cause abnormal firing of hippocampal place cells as evidenced, in part, by difficulties with spatial tasks such as the radial arm maze and the Morris water navigation task. Movement inputs Movement can also be an important spatial cue. Mice use their self-motion information to determine how far and in which direction they have travelled, a process called path integration. This is especially the case in the absence of continuous sensory inputs. For example, in an environment with a lack of visuospatial inputs, an animal might search for the environment edge using touch, and discern location based on the distance of its movement from that edge. Path integration is largely aided by grid cells, which are a type of neuron in the entorhinal cortex that relay information to place cells in the hippocampus. Grid cells establish a grid representation of a location, so that during movement place cells can fire according to their new location while orienting according to the reference grid of their external environment. Episodic memory Place cells play an important role in episodic memory. One important aspect of episodic memory is the spatial context in which the event occurred. Hippocampal place cells have stable firing patterns even when cues from a location are removed and specific place fields begin firing when exposed to signals or a subset of signals from a previous location. This suggests that place cells provide the spatial context for a memory by recalling the neural representation of the environment in which the memory occurred. By establishing spatial context, place cells play a role in completing memory patterns. Furthermore, place cells are able to maintain a spatial representation of one location while recalling the neural map of a separate location, effectively differentiating between present experience and past memory. Place cells are therefore considered to demonstrate both pattern completion and pattern separation qualities. Pattern completion Pattern completion is the ability to recall an entire memory from a partial or degraded sensory cue. Place cells are able to maintain a stable firing field even after significant signals are removed from a location, suggesting that they can recall a pattern based on only part of the original input. Furthermore, the pattern completion exhibited by place cells is symmetric, because an entire memory can be retrieved from any part of it. For example, in an object-place association memory, spatial context can be used to recall an object and the