Learning and Memory Flashcards
What is memory?
Changes in the nervous system that occur during the acquisition, retention and recall of information about the world and one’s past experiences.
How may STP play a key role in WM? (Keeping a phone number in mind briefly).
Maintaining short-term neural activity through facilitation.
Define a cell assembly: , cells within an assembly are bound together by …
Network of neurons that is activated whenever a function is executed. Bound together by excitatory synaptic connections strengthened at the time the memory was formed.
Who showed that memories are stored in cell assemblies, and how?
Tonegawa et al. Animals fear conditioned. Light activation of granule cells active during conditioning in new environment elicited strong freezing response.
What does the hippocampus comprise?
A loop of connections that process multimodal sensory and spatial information from the superficial layers of the entorhinal cortex.
What is the output region of the hippocampus?
CA1.
Cytoarchitecture of the hippocampus:
Entorhinal cortex to hippocampus via perforant pathway. Synapse on dentate gyrus. DG axons synapse on CA3, Schaffer collateral to CA1.
Who showed tetanic high frequency stim (i.e., 100Hz). to Schaffer collateral evoked an EPSP much greater than before?
Bliss and Lomo, 1973.
LTP mechanism:
Depolarisation, removal of Mg2+ block allowing Ca2+ influx. Initiates signalling cascades. Activates CaMKII, phosphorylates AMPA channels, increasing conductance and favouring insertion of new ones.
What can postsynaptic cells also do in LTP? Other than phosphorylate AMPA?
Release retrograde messengers that activate protein kinases in PreS terminal to enhance subsequent NT release.
What blocks LTP in response to 100Hz stim.?
2-amino-5-phosphonovaleric acid.
What did Morris et al 1986 show?
Rats given APV could not learn to remember where a submerged platform was in a water maze. Blocking NMDARs disrupts hippocampus-dependent learning.
What was shown about the timing of APV application on water maze learning?
If applied after no effect. NMDARs thus essential for induction but not necessarily maintenance of LTP.
Spatial learning is enhanced in transgenic mice that …
Overexpress a subunit of NMDAR. Rate of learning in Morris maze faster.
What shows that NMDAR-dependent LTP plays a role in more than just spatial learning?
When NMDAR in CA1 blocked, mice also not able to master a nonspatial object recognition task or learn complex odour discrimination.
What study showed that LTP has longevity?
Abraham et al (2002). LTP induced in CA1 of awake animals can last many weeks.
In what sense is LTP associative?
Weak presynaptic input insufficient, paired with strong to suprathreshold. Large depolarisation propagates to synapses with weak input, relieving Mg2+ blockade there, inducing LTP.
Why is associative LTP good?
Enables a pattern of activity in one group of cells to become linked to a distinct pattern of activity in a separate but partially overlapping group of synaptically coupled cells. This means that related events can be associated with each other, as occurs in explicit memory.
In what sense is LTP synapse specific?
Unstimulated synapse does not undergo LTP despite strong stimulation of neighbouring synapses. Depolarised but no binding. No co-incidence.
Why is synapse-specific LTP useful?
Large amounts of information must be stored in one network. More stored through functional alterations at specific synapses than through blanket changes in a cell’s excitability.
Why is LTD important?
If synaptic connections only enhances, synaptic transmission may saturate (where further enhancement not possible).
Who showed that low frequency (1-5Hz) tetanic stim. at Schaffer collateral leads to a depressed response to stimulation of that input?
Dudek and Bear, 1992.
What is spike-timing dependency?
Biological process that adjusts the strength of synaptic connections between neurons based on the relative timing of their action potentials.
When does postsynaptic spike have to occur for LTD to be induced?
Prior to glutamate release.
Why does postsynaptic spike prior to Glu release lead to LTD?
Release of block before channel open, only small influx of Ca2+. Ca2+ responses selectively activate diff. types of enzymes. Large, kinases (put phosphate groups on receptor). Small, phosphatases.
What is the function of spike timing dependency?
Inputs that might be the cause of PostS neuron excitation made more likely to contribute in future.
Who showed that there are place cells in the hippocampus?
O’Keefe (1971). Cells in CA1 and CA3 fire selectively when animal located in specific position.
Combination of currently active place cells is sufficient to …
Read out precisely where the animal is in the environment.
