Distinct tuning properties of human hippocampal neurons along the longitudinal axis during working memory

Working memory (WM) is among the most sophisticated and fundamental capabilities of the mammalian brain. While the roles of prefrontal and sensory areas are heavily explored, there is little knowledge on how the hippocampus (HPC) contributes to this process. Here, we studied human HPC neuronal activities during a verbal WM task and reveal that neurons in the posterior HPC (PH) show more robust rate-modulations during WM. On the other hand, anterior HPC (AH) neurons are more prominently modulated by the phase of local and frontal cortex {theta} and {beta} oscillations, a phenomenon that is accompanied by enhanced phase-synchronization between frontal cortex and HPC. Moreover, absence of correlational correspondence suggested that rate and phase are independent coding mechanisms. These results open a window to explore the functional dissociations along the primate HPC antero-posterior axis, a phenomenon long known to exist in the rodent brain. Furthermore, we suggest that combination of a variety of coding mechanisms in the human HPC neuronal population supports execution of WM.