Cosyne 2007 Workshops
February 26-27, 2007
The Canyons, Utah
Lisa Giocomo
Differences in subthreshold oscillations of stellate cells map to differences in periodicity of grid cells
As a rat moves through an environment, neurons in layer II of medial entorhinal cortex (mEC) fire at regular repeating intervals to form a hexagonal grid. The periodicity of the grid changes along the dorsal to ventral axis of mEC, with smaller periodic distances between grid fields in dorsal mEC and larger periodic distances between grid fields in ventral mEC (Sargolini et al., 2006). Computational models have suggested that changes in intrinsic membrane potential oscillations of cells in medial entorhinal cortex could contribute to grid cell periodicity (O’Keefe and Burgess, 2005). Recently, our lab has examined the properties of layer II neurons along the dorsal to ventral axis of entorhinal cortex using in vitro whole-cell patch clamp techniques. Unlike previous in vitro slice studies, the position of individual horizontal slices was measured relative to the dorsal surface of the brain, allowing analysis of cellular properties at different locations along the dorsal to ventral axis. We found differences in the frequency of intrinsic subthreshold membrane potential oscillations and the resonance frequency of layer II mEC cells along the dorsal to ventral axis, which map to spatial changes in grid cell periodicity. Our data support the explicit prediction by Burgess and O’Keefe, based on their computational model of grid cell formation, that the difference in spatial frequency of grid cell firing fields would result from differences in temporal frequency of subthreshold oscillations of individual entorhinal neurons. Simulations in our lab of the Burgess and O’Keefe model have demonstrated that a difference in the baseline temporal frequency of somatic oscillations results in differences in spatial frequency of grid fields. These physiological results suggest further analyses relevant to computational models of grid cell formation and the function of medial entorhinal cortex.
