NREM).

• Not linked to dreaming, the brain is partly asleep.

• Runs in families and is common in children.

Sexsomnia:

• A rare condition where a person engages in sexual behavior while asleep.

• Can happen during deep sleep, like sleepwalking.

Importance of Sleep:

• Brains have natural systems that make us sleep.

• These systems slow down brain activity and reduce alertness.

Inhibitory brain processes help us sleep:

• Special chemicals (GABA) calm the brain, making you feel less awake and less responsive.

Why REM and dreams:

• REM sleep is a special stage where your brain is active, but your body is relaxed.

• It’s when most dreaming happens.

• Scientists believe REM and dreams may help with:

  • Memory processing.

  • Emotional regulation.

  • Brain development

Function of sleep:

1. Resting the Body: Sleep gives your muscles a break from daily activity.

2. Slow Down Metabolism: The body uses less energy during sleep, helps with energy conservation and body repair.

3. Cellular Maintenance in the Brain: Sleep allows neurons to clean-up and repair work.

4. Reorganizing Synapses: Synapses are adjusted and fine-tuned during sleep, helps the brain stay flexible and efficient.

5. Strengthening memories: Sleep helps store and organize new information. Especially during REM sleep, your brain replays and strengthens memories.

Sleep & Energy Conservation:

• Sleep helps to save energy.

• During sleep, the body lowers its temperature by about 1–2°C.

• Reduces muscle activity, less movement means less energy used.

Hibernation:

• In hibernating animals: Body temperature drops close to the surrounding environment.

• Heart rate and brain activity slow down dramatically.

• Brain cells shrink, and dendrites lose about 25% of their branches. These grow back when the animal warms up again.

Animals sleep differently based on their daily needs and survival strategies.

Key factors that affect sleep patterns:

Predator vs. prey status.

Time spent hunting or foraging.

Safety while sleeping.

Sleep & learning:

1. Sleep boosts learning: Getting enough sleep after learning helps to remember it better the next day.

2. Your brain replays what’s learnt: While sleeping, the brain replays the same activity patterns used during learning. This happens especially in the hippocampus.

3. Strengthening and cleaning up connections: Sleep helps the brain strengthen important connections and weaken unneeded ones, making memory more effective.

4. Sleep spindles = brain at work: After learning something new, your brain produces more sleep spindles. More spindles are linked to better learning and higher nonverbal IQ.

How much we sleep:

• Sleep takes up a large part of life:

  • Humans spend about one-third of their life sleeping.

  • Around 20% of that sleep is REM sleep.

• Different animals, different sleep patterns:

  • The amount of REM sleep varies between species.

  • Birds and mammals are the ones that experience REM sleep the most.

• More sleep = more REM:

  • In most animals, the more total sleep they get, the higher the percentage of REM.

  • People who sleep longer tend to have more REM sleep.

Function of REM sleep:

• Still researching:

  • Scientists aren’t 100% sure what REM sleep is for.

• Brain clean up:

  • During REM, the brain might get rid of unneeded connections.

• Learning motor skills:

  • REM may help strengthen physical skills you’ve recently learned.

• Eye movement theory (MAURICE, 1998):

  • REM sleep keeps your eyes healthy.

  • The rapid eye movements may bring oxygen to the corneas.

Dreaming:

2 main biological theories of dreaming:

1. Activation-synthesis hypothesis:

   • Dreams start with random brain activity in the pons.

   • This activity spreads to the cortex, which tries to make sense of it by creating a story of your dream.

2. Clinico-anatomical hypothesis:

   • Dreams are like thinking, but in a weird, dream-like way.

   • Doesn’t focus much on REM sleep or pons, instead, it looks at how the brain processes internal signals.

   • Dreams start from internal brain stimulation, mixed with: Recent memories and bits of sensory info.

Brain Areas Active During Dreaming:

• Parietal cortex: Helps with body awareness and space.

• Damage: No dreams or trouble combining body and visual info.

• Visual areas (outside V1): Create mental images in dreams.

• Hypothalamus & amygdala: Add emotion and motivation to dreams.