Theta and sharp-wave ripple characteristics recorded across NeuroNexus A1x16-5mm-100-413 linear probes were used to localize electrode sites within layers of the mouse hippocampus. Results in Nature Communications by Martina Riva et al. with Alessandra Pierani’s group at Université Paris Cité in collaboration with Liset Menendez de la Prida’s group at Instituto Cajal, CSIC identify reduced theta and enhanced gamma in mutant mice. Their differences are related to memory impairment and susceptibility to seizures and are caused by preventing programmed cell death (PCD) of normally transient Cajal-Retzius cells.