Phase Synchronization Analysis of Theta-Band of Local Field Potentials in the Anterior Cingulated Cortex of Rats under Fear Conditioning

This study aims to examine the phase synchronization of characteristic frequency band of local field potentials (LFPs) in anterior cingulated cortex (ACC) of rats under fear conditioning. The 16-channel LFPs were recorded in ACC of rats implicated in microelectrode array under fear conditioning. The rats were trained to freezing when they hear the conditioned tone. Theta-band synchronization of the neural signal in the hippocampus and in the lateral amygdale (LA) was found recently. So, discrete wavelet transform was used to decompose LFPs to extract theta-band of LFPs. 16-channel´s instantaneous phases of theta-band can be obtained through applying Hilbert transform to the theta-band. Finally, cross-correlation coherences were calculated between every channel phase and a reference channel. The coherence values were calculated with a sliding window of 50ms and a step of 10ms. The results show that the linear correlation between every channel and a reference channel increased during retrieval of fear memory in the theta-band. These phenomena indicate that recall of fear memory can be discriminated from the rest state of brain using linear properties of electro-physiological signals. This analysis of fear memory may provide some support to the neuro-physiological mechanisms of fear memory.