Structure and Function of the Hippocampus Flashcards
What structure is adjacent to the hippocampus?
Entorhinal Cortex
What parts of the hippocampus receives many of the inputs from the neocortex?
Dentate Gyrus
Which one is a glutame receptor?
NMDA
Which cortical region strongly connected to the hippocampal is associated with spatial processing?
Parahippocampal Cortex
An influx of which positively-charged ion gives rise to LTP?
Calcium
Which positively-charged ion must be moved out of membrane pores for LTP to occur?
Magnesium
Where does most LTP take place in the hippocampus?
Between CA3 and CA1 cells
What do NMDA knock-out mice do in the water maze?
Find the platform by trial and error each time
What task was used to investigate relational memory in rats?
Transitive Inference Task (Beakers)
What is the difference between recollection and familiarity?
Only recollection involves mental time travel
how did the hippocampus get its name?
hippocampus means seahorse of the similar structure / shape -> structure is very important for the functions (as functions change along the hippocampus
what does long-term memory at the level of individuals neurones reflect?
structural changes at the synapse
- when we learn something we aren’t just changing the chemical makeup of the brain but we are physically changing the synapse itself allowing us to learn new long-term memories
Which anaesthetic used as a recreation drug disrupts the ability to form memories?
Ketamine is an NMDA receptor (type of glutamate receptor) supporting memory function
- Ketamine causes memory disruption
Where is the hippocampus?
medial temporal lobes / cortex (buried deep inside)
what is the hippocampus structure?
- along its lengths, the hippocampus shows distinct cell fields that are tightly folded
- the connections between these cell types are relatively well-understood
what is structure like within the hippocampus?
- Inputs via dentate gyrus
- Associations between CA1 and CA3 fields
- Outputs via subiculum
describe the layering of the hippocampus
layers are wrapped around each other and usually connected up -> helping us understand how long-term memories are supported by the hippocampus
There are four main types of cell fields within the hippocampus, what are they?
- CA3 and CA1 Neurones
- Subiculum
- Dentate Gyrus
How is information received and outputted in the hippocampus?
- Hippocampus receives input primarily via the dentate gyrus
- Dentate gyrus projects to CA3 and CA1 subfields of the hippocampus
- They send their outputs to the subiculum (output via subiculum) (major output system of the hippocampus)
What components sit next to the hippocampus? [need to find out how the hippocampus is connected to the adjacent cerebral cortex]
In order of closest to furthest:
* Entorhinal Cortex
* Perirhinal Cortex
* Parahippocampal Cortex
what is the hippocampus structured from and how is this different from the entorhinal cortex?
hippocampus has an unusual structure and is allocortex (different micro-structure from the cerebral cortex)
While Entorhinal cortex is a neocortex
what is the role of the Entorhinal cortex?
acts as a gateway between information in the rest of the cerebral cortex and hippocampus
what is the Perirhinal cortex important for?
localised site important for object recognition (/representation)
* stronger response in this cortex when using object recognition
what is the parahippocampal cortex important for?
spatial layout coding
- more activation when representing location (location representation)
how do we bind different representations of experience [theory of hippocampal function]?
we can bind representation which were active at the same time together in the hippocampus
i.e. objects via Perirhinal (dog and cup) and Place via Parahippocampal (beach)
what happens when we encounter these representations again?
it can reignite the whole memory
why is the structure in the hippocampus critical for it’s function
- Hippocampus
- Entorhinal feeding information into the hippocampus (major gateway into hippocampus from rest of the cerebral cortex) -> primarily receives it information from the parahippocampal and perihinal cortex
How does the hippocampus form associations?
- Parahippocampal (Location) and Perihinal Cortex (Object) learn about familiar objects and locations, binding together these aspects of memory by projecting information up into the hippocampus
- The hippocampus then forms associations between these different types of input via Eichenbaum et al. ‘Relational Theory’
How does the hippocampus differ in function, dependent on the region?
Posterior: greater input from parahippocampal cortex (spatial memory)
* location and spatial representation
Anterior: Greater input from amygdala and perirhinal cortex (emotional memories/processing, item familiarity/salience)
* memories for detecting novelty (new/old items)
Why is it believed the hippocampus differs?
there are differences in the anterior and posterior hippocampus functions because of the way different connections vary (and different proximities to areas which represent different information)
- thought to be explained by the balance of perihinal and parahippocampal cortex as you go from the front to the back of the brain
how can differences for the anterior and posterior hippocampus be supported?
Moser et al. (1993): spatial learning in rats impaired by posterior not anterior lesions
Strange et al. (1999): double dissociation in humans
What are some features of the hippocampus which link to memory?
- hippocampus receives diverse inputs from most of the cortex, which gets funnelled through to the entorhinal cortex and protected up to the hippocampus
what modalities does the hippocampus receive connections from?
major inputs from the amygdala (emotion), perihinal cortex (objects) and parahippocapal cortex (spatial location)
* vision, sound, smell, emotions etc
the hippocampus binds different aspects of our experience to form a hetromodal episodic memory, why?
because of memories are multisensory
the hippocampus contain many feedback loops (i.e. CA1 to CA3), what are these critical for?
learning (every time you send signals, it’s another change to bring information to the hippocampus)
* ideal for associative learning -> form chains as associative memories which link together our different experiences over time
neurones within the hippocampus have special properties which enable them to?
support memory
long-term memory at the level of individual neurones…
…reflects structural changes at the synapse
Synaptic changes underpin memory, what is Hebbian learning?
- memories are stored in connections between neurones (‘cell assemblies’)
- LTM through Hebbian learning: ‘cells that fire together, wire together’ (cells that fire together, will then strengthen their cognition) <- basis of LTM
- this all happens in the brain because of long-term potentiation (LTP)
The Biological Aspect of Memory: if you apply a weak stimulus
*action happens in the synapse
1. if you apply a weak stimulus to a pre-synaptic cell, you will produce some changes (some action potential) at the synapse, which will include the release of a little glutamate (excitatory neurotransmitter) into the synapse
2. glutamate diffuses across the synapse
3. sodium channels on the post-synaptic cells will open briefly so Na+ ions can enter
4. causes some depolarisation, but because it is weak, this depolarisation is not enough to trigger a new action potential AND there will only be a small change in membrane potential
The Biological Aspects of Memory; if you apply a stronger stimulus
- present a stronger stimulus to the presynaptic neurone (big chain of action potentials in presynaptic neurone)
- triggers the release of lots of glutamate into the synaptic gap
- glutamate leaves the presynaptic cell, diffuses across the synapse, ion channels in post-synaptic cell open for longer (and more channels open), triggering a large influx of sodium ions into the post-synaptic cell
- this triggers an action potential in the post-synaptic cell -> mechanisms which two neurones are communicating
what will a strong stimulus cause?
strengthens communication at this particular synapse - called long term potentiation (LTP)
what is long term potentiation (LTP)?
the connection between the two neurones are strengthened (potentiated in the long term)
when is the communication at the synapse, strengthen in LTP?
when you have a strong stimulus in the pre-synaptic cell