Analysis of fear memory signals in the rat amygdala and thalamus

The aim of this study was to obtain an insight of how fear memory is encoded in the electrophysiological signals of the rat. We recorded local field potentials (LFPs) of the lateral amygdala (LA) and the medial geniculate nucleus (MGm) in the rat´s brain during retrieval of fear memory. The rats were trained to freeze when they hear the conditioned tone (CS+) using Pavlovian fear conditioning. Total 10 adult rats were used for this experiment and 10-second of noise-free LFPs was used for analysis. We found increased theta power spectrum of neural activity in the LA and the MGm during retrieval of fear memory similar with the previous report. The linear functional connectivity between the LA and the MGm also increased after fear conditioning, specifically during CS+ presentation. In addition, approximate entropy (ApEn), a nonlinear measure of complexity and irregularity of signals, indicated that there was more information processing during fear state. These results show that recall of fear memory can be distinguished from the rest state of brain using linear and nonlinear properties of electrophysiological signals. These electrophysiological properties of fear memory would be used in neuro-engineering field to modify or decode the neural activity for clinical application