The electrophysiological correlates of the working memory subcomponents: evidence from high-density EEG and coherence analysis (original) (raw)
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Synchronization between prefrontal and posterior association cortex during human working memory
Proceedings of the National Academy of Sciences, 1998
We measured coherence between the electroencephalogram at different scalp sites while human subjects performed delayed response tasks. The tasks required the retention of either verbalizable strings of characters or abstract line drawings. In both types of tasks, a significant enhancement in coherence in the range (4-7 Hz) was found between prefrontal and posterior electrodes during 4-s retention intervals. During 6-s perception intervals, far fewer increases in coherence were found. Also in other frequency bands, coherence increased; however, the patterns of enhancement made a relevance for working memory processes seem unlikely. Our results suggest that working memory involves synchronization between prefrontal and posterior association cortex by phase-locked, low frequency (4-7 Hz) brain activity.
2020
ABSTRACTBackgroundThe maintenance of items in working memory (WM) relies on a widespread network of brain areas where synchronization between electrophysiological recordings may reflect functional coupling. While the coupling from hippocampus to scalp EEG is well established, we provide here direct cortical recordings for a fine-grained analysis.MethodsA patient performed a WM task where a string of letters was presented all at once, thus separating the encoding period from the maintenance period. We recorded sEEG from the hippocampus, temporo-parietal ECoG from a 64-contact grid electrode, and scalp EEG.ResultsPower spectral density (PSD) showed a clear task dependence: PSD in the posterior parietal lobe (10 Hz) and in the hippocampus (20 Hz) peaked towards the end of the maintenance period.Inter-area synchronization was characterized by the phase locking value (PLV). WM maintenance enhanced PLV between hippocampal sEEG and scalp EEG specifically in the theta range [6 7] Hz.PLV fro...
The Synchronization of the Human Cortical Working Memory Network
NeuroImage, 2002
A verbal reasoning problem at the intersection of verbal working memory, problem-solving, and language comprehension was examined using event-related fMRI to distinguish differences in the differential timing of the response of the various cortical regions that compose the working memory network. Problems were developed such that the process demand as well as the timing of the manipulation of the contents of working memory (i.e., a demanding computation) was varied. Activation was observed in several regions including the dorsolateral prefrontal cortex, the inferior frontal gyrus, and the parietal lobe. Examination of the MR amplitude response revealed that the regions do not all activate simultaneously; instead, their activation time courses reveal differential responses that correspond to their theoretical processing role in the problem-solving task. The coordination of cortical area responses reveals how the various cortical regions synchronize and collaborate in order to accomplish a given cognitive function.
European Journal of Neuroscience, 2010
Working memory (WM) tasks require not only distinct functions such as a storage buffer and central executive functions, but also coordination among these functions. Neuroimaging studies have revealed the contributions of different brain regions to different functional roles in WM tasks; however, little is known about the neural mechanism governing their coordination. Electroencephalographic (EEG) rhythms, especially theta and alpha, are known to appear over distributed brain regions during WM tasks, but the rhythms associated with task-relevant regional coupling have not been obtained thus far. In this study, we conducted time–frequency analyses for EEG data in WM tasks that include manipulation periods and memory storage buffer periods. We used both auditory WM tasks and visual WM tasks. The results successfully demonstrated function-specific EEG activities. The frontal theta amplitudes increased during the manipulation periods of both tasks. The alpha amplitudes increased during not only the manipulation but also the maintenance periods in the temporal area for the auditory WM and the parietal area for the visual WM. The phase synchronization analyses indicated that, under the relevant task conditions, the temporal and parietal regions show enhanced phase synchronization in the theta bands with the frontal region, whereas phase synchronization between theta and alpha is significantly enhanced only within the individual areas. Our results suggest that WM task-relevant brain regions are coordinated by distant theta synchronization for central executive functions, by local alpha synchronization for the memory storage buffer, and by theta–alpha coupling for inter-functional integration.
Dependence of Working Memory on Coordinated Activity Across Brain Areas
Frontiers in Systems Neuroscience, 2022
Neural signatures of working memory (WM) have been reported in numerous brain areas, suggesting a distributed neural substrate for memory maintenance. In the current manuscript we provide an updated review of the literature focusing on intracranial neurophysiological recordings during WM in primates. Such signatures of WM include changes in firing rate or local oscillatory power within an area, along with measures of coordinated activity between areas based on synchronization between oscillations. In comparing the ability of various neural signatures in any brain area to predict behavioral performance, we observe that synchrony between areas is more frequently and robustly correlated with WM performance than any of the within-area neural signatures. We further review the evidence for alteration of inter-areal synchrony in brain disorders, consistent with an important role for such synchrony during behavior. Additionally, results of causal studies indicate that manipulating synchrony across areas is especially effective at influencing WM task performance. Each of these lines of research supports the critical role of inter-areal synchrony in WM. Finally, we propose a framework for interactions between prefrontal and sensory areas during WM, incorporating a range of experimental findings and offering an explanation for the observed link between intra-areal measures and WM performance.
Human Brain Mapping, 2005
Electroencephalogram (EEG) α (around 10 Hz) is the dominant rhythm in the human brain during conditions of mental inactivity. High amplitudes as observed during rest usually diminish during cognitive effort. During retention of information in working memory, however, power increase of α oscillations can be observed. This α synchronization has been interpreted as cortical idling or active inhibition. The present study provides evidence that during top-down processing in a working memory task, α power increases at prefrontal but decreases at occipital electrode sites, thereby reaching a state in which α power and frequency become very similar over large distances. Two experimental conditions were compared. In the first, visuospatial information only had to be retained in memory whereas the second condition additionally demanded manipulation of the information. During the second condition, stronger α synchronization at prefrontal sites and larger occipital α suppression was observed as compared to that for pure retention. This effect was accompanied by assimilation of prefrontal and occipital α frequency, stronger functional coupling between prefrontal and occipital brain areas, and α latency shifts from prefrontal cortex to primary visual areas, possibly indicating the control of posterior cortical activation by anterior brain areas. An increase of prefrontal EEG α amplitudes, which is accompanied by a decrease at posterior sites, thus may not be interpreted in terms of idling or “global” inhibition but may enable a tight functional coupling between prefrontal cortical areas, and thereby allows the control of the execution of processes in primary visual brain regions. Hum Brain Mapp, 2005. © 2005 Wiley-Liss, Inc.
Brain Topography, 2019
The encoding of visuospatial information is the foremost and indispensable step which determines the outcome in a visuospatial working memory (VSWM) task. It is considered to play a crucial role in limiting our ability to attend and process only 3-5 integrated items of information. Despite its importance in determining VSWM performance, the neural mechanisms underlying VSWM encoding have not been clearly differentiated from those involved during VSWM retention, manipulation and/or retrieval. The high temporal resolution of electroencephalography (EEG) and improved spatial resolution with dense array data acquisition makes it an ideal tool to study the dynamics in the functional brain connectivity during a cognitive task. In the present study, the changes in the functional brain connectivity due to memory load during VSWM encoding were studied using 128-channel EEG. Lagged linear coherence (LagR) was computed between 84 regions of interest (ROIs) defined according to the Brodmann areas for seven EEG frequency bands: delta (2-4 Hz), theta (4-8 Hz), alpha 1 (8-10.5 Hz), alpha 2 (10.5-13 Hz), beta 1 (13-20 Hz), beta 2 (20-30 Hz), and gamma (30-45 Hz). Interestingly, out of seven EEG frequency bands investigated in the current study, LagR of only theta band varied significantly in 13 brain connections due to memory load during VSWM encoding. LagR of theta band increased significantly at high memory load when compared to low memory load in twelve brain connections with the maximum change observed between right cuneus and right middle temporal gyrus (Cohen's d = 0.836), indicating the integration of brain processes to confront the increase in memory demands. Theta LagR decreased significantly between left postcentral gyrus and right precentral gyrus at high memory load as compared to low memory load, which might have a role for sustaining attention during encoding. Change in the LagR values due to memory load between fusiform gyrus and lingual gyrus in the right hemisphere had a positive correlation (r = 0.464, p = 0.003) with the error rate, signifying the crucial role played by these two regions in predicting the performance. The current study has not only identified the neural connections that are responsible for the formation of working memory traces during VSWM encoding, but also support the notion that encoding is a rate-limiting process underlying our memory capacity limit.
Neuronal synchrony reveals working memory networks and predicts individual memory capacity
Proceedings of the National Academy of Sciences, 2010
Visual working memory (VWM) is used to maintain sensory information for cognitive operations, and its deficits are associated with several neuropsychological disorders. VWM is based on sustained neuronal activity in a complex cortical network of frontal, parietal, occipital, and temporal areas. The neuronal mechanisms that coordinate this distributed processing to sustain coherent mental images and the mechanisms that set the behavioral capacity limit have remained unknown. We mapped the anatomical and dynamic structures of network synchrony supporting VWM by using a neuro informatics approach and combined magnetoencephalography and electroencephalography. Interareal phase synchrony was sustained and stable during the VWM retention period among frontoparietal and visual areas in α- (10–13 Hz), β- (18–24 Hz), and γ- (30–40 Hz) frequency bands. Furthermore, synchrony was strengthened with increasing memory load among the frontoparietal regions known to underlie executive and attention...
Theta coupling in the human electroencephalogram during a working memory task
Neuroscience Letters, 2004
The role of coupling between prefrontal and temporo-parietal brain areas within the theta frequency range of the human electroencephalogram was explored in a working memory task. During encoding of visual information higher theta amplitudes were observed in the right compared to the left hemisphere. Retrieval of visuospatial and verbal information elicited a more bilateral activation pattern. These effects were accompanied by theta coupling between dorsolateral prefrontal and right posterior temporal electrode sites during encoding. During retrieval prefrontal and bilateral temporo-parietal brain areas were coupled. These results support the idea of working memory functions being dependent on distributed prefrontal-temporal networks. q
Journal of Neuroscience, 2008
It is a fundamental question whether the medial temporal lobe (MTL) supports only long-term memory encoding, or contributes to working memory (WM) processes as well. Recent data suggest that the MTL is activated whenever multiple items or item features are being maintained in WM. This may rely on interactions between the MTL or the prefrontal cortex (PFC) and content-specific areas in the inferior temporal (IT) cortex. Here, we investigated the neural mechanism through which the MTL, PFC, and IT cortex interact during WM maintenance. First, we quantified phase synchronization of intracranial EEG data in epilepsy patients with electrodes in both regions. Second, we used directional coupling analysis to study whether oscillatory activity in the IT cortex drives the MTL or vice versa. Finally, we investigated functional connectivity in functional magnetic resonance imaging data of healthy subjects with seeds in the MTL and PFC. With increasing load, EEG phase synchronization between the IT cortex and anterior parahippocampal gyrus and within the MTL increased. Coupling was bidirectional in all load conditions, but changed toward an increased top-down (anterior parahippocampal gyrus 3 IT) coupling in the high gamma range (51-75 Hz) with increasing load. Functional connectivity between the MTL seed and the visual association cortex increased with load, but activity within the MTL and the PFC correlated with fewer voxels, suggesting that more specific neural networks were engaged. These data indicate that WM for multiple items depends on an increased strength of top-down control of activity within the IT cortex by the MTL.