To our knowledge, we provided the first microcircuit description of functionally identified cells in medial entorhinal cortex. Friction-based pipette-stabilization and juxtacellular labeling allowed the combined analysis of neural activity, circuitry, and behavior. We demonstrated Cabozantinib in vivo efficient (>50% success rates) cell recovery with excellent morphology from freely moving animals. The success

of the friction-based device is almost certainly related to the rigidity of the pipette positioning. As the pipette is securely locked into position, the resulting recordings withstand mechanical disturbances. As only a handful of neurons have been recovered from freely moving mammals previously, our approach opens up a new frontier in microcircuit research. Beyond cell identification, our methodology provides additional advantages over conventional extracellular recording techniques. First, it allows unequivocal unit separation, given the remarkably high signal-to-noise ratio of the recorded spike signals (average signal-to-noise = 11.64 ± 6.9; see Supplemental Experimental Procedures and Figure S1D). Second, it allows recording and identifying silent cells, whose impact on cortical computations is poorly understood. IWR-1 in vivo Third, activity of the recorded cells can be manipulated by current injections (Houweling and Brecht, 2008, Voigt et al., 2008 and Houweling

et al., 2010), making it possible to explore the effects of single-cell stimulations on freely moving animal behaviors. A major limitation of the current method is the use of the antagonizable anesthesia. Although under the same conditions as the present study

hippocampal physiology seemed to be preserved to a large extent (e.g., occurrence and properties of place cells were unaltered) (Lee et al., 2006, Lee et al., 2009 and Epsztein et al., 2010), we cannot exclude potential residual effects of the anesthesia after antagonization. In the present study we made three key observations. First, we identified two types of patches in medial entorhinal cortex: small patches in layer 2 and Oxalosuccinic acid large patches at the dorsomedial border. Second, we identified the connections between patches. Superficial layer cells connect to single large patches (via centrifugal axons), whereas cells from these structures connect back to small patches (via centripetal axons) and to other large patches (via circumcurrent axons). Third, we characterized the functional properties of identified cells in the different compartments of medial entorhinal cortex. Altogether, our data point to a congruence of connectivity and responses with cortical patches, implying that these units—described not only in rats but also in monkeys and humans (Hevner and Wong-Riley, 1992 and Solodkin and Van Hoesen, 1996)—shape entorhinal processing in a fundamental way. Grid cells display a periodic and regular hexagonal firing pattern while the rat explores an open field (Hafting et al., 2005).