Spectral characteristics of the hippocampal LFP during contextual fear conditioning

Abstract

Objective: The hippocampus has an important role in the acquisitionand recall of aversive memories. The objective of this study was toinvestigate the relationship among hippocampal rhythms. Methods:Microeletrodes arrays were implanted in the hippocampus of Wistarrats. The animals were trained and tested in a contextual fearconditioning task. The training consisted in applying shocks in thelegs. The memory test was performed 1 day (recent memory) or 18days (remote memory) after training. We proposed a measure basedon the FFT power spectrum, denominated “delta-theta ratio”, tocharacterize the different behaviors (active exploration and freezing)and the memories types. Results: The delta-theta ratio was able todistinguish recent and remote memories. In this study, the ratio forthe 18-day group was smaller than for the 1-day group. Moreover,this measure was useful to distinguish the different behavior states– active exploration and freezing. Conclusions: The results suggestdelta-theta oscillations could reflect the demands on informationprocessing during recent and remote memory recalls.

Keywords

• Hippocampus
• Memory
• Fear/physiology
• Amnesia retrograde