18th Annual Pinkel Endowed Lecture February 25, 2016 2:00 PM Rubenstein Auditorium Smilow Translational Research Center "Grid cells and entorhinal network dynamics" The medial entorhinal cortex (MEC) is part of the brain’s circuit for dynamic representation of self-location. A key component of this representation is the grid cell, whose spatial firing fields tile environments in a periodic hexagonal pattern, but the circuit contains also other functional cell types, such as head direction cells and border cells. In this lecture, I will discuss the mechanisms by which grid patterns are updated in accordance with the animal’s movement in the environment. I will show that running speed is represented in the firing rate of a ubiquitous but functionally dedicated population of MEC neurons. I will also show that speed is represented across a wider brain circuit that includes speed cells in the mesencephalic locomotor region, whose outputs may reach the MEC via speed cells in the diagonal band of Broca. Finally, I will ask how input from spatially modulated cells in the MEC is used to form place-specific firing in the hippocampus. I will show that global but specific inactivation of the MEC causes substantial remapping among place cells in the hippocampus, without disrupting the spatial firing properties of individual place cells. These findings point to MEC input as an element of the mechanism for controlling the active cell population and the spatial map of the hippocampus.