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The following article was published in the English version of the Bulletin of Neuroscience, by the author of Bulletin of Neuroscience.
Time is the basic dimension of human understanding of the world. How the human brain constructs time series, encodes and memorizes a series of events is a common concern in psychology and neuroscience. The prefrontal lobe and hippocampus are key brain regions for processing time-series information. Patients with damage to the prefrontal lobe often have difficulty organizing a sequence of movements in chronological order. Patients and animals with damaged hippocamps often have difficulty remembering a sequence of events in chronological order. But the key unsolved scientific question is how the prefrontal lobe and hippocampus interact in sequential working memory
Neuroscience Bulletin published a cover article in Issue 2, 2024 from the Center for Excellence in Brain Science and Intelligent Technology, Chinese Academy of SciencesYe ZhengThe research group and the Department of Functional Neurosurgery, Ruijin Hospital, Shanghai Jiao Tong University School of MedicineZhan ShikunThe team's research titled "Theta oscillations support prefrontal-hippocampal interactions in sequential working memory"**. The study revealed that the dorsolateral prefrontal lobe and hippocampus of the human brain support the processing of time-series information through theta oscillations.
Using stereotactic electroencephalography (SEEG), combined with magnetic resonance imaging, the researchers collected local field potential data from 43 dorsolateral prefrontal lobe sites and 56 hippocampal loci while 20 epilepsy patients performed a sequential working memory task (Figure 1A).
In the sequential working memory task, the subject memorizes the orientation of the four lines in clockwise order (Figure 1b). In the sequential condition, the four lines are presented in clockwise order, and the subject only needs to remember the direction of the lines in the order in which they are presented. Under random conditions, the four lines are shuffled in a random order, and the subject is required to rearrange the lines in clockwise order and remember which direction they are facing. The researchers found that subjects took longer to think about the direction of the line and had less accurate memory of the direction of the line in the random condition compared to the sequential condition (Figure 1c).
Figure 1aElectrode location in the hippocampus and dorsolateral prefrontal lobe (DLPFC). bSequential working memory tasks. cLonger thought time and greater recall error.
The researchers then analyzed the local field potential data and found a series of changes in the dorsolateral prefrontal and hippocampal theta oscillations. First, the energy of the hippocampal theta oscillation (3-10 Hz) is briefly enhanced when encoding sequence information. The energy of the dorsolateral prefrontal theta oscillation continues to increase while encoding and maintaining sequence information (Figure 2A). Second, the phase consistency of the dorsolateral prefrontal Theta oscillations and hippocampal theta oscillations continued to increase while encoding and maintaining sequence information (Fig. 2B). More importantly, in theta oscillations, the flow of information from the dorsolateral prefrontal lobe to the hippocampus was significantly greater than that from the hippocampus to the dorsolateral prefrontal lobe. The flow of information from the dorsolateral prefrontal lobe to the hippocampus continues to enhance while encoding and maintaining sequence information (Figure 2C). The stronger the phase consistency of the dorsolateral prefrontal Theta oscillations and the hippocampal Theta oscillations, the greater the flow of information from the dorsolateral prefrontal lobe to the hippocampus, and the more accurate the subject's memory of the line orientation (Figure 2D).
Figure 2aEnhancement of energy of theta oscillations in the hippocampus and dorsolateral prefrontal lobes. bIncreased phase consistency of dorsolateral prefrontal and hippocampal theta oscillations. cThe dorsolateral prefrontal lobe to the hippocampus is enhanced. dThe stronger the phase consistency of the Theta oscillation, the more accurate the memory.
In summary,This study revealed for the first time that the prefrontal-hippocampal loop of the human brain supports the processing of time series information through Theta oscillations, confirming that the prefrontal-hippocampal loop plays a key role in time cognitionIn addition to the traditional research on hippocampal and spatial cognition, it suggests new research directions.
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su m, hu k, liu w, wu y, wang t, cao c, et al. theta oscillations support prefrontal-hippocampal interactions in sequential working memory. neurosci bull 2024, 40:147–156.
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