The Neural Circuitry of Memory

• Richard F. Thompson (University of S. California): Memories are stored in localized neural circuits, i.e., "unique, reusable pathways in the brain along which signals flow"
  

Experiment: Eyeblink Conditioning in Rabbit

 “[I]f a rabbit repeatedly hears a tone that’s followed by an unpleasant puff of air blown into its eye, the conditioned response it develops is to blink automatically every time it hears the tone. Moreover, it learns to blink with perfect timing to deflect the anticipated air-puff. This “eyeblink conditioning” is the experimental paradigm Thompson has used most frequently in his investigations” (Blakeslee, 2022)

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. 

Note that his discovery is about conditioned responses to events, that is, NOT about declarative memory for facts or experiences, but for learned reactions to events that happen to us that eventually become habitual or automatic.

• Eric Kandel (Columbia University)
  
  
• 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, some research finds that a few 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. Note, though, that this finding is very hotly debated.

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

Schemas As we saw in a previous class, a schema is an organized cluster of knowledge about particular objects or events or concepts We remember what clashes with the schema

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

Connectionist (or Parallel Distributed Processing [PDP]) Model of Memory   “is based on the idea that the brain does not function in a series of activities but rather performs a range of activities at the same time, parallel to each other… it proposes that cognitive processes can be represented by a model in which activation flows through networks that link together neuron-like units or nodes, i.e. Parallel - more than one process occurring at a time; distributed processing - processing occurring in a number of different locations.” <massey.nz> the memory is NOT a single “thing or place” but is stored in the activation pattern

---