Decreased interhemispheric coordination in schizophrenia: a resting state fMRI study

Altered interhemispheric functional coordination in chronic tinnitus patients

Purpose. Recent studies suggest that tinnitus may be due in part to aberrant callosal structure and interhemispheric interaction. To explore this hypothesis we use a novel method, voxel-mirrored homotopic connectivity (VMHC), to examine the resting-state interhemispheric functional connectivity and its relationships with clinical characteristics in chronic tinnitus patients. Materials and Methods. Twenty-eight chronic tinnitus patients with normal hearing thresholds and 30 age-, sex-, education-, and hearing threshold-matched healthy controls were included in this study and underwent the resting-state fMRI scanning. We computed the VMHC to analyze the interhemispheric functional coordination between homotopic points of the brain in both groups. Results. Compared to the controls, tinnitus patients showed significantly increased VMHC in the middle temporal gyrus, middle frontal gyrus, and superior occipital gyrus. In tinnitus patients, a positive correlation was found between tinnitus duration and VMHC of the uncus. Moreover, correlations between VMHC changes and tinnitus distress were observed in the transverse temporal gyrus, superior temporal pole, precentral gyrus, and calcarine cortex. Conclusions. These results show altered interhemispheric functional connectivity linked with specific tinnitus characteristics in chronic tinnitus patients, which may be implicated in the neuropathophysiology of tinnitus.

Increased interhemispheric functional connectivity in college students with non-clinical depressive symptoms in resting state

The underlying neural basis of non-clinical depressive symptoms (nCDSs) remains unclear. Interhemispheric functional connectivity has been suggested as one of the most robust characteristics of brain's intrinsic functional architecture. Here, we investigated the functional connectivity between homotopic points in the brain using the voxel-mirrored homotopic connectivity (VMHC) approach. We performed VMHC analysis on resting-state functional magnetic resonance imaging (rs-fMRI) data from 17 individuals with nCDSs and 20 healthy controls (HCs) who were enrolled from a sample of 1105 college students. We found increased VMHCs in the bilateral posterior cerebellum and fusiform gyrus in nCDSs subjects compared with HCs. Furthermore, receiver operating characteristic (ROC) curves indicated that VMHC values in the posterior cerebellum lobes could use to differente nCDSs from HCs [area under the curve (AUC), 0.756; p<0.01]. We suggest increased VMHCs indicate a possible compensatory mechanism involved in the pathophysiology of nCDSs. VMHC values of the posterior cerebellum lobes might serve as a reliable biomarker for identifying nCDSs.

Abnormal asymmetry of brain connectivity in schizophrenia

Recently, a growing body of data has revealed that beyond a dysfunction of connectivity among different brain areas in schizophrenia patients (SCZ), there is also an abnormal asymmetry of functional connectivity compared with healthy subjects. The loss of the cerebral torque and the abnormalities of gyrification, with an increased or more complex cortical folding in the right hemisphere may provide an anatomical basis for such aberrant connectivity in SCZ. Furthermore, diffusion tensor imaging studies have shown a significant reduction of leftward asymmetry in some key white-matter tracts in SCZ. In this paper, we review the studies that investigated both structural brain asymmetry and asymmetry of functional connectivity in healthy subjects and SCZ. From an analysis of the existing literature on this topic, we can hypothesize an overall generally attenuated asymmetry of functional connectivity in SCZ compared to healthy controls. Such attenuated asymmetry increases with the duration of the disease and correlates with psychotic symptoms. Finally, we hypothesize that structural deficits across the corpus callosum may contribute to the abnormal asymmetry of intra-hemispheric connectivity in schizophrenia.

Decreased inter-hemispheric connectivity in anterior sub-network of default mode network and cerebellum: significant findings in major depressive disorder

The issue of inter-hemispheric connectivity is an emerging new area in understanding the pathophysiology of depression. This study was designed to analyse the pattern of inter-hemispheric connectivity in patients with major depressive disorder (MDD). The resting-state functional magnetic resonance imaging (RFMRI) was acquired in all enrolled patients and controls. We used a method of voxel-mirrored homotopic connectivity (VMHC) to estimate the significant differences in inter-hemispheric connectivity between 44 patients with first-episode medication-naïve MDD and 27 normal controls. The patients and controls were matched for age and gender. The patients with first-episode medication-naïve MDD showed lower VMHC than normal controls in bilateral medial frontal cortex, anterior cingulate and cerebellar posterior lobe. The strength of inter-hemispheric connectivity VMHC value was negatively correlated with clinical severity of MDD. From the results, we suggested that decreased inter-hemispheric connectivity in the anterior sub-network of the default mode network and the cerebellar posterior lobe might represent an emerging finding in the pathophysiology for MDD.

Altered Functional Connectivity Patterns of the Insular Subregions in Psychogenic Nonepileptic Seizures

Neuroimaging studies have demonstrated that psychogenic nonepileptic seizures (PNES) are characterized by unstable cognitive-emotional and motor system, which is engaged in hyperactivity of limbic regions and sensorimotor area. The insula, which is a part of the limbic system, includes various subregions with some distinct connectivity patterns separately. However, whether these insular subregions show different connectivity patterns respectively in PNES remains largely unknown. We aimed to investigate the functional connectivity (FC) of insular subregions in PNES and extend the understanding of the complex pathophysiological mechanisms of this disease. A resting-state FC based on the insular subregions were conducted in 18 patients and 20 healthy controls. We examined the differences in FC values between PNES patients and controls using two sample t test. Our results showed patients had significantly stronger FC between insular subregions and sensorimotor network, lingual gyrus, superior parietal gyrus and putamen, which suggested a hyperlink pattern of insular subregions involved in abnormal emotion regulation, cognitive processes and motor function in PNES. Pearson correlation analysis between the mean FC values within abnormal regions and the frequency of PNES further indicated PNES exhibited abnormal functional organization whose stressful emotion of patients have great direct influence on their motor functions. The differentially impaired functional connectivity patterns of insular subregions might provide new insights into the complex neurological mechanism of PNES.

The alterations in inter-hemispheric functional coordination of patients with panic disorder: the findings in the posterior sub-network of default mode network

OBJECTIVE

Voxel-mirrored homotopic connectivity (VMHC) has been studied in several neuropsychiatric illnesses. The inter-hemispheric interactions probably could explain the important aspects for the pathophysiology of panic disorder (PD). Therefore, we initiated this study to estimate the differences in VMHC values between the PD patients and controls.

METHODS

Thirty first-episode medication-naïve patients with PD and 21 controls were enrolled with age and gender controlled. All the participants received the scanning of resting-state functional magnetic resonance imaging (R-FMRI). The R-FMRI images were preprocessed and analyzed to obtain the VMHC values. The two-sample t test of VMHC data between PD patients and controls was performed. We also explored the relationship between the VMHC values and clinical characteristics.

RESULTS

The controls had significantly higher VMHC values than patients in the posterior cingulate cortex and precuneus (false discovery rate corrected p<0.005). The one-sided results by the unilateral hemisphere mask also confirmed that the results were indeed found in the right hemisphere. The VMHC value in the posterior cingulate cortex was also negatively correlated with panic severity.

CONCLUSION

The alterations of inter-hemispheric coordination in cingulate-precuneus may play a role in the pathophysiology of PD.

Modulation of interhemispheric functional coordination in electroconvulsive therapy for depression

Considerable evidence suggests that depression is related to interhemispheric functional coordination deficits. For depression, electroconvulsive therapy (ECT) is the most rapid and effective therapy, but its underlying mechanism remains unknown. The aim of this study was to explore the impact of ECT on the interhemispheric functional coordination in depression patients. We used resting-state functional magnetic resonance imaging to observe the change of interhemispheric functional coordination with the method of voxel-mirrored homotopic connectivity (VMHC) in 11 depressed patients before and after ECT, compared with 15 healthy controls. The results showed that, compared with depression patients before ECT, VMHC was significantly increased in superior frontal gyri (BA 8), middle frontal gyri (two clusters: BA 8/9 and BA 10) and angular gyri (BA 39) in depression patients after ECT. Compared with healthy controls, VMHC in those areas was significantly lower in the middle frontal gyri (BA 8/9) and angular gyri (BA 39) in depression patients before ECT, but no significant difference was observed in the superior frontal gyri (BA 8) and middle frontal gyri (BA 10). There was no significant correlation between the changes of Hamilton Depression Rating Scale scores and changed VMHC values in those four areas in depression patients. The results suggest that ECT selectively modulated interhemispheric functional coordination in depression patients. Such may play an important mechanistic role in the treatment of depression, and may afford a useful avenue for optimizing treatment.

Time-shift homotopic connectivity in mesial temporal lobe epilepsy

BACKGROUND AND PURPOSE

Voxel-mirrored intrinsic functional connectivity allows the depiction of interhemispheric homotopic connections in the human brain, whereas time-shift intrinsic functional connectivity allows the detection of the extent of brain injury by measuring hemodynamic properties. We combined time-shift voxel-mirrored homotopic connectivity analyses to investigate the alterations in homotopic connectivity in mesial temporal lobe epilepsy and assessed the value of applying this approach to epilepsy lateralization and the prediction of surgical outcomes in mesial temporal lobe epilepsy.

MATERIALS AND METHODS

Resting-state functional MR imaging data were acquired from patients with unilateral mesial temporal lobe epilepsy (n=62) (31 left- and 31 right-side) and healthy controls (n=33). Dynamic interhemispheric homotopic architecture seeding from each hemisphere was individually calculated by 0, 1, 2, and 3 repetition time time-shift voxel-mirrored homotopic connectivity. Voxel-mirrored homotopic connectivity maps were compared between the patient and control groups by using 1-way ANOVA for each time-shift condition, separately. Group comparisons were further performed on the laterality of voxel-mirrored homotopic connectivity in each time-shift condition. Finally, we correlated the interhemispheric homotopic connection to the surgical outcomes in a portion of the patients (n=20).

RESULTS

The patients with mesial temporal lobe epilepsy showed decreased homotopic connectivity in the mesial temporal structures, temporal pole, and striatum. Alterations of the bihemispheric homotopic connectivity were lateralized along with delays in the time-shift in mesial temporal lobe epilepsy. The patients with unsuccessful surgical outcomes presented larger interhemispheric voxel-mirrored homotopic connectivity differences.

CONCLUSIONS

This study showed whole patterns of dynamic alterations of interhemispheric homotopic connectivity in mesial temporal lobe epilepsy, extending the knowledge of abnormalities in interhemispheric connectivity in this condition. Time-shift voxel-mirrored homotopic connectivity has the potential for lateralization of unilateral mesial temporal lobe epilepsy and may have the capability of predicting surgical outcomes in this condition.

Aberrant interhemispheric functional coordination in patients with HBV-related cirrhosis and minimal hepatic encephalopathy

Aberrant brain functional connectivity has been considered as the important mechanism underlying minimal hepatic encephalopathy (MHE); however, little is known about the change in interhemispheric connection in MHE patients. Twenty patients with HBV-related cirrhosis and MHE and 15 healthy controls were included in this study and underwent the resting-state fMRI scanning and diffusion tensor imaging. The functional connectivity between symmetric interhemispheric voxels was computed by a technique called voxel-mirrored homotopic connectivity (VMHC), in which the time series for each voxel in one hemisphere was correlated with that of its homotopic voxel. Diffusion tensor imaging was conducted to measure the mean diffusivity (MD) and fractional anisotropy (FA) values in corpus callosum (CC). Compared with controls, MHE patients showed decreased regional VMHC in medial frontal gyrus, superior frontal gryus, anterior cingulate gyrus, inferior parietal lobule, postcentral gyrus, lingual gyrus, and middle occipital gyrus. MHE patients had significant decreased FA value in CC genu and CC splenium and increased MD value in CC genu. Pearson correlation analyses showed that the VMHC in anterior cingulate gyrus/medial frontal gyrus was correlated with FA/MD values of CC genu. These findings may suggest aberrant interhemispheric coordination in MHE and may provide new insight into the disease-related mechanisms.

Functionally aberrant electrophysiological cortical connectivities in first episode medication-naive schizophrenics from three psychiatry centers

Functional dissociation between brain processes is widely hypothesized to account for aberrations of thought and emotions in schizophrenic patients. The typically small groups of analyzed schizophrenic patients yielded different neurophysiological findings, probably because small patient groups are likely to comprise different schizophrenia subtypes. We analyzed multichannel eyes-closed resting EEG from three small groups of acutely ill, first episode productive schizophrenic patients before start of medication (from three centers: Bern N = 9; Osaka N = 9; Berlin N = 12) and their controls. Low resolution brain electromagnetic tomography (LORETA) was used to compute intracortical source model-based lagged functional connectivity not biased by volume conduction effects between 19 cortical regions of interest (ROIs). The connectivities were compared between controls and patients of each group. Conjunction analysis determined six aberrant cortical functional connectivities that were the same in the three patient groups. Four of these six concerned the facilitating EEG alpha-1 frequency activity; they were decreased in the patients. Another two of these six connectivities concerned the inhibiting EEG delta frequency activity; they were increased in the patients. The principal orientation of the six aberrant cortical functional connectivities was sagittal; five of them involved both hemispheres. In sum, activity in the posterior brain areas of preprocessing functions and the anterior brain areas of evaluation and behavior control functions were compromised by either decreased coupled activation or increased coupled inhibition, common across schizophrenia subtypes in the three patient groups. These results of the analyzed three independent groups of schizophrenics support the concept of functional dissociation.

Increased interhemispheric resting-state in idiopathic generalized epilepsy with generalized tonic-clonic seizures: a resting-state fMRI study

PURPOSE

The aim is to examine the resting state functional connectivity (RSFC) between the two hemispheres and its relationships with clinical characteristic in idiopathic generalized epilepsy with generalized tonic-clonic seizures only (IGE-GTCS) patients using a technique called "voxel-mirrored homotopic connectivity (VMHC)".

METHODS

The resting-state functional MRI (Rs-fMRI) was used to measure the RSFC in patients with IGE-GTC and age-gender matched healthy subjects. The between-group difference in interhemispheric RSFC was examined after the interhemispheric RSFC map was obtained by an automated VMHC approach.

RESULTS

Compared to the controls, the IGE-GTCS patients showed significant increases in VMHC in the bilateral anterior cingulate and medial prefrontal gyrus. No areas showed decreased VMHC in patients. Moreover, the VMHC in bilateral thalamus, orbital frontal cortex as well as cerebellum showed significant negative correlations with the illness duration.

CONCLUSIONS

The current findings provide preliminary evidence of increased interhemispheric RSFC in patients with IGE-GTCS during the interictal period. These VMHC deficits in these regions and the inverse relations between VMHC and clinical characteristic may play an important role in the pathophysiology of IGE-GTCS. Our study may contribute to the understanding of neuro-pathophysiological mechanism of epilepsy and psychosocial function impairments in patients with IGE-GTCS.

Disrupted resting-state functional connectivity in minimally treated chronic schizophrenia

OBJECTIVE

The pathophysiology of chronic schizophrenia may reflect long term brain changes related to the disorder. The effect of chronicity on intrinsic functional connectivity patterns in schizophrenia without the potentially confounding effect of antipsychotic medications, however, remains largely unknown.

METHOD

We collected resting-state fMRI data in 21 minimally treated chronic schizophrenia patients and 20 healthy controls. We computed regional functional connectivity strength for each voxel in the brain, and further divided regional functional connectivity strength into short-range regional functional connectivity strength and long-range regional functional connectivity strength. General linear models were used to detect between-group differences in these regional functional connectivity strength metrics and to further systematically investigate the relationship between these differences and clinical/behavioral variables in the patients.

RESULTS

Compared to healthy controls, the minimally treated chronic schizophrenia patients showed an overall reduced regional functional connectivity strength especially in bilateral sensorimotor cortex, right lateral prefrontal cortex, left insula and right lingual gyrus, and these regional functional connectivity strength decreases mainly resulted from disruption of short-range regional functional connectivity strength. The minimally treated chronic schizophrenia patients also showed reduced long-range regional functional connectivity strength in the bilateral posterior cingulate cortex/precuneus, and increased long-range regional functional connectivity strength in the right lateral prefrontal cortex and lingual gyrus. Notably, disrupted short-range regional functional connectivity strength mainly correlated with duration of illness and negative symptoms, whereas disrupted long-range regional functional connectivity strength correlated with neurocognitive performance. All of the results were corrected using Monte-Carlo simulation.

CONCLUSIONS

This exploratory study demonstrates a disruption of intrinsic functional connectivity without long-term exposure to antipsychotic medications in chronic schizophrenia. Furthermore, this disruption was connection-distance dependent, thus raising the possibility for differential neural pathways in neurocognitive impairment and psychiatric symptoms in schizophrenia.

Anatomical distance affects functional connectivity in patients with schizophrenia and their siblings

BACKGROUND

The efficiency of human brain depends on the integrity of both long- and short-range connections, but the long-range connections need to be "penalized" to reduce overall wiring costs. This principle, termed as the anatomical distance function (ADF), refers to the presence of an inverse relationship between anatomical distance and connectivity. A crucial developmental feature that occurs in normal adolescence is the weakening of ADF, which is characterized by a selective strengthening of long-distance connections. Schizophrenia is associated with widespread dysconnectivity that is linked to aberrant cortical development.

METHODS

We studied the ADF in adults with schizophrenia (n = 28), their age-matched siblings (n = 28), and healthy controls (n = 60). We investigated the proportional abnormalities in the long-range connections involving interhemispheric, subcortical, frontal, and salience network regions and localized the connections showing most significant changes in schizophrenia. The groups were discriminated on the basis of short- and long-range connectivity using a machine-learning algorithm.

RESULTS

Both patients and their siblings showed abnormally pronounced ADF. This was associated with a disproportionate reduction in the number of long-range connections, affecting the subcortical, interhemispheric, and the salience network connections. The abnormalities in long-range connections had superior ability to accurately identify group membership.

CONCLUSIONS

A crucial organizing principle of the brain architecture that becomes apparent during normal adolescence is disturbed in schizophrenia. While siblings show some evidence of compensating for this deficit, patients lack putative compensatory changes. Age-related shift in ADF provides an explanatory framework for the developmental emergence of widespread dysconnectivity that is influenced by genetic risk in schizophrenia.

Decreased resting-state interhemispheric coordination in first-episode, drug-naive paranoid schizophrenia

BACKGROUND

Dysconnectivity hypothesis posits that schizophrenia relates to abnormalities in neuronal connectivity. However, little is known about the alterations of the interhemispheric resting-state functional connectivity (FC) in patients with paranoid schizophrenia. In the present study, we used a newly developed voxel-mirrored homotopic connectivity (VMHC) method to investigate the interhemispheric FC of the whole brain in patients with paranoid schizophrenia at rest.

METHODS

Forty-nine first-episode, drug-naive patients with paranoid schizophrenia and 50 age-, gender-, and education-matched healthy subjects underwent a resting-state functional magnetic resonance imaging (fMRI) scans. An automated VMHC approach was used to analyze the data.

RESULTS

Patients exhibited lower VMHC than healthy subjects in the precuneus (PCu), the precentral gyrus, the superior temporal gyrus (STG), the middle occipital gyrus (MOG), and the fusiform gyrus/cerebellum lobule VI. No region showed greater VMHC in the patient group than in the control group. Significantly negative correlation was observed between VMHC in the precentral gyrus and the PANSS positive/total scores, and between VMHC in the STG and the PANSS positive/negative/total scores.

CONCLUSIONS

Our results suggest that interhemispheric resting-state FC of VMHC is reduced in paranoid schizophrenia with clinical implications for psychiatric symptomatology thus further contribute to the dysconnectivity hypothesis of schizophrenia.

Decreased resting-state interhemispheric functional connectivity in unaffected siblings of schizophrenia patients

BACKGROUND

Neuroimaging studies in unaffected siblings of schizophrenia patients can provide clues to the pathophysiology for the development of schizophrenia. However, little is known about the alterations of the interhemispheric resting-state functional connectivity (FC) in siblings, although the dysconnectivity hypothesis is prevailing in schizophrenia for years. In the present study, we used a newly validated voxel-mirrored homotopic connectivity (VMHC) method to identify whether aberrant interhemispheric FC was present in unaffected siblings at increased risk of developing schizophrenia at rest.

METHODS

Forty-six unaffected siblings of schizophrenia patients and 50 age-, sex-, and education-matched healthy controls underwent a resting-state functional magnetic resonance imaging (fMRI). Automated VMHC was used to analyze the data.

RESULTS

The sibling group had lower VMHC than the control group in the angular gyrus (AG) and the lingual gyrus/cerebellum lobule VI. No region exhibited higher VMHC in the sibling group than in the control group. There was no significant sex difference of the VMHC values between male siblings and female siblings or between male controls and female controls, although evidence has been accumulated that size and shape of the corpus callosum, and functional homotopy differ between men and women.

CONCLUSIONS

Our results first suggest that interhemispheric resting-state FC of VMHC is disrupted in unaffected siblings of schizophrenia patients, and add a new clue of abnormal interhemispheric resting-state FC to the pathophysiology for the development of schizophrenia.

The diminished interhemispheric connectivity correlates with negative symptoms and cognitive impairment in first-episode schizophrenia

BACKGROUND

Previous studies imply that interhemispheric disconnectivity plays a more important role on information processing in schizophrenia. However, the role of the aberrant interhemispheric connection in the pathophysiology of this disorder remains unclear. Recently, resting-state functional Magnetic Resonance Imaging (fMRI) has reported to have potentials of mapping functional interactions between pairs of brain hemispheres.

METHODS

Resting-state whole-brain functional connectivity analyses were performed on 41 schizophrenia patients and 33 healthy controls.

RESULTS

The first-episode schizophrenia patients showed significant aberrant interhemispheric connection in the globus pallidus, medial frontal gyrus and inferior temporal gyrus. The correlation of Wechsler Adult Intelligence Scale scores with odds ratio of the aberrant interhemispheric connections revealed positive correlation in the pallidum (rho=0.335, p=.003) and medial frontal gyrus (rho=0.260, p=.025). The connection in the pallidum was also positively correlated with duration of illness (rho=-0.407, p=.009). Whereas, the aberrant interhemispheric connection in the inferior temporal gyrus was positively correlated with scores of Scale for the Assessment of Negative Symptoms (rho=0.393, p=.012).

CONCLUSION

The present study provides fMRI evidence for the aberrant interhemispheric resting-state functional connectivity within resting-state networks in first-episode schizophrenia patients. These aberrant interhemispheric connections, in particular the pallidum, due to its anatomical and functional connectivities, may be the primary disturbance for cognitive impairment, negative symptoms and chronicity of schizophrenia.

Resting-state functional connectivity and reading abilities in first and second languages

An intriguing discovery in recent years is that resting-state functional connectivity (RSFC) is associated with cognitive performance. The current study investigated whether RSFC within the reading network was correlated with Chinese adults' reading abilities in their native language (L1, Chinese) and second language (L2, English). Results showed that RSFC within the reading network was positively correlated to reading abilities in L1 and L2, and RSFC between reading areas and the default network was negatively correlated to reading abilities in L1 and L2. Further conjunction and contrast analyses revealed that L1 and L2 shared similar RSFC correlates including connectivities between the areas for visual analysis (e.g., bilateral posterior fusiform gyrus, lateral occipital cortices, and right superior parietal lobules) and those for phonological processing (e.g., bilateral precentral gyri and postcentral gyrus, Wernicke's area). These results indicate that RSFC is a potential neural marker for reading abilities in both L1 and L2, with important theoretical implications for reading in L1 and L2.

Decreased interhemispheric coordination in treatment-resistant depression: a resting-state fMRI study

Background

Previous studies have demonstrated that patients with treatment-resistant depression (TRD) and treatment-sensitive depression (TSD) differed at neural level. However, it remains unclear if these two subtypes of depression differ in the interhemispheric coordination. This study was undertaken for two purposes: (1) to explore the differences in interhemispheric coordination between these two subtypes by using the voxel-mirrored homotopic connectivity (VMHC) method; and (2) to determine if the difference of interhemispheric coordination can be used as a biomarker(s) to differentiate TRD from both TSD and healthy subjects (HS).

Methods

Twenty-three patients with TRD, 22 with TSD, and 19 HS participated in the study. Data of these participants were analyzed with the VMHC and seed-based functional connectivity (FC) approaches.

Results

Compared to the TSD group, the TRD group showed significantly lower VMHC values in the calcarine cortex, fusiform gyrus, hippocampus, superior temporal gyrus, middle cingulum, and precentral gyrus. Lower VMHC values were also observed in the TRD group in the calcarine cortex relative to the HS group. However, the TSD group had no significant change in VMHC value in any brain region compared to the HS group. Receiver operating characteristic curves (ROC) analysis revealed that the VMHC values in the calcarine cortex had discriminatory function distinguishing patients with TRD from patients with TSD as well as those participants in the HS group.

Conclusions

Lower VMHC values of patients with TRD relative to those with TSD and those in the HS group in the calcarine cortex appeared to be a unique feature for patients with TRD and it may be used as an imaging biomarker to separate patients with TRD from those with TSD or HS.

Interhemispheric functional connectivity and its relationships with clinical characteristics in major depressive disorder: a resting state fMRI study

BACKGROUND

Abnormalities in large-scale, structural and functional brain connectivity have been increasingly reported in patients with major depressive disorder (MDD). However, MDD-related alterations in functional interaction between the cerebral hemispheres are still not well understood. Resting state fMRI, which reveals spontaneous neural fluctuations in blood oxygen level dependent signals, provides a means to detect interhemispheric functional coherence. We examined the resting state functional connectivity (RSFC) between the two hemispheres and its relationships with clinical characteristics in MDD patients using a recently proposed measurement named "voxel-mirrored homotopic connectivity (VMHC)".

METHODOLOGY/PRINCIPAL FINDINGS

We compared the interhemispheric RSFC, computed using the VMHC approach, of seventeen first-episode drug-naive patients with MDD and seventeen healthy controls. Compared to the controls, MDD patients showed significant VMHC decreases in the medial orbitofrontal gyrus, parahippocampal gyrus, fusiform gyrus, and occipital regions including the middle occipital gyrus and cuneus. In MDD patients, a negative correlation was found between VMHC of the fusiform gyrus and illness duration. Moreover, there were several regions whose VMHC showed significant negative correlations with the severity of cognitive disturbance, including the prefrontal regions, such as middle and inferior frontal gyri, and two regions in the cereballar crus.

CONCLUSIONS/SIGNIFICANCE

These findings suggest that the functional coordination between homotopic brain regions is impaired in MDD patients, thereby providing new evidence supporting the interhemispheric connectivity deficits of MDD. The significant correlations between the VMHC and clinical characteristics in MDD patients suggest potential clinical implication of VMHC measures for MDD. Interhemispheric RSFC may serve as a useful screening method for evaluating MDD where neural connectivity is implicated in the pathophysiology.