PSYC 310 Lecture Notes - Lecture 8: Housekeeping Gene, Doxycycline, Tail Suspension Test
7 May 2018
School
Department
Course
Professor
PSYC 318
Behavioural Neuroscience II
February 21st, 2018
Lecture 13/24: The Hippocampus and Memory Engrams
• Memory:
o Short-term, working memory vs. long-term memory
o No clear distinction between these two: it often depends on the content of that
memory, neural circuits involved, cell types, molecular machinery encoding the memory
o Following a memory over time is difficult and not obvious
o Long-term memory
▪ Explicit memory vs. implicit memory
• Explicit memory: conscious, interntional recollections of experiences of
information
• Implicit memory: previous experience alters future behavior without
conscious awareness of what was learned
▪ Declarative memory vs. procedural memory
• Declarative memory: memories that can be declared, verbalized, stated
in words
o Only used to describe a phenomenon of human memory
o We dot ko if rodets are osiousl aare of eor, so
e use ter epliit eories for the that ust e ased o
knowledge of the world (learned)
• Procedural memory: motor memory, perception memory: for the
performance of particular types of actions
o Reinforcement learning strategies and incorporated dopamine
signaling: to better how we can do something over time
▪ In Explicit memory: Episodic memory vs. Semantic memory
• Semantic: details of world that hold true across episodes
• Episodic: Past, personal experiences that can be explicitly stated
▪ In Implicit memory: Procedural memory vs. non-procedural, unconscious
memory
• Non-procedural e.g. perceptual memories for group categorization
• Motor memories
o Both forms of explicit memory require hippocampus in order to be learned
▪ Over time semantic memories probably become hippocampal independent and
get permanently consolidated in neurons throughout the cortex
▪ Hippocampus can look up a record of what happened, reactivate neural circuits
that were last active at the time:
• Hippocampus stores a node that represents the episode
• What it is doing to bring memory back is reactivating cortical neurons
that perceived sensory stimuli at the time
• Nothing is actually stored in hippocampus, just directions to information
from cortex
• We think semantic information is entirely stored in the cortex
find more resources at oneclass.com
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• In order for cortex to learn consistent information over time it needs
hippocampus to remember each episode
• Episodic memories seem to always be dependent on hippocampal
activity
• The hippocampus
o Human vs. rodent brain slice
▪ HC at top in dark region: dense collections of cell bodies
▪ Structures labeled: dentate gyrus, CA1, CA2, CA3 getting information from
entorhinal cortex that feeds into dentate CA1 2 3 out
o We think HC is a record keeper of what neurons in cortex were activated at each
moment
o HC also needed for memory recall
▪ The reord keeper has a hard tie differetiatig if the eet as restritie to
right now or if HC was actively recalling a memory
o When we electrically stimulate HC in humans, they often start remembering different
episodes of their life
▪ Suggests that we are triggering memory recall events a person can play out or
think about in real time
▪ How can we gain control over neurons in HC that reflect distinct memory? Can
we activate them to trick animal into remembering certain events/storing
memories?
• The amygdala
o Very involved in emotions: when we lesion it in humans most pronounced consequence
is reduced fear
o In rodents we think it is critical for driving all different kinds of emotions, not just fear
o We can trigger different emotional responses by triggering different cell types or areas in
the HC
▪ Consistent: we think these neurons are hard-wired from birth to trigger certain
emotions
▪ Output of these neurons will never change: when you stimulate certain ones
oull always get fear, for example
o Some clusters of neurons in the amygdala promotes specific behaviors or emotions of
either positive or negative valence
▪ Valence: intrinsic attractiveness (positive valence) or avoidance (negative
valence) of an event, object or situation
▪ Hard to determine this in neurons
• Memory engrams in the HC
o When you have a memory of something good HC has to store it:
o Should I store it in areas that have positive neurons or negative neurons? Are there pre-
designed spots OR can neurons that make up a memory have changed effects after
stimulation over time?
o It is generally believed that memories are encoded by sparse populations of neurons
distributed throughout the HC
▪ Not close together: distributed throughout the HC
▪ We need to get optogenetic control over a sparse population distrusted across
the HC
o Discrete ensembles of HC neurons active at any given moment in time: as animals move
around different cells become active
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
In explicit memory: episodic memory vs. semantic memory: semantic: details of world that hold true across episodes, episodic: past, personal experiences that can be explicitly stated. Can we activate them to trick animal into remembering certain events/storing memories: the amygdala, very involved in emotions: when we lesion it in humans most pronounced consequence is reduced fear. Dna from birth: any time animal makes c-fos they make tta, use a virus to express tta-dependent gene promoter (tre) that drives. Label cfos positive neurons in green, blue is a cell body stain (in dentate gyrus) In some mice taken off antibiotics for two days but left them in their home cage, If you wait 1 month the chr2 expression totally disappears. If a(cid:374)i(cid:373)als did(cid:374)(cid:859)t get sho(cid:272)ked i(cid:374) the (cid:374)e(cid:449) roo(cid:373) the(cid:455) do(cid:374)(cid:859)t freeze (cid:449)he(cid:374) you reactivate neurons to remind them of events: you need to give them a reason to fear the memory to get behavioral expression.
