Lixia Tian

Regional homogeneity approach to fMRI data analysis.

Kendalls coefficient concordance (KCC) can measure the similarity of a number of time series. It has been used for purifying a given cluster in functional MRI (fMRI). In the present study, a new method was developed based on the regional homogeneity (ReHo), in which KCC was used to measure the similarity of the time series of a given voxel to those of its nearest neighbors in a voxel-wise way. Six healthy subjects performed left and right finger movement tasks in event-related design; five of them were additionally scanned in a rest condition. KCC was compared among the three conditions (left finger movement, right finger movement, and the rest). Results show that bilateral primary motor cortex (M1) had higher KCC in either left or right finger movement condition than in rest condition. Contrary to prediction and to activation pattern, KCC of ipsilateral M1 is significantly higher than contralateral M1 in unilateral finger movement conditions. These results support the previous electrophysiologic findings of increasing ipsilateral M1 excitation during unilateral movement. ReHo can consider as a complementary method to model-driven method, and it could help reveal the complexity of the human brain function. More work is needed to understand the neural mechanism underlying ReHo.

Altered functional connectivity in early Alzheimer's disease: a resting-state fMRI study.

Previous studies have led to the proposal that patients with Alzheimers disease (AD) may have disturbed functional connectivity between different brain regions. Furthermore, recent resting‐state functional magnetic resonance imaging (fMRI) studies have also shown that low‐frequency (<0.08 Hz) fluctuations (LFF) of the blood oxygenation level‐dependent signals were abnormal in several brain areas of AD patients. However, few studies have investigated disturbed LFF connectivity in AD patients. By using resting‐state fMRI, this study sought to investigate the abnormal functional connectivities throughout the entire brain of early AD patients, and analyze the global distribution of these abnormalities. For this purpose, the authors divided the whole brain into 116 regions and identified abnormal connectivities by comparing the correlation coefficients of each pair. Compared with healthy controls, AD patients had decreased positive correlations between the prefrontal and parietal lobes, but increased positive correlations within the prefrontal lobe, parietal lobe, and occipital lobe. The AD patients also had decreased negative correlations (closer to zero) between two intrinsically anti‐correlated networks that had previously been found in the resting brain. By using resting‐state fMRI, our results supported previous studies that have reported an anterior–posterior disconnection phenomenon and increased within‐lobe functional connectivity in AD patients. In addition, the results also suggest that AD may disturb the correlation/anti‐correlation effect in the two intrinsically anti‐correlated networks. Hum Brain Mapp 2006.

Regional coherence changes in the early stages of Alzheimer’s disease: A combined structural and resting-state functional MRI study

Recent functional imaging studies have indicated that the pathophysiology of Alzheimers disease (AD) can be associated with the changes in spontaneous low-frequency (<0.08 Hz) blood oxygenation level-dependent fluctuations (LFBF) measured during a resting state. The purpose of this study was to examine regional LFBF coherence patterns in early AD and the impact of regional brain atrophy on the functional results. Both structural MRI and resting-state functional MRI scans were collected from 14 AD subjects and 14 age-matched normal controls. We found significant regional coherence decreases in the posterior cingulate cortex/precuneus (PCC/PCu) in the AD patients when compared with the normal controls. Moreover, the decrease in the PCC/PCu coherence was correlated with the disease progression measured by the Mini-Mental State Exam scores. The changes in LFBF in the PCC/PCu may be related to the resting hypometabolism in this region commonly detected in previous positron emission tomography studies of early AD. When the regional PCC/PCu atrophy was controlled, these results still remained significant but with a decrease in the statistical power, suggesting that the LFBF results are at least partly explained by the regional atrophy. In addition, we also found increased LFBF coherence in the bilateral cuneus, right lingual gyrus and left fusiform gyrus in the AD patients. These regions are consistent with previous findings of AD-related increased activation during cognitive tasks explained in terms of a compensatory-recruitment hypothesis. Finally, our study indicated that regional brain atrophy could be an important consideration in functional imaging studies of neurodegenerative diseases.

Altered resting-state functional connectivity patterns of anterior cingulate cortex in adolescents with attention deficit hyperactivity disorder

Dorsal anterior cingulate cortex (dACC) has been found to function abnormally in attention deficit hyperactivity disorder (ADHD) patients in several former functional MRI (fMRI) studies. Resting-state low-frequency fluctuations (LFFs) of blood oxygen level-dependent (BOLD) fMRI signals have been proved to be quite informative. This study used resting-state LFFs to investigate the resting-state functional connectivity pattern differences of dACC in adolescents with and without ADHD. As compared to the controls, the ADHD patients exhibited more significant resting-state functional connectivities with the dACC in bilateral dACC, bilateral thalamus, bilateral cerebellum, bilateral insula and bilateral brainstem (pons). No brain region in the controls was found to exhibit more significant resting-state functional connectivity with the dACC. We suggest these abnormally more significant functional connectivities in the ADHD patients may indicate the abnormality of autonomic control functions in them.

Functional dysconnectivity of the dorsolateral prefrontal cortex in first-episode schizophrenia using resting-state fMRI

The known regional abnormality of the dorsolateral prefrontal cortex (DLPFC) and its role in various neural circuits in schizophrenia has given prominence to its importance in studies on the dysconnection associated with schizophrenia. Abnormal functional connectivities of the DLPFC have been found during various goal-directed tasks; however, the occurrence of the abnormality during rest in patients with schizophrenia has rarely been reported. In the present study, we selected bilateral Brodmanns area 46 as region of interest and analyzed the differences in the DLPFC functional connectivity pattern between 17 patients with first-episode schizophrenia (FES) and 17 matched controls using resting-state fMRI. We found that the bilateral DLPFC showed reduced functional connectivities to the parietal lobe, posterior cingulate cortex, thalamus and striatum in FES patients. We also found enhanced functional connectivity between the left DLPFC and the left mid-posterior temporal lobe and the paralimbic regions in FES patients. Our results suggest that functional dysconnectivity associated with the DLPFC exists in schizophrenia during rest. This may be partially related to disturbance in the intrinsic brain activity.

Hemisphere- and gender-related differences in small-world brain networks: A resting-state functional MRI study

We employed resting-state functional MRI (R-fMRI) to investigate hemisphere- and gender-related differences in the topological organization of human brain functional networks. Brain networks were first constructed by measuring inter-regional temporal correlations of R-fMRI data within each hemisphere in 86 young, healthy, right-handed adults (38 males and 48 females) followed by a graph-theory analysis. The hemispheric networks exhibit small-world attributes (high clustering and short paths) that are compatible with previous results in the whole-brain functional networks. Furthermore, we found that compared with females, males have a higher normalized clustering coefficient in the right hemispheric network but a lower clustering coefficient in the left hemispheric network, suggesting a gender-hemisphere interaction. Moreover, we observed significant hemisphere-related differences in the regional nodal characteristics in various brain regions, such as the frontal and occipital regions (leftward asymmetry) and the temporal regions (rightward asymmetry), findings that are consistent with previous studies of brain structural and functional asymmetries. Together, our results suggest that the topological organization of human brain functional networks is associated with gender and hemispheres, and they provide insights into the understanding of functional substrates underlying individual differences in behaviors and cognition.

Brain spontaneous functional connectivity and intelligence

Many functional imaging studies have been performed to explore the neural basis of intelligence by detecting brain activity changes induced by intelligence-related tasks, such as reasoning or working memory. However, little is known about whether the spontaneous brain activity at rest is relevant to the differences in intelligence. Here, 59 healthy adult subjects (Wechsler Adult Intelligence Scale score, 90-138) were studied with resting state fMRI. We took the bilateral dorsolateral prefrontal cortices (DLPFC) as the seed regions and investigated the correlations across subjects between individual intelligence scores and the strength of the functional connectivity (FC) between the seed regions and other brain regions. We found that the brain regions in which the strength of the FC significantly correlated with intelligence scores were distributed in the frontal, parietal, occipital and limbic lobes. Stepwise linear regression analysis also revealed that the FCs within the frontal lobe and between the frontal and posterior brain regions were both important predictive factors for the differences in intelligence. These findings support a network view of intelligence, as suggested in previous studies. More importantly, our findings suggest that brain activity may be relevant to the differences in intelligence even in the resting state and in the absence of an explicit cognitive demand. This could provide a new perspective for understanding the neural basis of intelligence.

Enhanced resting-state brain activities in ADHD patients: A fMRI study

Resting-state functional MRI (fMRI) could be an advantageous choice for clinical applications by virtue of its clinical convenience and non-invasiveness. Without explicit stimulus, resting-state brain activity patterns cannot be obtained using any model-driven method. In this study, we advanced a measure named resting-state activity index (RSAI) to evaluate the resting-state brain activities. Using RSAI, we first investigated the resting-state brain activity patterns in normal adolescents to test the validity of this RSAI measure. Then we compared the resting-state brain activity patterns of Attention deficit hyperactivity disorder (ADHD) patients to those of their matched controls. According to the resultant brain activity patterns, we suggest that RSAI could be an applicable measure to evaluate resting-state brain activities. As compared to the controls, the ADHD patients exhibited more significant resting-state activities in basic sensory and sensory-related cortices. This finding was in accordance with ADHD symptoms of inattention.

Regional homogeneity of resting state fMRI signals predicts Stop signal task performance

It has been suggested that resting-state functional magnetic resonance imaging (RS-fMRI) is a promising tool to study the relation between spontaneous brain activity and behavioral performance. However, little is known about whether the local synchronization of spontaneous brain activity could predict response inhibition. In the current study, we used regional homogeneity (ReHo) to measure the local synchronization of RS-fMRI signals, and then investigated the relationship between ReHo and individual differences in response inhibition, as evaluated by the stop signal reaction time (SSRT) in a Stop signal task. The results showed that ReHo of RS-fMRI signals could successfully predict SSRT. Specifically, positive ReHo-SSRT correlations were observed in the bilateral inferior frontal cortex (IFC) and three critical components of the default mode network (DMN), and negative ReHo-SSRT correlations were observed in the rolandic area/posterior insula and the bilateral middle occipital cortex. The present results indicate the possible influence of the IFC and rolandic area/posterior insula on the efficiency of response inhibition, and demonstrate the importance of the DMN for the efficiency of cognitive task performance.

The relationship within and between the extrinsic and intrinsic systems indicated by resting state correlational patterns of sensory cortices

Much Research has been done on extrinsic and intrinsic systems, which consist of brain regions associated with the processing of externally and internally oriented stimuli, respectively. However, understanding of the underlying relationships within and between these two systems is relatively limited. To improve our understanding of these underlying relationships, we investigated the positive and negative correlations of three regions of interest (ROIs) located in the auditory, visual and somatosensory systems by using resting state functional MRI (fMRI) with a large sample size. We found that all three sensory systems exhibited significant negative correlation with the intrinsic system. In contrast, positive correlations between these sensory cortices and brain regions outside their respective system were limited. The present study extended former findings by indicating that multiple subsystems rather than a single subsystem of the extrinsic system are inherently negatively correlated with the intrinsic system. We suggest that these negative correlations between the extrinsic and intrinsic systems may explain the phenomenon that externally and internally oriented processes can always disturb or even interrupt each other.