Alterations in the functional connectivity of a verbal working memory-related brain network in patients with left temporal lobe epilepsy

The neural basis of executive functioning deficits in adolescents with epilepsy: a resting-state fMRI connectivity study of working memory

Working memory deficits are common in youth with epilepsy and consistently associated with long-term negative outcomes. Existing research on the neural basis of working memory disruptions in pediatric epilepsy is limited. The question of whether differences in the functional connectivity of neural networks underlie working memory disruptions in pediatric patients with epilepsy remains unanswered. A total of 49 adolescents between the ages of 13-17 years participated in this study. Twenty-nine adolescents had confirmed epilepsy (n = 17 generalized epilepsy, n = 6 localization-related, n = 6 unclassified). The control group included 20 healthy adolescents. A total of 10-min resting state functional magnetic resonance imaging was obtained for all participants. NeuroSynth-derived regions of interest were used as nodes that comprise working memory neural networks. Group differences in resting state functional connectivity were examined between adolescents with epilepsy and controls. Functional connectivity was computed as the temporal correlation of functional magnetic resonance imaging signal fluctuations between any two regions of interest. Compared to controls, adolescents in the epilepsy group demonstrated both hypoconnectivity and hyperconnectivity in cortical areas that map onto fronto-parietal and cingulo-opercular networks, as well as cerebellar regions. Functional connectivity between pairs of regions of interest was also significantly associated with behavioral measures of working memory across epilepsy and control groups. This study demonstrates that the presence of abnormal patterns in resting state neural network connectivity may underlie the working memory disruptions that frequently characterize the neurocognitive profile of youth with epilepsy.

Voxel-wise functional connectivity of the default mode network in epilepsies: a systematic review and meta-analysis

Background:

Default Mode Network (DMN) is recognized to be involved in the generation and propagation of epileptic activities in various epilepsies. Converging evidence has suggested disturbed Functional Connectivity (FC) in epilepsies, which was inferred to be related to underlying pathological mechanisms. However, abnormal changes of FC in DMN revealed by different studies are controversial, which obscures the role of DMN in distinct epilepsies.

Objective:

The present work aims to investigate the voxel-wise FC in DMN across epilepsies.

Methods:

A systematic review was conducted on 22 published articles before October 2020, indexed in PubMed and Web of Science. A meta-analysis with a random-effect model was performed using the effect-size signed differential mapping approach. Subgroup analyses were performed in three groups: Idiopathic Generalized Epilepsy (IGE), mixed Temporal Lobe Epilepsy (TLE), and mixed Focal Epilepsy (FE) with different foci.

Results:

The meta-analysis suggested commonly decreased FC in mesial prefrontal cortices across different epilepsies. Additionally decreased FC in posterior DMN was observed in IGE. The TLE showed decreased FC in temporal lobe regions and increased FC in the dorsal posterior cingulate cortex. Interestingly, an opposite finding in the ventral and dorsal middle frontal gyrus was observed in TLE. The FE demonstrated increased FC in the cuneus.

Longitudinal assessment of resting-state fMRI in temporal lobe epilepsy: A two-year follow-up study

In this study, we aimed to detect longitudinal alterations in local spontaneous brain activity and functional connectivity (FC) of the default mode network (DMN) in patients with temporal lobe epilepsy (TLE) over a two-year follow-up. We used amplitude of low-frequency fluctuation (ALFF) analysis and independent component analysis (ICA) to explore differences in local spontaneous brain activity and FC strength. In total, 33 participants (16 patients with TLE and 17 age- and gender-matched healthy controls (HCs)) were recruited in this study. All participants performed the Attention Network Test (ANT) for evaluation of the executive control function. Compared with healthy patients at baseline, patients with TLE at follow-up exhibited increased ALFF values in the left medial frontal gyrus, as well as reduced FC values in the left inferior parietal gyrus (IPG) within the DMN. Patients with TLE revealed executive dysfunction, but no progressive deterioration was observed during follow-up. This study revealed the abnormal distribution of ALFF values and Rs-FC changes over a two-year follow-up period in TLE, both of which demonstrated different reorganization trajectories and loss of efficiency.

Aberrant executive control networks and default mode network in patients with right-sided temporal lobe epilepsy: a functional and effective connectivity study

Objective: We aimed to explore functional connectivity (FC) and effective connectivity (EC) of the executive control networks (ECNs) and the default mode network (DMN) in patients with right-sided TLE (rTLE) by applying independent component analysis (ICA) and Granger causal analysis (GCA).Methods: Twenty-seven patients with rTLE and 20 healthy controls (HCs) matched for age, gender underwent resting-state functional magnetic resonance imaging and Attention Network Test (ANT).Results: The FC analysis showed compared to HCs, patients with rTLE demonstrated reduced FC strength in the right inferior parietal gyrus (IPG) and the right middle temporal gyrus (MTG). The left superior temporal gyrus (STG) displayed reduced FC values whereas the left thalamus revealed increased FC values in rTLE. ROI-wise GCA revealed that patients with rTLE displayed increased EC from the left thalamus to the left STG, and as well as enhanced EC from the right IPG to the right MTG compared to HCs. Voxel-wise GCA showed positive EC from the left thalamus to the left insula while the right middle occipital gyrus (MOG) exhibited increased EC to the right MTG in patients. The ANT results demonstrated executive dysfunction in patients compared to HCs. The increased FC in the left thalamus showed a negative association with ECF in patients.Conclusion: We speculated that recurrent seizures take effect on disruption among the brain networks, and self-modulation occurs simultaneously to compensate for cognitive decline. Our findings revealed new insights on the neuropathophysiological mechanisms of rTLE.

Disruption and lateralization of cerebellar-cerebral functional networks in right temporal lobe epilepsy: A resting-state fMRI study

Numerous studies have highlighted important roles for the cerebellum in cognition and movement, based on numerous fiber connections between the cerebrum and cerebellum. Abnormal cerebellar activity caused by epileptic discharges has been reported in previous studies, but researchers have not clearly determined whether aberrant cerebellar activity contributes to the disruption of the cerebellar-cerebral networks in right temporal lobe epilepsy (rTLE). Here, thirty patients with rTLE and 30 age- and sex-matched healthy controls (HCs) were recruited. All participants underwent the Attention Network Test (ANT) and resting-state functional magnetic resonance imaging (rs-fMRI) scanning. Cerebellar functional networks were extracted and analyzed by defining seeds in the cerebellum. A correlation analysis was performed between attentional performance and voxels that showed differences in functional connectivity (FC) in patients compared with HCs. Relative to HCs, patients exhibited significantly decreased FC in the dentate nucleus (DN) network (right DN with the left postcentral gyrus, left precentral gyrus, left cuneus, and left calcarine gyrus) and motor network (right cerebellar lobule V with the right putamen) and increased FC in the executive control network (right cerebellar crus I with the right inferior parietal lobule). Alerting, orienting, and executive control performances were impaired in patients with rTLE. Furthermore, the executive control effect was significantly correlated with aberrant FC strength between the right DN and the left precentral/postcentral gyrus. Our findings highlight that the disrupted cerebellar-cerebral functional network ipsilateral to the epileptogenic focus causes both impairments in and compensatory effects on attentional deficits in patients with rTLE. These findings contribute to our understanding of the cerebellar damage caused by epileptic discharges and the corresponding effect on attentional performance.

Functional independence in resting-state connectivity facilitates higher-order cognition

Growing evidence suggests that intrinsic functional connectivity (i.e. highly structured patterns of communication between brain regions during wakeful rest) may encode cognitive ability. However, the generalizability of these findings is limited by between-study differences in statistical methodology and cognitive domains evaluated. To address this barrier, we evaluated resting-state neural representations of multiple cognitive domains within a relatively large normative adult sample. Forty-four participants (mean(sd) age=31(10) years; 18 male and 26 female) completed a resting-state functional MRI scan and neuropsychological assessments spanning motor, visuospatial, language, learning, memory, attention, working memory, and executive function performance. Robust linear regression related cognitive performance to resting-state connectivity among 200 a priori determined functional regions of interest (ROIs). Only higher-order cognitions (such as learning and executive function) demonstrated significant relationships between brain function and behavior. Additionally, all significant relationships were negative - characterized by moderately positive correlations among low performers and weak to moderately negative correlations among high performers. These findings suggest that functional independence among brain regions at rest facilitates cognitive performance. Our interpretation is consistent with graph theoretic analyses which represent the brain as independent functional nodes that undergo dynamic reorganization with task demand. Future work will build upon these findings by evaluating domain-specific variance in resting-state neural representations of cognitive impairment among patient populations.

Statistical parametric mapping for analyzing interictal magnetoencephalography in patients with left frontal lobe epilepsy

PURPOSE

Frontal lobe epilepsy is a common epileptic disorder and is characterized by recurring seizures that arise in the frontal lobes. The purpose of this study is to identify the epileptogenic regions and other abnormal regions in patients with left frontal lobe epilepsy (LFLE) based on the magnetoencephalogram (MEG), and to understand the effects of clinical variables on brain activities in patients with LFLE.

METHOD

Fifteen patients with LFLE (23.20 ± 8.68 years, 6 female and 9 male) and 16 healthy controls (23.13 ± 7.66 years, 6 female and 10 male) were included in resting-stage MEG examinations. Epileptogenic regions of LFLE patients were confirmed by surgery. Regional brain activations were quantified using statistical parametric mapping (SPM). The correlation between the activations of the abnormal brain regions and the clinical seizure parameters were computed for LFLE patients.

RESULTS

Brain activations of LFLE patients were significantly elevated in left superior/middle/inferior frontal gyri, postcentral gyrus, inferior temporal gyrus, insula, parahippocampal gyrus and amygdala, including the epileptogenic regions. Remarkable decreased activations were found mainly in the left parietal gyrus and precuneus. There is a positive correlation between the duration of the epilepsy (in month) and activations of the abnormal regions, while no relation was found between age of seizure onset (year), seizure frequency and the regions of the abnormal activity of the epileptic patients.

CONCLUSION

Our findings suggest that the aberrant brain activities of LFLE patients were not restricted to the epileptogenic zones. Long duration of epilepsy might induce further functional damage in patients with LFLE.

Functional substrate for memory function differences between patients with left and right mesial temporal lobe epilepsy associated with hippocampal sclerosis

OBJECTIVE

Little is known about the functional substrate for memory function differences in patients with left or right mesial temporal lobe epilepsy (mTLE) associated with hippocampal sclerosis (HS) from an electrophysiological perspective. To characterize these differences, we hypothesized that hippocampal theta connectivity in the resting-state might be different between patients with left and right mTLE with HS and be correlated with memory performance.

METHODS

Resting-state hippocampal theta connectivity, identified via whole-brain magnetoencephalography, was evaluated. Connectivity and memory function in 41 patients with mTLE with HS (left mTLE=22; right mTLE=19) were compared with those in 46 age-matched healthy controls and 28 patients with focal cortical dysplasia (FCD) but without HS.

RESULTS

Connectivity between the right hippocampus and the left middle frontal gyrus was significantly stronger in patients with right mTLE than in patients with left mTLE. Moreover, this connectivity was positively correlated with delayed verbal recall and recognition scores in patients with mTLE. Patients with left mTLE had greater delayed recall impairment than patients with right mTLE and FCD. Similarly, delayed recognition performance was worse in patients with left mTLE than in patients with right mTLE and FCD. No significant differences in memory function between patients with right mTLE and FCD were detected. Patients with right mTLE showed significantly stronger hippocampal theta connectivity between the right hippocampus and left middle frontal gyrus than patients with FCD and left mTLE.

CONCLUSION

Our results suggest that right hippocampal-left middle frontal theta connectivity could be a functional substrate that can account for differences in memory function between patients with left and right mTLE. This functional substrate might be related to different compensatory mechanisms against the structural hippocampal lesions in left and right mTLE groups. Given the positive correlation between connectivity and delayed verbal memory function, hemispheric-specific hippocampal-frontal theta connectivity assessment could be useful as an electrophysiological indicator of delayed verbal memory function in patients with mTLE with HS.