The data show that representations in MEC and PPC change independently of one another. Eight rats were given microdrive implants with tetrodes penetrating layers II, III, or V of MEC in one hemisphere, and deeper layers (>500 μm) of PPC in the contralateral hemisphere (Figure 1). Coordinates for PPC implantation (∼2.5 mm lateral of midline and ∼−4.0 mm posterior to

Bregma) were consistent with anatomical descriptions of rodent PPC based on thalamocortical and cortico-cortical connections (Chandler et al., 1992, Kolb and Walkey, 1987 and Reep et al., 1994), as well as studies characterizing navigational deficits following lesions to PPC (Kolb and Walkey, 1987 and Save and Moghaddam, 1996). The same implantation site was targeted across subjects, making

small variations to avoid surface vasculature. Overall, electrode penetrations in this study appeared slightly posterior to those of Nitz (Figure S7 Caspase inhibitor in Nitz [2006]) and corresponded to the rostral and lateral-most locations reported by Chen et al. (1994a) (see Figures S1A and S1B available online for all recording locations). All recordings were performed in accordance with the Norwegian Animal Welfare Act and the European Convention for the Protection of Vertebrate Animals Used for AZD2281 datasheet Experimental and Other Scientific Purposes. All eight rats yielded well-isolated cells in MEC, and PPC units were recorded simultaneously in five of the animals (Figures 1 and S1A). Recordings were made while rats foraged for cookie crumbs in a 1.5 × 1.5 m box with black Perspex walls and a black

vinyl floor. Animals’ paths were tracked using dual infrared head-mounted LEDs. Cells in MEC showed a variety of spatial responses including grid patterns, head direction selectivity, and firing in proximity to box walls, whereas PPC cells showed of poor spatial tuning (Figure 2, column 1). Grid cells were identified by comparing rotational symmetry (“grid scores”) in individual spatial autocorrelation maps with the distribution of symmetry in autocorrelation maps for shuffled versions of the spike-position data (Langston et al., 2010, Wills et al., 2010 and Boccara et al., 2010) (Figure S2). Cells in the observed data with grid scores above the 99th percentile of the distribution from the shuffled data were defined as grid cells. Using this statistical approach, we identified 53 grid cells in MEC. In PPC, only 1 of 98 cells exceeded the statistical criterion for grid cells. This was not more than expected by random selection from the shuffled distribution (Z = 0.02, p > 0.95; large-sample binomial test with expected P0 of 0.01). Spatial information content and coherence were low in PPC cells, though a few cells preferred the walls or corners of the box. In some cases this resulted in scores for spatial information content (two cells, Z = 1.04, p > 0.3) and spatial coherence (four cells, Z = 3.07, p < 0.