The ins and outs of hippocampal circuits

The anatomy of the entorhinal-hippocampal circuit suggests how spatial information may flow into and out of the CA1 region. In this issue of Neuron, two groups use in vivo physiology to make predictions about the circuit mechanisms involved in the encoding and maintenance of spatial memory. Brun et al. show that lesions of the cells providing direct input from the mEC to CA1 lead to a decrease in spatial tuning, while Cheng and Frank report that the exploration of novel space leads to a transient increase in the temporally correlated firing of pairs of CA1 cells outside of their place fields specifically during ripple-like high-frequency events in the local field potential.