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