Hippocampal place cells fire when an animal is in a specific location. But what defines "location"? Explore how visual landmarks anchor a place cell's firing field.
Click anywhere in the maze to move the rat. Watch the place cell response change in real time.
Real-time spiking activity of the recorded place cell
Average place cell firing rate when the rat is in each arm
In 1971, John O'Keefe and Jonathan Dostrovsky discovered neurons in the rat hippocampus that fire whenever the animal occupies a specific location in its environment. These place cells collectively tile the environment, forming an internal cognitive map — a discovery that earned O'Keefe a share of the 2014 Nobel Prize in Physiology or Medicine.
Each place cell has a place field — a circumscribed region of the environment where the cell fires at high rates (typically 20–80 Hz), while remaining nearly silent elsewhere (0–2 Hz). The firing rate as a function of position is often modeled as a 2D Gaussian:
\[ f(\mathbf{x}) = f_{\text{bg}} + f_{\text{peak}} \cdot \exp\!\left(-\frac{\|\mathbf{x} - \mathbf{x}_{\text{field}}\|^2}{2\sigma^2}\right) \]
where \(\mathbf{x}\) is the rat's position, \(\mathbf{x}_{\text{field}}\) is the center of the place field, \(\sigma\) controls the field width, \(f_{\text{peak}}\) is the peak firing rate, and \(f_{\text{bg}}\) is the background rate.
A critical question is: what anchors a place field? Is it the absolute position in the room, or the rat's position relative to visual cues? Classic experiments by Muller & Kubie (1987) and others addressed this using a three-armed radial maze with a single visual landmark (a cue card).
The key finding, illustrated in this demo:
This demonstrates that place cell firing is anchored to the visual landmark, not to idiothetic (self-motion) cues or the maze geometry alone. The hippocampus constructs a spatial representation relative to salient environmental cues — a key principle of allocentric spatial coding.