Schmidt hippocampus 2 Flashcards
What do action potentials reflect?
Our sensory perceptions, cognitive functions and behaviour.
Outline the first example of rate coding
Spike trains from recordings vary depending on the orientation of a presented visual stimulus
The rate of these recordings can be summarised in a graph
With stimulus orientation (degrees) on the X axis and neural response (spikes/second) on the Y axis
The firing rate changes depending on the orientation of the stimulus
Outline the second example of rate coding
A rat is sitting in a box with food sprinkled around it
The presented graph displays lines which follow the trajectory of the rat, whilst also recording from the EHC to investigate neural activity
Each red dot on the graph is the position of the animal when the neuron we are recording from fires an AP
Very systematic, there are visible clusters where the neuron is very active
Implications for grid cells in the EHC
What are the uses of neural coding?
You can find relations between the firing of different neurons by looking at their respective spike trains along with the use of statistical analyses.
For example, the firing activity is the same but one neuron fires slightly later
Spike times can be correlated and used for correlation coding
Could they be receiving a similar input?
What are place cells?
Cells that respond solely or maximally when situated in a particular location e.g. 8 different cells firing for 8 different sections of a track
There may be some overlap but not much
Where are place cells usually located?
They are usually pyramidal neurons in the CA3 and CA1
What are the different factors of a place cell?
For each place cell there is an associated place field
Directionality (open field vs. linear track) may affect how active a place cell is
There is a multi-sensory representation of the input for place cells e.g. olfactory, visual etc.
They are connected to movement so not as active when subject is stood still
What can you see when recording from place cells in the CA1?
As a rat walks along a surface you will see some that are very active and others that are very quiet, but it is not quite clear on the specific pattern due to overlapping
What happens during remapping in Fynn et al. (2007) when there are different boxes e.g. square, circle then square, at the same location?
When they change it to a circle box, neuron is no longer active as not inside the new boundaries, but when changed back to square the neuron becomes active again in same area of the box
Can measure the rate overlap and spatial correlation between different environmental changes
What happens in Fynn et al. (2007) when the same boxes are used but in different locations?
Very similar to previous experiment, locations A and B show a strong decrease in rate overlap and spatial correlation (remapping)
The firing rate is stronger in the A’ once it has been brought back from B
What can be seen in Fynn et al. (2007) when they change the colour of the box walls?
A different result is seen for spatial correlation. A high spatial correlation is recorded meaning that most place cells kept at the same location - they didn’t remap
However, the rate changes still
What are grid cells?
They are similar to place cells in that they care about spatial location of the animal but are active at several points in the environment.
These locations follow a systematic grid pattern unlike place cells
Where are grid cells found?
In the EHC which is the input and output region of the hippocampus
What are other spatial location cell types?
- Head direction cells: found in subiculum, they become more active when the animal is facing a certain direction, location doesn’t matter
- Border cells: also found in hippocampal formation, and are active near walls of an environment
What is the Cognitive Mapping Theory (O’Keefe & Nadel, 1978)?
Proposes that the hippocampus is an allocentric map which we use to navigate around the environment
It relates to the activity of different place cells
