PSYC 310 Lecture Notes - Lecture 6: Eyelid, Memory Consolidation, American Psychologist
7 May 2018
School
Department
Course
Professor
PSYC 318
Behavioural Neuroscience II
February 28th, 2018
Lecture 16/24: The influence of neurogenesis on memory
• Paper: “Hippocampal Neurogenesis Regulates Forgetting During Adulthood and Infancy”
o If there is a lot of neurogenesis in dentate gyrus, the retention of episodic memory is
impaired
o HC neurogenesis changes circuits involved in memory recall.
▪ Does this promote forgetting?
▪ Presumably, memory consolidation must occur in cortex before neurogenesis-
induced memory decay happens
• Paper 19: Final Summary
o Young mice have a lot of neurogenesis in the early weeks of life in their dentate gyrus
▪ As they get older the neurogenesis rate lowers and it is pretty low by 2-3 months
old
o If you’re an adult mouse you have better memory
o One month of exercise forgetting of HC-dependent (episodic) memories that you
learned before (e.g. fear conditioning like in the shock rooms, or neutral rooms or the
hidden platform Morris water maze task)
▪ The effects you get from exercise on your memory all depends on neurogenesis
rates
o If you pharmacologically induce neurogenesis you promote forgetting
▪ Reducing neurogenesis lessens the likelihood of forgetting
▪ Rodent species like guinea pigs who don’t show high levels of neurogenesis at
birth don’t show infantile amnesia, probably because neurogenesis is not
impairing their memory
• If you somehow increase amount of neurogenesis in them, this promotes
forgetting
• Neurogenesis promotes learning ability but hinders memory retrieval
o With a lot of neurogenesis, you can learn quite a bit
o With too little neurogenesis you learn not as much but retain it much better
o Balance between the two: what is the right amount of neurogenesis so that you can learn
and you can remember what you learn?
• Kids learn a lot of information when they’re young but growing up they tend to forget many
episodic memories (events that happened when they were very young)
o Findings in study in rodents:
▪ Newly born cell rate of surviving depends on the age of new cells and functional
relevance.
• Neurogenesis in rodents is high at birth but throughout aging it steadily decreases
o This is not true for primates (humans), in this case the rate of neurogenesis stops around
puberty
Memory traces & memory engrams:
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• A memory trace is a theoretical, psychological construct that’s used to study underlying
structures of memory
• A memory engram is a hypothetical permanent change in the brain that explains the existence of
certain memories: it is a molecular, biological change in the brain
• In search of the engram
o Karl Lashley (1890-1958)
▪ He was a prominent American psychologist who searched for the biological
locus of the engram
▪ Hypothesis was that the engram exists somewhere in the cortex…
▪ So he thought that lesioning cortex could impair memory
• Lashley’s experiments:
o Taught maze to rodents, initially not very good
▪ Then he lesioned parts of cortex
▪ The more he lesioned, the more errors the rat made in the maze
▪ He based it off the amount of cortex lesioned, not specific regions
• General findings:
o Memory deficits were related to the size of the lesion, not location
o Conclusion: Theory of Equipotentiality
• Cortical areas contribute equally to memory. This idea fit with the
broader concept of Holism (Gestalt) – the idea that natural systems and
their properties should be viewed as wholes, rather than as collections of
parts
o Problem:
▪ Task too complex, rats might solve maze using different strategies (sight, smell,
touch)
o Lasting contribution:
▪ Memories might be distributed among the vast number of neurons in the cerebral
cortex
• Donald Hebb
o Hebb argued in 1949 that long-term memory must be stored in physical changes in the
brain.
o His major contribution was the idea that strong or consistent reverberatory activity must
lead to physical changes in the brain that are responsible for stable memory storage.
▪ Famous saying was: “Cells that fire together, wire together”
o He believed that the memory engram must be located somewhere, but that it was
probably highly distributed among neurons in what was labeled as a neuronal ensemble
• A Hebbian Explanation of Pavlov’s Dogs:
o For this learning to occur, neurons triggering salvation receive input both from food
detecting neurons but also from those receptive to environmental stimuli (e.g. the sound
of a bell ringing)
▪ The system originally was wired such that every time food was detected, the
animal would salivate.
▪ The bell-associated neurons initially had a weak influence over the salivation
neurons, but wiring does exist and so it is possible to learn
▪ If the bell-associated neurons are consistently active at the same time as the
salivation-associated ones, then synaptic influence grew strong enough so that by
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Lecture 16/24: the influence of neurogenesis on memory: paper: hippocampal neurogenesis regulates forgetting during adulthood and infancy . This is called the delay procedure: there"s a slight delay between the onset of the. Inferior olive stimulation also consistent: pontine nucleus stimulation changes, before no eye blink, after eye blink. Tone shuts off, though, before air puff is delivered. 0. 5 second gap between the end of tone and the air puff (not delay conditioning: trace conditioning and the hippocampus, tone comes on for 100ms, you need the hippocampus to learn trace conditioning, trace conditioning and the hippocampus: If you lesion hippocampus one day later, memory is entirely gone: memory is stored in hippocampus. If wait a month then lesion hippocampus, learning is maintained: eventually stored in cortex, hippocampus can hold memory over a gap period, circuitry of eyeblink conditioning, trace vs delay conditioning and the hippocampus. If you switch to trace conditioning procedure (add half second gap)
