Place cells fire when an animal is in a specific location in its environment. Researchers found that: 1) Place cells in rats fired reliably when the rat visited the goal location of a maze, even when the rat made errors due to removed visual cues. 2) Place cell firing maps show the locations where a cell reliably fires as the rat moves around its environment. These maps have stable firing fields over multiple sessions. 3) When an environment is changed, such as its shape or prominent landmarks, place cells may remap and represent the new environment with different firing patterns.

1. Place cells

2. Place cells reflect where
the rat “thinks” it is
• O’Keefe and Speakman (1987)
trained rats to find a goal arm from
Place cell multiple start locations on an
Firing field
elevated plus maze
GOAL
• The goal was always in a fixed
Training location with respect to visual
error cues surrounding the maze
Shifted
Firing field • Some place cells fired reliably on
each visit to the goal arm
• When the spatial cues were
Original removed, rats made errors in
Firing field identifying the goal arm, but place
GOAL cells always fired as if the rat’s
Testing guess was correct

3. Computing the Firing Rate Map
SPIKE MAP
FIRING RATE
MAP
VISIT MAP

4. Even distribution of
field 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!

5. 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.

6. Long-term stability of place fields
SESSION
#1
6
DAYS
SESSION
#2

7. 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.

8. 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

9. Place cells seem to rescale their
firing fields along with a resized
environment

10. Removal of the cue card often does
not disrupt place fields

11. Place cells can
maintain their
firing fields in
complete
darkness!

12. Fooling place cells
PRE WALL
POST
20 min. 20 min.
FLOOR
90º SLOW CW 90º FAST CW
20 min. 20 min. 20 min. 20 min.
Before After Before After

13. 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

14. Place cells can encode the same location
differently depending on behavioral context

15. Rats vs. Humans