Today's physics colloquium (4:15, tea at 3:30) is being given by the 2014 Nobel Prize Winners in Medicine or Physiology, covering the work that won them the prize. Should be interesting!
Best,
Ian
Harvard Physics Colloquium
Monday, April 27, 2015
4:15 p.m.-5:15 p.m. in Jefferson 250
Tea served in Jefferson 450 @ 3:30 p.m.
"Grid Cells and Neural Maps for Space"
May-Britt and Edvard Moser
NTNU
For announcement poster please go to: http://www.physics.harvard.edu/events/colloquium.pdf
The medial entorhinal cortex (MEC) is part of the brain’s circuit for dynamic representation of self-location. The metric of this representation is provided by grid cells, cells with spatial firing fields that tile environments in a periodic hexagonal pattern, like holes in a bee hive.
In the first part of the talk, we will examine the mechanisms that determine how the grid pattern is positioned relative to the external environment. Data were collected from grid cells while rats foraged randomly in square enclosures. We will show that the axes of the grid are offset from the walls of the environment by an angle that minimizes symmetry with the wall axes. The offset is always accompanied by an elliptic distortion of the grid pattern. Offset and distortion can both be removed by a shear transformation along one or several walls of the box, pointing to shear forces from specific geometric references as elements of the mechanism for anchoring grids to the external world.
In the second part of the talk, we will focus on the mechanism by which grid patterns are updated in accordance with the animal’s movement in the environment. For grid cells to be updated efficiently, the cells need information about the animal’s instantaneous running speed. We will show that running speed is represented in the firing rate of a ubiquitous but functionally dedicated population of neurons in the medial entorhinal cortex. This entorhinal subpopulation is characterized by a positive, linear response to running speed and low overlap with other entorhinal cell types, such as grid, head direction and border cells.
The final part of the talk will address the mechanisms by which grid cells interact with place cells in the hippocampus. We will show that the hippocampus receives inputs from a variety of functional cell types in the medial entorhinal cortex, including grid cells and border cells. We will also show that place cells in the CA1 of the hippocampus are part of a prefrontal-thalamic-neural circuit for representation of routes through the environment, where the nucleus reuniens links medial prefrontal cortex with the hippocampus. The findings imply that space and spatial navigation recruit widespread cortical circuits, with the thalamus operating as a key node for long-range communication between cortical regions involved in navigation.