Schmidt hippocampus 1 Flashcards
Who was patient H.M?
Had bilateral removal of medial temporal lobes and hippocampus to cure his epilepsy
Resulted in anterograde amnesia and partial retrograde amnesia
Huge impact on memory research
Highlighted clear connection of brain regions to memory
What is the controversy of hippocampal function?
Originally thought to be involved with anxiety due to pharmacological studies but is no longer a dominant theory
Believed to be more involved with memory and spatial navigation
What is one problem with studies looking at hippocampus function?
A lot are based on lesion studies so it is difficult to be so specific and also use the right behavioural testing
Meaning there are sometimes issues with interpretation
Which type of memory is related to the medial temporal lobe?
Declarative memory, episodic memory
Why do we use animals in cognitive research?
There is limited ethics with human studies and are therefore more techniques available in animal studies
But can you measure cognitive abilities in animals?
Relates to the argument that cortex is special and has special organisation that allows for higher cognitive function
Mammals have cortex but birds don’t
But may not be the only way higher cognitive functioning is achieved
Can look at studies with birds
What did the studies of birds and theory of mind show?
A study of magpies and a mirror showed that some displayed aggressive behaviour indicating that they think their mirror image is a rival
BUT depends on the bird as some behaved differently e.g. looking behind the mirror and checking whats happening in the mirror with their own actions (contingency learning)
Indicating that they knew something was different
What did studies of crows show?
Crows in a lab setting use a metal rod to get food out of a tube demonstrating causal reasoning
After investigating animal studies can you study cognitive abilities in animals?
Yes they also have impressive cognitive abilities
Even animals without cortex (birds) show evidence for insight-related cognition
But there might be simpler ‘pre-cursors’ for cognitive abilities in some animals, so don’t have episodic memory but have something similar
Provides interesting insights for research
What is the hippocampus?
A banana-like shaped region going from the central part of the brain to the more lateral part.
Described as a tri-synaptic pathway because there are 3 main processing steps that reflect the flow of information through the hippocampus
What are the 3 main processing steps?
- The pathway is mediated by the perforant pathway as the input to the hippocampus, which leads to the dentate gyrus
- Mossy fibres then project from the DG to the CA3
- The Schaffer collaterals connect the CA3 to the CA1
These steps are simplified as there are a lot of processes going on within this flow of information
What are the subregions of the hippocampus?
Dentate Gyrus CA3 CA1 Subiculum (there is a CA2 subregion but it isn't as prominent and not been studied as much)
What are the two types of neurons within the regions of the hippocampus?
- Projection neurons i.e. across subregions
2. Inhibitory interneurons i.e. within subregions
What is the Dentate Gyrus?
The input region of the hippocampus with densely packed granule cells. Also lots of different inhibitory interneurons
Found to have high rates of neurogenesis which is the formation of new neurons - thought to be related to memory
What are granule cells?
Excitatory projection neurons
What are the CA3 and CA1 subregions?
They mostly consist of pyramidal projection neurons
But also have a lot of inhibitory interneurons
CA3 has a dense recurrent network such that the pyramidal neurons are also connected to each other - this provoked ideas about formation of memories
What is the CA3 and CA1 network like?
A complex network of pyramidal neurons and interneurons
Cannabinoids act on these microcircuits through cannabinoid receptors
What is the Subiculum?
The output region of the hippocampus, has 2 types of principal neurons:
- regular firing neurons
- bursting neurons
These are to do with the patterns of action potentials
Overall less well studied area of the hippocampus
What is the hippocampal formation?
Part of the limbic system and also has connection with the entorhinal cortex and other structures
Has significant projections from the entorhinal cortex (which has 6 layers) to the hippocampus
But the connections are very complex
What are the projections between the entorhinal cortex and the hippocampus?
- perforant pathway: layer II of the EHC to CA3 in the hippocampus
- tempero-ammonic pathway: layer III of the EHC to CA1 of the hippocampus
How does the neural activity in the hippocampus relate to learning and memory?
Have to look at it in the context of firing patterns of the hippocampal neurons
What causes action potentials?
Primarily caused by the flux of sodium and potassium ions due to the opening and closing of ion channels
How do we measure the flow of ions in the brain?
Using electrodes.
From the recorded signal we can determine the time when a certain neuron fired an action potential
The resulting spike trains are key in relating neuronal activity with behaviour
