Independence of firing correlates of anatomically proximate hippocampal pyramidal cells

In neocortex, neighboring neurons frequently exhibit correlated encoding properties. There is conflicting evidence whether a similar phenomenon occurs in hippocampus. To assess this quantitatively, a comparison was made of the spatial and temporal firing correlations within and between local groups of hippocampal cells, spaced 350-1400 mum apart. No evidence of clustering was found in a sample of >3000 neurons. Moreover, cells active in two environments were uniformly interspersed at a scale of <100 <mu>m, as assessed by the activity-induced gene Arc. Independence of encoding characteristics implies uncorrelated inputs, which could enhance the capacity of the hippocampus to store arbitrary associations.