ABSTRACT
The prefrontal cortex and hippocampus may support sequential working memory beyond episodic memory and spatial navigation. This stereoelectroencephalography (SEEG) study investigated how the dorsolateral prefrontal cortex (DLPFC) interacts with the hippocampus in the online processing of sequential information. Twenty patients with epilepsy (eight women, age 27.6 ± 8.2 years) completed a line ordering task with SEEG recordings over the DLPFC and the hippocampus. 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. First, the ordering-related increase in thinking time and recall error was associated with a transient theta power increase in the hippocampus and a sustained theta power increase in the DLPFC (3-10 Hz). In particular, the hippocampal theta power increase correlated with the memory precision of line orientation. Second, theta phase coherences between the DLPFC and hippocampus were enhanced for ordering, especially for more precisely memorized lines. Third, the theta band DLPFC → hippocampus influence was selectively enhanced for ordering, especially for more precisely memorized lines. This study suggests that theta oscillations may support DLPFC-hippocampal interactions in the online processing of sequential information.
Subject(s)
Adult , Female , Humans , Young Adult , Male , Epilepsy , Hippocampus , Memory, Short-Term , Mental Recall , Prefrontal Cortex , Theta RhythmABSTRACT
Objective Temporal lobe epilepsy (TLE),frequently accompanied by working memory dysfunction,is an important form of adult epilepsy syndrome.Study on neural mechanisms of TLE with working memory dysfunction has important scientific value and clinical significance.Theta oscillations are synchronous activity of the brain in the 4-8 Hz frequency range.It is well recognized that there is a close relationship between the theta oscillations and working memory behavior.TLE patients with working memory dysfunction were taken as the research subjects,and the theta oscillations absence in TLE with working memory behavioral disorder was carried out,which provide the reference for further research into the neural mechanisms of TLE with working memory dysfunction.Methods The 34-channel electroencephalographs (EEGs) were recorded from TLE group (18 TLE patients) and control groups (18 healthy subjects) while subjects were performing visual working memory (delayed matching-tosample) tasks.The EEGs during the 3 s delay period was analyzed as experimental data.Fourier transform was used to assess the EEGs spectrum.The channel with the strongest spectrum was selected as the feature channel.Short-time Fourier transform algosiths was employed to calculate the time-frequency representation of the feature channel for the TLE and control groups.Frequency band with the strongest spectrum was selected for control group as the feature frequency band in working memory.Then,the topographical maps of the feature frequency band spectrum were calculated for the TLE and control groups.Results Compared with the control group,the working memnory behavioral performance of the TLE group was lower:accuracy of the TLE group was significantly lower than that of the control group (P＜0.05),and reaction time of the TLE group was significantly longer than that of the control group (P＜0.001).The feature channel in working memnory was frontal midline (Fz) and the feature frequency band was theta band.The Fz spectrum of the feature frequency for TLE was lower than that for control (P＜0.05).The frontal spectrum (seven channels) of the feature frequency for TLE was lower than that of control (P＜0.01).Conclusions Theta oscillations for TLE with working memory behavioral disorder is absent,which maybe one of the possible neural mechanism of TLE with working memory dysfunction.