Kai Li

Altered spontaneous neuronal activity of the default-mode network in mesial temporal lobe epilepsy.

Increasing evidence from behavioral and neuroimaging studies suggests that mesial temporal lobe epilepsy (mTLE) is possibly associated with the default-mode brain function. However, the alteration of coherent neural activities in such a default-mode network (DMN) in mTLE has yet to be investigated. The present study analyzed the resting-state functional MRI data from two groups of mTLE patients with left and right hippocampal sclerosis using independent component analysis. In comparison with healthy controls, decreased functional connectivity in the dorsal mesial prefrontal cortex, mesial temporal lobe and inferior temporal cortex was observed in these two patient groups. Moreover, the right but not left mTLE patients showed bilaterally decreased functional connectivity in the mesial temporal lobe and increased functional connectivity in the posterior cingulate cortex. The decreased functional connectivity of the mesial temporal lobe was related to the epilepsy duration, suggesting that the posterior cingulate cortex may play a compensatory role for the altered DMN in the right mTLE. These findings indicate that the DMN is widely affected even if a single network node is impaired. An extensive regional overlap between the DMN and the previously described epileptic network suggests that the widespread functional impairments in mTLE may attribute to an aberrant DMN. The distinct patterns of the DMN between the left and right mTLE support a view that there are different pathological mechanisms underlying these two types of epilepsies.

Granger causal influence predicts BOLD activity levels in the default mode network

Although the brain areas in the default‐mode network (DMN) act in a coordinated way during rest, the activity levels in the individual areas of the DMN are highly heterogeneous. The relation between the activity levels and the pattern of causal interaction among the DMN areas remains unknown. In the present fMRI study, seven nodes of the DMN were identified and their activity levels were rank‐ordered based on a power spectral analysis of the resting blood oxygenation level‐dependent (BOLD) signals. Furthermore, the direction of information flow among these DMN nodes was determined using Granger causality analysis and graph‐theoretic methods. We found that the activity levels in these seven DMN nodes had a highly consistent hierarchical distribution, with the highest activity level in the posterior cingulate/precuneus cortices, followed by ventral medial prefrontal cortex and dorsal medial prefrontal cortex, and with the lowest level in the left inferior temporal gyrus. Importantly, a significant correlation was found between the activity levels and the In‐Out degrees of information flow across the DMN nodes, suggesting that Granger causal influences can be used to predict BOLD activity levels. These findings shed light on the dynamical organization of cortical neuronal networks and may provide the basis for characterizing network disruption by brain disorders. Hum Brain Mapp, 2010.

Altered resting state networks in epileptic patients with generalized tonic–clonic seizures

Recent functional magnetic resonance imaging (fMRI) studies have demonstrated that the resting state networks (RSNs) are impaired in various neuropsychiatric disorders. However, little is known about the changes in the functional architecture of the RSNs in idiopathic generalized epilepsy patients with generalized tonic-clonic seizures (GTCS). Resting state fMRI data were acquired from 16 GTCS patients and 16 healthy subjects. The data were acquired during interictal without combined EEG confirmation. Functional connectivity among the RSNs was examined using individual-based independent component analysis. Six RSNs were identified in both the GTCS and control groups. Compared with the healthy subjects, decreased functional connectivity in the self-referential, somatosensory, visual, and auditory networks, and both the decreased and increased functional connectivities in the classic default-mode and dorsal attention networks were found in the GTCS patients. Furthermore, the present study revealed a negative correlation between the seizure duration and functional connectivity changes in the medial prefrontal cortex in the GTCS patients. These results indicate that there are impairments in the RSNs and possible reorganization of the default-mode network and dorsal attention network in patients with GTCS. Our findings may also suggest that the medial prefrontal cortex and its associated network play a role in the development of GTCS.

Altered Resting-State Brain Activity at Functional MR Imaging during the Progression of Hepatic Encephalopathy

PURPOSEnTo explore the spatial patterns of the amplitude of low-frequency fluctuation (ALFF) in patients with hepatic encephalopathy (HE) of varying severity and to correlate these fluctuations with clinical markers of HE.nnnMATERIALS AND METHODSnThis study was approved by the local ethics committee, and written informed consent was obtained from all participants. Twenty-nine patients with HE (15 with overt and 14 with minimal HE) and 17 healthy control subjects underwent resting-state functional magnetic resonance (MR) imaging. The ALFF, an index reflecting the amplitudes of spontaneous brain activity, was compared among patients with overt HE, patients with minimal HE, and control subjects with analysis of variance tests and t tests between each pair. Pearson correlation analysis was performed between the ALFF and the venous blood ammonia level and Child-Pugh score of all patients with HE.nnnRESULTSnCompared with control subjects, patients with overt and minimal HE showed decreased ALFF mainly in regions within the default-mode network (DMN) and increased ALFF in the cerebellum and middle temporal gyrus. Compared with patients with minimal HE, those with overt HE showed decreased ALFF in DMN regions and increased ALFF in the posterior insular cortex (P<.05, corrected for multiple comparisons). Both the venous blood ammonia levels and Child-Pugh scores of individual patients with HE showed negative correlation with ALFF within some DMN regions, whereas they showed positive correlation with ALFF in the posterior insular cortex (P<.05, corrected for multiple comparisons).nnnCONCLUSIONnPatients with HE have diffuse abnormalities in intrinsic brain activity. The levels of decreased ALFF in the DMN and increased ALFF in the posterior insular cortex are dependent on the severity of HE, suggesting continuous impairment of the DMN and a compensatory role of the insula during the progression of HE. Resting-state functional MR imaging with ALFF analysis may be a noninvasive modality with which to detect the progression of HE.

Altered regional synchronization in epileptic patients with generalized tonic-clonic seizures.

Epilepsy is a common neurological disorder characterized by hyper-synchronous abnormalities of neurons. Resting state brain activity measured by fMRI might evaluate the synchronization of the disorder. To investigate the alteration of the haemodynamic synchronization in epilepsy, resting-state fMRI (RS-fMRI) was performed on 25 patients with primarily generalized tonic-clonic seizures (GTCS), along with 25 age- and sex-matched healthy subjects. Regional homogeneity (ReHo), a measurement of the synchronization of spontaneous RS-fMRI signal oscillations within spatially neighboring voxels, was examined. Compared with the healthy controls, the patients with GTCS showed bilaterally and symmetrically altered ReHo in the cortical and subcortical structures. In addition, a correlation analysis of the ReHo measurement versus the epilepsy duration was performed, and highly negative correlations were observed in thalamus, insula and the regions followed the pattern of default state of brain function. The current findings demonstrate that altered regional synchronization of brain activity exists in the patients with GTCS during interictal period, and there is potential in utilizing the ReHo method in RS-fMRI analyses of epilepsy.

Increased Activity Imbalance in Fronto-Subcortical Circuits in Adolescents with Major Depression

Background A functional discrepancy exists in adolescents between frontal and subcortical regions due to differential regional maturational trajectories. It remains unknown how this functional discrepancy alters and whether the influence from the subcortical to the frontal system plays a primacy role in medication naïve adolescent with major depressive disorder (MDD). Methodology/Principal Findings Eighteen MDD and 18 healthy adolescents were enrolled. Depression and anxiety severity was assessed by the Short Mood and Feeling Questionnaire (SMFQ) and Screen for Child Anxiety Related Emotional Disorders (SCARED) respectively. The functional discrepancy was measured by the amplitude of low-frequency fluctuations (ALFF) of resting-state functional MRI signal. Correlation analysis was carried out between ALFF values and SMFQ and SCARED scores. Resting brain activity levels measured by ALFF was higher in the frontal cortex than that in the subcortical system involving mainly (para) limbic-striatal regions in both HC and MDD adolescents. The difference of ALFF values between frontal and subcortical systems was increased in MDD adolescents as compared with the controls. Conclusions/Significance The present study identified an increased imbalance of resting-state brain activity between the frontal cognitive control system and the (para) limbic-striatal emotional processing system in MDD adolescents. The findings may provide insights into the neural correlates of adolescent MDD.

Impairments of Thalamic Nuclei in Idiopathic Generalized Epilepsy Revealed by a Study Combining Morphological and Functional Connectivity MRI

Objective Neuroimaging evidence suggested that the thalamic nuclei may play different roles in the progress of idiopathic generalized epilepsy (IGE). This study aimed to demonstrate the alterations in morphometry and functional connectivity in the thalamic nuclei in IGE. Methods Fifty-two patients with IGE characterized by generalized tonic-clonic seizures and 67 healthy controls were involved in the study. The three-dimensional high-resolution T1-weighted MRI data were acquired for voxel-based morphometry (VBM) analysis, and resting-state blood-oxygenation level functional MRI data were acquired for functional connectivity analysis. The thalamic nuclei of bilateral medial dorsal nucleus (MDN) and pulvinar, as detected with decreased gray matter volumes in patients with IGE through VBM analysis, were selected as seed regions for functional connectivity analysis. Results Different alteration patterns were found in functional connectivity of the thalamic nuclei with decreased gray matter volumes in IGE. Seeding at the MDN, decreased connectivity in the bilateral orbital frontal cortex, caudate nucleus, putamen and amygdala were found in the patients (P<0.05 with correction). However, seeding at the pulvinar, no significant alteration of functional connectivity was found in the patients (P<0.05 with correction). Conclusions Some specific impairment of thalamic nuclei in IGE was identified using morphological and functional connectivity MRI approaches. These findings may strongly support the different involvement of the thalamocortical networks in IGE.

Altered cortical and subcortical local coherence in PTSD: evidence from resting-state fMRI.

Background Post-traumatic stress disorder (PTSD) is often characterized by region-specific brain activation/deactivation and functional abnormalities in corticolimbic circuitry, as elucidated by task-dependent functional neuroimaging. However, little is known about the abnormalities in the local coherence of cortical and subcortical activity occurring during the resting state. Purpose To evaluate the functional discrepancy of local coherence between cortical and subcortical regions in PTSD patients using resting-state functional magnetic resonance imaging (fMRI). Material and Methods Resting-state fMRI (RS-fMRI) was performed on 14 outpatients with PTSD, along with 14 age- and sex-matched normal control subjects. Regional homogeneity (ReHo), a measurement of the coherence of spontaneous RS-fMRI signal oscillations within spatially neighboring voxels, was examined. Results Compared with the normal controls, PTSD patients showed increased local coherence in subcortical regions, including amygdala, hippocampus, thalamus, and putamen, and decreased local coherence in cortical regions, including medial prefrontal cortex and dorsolateral prefrontal cortex. Moreover, a correlation analysis of the ReHo measurement versus the severity of the disorder was performed, and highly positive correlation were observed in the right amygdala. Conclusion The present study identified a functional discrepancy of local coherence between cortical and subcortical regions in PTSD patients compared with normal controls. The findings revealed that resting-state abnormalities might lead to further improvement of the understanding of the neural substrates of cognitive impairment and symptoms in PTSD.

Gender Differences of Brain Glucose Metabolic Networks Revealed by FDG-PET: Evidence from a Large Cohort of 400 Young Adults

Background Gender differences of the human brain are an important issue in neuroscience research. In recent years, an increasing amount of evidence has been gathered from noninvasive neuroimaging studies supporting a sexual dimorphism of the human brain. However, there is a lack of imaging studies on gender differences of brain metabolic networks based on a large population sample. Materials and Methods FDG PET data of 400 right-handed, healthy subjects, including 200 females (age: 25∼45 years, mean age±SD: 40.9±3.9 years) and 200 age-matched males were obtained and analyzed in the present study. We first investigated the regional differences of brain glucose metabolism between genders using a voxel-based two-sample t-test analysis. Subsequently, we investigated the gender differences of the metabolic networks. Sixteen metabolic covariance networks using seed-based correlation were analyzed. Seven regions showing significant regional metabolic differences between genders, and nine regions conventionally used in the resting-state network studies were selected as regions-of-interest. Permutation tests were used for comparing within- and between-network connectivity between genders. Results Compared with the males, females showed higher metabolism in the posterior part and lower metabolism in the anterior part of the brain. Moreover, there were widely distributed patterns of the metabolic networks in the human brain. In addition, significant gender differences within and between brain glucose metabolic networks were revealed in the present study. Conclusion This study provides solid data that reveal gender differences in regional brain glucose metabolism and brain glucose metabolic networks. These observations might contribute to the better understanding of the gender differences in human brain functions, and suggest that gender should be included as a covariate when designing experiments and explaining results of brain glucose metabolic networks in the control and experimental individuals or patients.

18F‑fluorodeoxyglucose positron emission tomography/computed tomography findings of gastric lymphoma: Comparisons with gastric cancer

The role of 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) in numerous malignant tumors, including gastric lymphoma, is well-established. However, there have been few studies with regard to the 18F-FDG PET/CT features of gastric lymphoma. The aim of the present study was to characterize the 18F-FDG PET/CT features of gastric lymphoma, which were compared with those of gastric cancer. Prior to treatment, 18F-FDG PET/CT was performed on 24 patients with gastric lymphoma and 43 patients with gastric cancer. The 18F-FDG PET/CT pattern of gastric wall lesions was classified as one of three types: Type I, diffuse thickening of the gastric wall with increased FDG uptake infiltrating more than one-third of the total stomach; type II, segmental thickening of the gastric wall with elevated FDG uptake involving less than one-third of the total stomach; and type III, local thickening of the gastric wall with focal FDG uptake. The incidence of the involvement of more than one region of the stomach was higher in the patients with gastric lymphoma than in those with gastric cancer. Gastric FDG uptake was demonstrated in 23 of the 24 patients (95.8%) with gastric lymphoma and in 40 of the 43 patients (93.0%) with gastric cancer. Gastric lymphoma predominantly presented with type I and II lesions, whereas gastric cancer mainly presented with type II and III lesions. The maximal thickness was larger and the maximal standard uptake value (SUVmax) was higher in the patients with gastric lymphoma compared with those with gastric cancer. A positive correlation between the maximal thickness and SUVmax was confirmed for the gastric cancer lesions, but not for the gastric lymphoma lesions. There was no difference in the maximal thickness and SUVmax of the gastric wall lesions between the patients without and with extragastric involvement, for gastric lymphoma and gastric cancer. Overall, certain differences exist in the findings between gastric lymphoma and gastric cancer patients on 18F-FDG PET/CT images, which may contribute to the identification of gastric lymphoma.