Synchronization of the prefrontal cortex with the hippocampus and posterior parietal cortex is navigation strategy-dependent during spatial learning

1.During goal-directed spatial learning, subjects progressively change their navigation strategies to increase their navigation efficiency, an operation supported by the medial prefrontal cortex (mPFC). However, how the mPFC may integrate relevant information in a wider memory networks involving the hippocampus (HPC) and the posterior parietal cortex (PPC) is poorly understood. We recorded local-field potential and neuronal firing simultaneously from the mPFC, HPC and PPC in mice subjected to spatial memory acquisition in the Barnes maze. During navigation trials, animals demonstrated two consecutive behavioral stages: searching and exploration. Throughout training, mice gradually switched from less efficient (non-spatial) to more efficient (spatial) goal-oriented strategies exclusively during the searching stage. 4-Hz and theta (6-12 Hz) oscillations were detected during spatial navigation in the three recorded areas associated with episodes of immobility and locomotion, respectively. The entrainment of prefrontal gamma oscillations (60-100 Hz) by hippocampal and parietal 4-Hz and theta oscillations, as well as the incidence of prefrontal gamma, was higher when mice implemented spatial strategies during the searching stage. Interestingly, 4-Hz and theta from HPC and PPC also synchronized the spike-timing of prefrontal neurons, which was maximum during spatial strategies in the searching stage. Finally, neurons recorded in the mPFC increased their task stage firing selectivity when they used spatial strategy. Altogether, these results provide evidence for the neural mechanisms underlying the prefrontal large-scale coordination with distributed neural networks during spatial learning.