Cognition, Sleep, and Memory Review

PART 1: COGNITION AND SLEEP

  • Memory Systems

    • Systematic approaches for remembering small amounts of information, e.g., phone numbers.
    • Retention of information involves various memory types.
    • Types of Memory: Short-term memory, long-term memory, working memory.
    • Methods of Remembering: Chunking, associating, visual aid use.

  • Stages of Sleep

    • Multiple stages: REM (Rapid Eye Movement) and NREM (Non-Rapid Eye Movement).
    • Significant events occur at various stages, affecting overall health and cognitive functions.

MEASURING BRAIN ACTIVITY: EEG

  • Electroencephalogram (EEG)
    • A diagnostic test for detecting electrical activity of the brain, represented as waves.
    • Electrical activity primarily recorded includes excitatory postsynaptic potentials (EPSPs).
    • Synchronized neuronal activity results in larger voltage changes.
    • Wave frequency correlates with concentration and alertness levels.

GRADED POTENTIAL

  • Mechanism:
    • Opening of ligand-gated Na+ channels results in depolarization as Ca+ or Na+ flows into the neuron, potentially leading to an action potential.
    • Opening of ligand-gated Cl- or K+ channels results in hyperpolarization, inhibiting action potential due to K+ leaving or Cl- entering the neuron.
  • Membrane Potentials:
    • Depolarization: Less negative inside the neuron (due to Na+ influx).
    • Hyperpolarization: More negative inside the neuron (due to K+ efflux).

TYPES OF ELECTRICAL ACTIVITY

  • Graded Potentials
    • Occur at the receptive regions of a neuron; short-lived and depend on stimulus magnitude.
    • Larger stimuli lead to increased ion flow and greater current.
  • Action Potentials
    • Occur at the axon; involve depolarization followed by repolarization, propagating along the axon to the terminal ends.

COMPARING GRADED AND ACTION POTENTIALS

  • Differences:
    • Graded Potentials: Amplitude varies, can be summed, has no threshold or refractory period, and decreases in amplitude with distance.
    • Action Potentials: All-or-none response, cannot be summed, has a threshold (~15 mV depolarization), possesses a refractory period, and conducts without decrement.

CNS STRUCTURES INVOLVED IN COGNITION

  • Key Areas for Higher Order Functions:
    • Reticular formation; regulates alertness.
    • Limbic system; regulates emotional responses.
    • Thalamus; sensory information relay.
    • Temporal lobe and Frontal lobe; crucial for cognition.

RETICULAR FORMATION

  • Composed of gray matter vertically through midbrain, pons, and medulla, extends into diencephalon and spinal cord.
  • Maintains mental alertness through motor and sensory components:
    • Skeletal muscle regulation, breathing, heart rate, and blood pressure.
    • Sensory information relay to the cerebrum.
    • Activation due to disruptions in sleep; decreased function in relaxation contexts.

COGNITION AND CONSCIOUSNESS

  • Defined as the state of alertness necessary for higher mental processing, including awareness and voluntary control.
  • Involves coordinated function of various brain regions, enabling response and engagement with the environment.

STATES OF UNCONSCIOUSNESS

  • Sleep: Reduced consciousness is not pathological.
  • Fainting: Temporary loss of alertness due to various causes.
  • Coma: Inability to awaken or respond despite stimuli.
  • Persistent vegetative state: No awareness with some spontaneous activity.

SLEEP AND SLEEP CYCLES

  • Brain Wave Frequencies: Differentiated in states of consciousness.
    • Waves like alpha, beta, theta, delta indicate various states from awake to deep sleep.

BRAIN STRUCTURES INVOLVED IN SLEEP

  • Regulatory Structures:
    • Reticular formation (sleep and wake transitions).
    • Hypothalamus (sleep onset and duration).
    • Hippocampus (active during dreaming).
    • Amygdala (emotional center during dreams).
    • Thalamus (prevents sensory signal during sleep).
    • Pons (initiates REM sleep).

RECOMMENDED AMOUNTS OF SLEEP

  • Birth to 1 year:
    • 16-18 hours per day, irregular rhythms, circadian rhythms develop at around 3 months.
  • 1-9 years of age:
    • 11 hours nightly, growth and axon myelination.
  • 10-20 years:
    • 9 hours nightly, increased synapses and maturation of brain areas.

WHY WE NEED SLEEP

  • Necessary for:
    • Neural maturation and restoration.
    • Facilitating learning and memory.
    • Decluttering by removing unimportant synapses.
    • Clearing metabolic waste and conserving energy.

TYPES OF BIOLOGICAL RHYTHMS

  • Circadian Rhythm: Natural sleep-wake cycle, influenced by environmental cues.
    • Affects hormonal release (e.g., melatonin, cortisol).
  • Phase Shift Rhythms: Adjusting sleep patterns can lead to jet lag.

INTERNAL CLOCKS AND ENVIRONMENTAL CUES

  • Hypothalamus as Pacemaker:
    • Receives light input and regulates bodily functions including melatonin production.
  • Light Effects:
    • Blue light reduces melatonin and increases wakefulness; yellow light helps induce sleep.

SLEEP INDUCTION: NEUROTRANSMITTERS

  • REM sleep shows high metabolism where ADP accumulation inhibits wakefulness.
  • Exercise is noted to aid in falling asleep.
  • Neurotransmitters: Involved in excitatory/inhibitory actions that modulate sleep and wakefulness.

DREAMS

  • Challenges in Dream Research:
    • Difficulties in defining dreams, linking neural circuits, and differentiating dream functions.

WHAT WE DO KNOW ABOUT DREAMING

  1. Role in cognitive development correlates with brain development and recall abilities.
  2. Changes in dream content with cognitive and emotional growth.
  3. Stability of dream content from late teenage years onward.

ACTIVATION-SYNTHESIS MODEL

  • Proposes dreaming results from activation of brain regions and internal sensory inputs during REM sleep, with blocking of external stimuli.

SLEEP DISORDERS

  • REM Sleep Disorder: Lack of skeletal muscle atonia, enabling movement during dreams. Associated with conditions such as Parkinson's disease.
  • Somnambulism: Sleepwalking occurring during N3 stage; movements are purposeful but not dream actions.

PART 2: MEMORY

  • Memory:
    • Encoding, storing, and retrieving neural processes, not merely physical objects.
  • Brain Regions Involved: Amygdala, thalamus, temporal lobe, hippocampus, caudate nucleus, prefrontal cortex.

PROPOSED MEMORY CIRCUITS

  • No single area for memory; functions rely on integrated circuits, influenced by the limbic system.

LIMBIC SYSTEM

  • Comprised of primitive brain structures that enhance or inhibit memory through emotional connections.
  • Key components: Amygdala, hippocampus, thalamus.

AMYGDALA

  • Involved in identifying danger (fear responses) and storing emotional memories.

HIPPOCAMPUS

  • Facilitates memory consolidation and spatial orientation; its activity is crucial during slow-wave and REM sleep for memory storage.

THALAMUS

  • Acts as a relay station linking sensory perception to other brain regions, integral for memory functioning.

TEMPORAL LOBE

  • Engaged in memory association and emotional responses, particularly visual memories.

TYPES OF MEMORY

  • Memory Consolidation: Requires sleep for optimum efficiency, involving the medial temporal lobe, hippocampus, and amygdala.

Memory Types

  1. Working/Short-Term Memory: Temporary retention of information, requiring neuron connection generation; methods include chunking and chaining.
  2. Long-Term Memory:
    • Can be non-declarative (implicit) or declarative (explicit).
    • Declarative subdivided into semantic (facts) and episodic (events).

LONG-TERM MEMORY STORAGE

  • Consolidation Mechanisms:
    • Changes in neurons and synapses after prolonged activation.

AMNESIA TYPES

  1. Anterograde Amnesia: Difficulty forming new memories after an event, while retaining old memories.
  2. Retrograde Amnesia: Loss of recent memories prior to a trauma.
  3. Transient Global Amnesia: Temporary inability to recall recent events lasting about 24 hours.

ADDICTION AND THE REWARD CIRCUIT

  • Studying how the brain responds to rewards and drugs, focusing on neurotransmitters and their effects on brain chemistry.

OPIOID ADDICTION

  • Mechanism of opioids on neurotransmitter release and subsequent tolerance and dependence on the substances.

SEROTONIN

  • Involved in wakefulness, cravings, and can affect addiction patterns and various treatments for disorders.

DOPAMINE

  • Central to various neurological conditions; its role in addiction underlines its importance in treating conditions like Parkinson's disease and schizophrenia.