Functional connectivity homogeneity correlates with duration of temporal lobe epilepsy.
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ABSTRACT:
SUBMITTER: Haneef Z
PROVIDER: S-EPMC4458387 | biostudies-literature | 2015 May
REPOSITORIES: biostudies-literature
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Project description:Temporal lobe epilepsy (TLE) affects brain areas beyond the temporal lobes due to connections of the hippocampi and other temporal lobe structures. Using functional connectivity magnetic resonance imaging (MRI), we determined the changes of hippocampal networks in TLE to assess for a more complete distribution of abnormality.Regions of interest (ROIs) were defined in the right and left hippocampi in three groups of participants: left TLE (n = 13), right TLE (n = 11), and healthy controls (n = 16). Brain regions functionally connected to these ROIs were identified by correlating resting-state low-frequency functional MRI (fMRI) blood oxygenation level-dependent (BOLD) signal fluctuations. The grouped results were compared using independent sample t-test.TLE was associated with increased hippocampal connectivity involving several key areas of the limbic network (temporal lobe, insula, thalamus), frontal lobes, angular gyrus, basal ganglia, brainstem, and cerebellum, along with reduced connectivity involving areas of the sensorimotor cortex (visual, somatosensory, auditory, primary motor) and the default mode network (precuneus). Left TLE had more marked connectivity changes than right TLE.The observed connectivity changes in TLE indicate dysfunctional networks that underlie widespread brain involvement in TLE. There are identifiable differences in the connectivity of the hippocampi between left and right TLE.
| S-EPMC3946924 | biostudies-literature
Project description:In mesial temporal lobe epilepsy (MTLE) the epileptogenic area is confined to the mesial temporal lobe, but other cortical and subcortical areas are also affected and cognitive and psychiatric impairments are usually documented. Functional connectivity methods are based on the correlation of the blood oxygen level dependent (BOLD) signal between brain regions, which exhibit consistent and reproducible functional networks from resting state data. The aim of this study is to compare functional connectivity of patients with MTLE during the interictal period with healthy subjects. We hypothesize that patients show reduced functional connectivity compared to controls, the interest being to determine which regions show this reduction.We selected electroencephalography-functional magnetic resonance imaging (EEG-fMRI) resting state data without EEG spikes from 16 patients with right and 7 patients with left MTLE. EEG-fMRI resting state data of 23 healthy subjects matched for age, sex, and manual preference were selected as controls. Four volumes of interest in the left and right amygdalae and hippocampi (LA, RA, LH, and RH) were manually segmented in the anatomic MRI of each subject. The averaged BOLD time course within each volume of interest was used to detect brain regions with BOLD signal correlated with it. Group differences between patients and controls were estimated.In patients with right MTLE, group difference functional connectivity maps (RMTLE - controls) showed for RA and RH decreased connectivity with the brain areas of the default mode network (DMN), the ventromesial limbic prefrontal regions, and contralateral mesial temporal structures; and for LA and LH, decreased connectivity with DMN and contralateral hippocampus. Additional decreased connectivity was found between LA and pons and between LH and ventromesial limbic prefrontal structures. In patients with left MTLE, functional connectivity maps (LMTLE - controls) showed for LA and LH decreased connectivity with DMN, contralateral hippocampus, and bilateral ventromesial limbic prefrontal regions; no change in connectivity was detected for RA; and for RH, there was decreased connectivity with DMN, bilateral ventromesial limbic prefrontal regions, and contralateral amygdala and hippocampus.In unilateral MTLE, amygdala and hippocampus on the affected and to a lesser extent on the healthy side are less connected, and are also less connected with the dopaminergic mesolimbic and the DMNs. Changes in functional connectivity between mesial temporal lobe structures and these structures may explain cognitive and psychiatric impairments often found in patients with MTLE.
| S-EPMC3767602 | biostudies-literature
Project description:BackgroundThe functional architecture of the human brain has been extensively described in terms of functional connectivity networks, detected from the low-frequency coherent neuronal fluctuations that can be observed in a resting state condition. Little is known, so far, about the changes in functional connectivity and in the topological properties of functional networks, associated with different brain diseases.Methodology/principal findingsIn this study, we investigated alterations related to mesial temporal lobe epilepsy (mTLE), using resting state functional magnetic resonance imaging on 18 mTLE patients and 27 healthy controls. Functional connectivity among 90 cortical and subcortical regions was measured by temporal correlation. The related values were analyzed to construct a set of undirected graphs. Compared to controls, mTLE patients showed significantly increased connectivity within the medial temporal lobes, but also significantly decreased connectivity within the frontal and parietal lobes, and between frontal and parietal lobes. Our findings demonstrated that a large number of areas in the default-mode network of mTLE patients showed a significantly decreased number of connections to other regions. Furthermore, we observed altered small-world properties in patients, along with smaller degree of connectivity, increased n-to-1 connectivity, smaller absolute clustering coefficients and shorter absolute path length.Conclusions/significanceWe suggest that the mTLE alterations observed in functional connectivity and topological properties may be used to define tentative disease markers.
| S-EPMC2799523 | biostudies-literature
Project description:Focal brain lesions are assumed to produce language deficits by two basic mechanisms: local cortical dysfunction at the lesion site, and remote cortical dysfunction due to disruption of the transfer and integration of information between connected brain regions. However, functional imaging studies investigating language outcome after aphasic stroke have tended to focus only on the role of local cortical function. In this positron emission tomography functional imaging study, we explored relationships between language comprehension performance after aphasic stroke and the functional connectivity of a key speech-processing region in left anterolateral superior temporal cortex. We compared the organization of left anterolateral superior temporal cortex functional connections during narrative speech comprehension in normal subjects with left anterolateral superior temporal cortex connectivity in a group of chronic aphasic stroke patients. We then evaluated the language deficits associated with altered left anterolateral superior temporal cortex connectivity in aphasic stroke. During normal narrative speech comprehension, left anterolateral superior temporal cortex displayed positive functional connections with left anterior basal temporal cortex, left inferior frontal gyrus and homotopic cortex in right anterolateral superior temporal cortex. As a group, aphasic patients demonstrated a selective disruption of the normal functional connection between left and right anterolateral superior temporal cortices. We observed that deficits in auditory single word and sentence comprehension correlated both with the degree of disruption of left-right anterolateral superior temporal cortical connectivity and with local activation in the anterolateral superior temporal cortex. Subgroup analysis revealed that aphasic patients with preserved positive intertemporal connectivity displayed better receptive language function; these patients also showed greater than normal left inferior frontal gyrus activity, suggesting a possible 'top-down' compensatory mechanism. These results demonstrate that functional connectivity between anterolateral superior temporal cortex and right anterior superior temporal cortex is a marker of receptive language outcome after aphasic stroke, and illustrate that language system organization after focal brain lesions may be marked by complex signatures of altered local and pathway-level function.
| S-EPMC2792371 | biostudies-literature
Project description:We have previously shown that the connectivity of the hippocampus to other regions of the default mode network (DMN) is a strong indicator of memory ability in people with temporal lobe epilepsy (TLE). Recent work in the cognitive neuroscience literature has suggested that the anterior and posterior aspects of the hippocampus have distinct connections to the rest of the DMN and may support different memory operations. Further, structural analysis of epileptogenic hippocampi has found greater atrophy, characterized by mesial temporal sclerosis, in the anterior region of the hippocampus. Here, we used resting state FMRI data to parcellate the hippocampus according to its functional connectivity to the rest of the brain in people with left lateralized TLE (LTLE) and right lateralized TLE (RTLE), and in a group of neurologically healthy controls. We found similar anterior and posterior compartments in all groups. However, there was weaker connectivity of the epileptogenic hippocampus to multiple regions of the DMN. Both TLE groups showed reduced connectivity of the posterior hippocampus to key hubs of the DMN, the posterior cingulate cortex (PCC) and the medial pre-frontal cortex (mPFC). In the LTLE group, the anterior hippocampus also showed reduced connectivity to the DMN, and this effect was influenced by the presence of mesial temporal sclerosis. When we explored brain-behavior relationships, we found that reduced connectivity of the left anterior hippocampus to the DMN hubs related to poorer verbal memory ability in people with LTLE, and reduced connectivity of the right posterior hippocampus to the PCC related to poorer visual memory ability in those with RTLE. These findings may inform models regarding functional distinctions of the hippocampal anteroposterior axis.
| S-EPMC6714062 | biostudies-literature
Project description:In the present study, we adopted a novel method-local diffusion homogeneity (LDH)-to characterize the structure feature in mesial temporal lobe epilepsy (MTLE). Diffusion-weighted images were acquired from 11 left MTLE patients, 16 right MTLE patients, and 20 healthy controls from May 2014 to January 2015. Local diffusion homogeneity was compared among patient groups and controls by 2 sample t test. The discriminative value of LDH abnormalities was examined by receiver operating characteristic (ROC) curve analysis. Correlations with disease duration and onset age in both patient groups were assessed using Pearson's coefficient. Both patient groups exhibited lower LDH in the anterior corpus callosum (P < 0.05, corrected), and this regional anomaly exhibited excellent classification performance in left MTLE patients (sensitivity = 82%, specificity = 100%), right MTLE patients (sensitivity = 81%, specificity = 90%), and the entire patient cohort (sensitivity = 82%, specificity = 95%). In summary, left and right MTLE patients show common pathological changes in the anterior corpus callosum. This regional LDH abnormality is a potential quantitative biomarker for MTLE.
| S-EPMC5265813 | biostudies-literature
Project description:The mesial temporal lobe is a key region for episodic memory. Accordingly, memory impairment is frequent in patients with mesial temporal lobe epilepsy. However, the functional relevance of potentially epilepsy-induced reorganisation for memory formation is still not entirely clear. Therefore, we investigated whole-brain functional correlates of verbal and non-verbal memory encoding and subsequent memory formation in 56 (25 right sided) mesial temporal lobe epilepsy patients and 21 controls. We applied an fMRI task of learning scenes, faces, and words followed by an out-of-scanner recognition test. During encoding of faces and scenes left and right mesial temporal lobe epilepsy patients had consistently reduced activation in the epileptogenic mesial temporal lobe compared with controls. Activation increases in patients were apparent in extra-temporal regions, partly associated with subsequent memory formation (left frontal regions and basal ganglia), and patients had less deactivation in regions often linked to the default mode and auditory networks. The more specific subsequent memory contrast indicated only marginal group differences. Correlating patients' encoding activation with memory performance both within the paradigm and with independent clinical measures demonstrated predominantly increased contralateral mesio-temporal activation supporting intact memory performance. In left temporal lobe epilepsy patients, left frontal activation was also correlated with better verbal memory performance. Taken together, our findings hint towards minor extra-temporal plasticity in mesial temporal lobe epilepsy patients, which is in line with pre-surgical impairment and post-surgical memory decline in many patients. Further, data underscore the importance of particularly the contralateral mesial temporal lobe itself, to maintain intact memory performance.
| S-EPMC8220377 | biostudies-literature
Project description:Neuroticism, a core personality trait characterized by a tendency towards experiencing negative affect, has been reported to be higher in people with temporal lobe epilepsy (TLE) compared with healthy individuals. Neuroticism is a known predictor of depression and anxiety, which also occur more frequently in people with TLE. The purpose of this study was to identify abnormalities in whole-brain resting-state functional connectivity in relation to neuroticism in people with TLE and to determine the degree of unique versus shared patterns of abnormal connectivity in relation to elevated symptoms of depression and anxiety. Ninety-three individuals with TLE (55 females) and 40 healthy controls (18 females) from the Epilepsy Connectome Project (ECP) completed measures of neuroticism, depression, and anxiety, which were all significantly higher in people with TLE compared with controls. Resting-state functional connectivity was compared between controls and groups with TLE with high and low neuroticism using analysis of variance (ANOVA) and t-test. In secondary analyses, the same analytics were performed using measures of depression and anxiety and the unique variance in resting-state connectivity associated with neuroticism independent of symptoms of depression and anxiety identified. Increased neuroticism was significantly associated with hyposynchrony between the right hippocampus and Brodmann area (BA) 9 (region of prefrontal cortex (PFC)) (p < 0.005), representing a unique relationship independent of symptoms of depression and anxiety. Hyposynchrony of connection between the right hippocampus and BA47 (anterior frontal operculum) was associated with high neuroticism and with higher depression and anxiety scores (p < 0.05), making it a shared abnormal connection for the three measures. In conclusion, increased neuroticism exhibits both unique and shared patterns of abnormal functional connectivity with depression and anxiety symptoms between regions of the mesial temporal and frontal lobe.
| S-EPMC7483612 | biostudies-literature
Project description:The thalamus has been implicated in various stages of medial temporal lobe epilepsy (MTLE) seizure evolution. The relative density and functional significance (in epileptogenesis) of thalamic projections to MTL subregions, however, remains to be determined. This study used structural and diffusion magnetic resonance imaging (MRI) to evaluate thalamic connection density with distinct MTL subregions in terms of location and volume. Nineteen MTLE patients with unilateral hippocampal sclerosis (HS; 12 right; 10 female) were compared to 19 age-matched controls. Five regions of interest (ROIs) per hemisphere were created in native space: thalamus, amygdala, entorhinal cortex, hippocampus, and parahippocampus. Separate probabilistic tractography analyses were performed between the thalamus and each ipsilateral MTL subregion (four per hemisphere). Individual connectivity profiles and regional volumes were assessed. The medial pulvinar consistently showed the highest connection density with the hippocampus in healthy controls and in MTLE patients. Decreased thalamic connected volume was observed for thalamohippocampal pathways in patients with MTLE, and indicates pathway-specific deafferentation. Regional hippocampal and thalamic atrophy was also observed, indicating gray and white matter loss in the thalamohippocampal pathway. Consistent localization of dense medial pulvinar (PuM) connectivity with the hippocampus suggests chronic PuM stimulation could modulate the MTLE seizure network. Decreased thalamic connected volume is a promising biomarker for epileptogenesis that merits longitudinal validation. A PowerPoint slide summarizing this article is available for download in the Supporting Information section here.
| S-EPMC4791041 | biostudies-literature
Project description:OBJECTIVE:The current practice under which patients with refractory epilepsy are surgically treated is based mainly on the identification of specific cortical areas, mainly the epileptogenic zone, which is believed to be responsible for generation of seizures. A better understanding of the whole epileptic network and its components and properties is required before more effective and less invasive therapies can be developed. The aim of the present study was to partially characterize the evolution of the functional network during the preictal-ictal transition in partial seizures in patients with temporal lobe epilepsy (TLE). METHODS:Scalp and foramen ovale (FOE) recordings from twenty-two TLE patients were analyzed under the complex network perspective. The density of links, average path length, average clustering coefficient, and modularity were calculated during the preictal and the ictal stages. Both linear-Pearson correlation-and non-linear-phase synchronization-measures were used as proxies of functional connectivity between the electrode locations areas. The transition from one stage to the other was evaluated in the whole network and in the mesial sub-networks. The results were compared with a voltage-dependent measure, namely, the spectral entropy. RESULTS:Changes in the global functional network during the transition from the preictal to the ictal stage show, in the linear case, that in sixteen cases (72.7%) the density of the links increased during the seizure, with a decrease in the average path length in fifteen cases (68.1%). There was also a preictal and ictal imbalance in functional connectivity during both stages (77.2% to 86.3%). The SE dropped during the seizure in 95.4% of the cases, but did not show any tendency towards lateralization. When using the nonlinear measure of functional connectivity, the phase synchronization, similar results were obtained. CONCLUSIONS:In TLE patients, the transition to the ictal stage is accompanied by increasing global synchronization and a more ordered spectral content of the signals, indicated by lower spectral entropy. The interictal connectivity imbalance (lower ipsilateral connectivity) is sustained during the seizure, irrespective of any appreciable imbalance in the spectral entropy of the mesial recordings.
| S-EPMC4619301 | biostudies-literature