Head direction (HD) cells (Taube et al 1990) fire only when an animal's head points in a specific direction, regardless of location. They form a "neural compass." The 60-neuron ring shown here is an attractor network: excitatory connections between nearby neurons and inhibitory connections between distant neurons create a stable "bump" of activity that can rotate continuously around the ring.
Network dynamics: The bump velocity is driven by "velocity cells" that shift the bump based on angular head velocity input. The bump maintains its position (direction memory) even in darkness. HD cells are found in ADN, PoSTh, RSC, and entorhinal cortex — the HD signal propagates throughout the spatial navigation circuit.
Tuning curve: Each cell has a preferred direction (PD) and fires with a ~90° half-width Gaussian profile. The population vector sum of all active cells gives the current heading estimate.