In-Depth Notes on Memory Constructs and Disorders

Constructs of Memory

• Overview of constructs that represent different brain functions related to memory.
  • Includes auditory processing, case studies, memory disorders.

Auditory Domain

• Understanding how auditory signals (sound waves) are converted into electrical signals sensed by the brain.
  • Auditory pathway is divided into peripheral and central components.

Peripheral Auditory Pathway

• Begins with sound waves entering the pinna (outer ear).
• Sound travels through the ear canal to the eardrum (tympanic membrane), causing it to vibrate.
• Vibrations are amplified by the ossicles (malleus, incus, stirrup) and transmitted to the cochlea.
• Cochlea contains hair cells that convert mechanical vibrations into electrical signals.
  • Hair cells resemble tiny hairs, crucial for sound signal detection.

Central Auditory Pathway

• Signals from the auditory nerve go to the brainstem, then to structures like:
  • Cochlear nucleus
  • Superior olives
  • Inferior colliculus
  • Thalamus (medial geniculate nucleus)
  • Primary auditory cortex (A1, located in the superior temporal lobe).
• There are parallels between auditory and visual processing pathways:
  • Auditory information processing involves more brainstem regions as compared to vision.
  • Visual information primarily flows to the lateral geniculate nucleus.

Dorsal and Ventral Streams in Auditory Processing

• Dorsal stream (how and where): Helps localize sound sources.

  • Separates sound streams for understanding speech amidst noise (e.g., restaurant scenario).
  • Supports speech production.

• Ventral stream (what): Groups features of sounds (e.g., pitch, timbre) to identify auditory objects (like music).

Tonotopic Organization

• Cochlea exhibits tonotopic organization; different frequencies processed at different cochlear locations.
• Maintained throughout auditory pathways to primary auditory cortex.

Auditory Tests

• Pure tone audiograms used to test hearing acuity across different frequencies.
• Speech in noise tests (like Quicksin) assess understanding of speech in background noise.

Memory Constructs

• Different categories of memory include:
  • Sensory memory (milliseconds to seconds)
  • Short-term/working memory (seconds to minutes)
  • Long-term memory (minutes to years)

Taxonomy of Memory

• Explicit Memory: Conscious recollection of facts or events.

  • Episodic Memory: Personal experiences, context-specific recollections.
  • Semantic Memory: General factual knowledge without personal context.

• Implicit Memory: Unconscious memory, includes skills and habits (like riding a bike).

Memory Processes

• Steps in memory processing include:
  • Registration: Sensory perception.
  • Encoding: Associating sensory experiences (e.g., taste, smell, sight).
  • Consolidation: Stabilizing memory traces into long-lasting representations.
  • Storage: Maintaining encoded information for future retrieval.
  • Retrieval: Recalling stored information, can lead to re-encoding.

Amnesia and Disorders

• Amnesia: Severe memory deficits, often dissociated from other cognitive functions. Types include:
  • Retrograde Amnesia: Inability to recall memories before an injury.
  • Anterograde Amnesia: Inability to form new memories after an injury.
  • Rebud's Law: Recent memories are more affected than older memories.

Case Studies of Amnesia

• Patient H.M.: Underwent brain surgery leading to profound anterograde amnesia while sparing some functional memory.
• Clive Wearing: Exhibits profound anterograde amnesia due to viral encephalitis, retaining some semantic memory and procedural skills.

Dementia

• Types include Alzheimer's, Frontal Temporal Dementia, etc.
  • Alzheimer's is a leading cause correlated with substantial cognitive decline.
  • MCI (Mild Cognitive Impairment): Intermediate stage, may signify risk but doesn’t always lead to dementia.

Key Concepts in Memory and Cognition

• Normal aging leads to declines in episodic memory but often leaves semantic memory intact.
• Dementia involves global cognitive impairments, affecting daily life, seen progressively over time.
• Importance of diagnostics in differentiating between normal aging and dementia signs.

Summary

• Understanding memory entails differentiating between various constructs of memory, their processes, disorders, and their neural correlates, highlighting complexity in cognitive functioning and memory health.