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BIO SCI N156: Lecture 20: Hippocampal-Neocortical Interactions in Systems…
BIO SCI N156: Lecture 20: Hippocampal-Neocortical Interactions in Systems Memory Consolidation
Optogenetics
Activation of the hippocampus index activates a contextual fear memory
Channelrhodopsin-2 tagged with a fluorescent tag
Can reactivate the cells that were active during learning
Shining blue light in a novel chamber, the mice displayed fear in a context they had never been shocked in
Implanting a false memory
By activating the dentate with light, the neurons get coupled with a false memory that they were shocked in a particular environment
Pattern separation
Facilitates the formation of unique episodic memories
Cell population activity in the EC is highly overlapped
Sparse activation of the DG and low contact probability of mossy fibers to CA3 cells manifests as unique cell ensemble activity for two separate input patterns
Dentate gyrus
EC has relatively few cells compared to dentate gyrus
EC has high level of activity
Local circuits have a lot of inhibition
A fraction of the many cells are active
Dentate considered one of the most sparse areas of forebrain
Sparsity = the relative proportion of neurons active in a region at a given time
Highly selective
An excellent "pattern separator"
Represents a bottleneck in the processing system
DG mossy fiber synapses on CA3 neurons are very strong
Single DG neuron can drive firing in target CA3 neurons
Recurrent CA3 network
CA3 has strong connectivity with itself
CA3-CA3 synapses = CA3 recurrent collaterals
Exhibit NMDA-R dependent LTP
For a CA3 neuron, 80% of its inputs are from other CA3 neurons
A key structure for "pattern completion"
When a partial cue is given, the rest of the cortex can be activated to retrieve the memory
Two types of consolidation
Cellular
Consequences of synaptic biochemical events initiated by original events
Time frame of hours
Systems
Consequence of an interaction between medial temporal hippocampal system and neocortex
Time frame largely unspecified - days, weeks, months, years
Re-examination of the role of the hippocampus in systems consolidation of declarative memories