All active hippocampal pyramidal cells are place cells

Hippocampal place cells – neurons whose activity is modulated by spatial position – are considered an essential substrate of spatial cognition. Despite decades of research, the fraction of hippocampal place cells remains debated, with studies reporting between 20% and 90% of the recorded populations. This raises the question of whether distinct subsets of cells – place cells and non-place cells – genuinely exist in the hippocampus. Here, we developed an analytical approach that estimates place cells’ fraction by fitting measured neuronal activity to simulated datasets with different fractions of place cells. We found that in familiar environments, all neurons recorded from the mouse dorsal CA1 are place cells. In novel environments, place cells’ fraction is lower, yet many cells naively classified as non-place cells are in fact modulated by position, but their fields are unstable. Overall, our findings suggest there are no distinct subsets but rather that all active cells are spatially informative.