Lecture 17: The Neuroscience of Sleep

Introduction

  • University Information:
    • University of Lethbridge
    • Presented by Dr. Chelsea Ekstrand
    • Date: November 25, 2025

Learning Objectives

  • Discuss the significance and concepts of sleep.
  • Examine the reasons behind sleep, encompassing four distinct theories.
  • Understand methodologies used in studying sleep patterns.
  • Explore circadian rhythms and the brain's process of cleaning during sleep.
  • Investigate the impact of sleep on memory and the learning process.

Effects of Sleep Deprivation

Consequences of Insufficient Sleep

  • After 24 hours:
    • Equivalent to a Blood Alcohol Concentration (BAC) of 0.10%.
  • After 36 hours:
    • Hormonal dysregulation occurs.
  • After 48 hours:
    • Immune system disruption.
  • After 72 hours:
    • Hallucinations may occur.
  • Exceeding 3 days:
    • Risk of organ failure or death.

Consequences of Excessive Sleep

  • Cognitive Effects:
    • Cognitive impairment, causing decreased mental function.
  • Physical Effects:
    • Daytime drowsiness, sluggishness, low energy levels.
  • Health Issues:
    • Headaches and associated depression.
  • Sleep Disorders:
    • Trouble sleeping, leading to a cycle of insomnia.
  • Long-term Risks:
    • Obesity and higher mortality rates associated with excessive sleep patterns.

Theories of Why We Sleep

Overview

  • There are four theories explaining the functionalities and purposes behind sleep:
    • Inactivity Theory
    • Energy Conservation Theory
    • Restorative Theories
    • Brain Plasticity Theory

Inactivity Theory

  • Also known as the evolutionary theory
    • Functionality:
    • Sleep acts as a survival mechanism, reducing risks of predation by keeping animals still and quiet during vulnerable periods.

Energy Conservation Theory

  • Focuses on competition for energy resources.
  • Mechanism:
    • Sleep decreases overall energy demand on the body.
    • Physiological Changes:
    • Energy metabolism is notably reduced during sleep.
  • Example:
    • After consuming a large meal, lions can sleep for up to 24 hours.

Restorative Theories

  • Posit that sleep restores physiological functions lost during waking hours.
  • Mechanisms:
    • Facilitates repair and rejuvenation of bodily systems.
    • Adenosine Clearance:
    • Sleep assists in clearing adenosine, a byproduct of neural activity, from the brain, which induces feelings of sleepiness.

Brain Plasticity Theory

  • Proposes that sleep is linked to structural and organizational changes in the brain.
  • Key Components:
    • Sleep is essential for brain development and cognitive functions.
    • Effects of Sleep Deprivation:
    • Impairs the ability to learn and acquire new information.

Methods of Studying Sleep

Animal Studies

  • Can involve invasive techniques but yield insights that are beneficial for understanding human sleep conditions.
  • Applicable Conditions:
    • Insomnia, restless leg syndrome, sleep apnea.
  • Specialized Sleep:
    • Some animals can exhibit unihemispheric sleep, resting one side of the brain while the other remains alert.

Human Studies

  • Polysomnography:
    • A comprehensive method of studying sleep which records:
    • Brain waves using EEG (Electroencephalography).
    • Blood oxygen levels.
    • Heart rate and breathing patterns.
  • Outcome:
    • Monitors distinct stages of sleep based on collected data.

Electroencephalography (EEG)

  • Procedure:
    • Involves the use of a pen recorder to capture brain activity through electrodes placed at specific locations.
  • Significance of Wave Patterns:
    • Irregular high-frequency noise indicates independent neuron activity, while regular low-frequency noise represents synchronized neuronal activity.

Sleep Stages

Classification of Sleep Stages

  1. Stage 1:
    • NREM sleep; transition from wakefulness to sleep.
  2. Stage 2:
    • Light NREM sleep; easily woken.
  3. Stage 3:
    • Deeper NREM sleep.
  4. Stage 4:
    • Deep NREM sleep; characterized by the lowest heartbeat, breathing, and brain wave activity.
  5. REM Sleep:
    • Characterized by rapid eye movement and increased brain activity.

Circadian Rhythms and Brain Cleaning During Sleep

Circadian Rhythms

  • Defined as physical, mental, and behavioral changes that adhere to a daily cycle.
  • Regulation:
    • Responds to the light-darkness cycle and is genetically predetermined.
  • Biological Clocks:
    • Proteins that interact within every tissue in the body act as biological clocks.
  • Suprachiasmatic Nucleus (SCN):
    • Acts as the central control of circadian rhythms, commonly referred to as the “queen of clocks.”

Sleep and Brain Cleaning

  • During sleep, cerebrospinal fluid (CSF) flow is notably active, facilitating brain cleaning.
  • Glymphatic System:
    • A sophisticated system for removing toxins and waste from the brain during sleep.
    • Employs specialized cells to flush out undesirable molecules and facilitate healthy brain function.

The Role of Sleep in Memory and Learning

Sleep Impact on Learning and Memory

  • Key Processes:
    • Acquisition: Introducing new information to the brain.
    • Consolidation: Stabilizing and organizing memories.
    • Recall: Accessing stored information.
  • Importance of Sleep:
    • Critical for the consolidation process, enhancing learning outcomes.

Sleep Consolidation Mechanisms

  • Reactivation of memories during sleep is facilitated by sleep spindles (bursts of brain activity).
  • Procedures:
    • During wakefulness, the hippocampus integrates new information within the distributed cortical network.
    • Sleep reactivates this network, strengthening cortical connections and eventually reducing dependence on the hippocampus.

Sleep and Unlearning

  • Study Reference:
    • Andrillon et al. (2017), Nature
  • Findings:
    • Participants exposed to sound sequences while awake and asleep recognized sounds from REM and light NREM sleep but not from deep NREM sleep.
    • Learning new sounds during deep NREM sleep proved more difficult.

Summary and Future Learning

Key Study Topics

  • Effects of insufficient and excessive sleep.
  • Four theories explaining the necessity of sleep.
  • Methods employed in studying sleep patterns.
  • Identification of the brain regions responsible for circadian rhythms and brain cleaning processes.
  • Understanding the influence of sleep on memory and learning.

Upcoming Class Information

  • Activity 4: Opened November 24th, closing November 30th.
  • Quiz 3: Scheduled for December 4th
  • Next Class Date: November 27th, focusing on Science vs. brain training.