the apparatus with alcohol and for the 90u cue rotation. Place maps showing average cell firing rates at positions in the cylinder were constructed for individual sessions. At the end of each session, the animal was returned back to its cage, the recording chamber was cleaned, and the recording cables were untwisted. Also, between the first and the PF-8380 biological activity second sessions, the visual cue was rotated by 90u in a counter clockwise direction. At the end of the second session the cue was placed back in its original position by rotating it 90u clockwise, thereby making the sensory cues identical to those of session 1. Mice were repeatedly exposed to the same recording chamber over days until the end of the experiment. In case the cell being recorded drifted or was lost between sessions, that cell was excluded from the analyses. finding the maximum cross-correlation, pixel-by-pixel correlations were performed with a place map successively rotated in 1u steps. The size of the place field was defined as the number of pixels that had firing rates above the overall cell firing rate for the session. All correlation values were transformed into Fisher’s Z scores for parametric comparisons. Definitions of spatial information, coherence, spatial selectivity, and variability, of complex spike bursts are defined in the corresponding PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/22190017 sections of Results. The firing properties were calculated using data from all 3 sessions combined. Throughout the analyses, a two tailed unequal variance Student’s t-test for equality of means was used to compare groups. Histology After completion of recordings, recording locations were verified. Mice were overdosed with Nembutal, an electrolytic lesion was made by passing current through the recording electrode, and then perfused transcardially with 3.7% formalin. Brains were extracted and further fixed in 3.7% formalin for a week at room temperature. Coronal sections were cut through the entire hippocampus with a microtome cryostat. The sections were stained with cresyl violet and examined under a light microscope to determine recording sites. Data Analyses Only well-isolated single units confirmed to be in the CA1 region by histology were used in the analyses. Data obtained via data acquisition software were cluster-cut into single units. Each cluster-cut unit was confirmed 
to be a signal from a single neuron by verifying that no spike counts existed under the first 1 ms in the inter-spike interval histogram within a single unit. For place field analysis, Linux based R- program was used. The midpoint of two LEDs was calculated for each position sample, and used as the position of the animal’s head. For each pixel, the total number of spikes was divided by the total time spent by an animal in the pixel. Firing rates per pixel over the whole session were used to construct a color map representing a place field of each recording session. A stability index was obtained by calculating pixel-by-pixel correlation between place maps derived from two recording sessions chosen pair-wise. Another index for stability was deemed as the amount of rotation of the place maps between 2 sessions that yielded the maximum value of pixel-by-pixel cross-correlation. For Acknowledgments We would like to thank Dr. Hugh T. Blair and Mayank Mehta for comments that helped to shape this manuscript. ~~ Familial adenomatous polyposis and hereditary nonpolyposis colorectal cancer are autosomal dominant diseases that result from inherited genetic mutations i
