Amygdalar and hippocampal beta rhythm synchrony during human fear memory retrieval.

BACKGROUND: Fear, as one of the basic emotions, is crucial in helping humans to perceive hazards and adapt to social activities. Clinically, fear memory is also involved in a wide spectrum of psychiatric disorders. A better understanding of the neural mechanisms of fear thereby has both neuroscientific and clinical significance. In recent years, data from animal models have demonstrated the key role of the amygdala-hippocampal circuit in the development of fear. However, the neural processing of fear memory remains unclear in humans, which is mainly due to the limitation of indirect measure of neural activity. METHODS: Herein, we investigated fear memory by direct intracranial recordings from 8 intractable epilepsy patients with depth electrodes in both the hippocampus and ipsilateral amygdala. All the patients were subjected to a well-established Pavlovian fear memory paradigm consisted of the familiarization task, conditioning task, and retrieval task, respectively. Simultaneous local field potentials from the hippocampus and amygdala were recorded during different stages. The oscillatory activities from the amygdala and hippocampus were analyzed during fear memory retrieval compared with neutral stages. RESULTS: Consistent with previous rodent studies, our results showed that the amygdala was involved in fear memory retrieval rather than neutral memory retrieval, while the hippocampus was involved both in fear memory retrieval and neutral memory retrieval. In particular, we found that there was an enhanced synchronized activity between the amygdala and hippocampus at beta frequencies (14-30 Hz), which suggested that enhanced synchronized activity at beta frequencies between the amygdala and hippocampus play a pivotal role during retrieval of fear memory in human. CONCLUSIONS: Thus, our observation that the amygdala-hippocampal system contributing to fear memory retrieval in human with frequency-depended specificity has provided new insights into the mechanism of fear and have potential clinical relevance.

Neural processes of auditory perception in Heschl's gyrus for upcoming acoustic stimuli in humans.

In the natural environment, attended sounds tend to be perceived much better than unattended sounds. However, the physiological mechanism of how our neural systems direct the state of perceptual attention to prepare for the detection of upcoming acoustic stimuli before auditory stream segregation remains elusive. In this study, based on the direct intracerebral recordings from the auditory cortex in eight epileptic patients with refractory focal seizures, we investigated the neural processing of auditory attention by comparing the local field potentials before 'attentional' and 'distracted' conditions. Here we first showed a distinct build-up of slow, negative cortical potential in Heschl's gyrus. The amplitude increased steadily, starting from 600 to 800 ms before presentation of the tone until the onset of the evoked component P/N 60-80 when the patients were in the attentional condition. Because of their specific topographical distribution and modality-specific properties, we named these 'auditory preparatory potentials', which are also associated with increased gamma oscillations (30-150 Hz) and desynchronized low frequency activity (below 30 Hz). Thus, our findings suggest that the auditory cortex is pre-activated to facilitate the perception of forthcoming sound events, and contribute to the understanding of the neurophysiological mechanisms of auditory perception from a new perspective.

Dynamic Preictal Discharges in Patients With Mesial Temporal Lobe Epilepsy.

PURPOSE: It has been challenging to detect early changes preceding seizure onset in patients with epilepsy. This study investigated the preictal discharges (PIDs) by intracranial electroencephalogram of 11 seizures from 7 patients with mesial temporal lobe epilepsy. METHODS: The EEG segments consisting of 30 seconds before ictal onset and 5 seconds after ictal onset were selected for analysis. After PID detection, the amplitude and interval were measured. According to the timing of PID onset, the 30-second period preceding seizure onset was divided into two stages: before PID stage and PID stage. The autocorrelation coefficients during the two stages were calculated and compared. RESULTS: Preictal discharge amplitude progressively increased, while PID interval gradually decreased toward seizure onset. The autocorrelation coefficients of PID channels were significantly higher during PID stage than before PID stage. There was an overlap between channels with PIDs and seizure onset channels (80.77%). CONCLUSIONS: Preictal discharges emerge prior to ictal event, with a dynamic change and a spatial correlation with seizure onset zone. These findings deepen our understanding of seizure generation and help early prediction and localization of seizure onset zone.