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This page was last modified on Sept 14, 2021

The Physiology of Memory II

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)
    • Eyeblink Conditioning. Thompson and his lab demonstrated that there is neural tissue in the cerebellum (the lateral pontine nucleus) which must be there in order to cause an animal to learn a conditioned response to a stimulus (pairing a sound with a puff of air to cause a rabbit to blink its eye). He also demonstrated that there is another area of tissue right outside the cerebellum (the red nucleus) which has to be functioning in order for the response to happen. It appears that the signal for the response goes from the lateral pontine nucleus to the red nucleus and, then, to the rest of the brain.
lpn red nucleus

  • 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"]

YouTube Video (2'43") explaining in greater detail what Kandel discovered in working with the sea snail.


  • 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.

Memory Organization: How is our long-term memory organized?

How is our memory stored? How is it organized? Here is a possible approach to answering these questions
(though ultimately we are not yet sure of the answer)

  • Organized cluster of knowledge about particular objects or events or concepts
  • We remember what clashes with the schema

schema for "college"
Semantic Networks
= concepts joined together by pathways that link related concepts
  • recalling one of the nodes within the network may trigger recall of other nodes ==> spreading activation within a semantic network
semantic network for "college"
Connectionist (or Parallel Distributed Processing [PDP]) Model of Memory
  • in this model, remembering = at the same time [parallel] the brain is activating multiple networks of interrelated concepts [distributed]
  • the memory is NOT a single “thing or place” but is stored in the activation pattern

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

                  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