Grid cells are specialized neurons in the mammalian entorhinal cortex that act as an internal GPS, creating a hexagonal coordinate system to map the environment. They fire at multiple, regularly spaced locations, allowing animals to calculate position, distance, and direction. They are crucial for spatial memory and navigation. 

Key Aspects of Grid Cells:

• Location and Function: Found in the medial entorhinal cortex (MEC), these cells fire in a triangular or hexagonal grid pattern that tiles the space an animal moves through.
• Spatial Representation:
   They provide a metric for spatial maps, acting similarly to longitude and latitude lines on a map to track where an animal is.
Discovery: Discovered in 2005 (by researchers such as May-Britt and Edvard Moser), they are essential for understanding navigation and memory.
Types of Cells: They work in conjunction with place cells (in the hippocampus), head direction cells, and speed cells to create a comprehensive "cognitive map".
Synonyms/Related Terms: Often referred to as part of the "brain's navigation system," "mental coordinates," or "spatial representation cells". 

Usage Examples in Brain Function:

• Navigation: Tracking your current position in an open space.
• Spatial Memory: Recording the location of objects or places.
• Path Integration: Calculating distance traveled, which relies on speed and direction inputs.
• Contextual Organization: Potentially organizing memory and non-spatial information.