Brain injury degrades the precision of hippocampal spatial representations

Traumatic brain injury (TBI) disrupts spatial memory, but the circuit mechanisms are unknown. Here we used in vivo endoscopic calcium imaging to record CA1 activity dynamics in freely behaving mice with TBI. Spontaneous CA1 neuron activity is broadly preserved three months after brain injury. However, chronic TBI reorganizes hippocampal spatial representations by increasing the fraction of spatially unresponsive neurons, broadening place fields among spatially tuned neurons and diminishing the persistence of spatial representations across sessions. These circuit alterations are accompanied by impaired discrimination of a novel spatial environment. Thus, TBI reorganizes the cellular structure and precision of hippocampal spatial representations despite preserved overall CA1 activity, revealing a dissociation between neuronal activity and network function that may underlie persistent cognitive dysfunction.