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This page was last modified on Feb 2, 2018

The Memory Trace: The Physiology of Memory

Types of amnesia

Patient H.M. (Henry Gustav Mo
HM Obitlaison, 1926-2008) {W}

HM 2

Surgery 1953
Died 2008
  • Short-term working memory was fine.
  • He could not remember any experience longer than about 5 to 10 minutes
  • He also had very significant memory loss of events in his life from before his operation.
  • His overall intelligence remained intact and he could generally care for himself, carry on conversations, and enjoy himself with puzzles and other games.
Hippocampus HM

H.M. was experiencing (1) massive anterograde amnesia and (2) significant retrograde amnesia

The Neural Circuitry of Memory
  • Richard F. Thompson: memories are stored in localized neural circuits, i.e., "unique, reusable pathways in the brain along which signals flow" (p. 247)
lpn red

Thompson Rabbit Eyeblink
  • Eric Kandel: memories result from alterations in synaptic transmissions at specific sites, i.e. there are long-lasting changes in whether synapses fire or don't fire [= "Long-Term Potentiation"]
  • Neurogenesis: while we know that new neurons are not created in most of the brain after birth, recent research finds that some new neurons may develop in the dentate gyrus of the hippocampus (= neurogenesis). From research with Patient H.M., we know that the hippocampus is central to the storage of new memories. 

  • Overall, despite many years of study, we are still not fully sure either where or how long-term memories are stored in the brain.

Different Types of Memory Systems

Systems of Memory

A. Nondeclarative ("procedural memory") = Implicit; nonverbal, shown by completing a task
•    Actions & perceptual motor skills, e.g., riding a bike, driving a car, cooking a meal, etc.
•    Implicit knowledge: how to solve a puzzle, how to fix a broken object

• Conditioned reflexes, e.g., responding to sounds or other signals
• Emotional memories: the feelings which were part of an experience

[Endel Tulving]B. Declarative • “What is” Memory = Explicit, verbal, visual, auditory
= Factual information

Endel Tulving (see photo) suggests two separate systems
1. Semantic Memory: knowledge of the world, "facts" which are independent of any specific time

2. Episodic Memory: Personal, time-bound, recollections which are linked to a particular point in time

Prospective vs. Retrospective Memory

  • Retrospective memories concern events in the past or information which is previously learned
  • "Prospective" memories involve remembering to perform tasks in the future.
    • E.g., carrying your umbrella, picking up your laundry from the cleaners, writing a "thank you" note to a friend


Endel Tulving also talks about the notion of an ability unique to humans which he calls "mental time travel" or more formally "chronesthesia. (Article from APA on this notion.)

By this, he means

  • the ability of human beings to go both backward and forward in time
  • to think about the past and to imagine the future
With this ability, humans can do things like
  • Plant seeds at the right time of the growing season
  • Harvest crops when they are at their peak
  • Keep records
  • Teach children what they can expect as they grow up


This page originally posted on 9/28/07