Plasticity In The Hippocampus Flashcards
(40 cards)
Where is the hippocampus?
Medial temporal lobe
From medial to lateral name the structure of the medial temporal lobe?
Hippocampus
Enterhinnal cortex
Perihinnal Cortez
Parahippocampal cortex
Why is the entorhinal cortex important?
Sends projections to the hippocampus
Contains grid cells which are active when rat is in multiple locations
When rat navigates around the clock in different locations some grid cells would become more active than others
Send signals to place cells in hippocampus
How are memories formed (grossly)?
Sensory information
Processed by cortical association areas
Sent to parahippocampal and entorhinal cortical areas
To hippocampus (back to engram cells in respective cortical association areas in loop AND Hippocampus to the thalamus and hypothalamus via the fornix)
What are the synapses in the trisynaptic pathway?
EC (perforant path) - granular cells in dentate gyrus
Mossy fibres (axons of granular cells) - pyramidal cells in CA3
CA3 - CA1
What 2 pathways go from ca3 to ca1? What’s the difference?
Schaffer collateral fibres projects to CA1 from ipsilateral hippocampus CA3 region
Associational commissural fibres project to CA1 from contralateral CA3
What does the CA in CA1 and 3 mean?
Cornu ammonis (rams horn)
What layers of the entorhinal cortex makes up most of the perforated path?
2 and 3
The perforated path is made from a medial section and lateral section. Where do they originate and terminate?
Medial - layers 2 and 4 to dentate gyrus
Lateral - layers 3 and 5 bipass the dentate gyrus and synapse on CA3 neurons
Where do CA1 neurons project to?
Proximal CA1 neurons to distal subiculum
Distal ca1 neurons to proximal subiculum
Where do neurons within the subiculum project to?
Proximal subiculum to medial EC
Distal subiculum to lateral EC
2 closed loops are formed as the distal subiculum received lateral EC inputs
Proximal subiculum receives medial EC inputs
What are the functions of the hippocampus?
Behavioural inhibition (removal = behavioural inhibition in animals) Memory Spatial map - place cells
What are place cells?
The GPS of the brain
Particular neurons in the hippocampus fire when we are in a particular location ‘place field’
Based on visual cues AND where we think we are in space (if familiar with the location)
PET scans of humans navigating through a video game show hippocampal activity
Who first discover LTP?
Bliss and lomo 1973
In the hippocampus of rabbit brains
Between perforant path and dentate gyrus
Experimentally how can LTP be produced?
Theta burst stimulation
3 trains of stimuli 20 seconds apart
Each train consists of 10 stimulus epochs delivered at 5Hz (200ms apart)
Each epoch consists of 4 pulses at 100Hz
What are the 4 properties of LTP?
Cooperativity
Persistence
Input specific
Associativity
What is meant by LTP cooperativity?
Weaker spacial summation of multiple synaptic inputs can induce an action potential. Synapses which contribute to this AP will be potentiated.
What is meant by spike time dependant plasticity?
LTP will occur if and action potential occurs within 100ms of transmitter release, important for cooperativity
As the synapses which contributes to the AP will be potentiated.
If Inout occurs after postsynaptic AP FIRING that will be depressed
What is meant by persistence?
LTP can last for hours/days/months
Due to protein synthesis and structural changes in the synapse
Role of PKM(Zeta)
What is meant by input specific LTP?
LTP Occurs only at synapses which are activated
Synaptic tag?
What is associativity?
A strong stimulus will potentiate a weaker stimulus if an AP is induced. Contributing fibres and post synaptic cell need to be activated together.
Therefore, the weaker input following potentiation may be able to induce an AP alone (could not do so before potentiation by sting input)
Thus the the strong input is now associated with the previous weak input
What learning theory is associativity associated with?
Classical conditioning
The strong input and weak input have been associated together as following potentiation both can cause an action potential in the same post synaptic cell
What feature of NMDAR/ makes them a ‘coincidence detector’?
They detect both change in post synaptic membrane potential AND glutamate release
What is the importance is AMPAR mediated depolarisation and NMDAR function?
Extent of depolarisation mediated by AMPARS control the extent of mg2+ release from NMDARs. Therefore, it governs the amount of calcium entry
Low levels active phosphatases (LTD)
High levels activate kinases (LTP)
