Week 6: Boundary vector cell model of place cells Flashcards
What type of neuron does the boundary vector model of place cell use?
standard artifical neurons with no dynamics
Boundary vector model based on experiments conducted by which investigated (2)
O’Keefe and Burgess, 1996 investigated:
what are the inputs to place cells?
What did O’Keefe and Burgress do (1996)? = Method (2)
- Made a square enviroment where
- Rat forages in a box where the size of the box is varied across dimensions and recorded their PC cells
What did O’Keefe and Burgess, 1996 find (2) = PC field did not change
- Data from a single same neuron where they extended box across 1 dimension (e.g., lenght) and in another direction (width) and extended in both directions (length and width)
- Some of the PC they recorded exhibited ‘simple’ place field firing, consistent across box-sizes = place field did not change…
What did O’Keefe and Burgess, 1996 = PC field changed (3)
- However, some PC appear to change with firing when the geometry of the box changed
- For example, firing field of PC that was close to east wall
- When the wall was extended on that dimension (towards east) , the firing field of one PC neuron changes and extends so that there is PC spikes all along the east side of the wall of the box
These are all for one neuron in which they measured…
Captures its average firing rate
Results of O’Keefe and Burgees 1996 when PC field changes shows that (3)
- Other place fields appear to respond at fixed distances from walls …
… with nearer walls more important than further ones.
=> The geometry of a space is an important factor (at least for a subset of PC cells)
Subsequently, Hartley et al., (2000) (after O’Keefe and Burgess 1996 study) coined the term boundary vector cells (BVC) to describe the
- cells that respond to presence of a wall
Boundary vector cells were not yet found experimentally
around the time of Hartley et al., (2000) research as they did theoretical predictions
Hartley et al., (2000) put hypothesised that.. (3)
- Each BVC tuned to respond when a barrier lies at a specific distance from the rat in a particular allocentric direction
- These BVC cells are allocentric cells meaning the direction (of barrier) defined relative to some element of enviroment (like external cue)
- Does not depend on animal’s orientation
Allocentric is a fancy term for
world centred
BVC cells recorded via
single-cell recordings
Hartley et al., (2000) hypothesied that
BVC and may give input to PC and influence their activity
Hartley et al., (2000) proposes that the BVC firing is determined by
product of two gaussian functions, defining distance and angle tuning to boundary:
Hartley et al., (2000) says sharper tuning for
shorter distances reflecting less unceranity in inputs to BVCs
Hartley et al., (2000) if you take set of BVCs with receptive fields in different direction that are active
they together signals the distance to a set of boundaries
Hartley put forward that BVC tuned to respond when a barrier lies at a specific distance from a rat in particular allocentric direction meaning that
BVC receptive field at given orientaiton (2)
- in the enviroment relative to the enviroment (not to animal’s orientation)
- As the animal approaches the wall, the wall of a specific barrier/boundary of box, covers more of the receptive field and firing rate of a particulae BVC goes up and is maxiamlly
Hartley model of place cell firing is
taking 3/4 BVC and given input weight to PC and simply sum boundary inputs * weight and put through transfer function
Hartley hypothesied that We know how far we are from the walls as (BVC)
we know where are are (PC cells)
Hartley theoretically predicted that enviromental geometry influences PC (i.e., BVC give inputs to PC)
by having BVC as geometric inputs to PCs in the gaussian functions
Diagram of BVC Model of PC Firing
Idea of BVC Model is that when I am at a given location where (4)
3 BVC cells are active
These different BVCs will be maximally active and respond to barriers at specific distances and directions
These three different active BVC give input to PC and is then maximally active at this location
Subtract background activity and get place fields at specific locations
How do BVC model of place cell firing model experimental data from O’Keefe and Burgess, 1996?
We calculate the activity of PC at all possible positions/locations (x,y) simultaneously since one location does not influence the other
In BVC Model of PC Firing we could do it
location by locaiton but nothing stops us at doing all locations
Remindar: The BVC Model of Place Firing Hartley et al., (2000) works of producing place field
Sum of 2 or more BVC inputs * its weights and put through transfer function which gives place fields
Hartley et al., (2000) modelled O’Keefe and Burgess 1996 using BVC model
2-4 BVC
2-4 BVC oriented at right angles to one another and thresholds are sufficient to fit most (i.e., give best match) of the PC fields in the data by O’Keefe and Burgess 1996
After using 2-4 BVC,
Stimulated results of the BVC showed that
- There is a close match of place fields between O’Keefe and Burgess data and Hartley’s model results
BVCs predict boundary-referenced firing of PCs across enviroment
Method - (4)
- Record some place cells in differerent shapes of enviroment (e.g., square, circle)
- Find BVCs that best fit to those place cells in (e.g., square/circle enviroment)
- Use the model BVCs to predict firing in other enviroments that have different shapes (e.g., right angle-triangle)
- Experimentally, then record the same PC cells as found in the step 3 in predicted enviroments (e.g., right-angle triangle)
Lever et al., (2009) and Solstad et al., (2008) discovered BVC in an area - (3)
rodent subiculum (area very close to hippocampus)
Rodent has a receptive field for west and everytime rodent is near the west wall of a box, a cell will fire
does not matter if curtain around box, remove the curtain or change shape of the enviroment, the specific BVC will always fire west to the wall
Massive achievement for a theoretical model developed of BVC Model of PC firing as they predict BVC cell and this experiment by
Lever et al., 2009 and Solstad et al., 2008 confirms this
