1 (Jandel Scientific, San Rafael, CA, USA), and the Statistical Package for the Social Sciences version 14 (SPSS). Student’s two-tailed t tests were used for comparisons. Two-way repeated ANOVA was carried out for EEG comparison between groups and within groups. All data are presented as mean ± SEM unless stated otherwise. p values of <0.05 were considered statistically significant. We thank Chanki

Kim, M.A. Aslam, Gireesh G., Sungsoo Jang, Soojung Lee, Il-hwan Choe, and Seung-eun Lee for technical as well as intellectual support. This work was supported by the National Honor Scientist Program of the Korean Government, and the WCI program of Korea Institute of Science and Technology. “
“The hippocampus is a key brain structure for learning and memory

in mammals (Andersen et al., 2007). When a rodent explores a new space, a long-lasting (Thompson Rapamycin and Best, 1990) map (O’Keefe and Dostrovsky, 1971 and O’Keefe and Nadel, 1978) defined by two classes of neurons rapidly appears (Hill, 1978, Wilson and McNaughton, 1993, Frank et al., 2004 and Leutgeb et al., 2004) in its hippocampus. A place cell fires action potentials (APs) selectively whenever the animal is in a particular region—called the cell’s place field—of the environment (O’Keefe and Dostrovsky, 1971), whereas silent cells fire few APs across the entire area (Thompson and Best, 1989). In distinct mazes, selleckchem different but partially overlapping subsets of CA1 pyramidal neurons have place fields (O’Keefe and Conway, 1978, Muller and Kubie, 1987, Thompson and Best, 1989 and Leutgeb et al., 2005), with at least half of all neurons silent in each maze (Thompson and Best, 1989 and Wilson and McNaughton, 1993). Thus, an environment is represented not only by where each place cell fires, but also by which cells are active versus silent there. Similarly,

the human hippocampus represents specific items (Quiroga et al., 2005) or episodes (Gelbard-Sagiv et al., 2008) with unique and sparse (Waydo et al., 2006) subsets of active cells among a larger population of silent neurons. Therefore, one of the most critical questions for understanding the formation of spatial memories in rodents as well Rolziracetam as declarative memories in humans is—what determines which cells will form the memory trace of a given environment, item, or episode? Specifically, regarding rodents and space—what determines whether a given cell becomes a place cell versus a silent cell in a given maze? At a basic level, the possibilities include (1) differences in the amount and spatial distribution of synaptic input and (2) differences in intrinsic properties that shape the cell’s response to inputs. Ultimately, for a neuron to have a place field, the membrane potential (Vm) by definition must consistently reach the AP threshold in a spatially selective manner. Conversely, Vm must generally stay below threshold for silent cells.