Memory reconsolidation is a process allowing previously consolidated memories to be updated. In order for memory reconsolidation to occur, a memory first needs to be reactivated. It has been shown recently that memory retrieval during awake/sleep phases may affect susceptibility to memory reactivation. Given the importance of hippocampal gamma frequencies in memory processes, the purpose of the present research was to study changes in gamma bands power during retrieval of instrumental appetitive memories. Local field potentials were recorded in the CA1 area of dorsal hippocampus of Sprague Dawley rats during retrieval of instrumental appetitive memory performed either during light or dark phases of the circadian cycle. Appetitive memory retrieval was performed by using a protocol of sucrose self-administration in operant chambers equipped with levers (Piva et al., 2018): rats were first trained to self-administer sucrose pellets and, after a 14-days forced abstinence stage, memory retrieval stage consisted in training context exposure. At the retrival stage performed during the light phase, a decreased low-gamma power was observed in CA1 when rats were not lever pressing compared to when they were lever pressing (actual instrumental memory retrieval). Moreover, results showed an inverse correlation between gamma power and rate of responding when retrieval was performed in the dark phase.

Our findings suggest that hippocampal gamma power is differently modulated when retrieval is performed during the light phase compared to the dark phase. Further investigations should explore the role of gamma oscillations as potential markers of instrumental appetitive memory reactivation in both light and dark conditions.

内存重新整合是一个允许更新先前合并的内存的过程。为了进行内存整合，首先需要重新激活内存。最近已经表明，在清醒/睡眠阶段的记忆检索可能会影响记忆重新激活的敏感性。考虑到海马伽马频率在记忆过程中的重要性，本研究的目的是研究在恢复工具性食欲性记忆期间伽马能带功率的变化。在昼夜节律周期的亮或暗阶段进行的工具性食欲记忆的恢复过程中，在Sprague Dawley大鼠的背海马CA1区记录了局部场电位。通过在配备杠杆的手术室中使用蔗糖自我管理的方案进行食欲记忆的恢复（Piva et al。，2018）：首先训练大鼠自我管理蔗糖颗粒，然后经过14天的强迫戒断阶段，记忆检索阶段包括训练上下文暴露。在光阶段进行的检索阶段，与未按下杠杆时相比，未按下老鼠时，CA1中观察到了较低的低伽马功率（实际仪器记忆检索）。此外，结果表明，在暗阶段执行检索时，伽马强度与响应速率之间呈反比关系。记忆检索阶段包括训练上下文暴露。在光阶段进行的检索阶段，与未按下杠杆的老鼠相比，未按下老鼠的CA1中观察到了较低的低伽马功率（实际仪器记忆检索）。此外，结果表明，在暗阶段执行检索时，伽马强度与响应速率之间呈负相关。记忆检索阶段包括训练上下文暴露。在光阶段进行的检索阶段，与未按下杠杆时相比，未按下老鼠时，CA1中观察到了较低的低伽马功率（实际仪器记忆检索）。此外，结果表明，在暗阶段执行检索时，伽马强度与响应速率之间呈负相关。

我们的发现表明，与在黑暗阶段相比，在亮相期间进行检索时，海马γ功率的调制方式有所不同。进一步的研究应探索在黑暗和黑暗条件下伽马振荡作为工具性食欲性记忆再激活的潜在标志物的作用。