Also, cholinergic modulation can change thresholds by several millivolts even with a constant baseline (Figenschou et al., 1996). Alternatively, having a higher proportion of APs triggered by dendritic spikes (Gasparini et al., 2004) could lead to an apparently lower threshold, with the proportion itself affected by differences in inputs and/or intrinsic factors. Selleck Pomalidomide Second, while the random input-based model predicts a continuum of “peak – threshold” values (regardless of whether the AP threshold is fixed or varies across cells) with higher values

for place cells, instead we found a bimodal distribution with a large, clear gap separating place fields from silent (Figure 4G) as well as active from nonactive (Figure S1V) directions. This was the feature that most clearly separated the two classes and, contrary to the random input-based model, suggests that place and silent

cells qualitatively differ within a given environment. This qualitative difference is further supported by the surprising flatness of the silent cells’ subthreshold fields (Figures 4A, 4E, and 4H). A nonrandom distribution of inputs could explain the lack of a continuum, but would be unlikely to explain the following result, as it involved somatic current injection. Third, even prior to any sensory input from the maze, future place and silent cells unexpectedly displayed differing burst propensities (Figures 5 and S1J) as did future active and non-active cells (Figure S1A′). Raf inhibitor Thus intrinsic properties may predetermine the division into place and silent cells. Does this mean that a fixed fraction of cells will have place fields regardless of the size of the environment? While fewer cells may express place fields in smaller and/or simpler mazes (Thompson and Best, 1989), in larger environments the number of place cells appears to be limited,

with additional spatial coverage achieved primarily by having each place cell express multiple fields (Fenton et al., 2008 and Davidson et al., 2009). Therefore, what intrinsic factors may predetermine is the restricted subset of cells that could potentially have place fields. Moreover, among the set of possible place cells, Histone demethylase the relative locations of their place fields also appear to be predetermined (Dragoi and Tonegawa, 2011). In the simple input-based model, the subthreshold field would essentially reflect the net synaptic conductance as a function of the animal’s location and be largely independent of properties such as the threshold or burst propensity, but these results show that they are all interrelated. Indeed, direct comparison of the “peak – baseline” and threshold shows that these features were negatively correlated (Figures S1O and S1F′) as opposed to uncorrelated (or positively correlated, which could occur if the input and threshold were uncorrelated but the threshold acted as a ceiling on the subthreshold peak).