其他摘要 | During our daily lives and work, we often need to think for ourselves in what order and in what way, rather than simply repeating what is already there, in order to perform complex tasks. For example, when trying to make a delicious meal, we not only need to put in the dishes and seasonings in the right order, but also need to be precise about the heat and the amount of seasoning. Sequential working memory happens to be the cognitive function that helps us precisely manipulate and maintain the order and content of multiple pieces of information. It has been shown that the prefrontal and hippocampus support learning and memory of information, but whether and how prefrontal hippocampal circuits support the online manipulation and maintenance of sequential information remains unknown. This thesis is divided into three parts to answer these questions. In the first part, three behavioral experiments were conducted to illustrate that maintenance and manipulation of sequential information are not isolated. When we are reordering multiple pieces of information, the accuracy of remembering individual pieces of information decreases. In the second part and the third part, the intracranial local field potential recording experiments based on stereo-electroencephalography (SEEG) show that theta and gamma oscillations are crucial for the prefrontal hippocampal circuits to engage in sequence working memory. There are general and specific neural mechanisms for manipulating and maintaining sequence information. The second part (experiment 4) was based on a line ordering task to investigate how the prefrontal hippocampal circuits support the online updating and generation of sequence information. Participants showed longer thinking times and more recall errors when asked to arrange random lines clockwise (random trials) than to maintain ordered lines (ordered trials) before recalling the orientation of a particular line. Compared with the ordered trials, first, the theta power in the prefrontal cortex increased substantially. The theta power increased transiently and was correlated with the memory precision of line orientation. Second, theta phase coherences between the dorsal lateral prefrontal cortex (DLPFC) and hippocampus were enhanced for ordering, especially for more precisely memorized lines. Third, the theta band DLPFC令hippocampus influence was selectively enhanced for ordering. Finally, gamma oscillations of lateral-prefrontal-hippocampal circuits represent the newly generated sequential information. In the third part, the other SEEG study (experiment 5) investigated whether ordering-related neural activity in prefrontal hippocampal circuits was also affected by memory load during maintenance. Participants also showed longer thinking times and more recall errors when asked to maintain four lines (load 4) than to maintain two lines (load 2) before recalling the orientation of a particular line. First, compared with load 2, only the dorsal anterior cingulate cortex (dACC) showed higher theta power and was not associated with memory precision.
Second, theta phase coherences between the DLPFC and hippocampus, between the dACC and hippocampus were higher at load 4 but was not affected by the memory precision. Third, the direction of the information flow was from the hippocampus to the DLPFC and dACC in all memory loads. Finally, the representative similarity of sequences by gamma oscillations increased with memory load in the hippocampus and ventral lateral prefrontal cortex and decreased with memory load in the dACC. This study suggests that the DLPFC and hippocampus may support the online manipulation of sequence information through theta oscillations. Besides, the lateral prefrontal-hippocampal circuits may support the generation of new sequence information through gamma oscillations. Overall, theta coherence in prefrontal and hippocampus was generalized in the maintenance and manipulation of sequence working memory, but directional effects were specific. More importantly, this study reveals for the first time that the prefrontal-hippocampal circuits supports online processing of time-series information through theta and gamma oscillations and confirms that the prefrontal-hippocampal circuits play a key role in temporal cognition, which provides a new research direction for traditional hippocampal and spatial cognition. |
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