Study Notes on Memory and Sleep

PHYSIO — MEMORY & SLEEP

MEMORY — Brain Areas & What They Do

1. Hippocampus — “The Filing Cabinet”

• Function:
  • Consolidates new declarative memories (facts + events) from short-term memory to long-term memory.
  • Critical for spatial memory, which includes memory for locations and navigation.
• Clinical Case - H.M. Case:
  • Following the removal of the hippocampus, H.M. exhibited:
  • Intact:
    • Short-term memory
    • Procedural memory
  • Impaired:
    • Forming new declarative long-term memories (LTM);
    • Some remnant of episodic memory is maintained.
• EPPP (Examination for Professional Practice in Psychology) angle:
  • Damage to the hippocampus results in anterograde amnesia for declarative memories, whereas procedural memory remains intact.

2. Basal Ganglia + Cerebellum — “Skill & Habit Centers”

• Function:
  • Responsible for procedural learning, including skills, habits, and motor routines.
• Consequences of Damage:
  • Results in difficulty learning new motor skills and performing learned skills.
• EPPP angle:
  • Implicit memory, which does not require conscious thought, relies heavily on these brain structures.

3. Amygdala — “Emotion Tagger”

• Function:
  • Assigns emotional significance to memories, increasing recall of emotional events.
• Clinical Implications:
  • People can better recall emotional events if the amygdala is functioning properly.
  • Damage to amygdala results in no significant difference in recall of emotional versus non-emotional memories.
• EPPP angle:
  • The role of emotion is crucial in strengthening memory consolidation.

4. Prefrontal Cortex — “The Organizer”

• Function:
  • Handles working memory, prospective memory (the ability to remember to perform actions in the future), item memory (what happened in past experiences), and source memory (where and when events occurred).
• Consequences of Damage:
  • Results in confusion, difficulty planning, and trouble recalling the context of memories.

5. Thalamus — “The Relay Hub”

• Function:
  • Plays a significant role in memory processing.
• Consequences of Damage:
  • Can lead to both anterograde and retrograde amnesia.
• Association with Korsakoff’s Syndrome:
  • Often involved indirectly through the mammillary bodies section.

NEURAL MECHANISMS OF MEMORY

1. Kandel’s Research — How Neurons Store Memory

• Subject:
  • Conducted research with sea slugs (Aplysia) to understand memory storage mechanisms.
• Findings:
  • Short-term memory correlates with increased serotonin release, strengthening synaptic transmission temporarily.
  • Long-term memory involves new synapse formation and structural synaptic changes, dependent upon RNA and protein synthesis.
  • Blocking RNA synthesis results in an absence of long-term memory formation, although short-term memory remains unaffected.

2. Long-Term Potentiation (LTP)

• Definition:
  • A process where repeated stimulation leads to stronger synaptic responses.
• Location:
  • Initially observed in glutamate receptors in the hippocampus, now noted in the amygdala and entorhinal cortex as well.
• Trigger Mechanism:
  • Induced by rapid, high-frequency stimulation.
• Benefits:
  • Increases synaptic strength and efficiency, considered a major cellular basis of learning and memory.
• EPPP angle:
  • Significance of LTP as a foundational mechanism in learning processes.

SLEEP — High-Yield for EPPP

Purpose of Sleep (2 Theory Categories)

1. Restoration Theory

• Sleep serves to repair daily wear and tear on the body and brain.

2. Evolutionary / Adaptive Theory

• Sleep serves to conserve energy and protect against nighttime threats.
• EPPP aspect:
  • Be prepared to evaluate which theory aligns with specific sleep-related explanations.

Stages of Sleep (EEG-Based)

• Two primary types: NREM (Stages N1–N3) and REM (Stage R).

🌙 N1 — “Lightest Sleep”

• Characteristics:
  • Transition from wake to sleep, marked by alpha to theta wave transition.
  • Typically involves drifting and a tendency to deny being asleep.

🌙 N2 — “True Sleep”

• Characteristics:
  • Presence of sleep spindles (fast bursts) and K-complexes (large slow waves) amidst theta waves.
  • Body temperature decreases, heart rate (HR) and breathing slow down, and muscles relax.

🌙 N3 — “Deep Sleep / Slow Wave Sleep (SWS)”

• Characteristics:
  • Characterized by delta waves; high amplitude and low frequency.
  • It is most challenging to wake a person from this stage, which is also restorative, and releases growth hormone.
  • The duration of this stage decreases throughout the night.

💤 REM (Stage R) — “Paradoxical Sleep”

• Characteristics:
  • EEG readings resemble an awake state with beta and some theta waves.
  • The body experiences paralysis, and dreams tend to be vivid, emotional, and narrative-driven.
  • Difficulty arises in waking a person, and REM periods elongate towards morning.
• EPPP note:
  • Most vivid dreams transpire during REM, while nightmares occur in NREM parasomnias; common among children.

Sleep Cycle Facts

• First sleep cycle predominantly features N3 with a shorter REM duration.
• Subsequent cycles reveal:
  • Increased duration of REM
  • Decreased duration of N3

Sleep Across the Lifespan

Infants:

• Sleep duration of 14–16 hours/day.
• Begin sleep with REM rather than NREM.
• By 3 months, normal sleep sequence (NREM → REM) commences, with all three NREM stages evident by 6 months.

Adults:

• Typical sleep duration is around 8 hours, with REM making up approximately 20–25% of total sleep time.

Older Adults:

• Require approximately the same amount of sleep but face challenges such as:
  • Longer durations to fall asleep
  • Increased frequency of nighttime awakenings
  • Less time spent in N3 (deep sleep)
  • More evenly distributed REM periods across the night
  • Advanced sleep phase (going to bed early and rising early).
• EPPP often queries on N3 decline related to aging and advanced sleep phase concepts.