Download - Place cells
Place cells
GOAL
Place cellFiring field
GOAL
OriginalFiring field
error
Training
Testing
ShiftedFiring field
• O’Keefe and Speakman (1987) trained rats to find a goal arm from multiple start locations on an elevated plus maze
• The goal was always in a fixed location with respect to visual cues surrounding the maze
• Some place cells fired reliably on each visit to the goal arm
• When the spatial cues were removed, rats made errors in identifying the goal arm, but place cells always fired as if the rat’s guess was correct
Place cells reflect where the rat “thinks” it is
Computing the Firing Rate Map
SPIKE MAP
VISIT MAP
FIRING RATE MAP
Even distribution offield centers
• In a cylindrical chamber, place cells can exhibit firing fields that are against walls, in the middle of the floor, etc.
• During free-foraging, place cells are randomly distributed throughout the environment.
• Preferred firing locations ARE NOT topographically organized!
Place cells adopt their preferred locations during the first few minutes of exposure to
a novel environment.At first place cells have large fields that cover almost the entire environment, but gradually the fields become smaller and more selective for one specific region.
Wilson MA & McNaughton BL (2003). Dynamics of the hippocampal ensemble code for space. Science 261:1055-8.
Long-term stability of place fields
SESSION#1
SESSION#2
6DAYS
Directionality of Place Fields• In open fields, place cells tend to be non-directional.
That is, they fire equally at their preferred firing location no matter what direction the rat is facing.
• On linear tracks, place cells tend to be directional. That is, they fire more when the rat runs in one direction than the other.
Influence of visual landmarks
• When prominent familiar landmarks are moved, place cell firing fields often move along with the landmarks
• For example, when a cue card is rotated in a circular arena, place cells move with the cue card
Place cells seem to rescale their firing fields along with a resized
environment
Removal of the cue card often does not disrupt place fields
Place cells canmaintain their firing fields in
complete darkness!
WALL
FLOOR
20 min. 20 min.
Before After
90º FAST CW
20 min. 20 min.
Before After
90º SLOW CW
PRE20 min.
POST20 min.
Fooling place cells
Remapping: place cells represent different environments with different “maps”
Square Box Round Box
• ~40% chance that a place cell will fire in a given environment
Place cells can encode the same location differently depending on behavioral context
Rats vs. Humans