This 2015 Canadian rodent study tried to establish that grid cells in the medial entorhinal cortex generated brain waves in the theta frequency range that controlled place cells in the hippocampus part of the limbic system.

The researchers stated:

“Our results deviate from the prediction.”

but a commentary Do the spatial frequencies of grid cells mold the firing fields of place cells? said the researchers:

“Obtained fascinating results, largely supporting the model.”

What’s fascinating to me is the volume of studies on the hippocampus that ignore its position as the seat of emotional memories. Human experiments involving the hippocampus are usually designed to not contain any emotional content.

Two studies showed functions of hippocampal place cells:

• Our memories have contexts with specific places and times
• Hippocampus replays memories and preplays to extend memories into future scenarios

A summary study of 118 other studies What do grid cells contribute to place cell firing? provided additional information on grid cells and hippocampal place cells, head direction cells, boundary cells, and cells that encode object locations.

The summary study related to the current study by stating that the research through early 2014 arguably found:

“Grid and place cell firing patterns are not successive stages of a processing hierarchy, but complementary and interacting representations that work in combination.”

http://www.pnas.org/content/112/13/4116.full “Place field expansion after focal MEC inactivations is consistent with loss of Fourier components and path integrator gain reduction”