BOLD response during visual perception of biological motion in obsessive-compulsive disorder

Objective  

Although research has shown that deficits in various cognitive functions may underlie obsessive-compulsive disorder (OCD), studies have not yet clarified the specificity and etiology of perception processing, particularly the perception of biological motion that is correlated with social cognition. We used functional magnetic resonance imaging (fMRI) to investigate neural activity associated with the perception of biological motion in OCD patients.     

Provocation of obsessive-compulsive symptoms: a quantitative voxel-based meta-analysis of functional neuroimaging studies

Objective

Recent functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) studies based on the symptom provocation paradigm have explored neural correlates of the cognitive and emotional processes associated with the emergence of obsessive–compulsive disorder (OCD) symptoms. Although most studies showed the involvement of cortico–subcortical loops originating in the orbitofrontal cortex and the anterior cingulate cortex, an increased activity within numerous other regions of the brain has inconsistently been reported across studies. To provide a quantitative estimation of the cerebral activation patterns related to the performance of the symptom provocation task by OCD patients, we conducted a voxel-based meta-analysis.

Methods

We searched the PubMed and MEDLINE databases for studies that used fMRI and PET and that were based on the symptom provocation paradigm. We entered data into a paradigm-driven activation likelihood estimation meta-analysis.

Results

We found significant likelihoods of activation in cortical and subcortical regions of the orbitofrontal and anterior cingulate loops. The left dorsal frontoparietal network, including the dorsolateral prefrontal cortex and precuneus, and the left superior temporal gyrus also demonstrated significant likelihoods of activation.

Conclusion

Consistent results across functional neuroimaging studies suggest that the orbitofrontal and anterior cingulate cortices are involved in the mediation of obsessive–compulsive symptoms. Based on recent literature, we suggest that activations within the dorsal frontoparietal network might be related to patients'' efforts to resist the obsessive processes induced by the provocation task. Further research should elucidate the specific neural correlates of the various cognitive and emotional functions altered in OCD.Medical subject headings: obsessive-compulsive disorder, magnetic resonance imaging, positron-emission tomography     

Compensatory hyperactivations as markers of latent working memory dysfunctions in patients with obsessive-compulsive disorder: an fMRI study

Objective

Behavioural studies have implicated working memory (WM) deficits in obsessive–compulsive disorder (OCD). However, findings are inconsistent, which could be explained by compensation strategies used by a subgroup of OCD patients. To test this hypothesis, we examined patients without a behavioural deficit in WM during performance of different WM tasks using functional magnetic resonance imaging (fMRI).

Methods

We scaned 11 patients and 11 matched control subjects while they performed 3 verbal and spatial item-recognition tasks.

Results

Patients and healthy subjects engaged the same set of brain regions. However, in direct comparison, the patients exhibited significantly greater task-related activation in several frontal and parietal brain areas known to underlie WM.

Conclusion

Patients without manifest WM deficits exhibit increased activation in frontal and parietal brain areas relative to healthy subjects during WM task performance. These hyperactivations may permit them to compensate for reduced efficiency of their WM systems and may thus serve as markers of latent WM dysfunctions.Medical subject headings: obsessive–compulsive disorder, memory, magnetic resonance imaging, cognition     

Brain structural correlates of sensory phenomena in patients with obsessive–compulsive disorder

Background

Sensory phenomena (SP) are uncomfortable feelings, including bodily sensations, sense of inner tension, “just-right” perceptions, feelings of incompleteness, or “urge-only” phenomena, which have been described to precede, trigger or accompany repetitive behaviours in individuals with obsessive–compulsive disorder (OCD). Sensory phenomena are also observed in individuals with tic disorders, and previous research suggests that sensorimotor cortex abnormalities underpin the presence of SP in such patients. However, to our knowledge, no studies have assessed the neural correlates of SP in patients with OCD.

Methods

We assessed the presence of SP using the University of São Paulo Sensory Phenomena Scale in patients with OCD and healthy controls from specialized units in São Paulo, Brazil, and Barcelona, Spain. All participants underwent a structural magnetic resonance examination, and brain images were examined using DARTEL voxel-based morphometry. We evaluated grey matter volume differences between patients with and without SP and healthy controls within the sensorimotor and premotor cortices.

Results

We included 106 patients with OCD and 87 controls in our study. Patients with SP (67% of the sample) showed grey matter volume increases in the left sensorimotor cortex in comparison to patients without SP and bilateral sensorimotor cortex grey matter volume increases in comparison to controls. No differences were observed between patients without SP and controls.

Limitations

Most patients were medicated. Participant recruitment and image acquisition were performed in 2 different centres.

Conclusion

We have identified a structural correlate of SP in patients with OCD involving grey matter volume increases within the sensorimotor cortex; this finding is in agreement with those of tic disorder studies showing that abnormal activity and volume increases within this region are associated with the urges preceding tic onset.     

A diffusion tensor imaging study of white matter in obsessive-compulsive disorder

Our objective was to test for differences between subjects with obsessive-compulsive disorder (OCD) and healthy controls with respect to white matter architecture within the cingulum bundle (CB) and anterior limb of the internal capsule (ALIC). We studied eight subjects with active OCD and 10 matched healthy controls using diffusion tensor magnetic resonance imaging (DT-MRI) at 1.5 T (Tesla). Fractional anisotropy (FA) was evaluated in both CB and ALIC. Both voxelwise and region-of-interest methods of analysis were employed. Within both the left CB and the left ALIC, subjects with OCD exhibited significantly greater FA than healthy controls. In the right CB, subjects with OCD exhibited significantly decreased FA versus healthy control subjects. Additionally, the OCD group exhibited abnormal asymmetry (left > right) of FA in the CB. These results provide preliminary evidence for abnormal architecture within the CB and ALIC in OCD. FA differences in these areas are consistent with the presence of abnormal connections between the nodes linked by these tracts. This could explain why surgically severing these tracts is therapeutic. Additional studies are needed to replicate these findings and to clarify their pathological and clinical significance.     

Enhanced rostral anterior cingulate cortex activation during cognitive control is related to orbitofrontal volume reduction in unipolar depression

Objective

In patients with major depressive disorder (MDD), enhanced activation of the rostral anterior cingulate cortex (rACC) during conflict resolution has been demonstrated with the use of functional magnetic resonance imaging (fMRI), which suggests dysregulation of the affective compartment of the ACC associated with error monitoring and cognitive control. Moreover, several previous studies have reported disrupted structural integrity in limbic brain areas and the orbitofrontal cortex in MDD. However, the relation between structural and functional alterations remains unclear. Therefore, the present study sought to investigate whether structural brain aberrations in terms of grey matter decreases directly in the medial frontal regions or in anatomically closely connected areas might be related to our previously reported functional alterations.

Methods

A sample of 16 female, drug-free patients with an acute episode of MDD and 16 healthy control subjects matched for age, sex and education were examined with structural high-resolution T₁-weighted MRI; fMRI images were obtained in the same session.

Results

Voxel-based morphometry (VBM) revealed grey matter decreases in the orbitofrontal and subgenual cortex, in the hippocampus-amygdala complex and in the middle frontal gyrus. The relative hyperactivation of the rACC in terms of inability to deactivate this region during the Stroop Color-Word Test showed an inverse correlation with grey matter reduction in the orbitofrontal cortex.

Conclusion

The present study provides strong evidence for an association between structural alterations in the orbitofrontal cortex and disturbed functional activation in the emotional compartment of the ACC in patients with MDD during cognitive control.Medical subject headings: magnetic resonance imaging, depressive disorder, depression     

Functional and biochemical alterations of the medial frontal cortex in obsessive-compulsive disorder

CONTEXT: The medial frontal cortex (MFC), including the dorsal anterior cingulate and the supplementary motor area, is critical for adaptive and inhibitory control of behavior. Abnormally high MFC activity has been a consistent finding in functional neuroimaging studies of obsessive-compulsive disorder (OCD). However, the precise regions and the neural alterations associated with this abnormality remain unclear. OBJECTIVE: To examine the functional and biochemical properties of the MFC in patients with OCD. DESIGN: Cross-sectional study combining volume-localized proton magnetic resonance spectroscopy and functional magnetic resonance imaging with a task encompassing inhibitory control processes (the Multi-Source Interference Task) designed to activate the MFC. SETTING: Healthy control participants and OCD patients recruited from the general community. PARTICIPANTS: Nineteen OCD patients (10 males and 9 females) and 19 age-, sex-, education-, and intelligence-matched control participants recruited from the general community. MAIN OUTCOME MEASURES: Psychometric measures of symptom severity, Multi-Source Interference Task behavioral performance, blood oxygen level-dependent activation, and proton magnetic resonance spectroscopy brain metabolite concentrations. RESULTS: Multi-Source Interference Task behavioral performance did not differ between OCD patients and control subjects. Reaction time interference and response errors were correlated with blood oxygen level-dependent activation in the dorsal anterior cingulate region in both groups. Compared with controls, OCD patients had greater relative activation of the supplementary motor area and deactivation of the rostral anterior cingulate during high- vs low-conflict (incongruent > congruent) trials. Patients with OCD also showed reduced levels of neuronal N-acetylaspartate in the dorsal anterior cingulate region, which was negatively correlated with their blood oxygen level-dependent activation of the region. CONCLUSIONS: Hyperactivation of the MFC during high- vs low-conflict conditions in patients with OCD may be a compensatory response to a neuronal abnormality in the region. This relationship may partly explain the nature of inhibitory control deficits that are frequently seen in this group and may serve as a focus of future treatment studies.     

Evidence for fractional anisotropy and mean diffusivity white matter abnormalities in the internal capsule and cingulum in patients with obsessive-compulsive disorder

Background

There is evidence to suggest that obsessive–compulsive disorder (OCD) is associated with structural abnormalities in cortico–striato–thalamic circuits, yet the extent of white matter abnormalities is not well established. In this study, we used diffusion tensor imaging (DTI) to examine white matter integrity in specific regions of interest (ROIs) in patients with OCD.

Methods

Patients with OCD and sex-, age- and IQ-matched healthy controls underwent DTI. The primary objective was to explore whether patients with OCD had white matter abnormalities in the anterior limb of the internal capsule (ALIC), the uncinate fasciculus, the genu of the corpus callosum and the cingulum. The secondary objective was to evaluate the relation between fractional anisotropy and mean diffusivity in these ROIs and other clinical variables (including age at onset of OCD, OCD severity and levels of depressive and anxiety symptomatology) in patients with OCD.

Results

There were 15 patients and 17 controls enrolled in our study. Compared with healthy controls, patients with OCD showed increased fractional anisotropy in bilateral regions of the ALIC adjacent to the body of the caudate, as well as decreased fractional anisotropy in the right anterior limb near the head of the caudate. Patients also had decreased mean diffusivity in the body of the right cingulum and the left anterior cingulum compared with controls. Correlational analyses revealed significant associations of fractional anisotropy and mean diffusivity in select circuits with OCD, depression and anxiety severity scores.

Limitations

Inclusion of patients with OCD receiving pharmacotherapy may have been a limitation. In addition, the patients were heterogeneous in terms of their obsessive–compulsive symptom profiles; we did not distinguish between different obsessive–compulsive symptom dimensions.

Conclusion

The study results provide further evidence for OCD-related white matter abnormalities in the ALIC and cingulum, consistent with a corticostriatal model of OCD.     

Stress response in postpartum women with and without obsessive-compulsive symptoms: an fMRI study

Background

During the postpartum period, some women might be under a considerable amount of stress and at increased risk for onset or exacerbation of obsessive–compulsive disorder (OCD). Little is known about the stress response correlates during the postpartum period and in patients with OCD. This study aimed to examine the cerebral, psychologic and endocrine correlates of the stress response in patients with OCD and during the postpartum period.

Methods

Women with postpartum OCD, healthy postpartum women and healthy mothers past the postpartum period underwent functional magnetic resonance imaging while facing a reliable psychosocial stressor (the Montreal Imaging Stress Task). Stress-related psychologic and endocrine responses (i.e., cortisol) were obtained.

Results

We enrolled 12 women with postpartum OCD, 16 healthy postpartum women and 11 healthy mothers past the postpartum period in our study. Compared with healthy postpartum counterparts, postpartum women with OCD had a heightened self-reported and endocrine stress response associated with a distinct brain activation pattern in response to psychosocial stress involving the orbitofrontal and temporal cortices. Moreover, compared with mothers assessed in a period of time beyond the postpartum period, healthy postpartum women did not differ in psychologic and cortisol response to stress, but recruited different brain regions, such as the dorsolateral pre-frontal cortex and the anterior cingulate cortex, during exposure to stress.

Limitations

Potential confounding factors, such as medication use, breastfeeding, parity and personality factors, may have modulated the stress-related endocrine response and could not be assessed in this study.

Conclusion

Obsessive–compulsive disorder and the postpartum period differentially influence the brain circuitry underlying psychosocial stress as well as the psychologic and endocrine responses.     

Abnormal small-world architecture of top-down control networks in obsessive-compulsive disorder

Background

Obsessive–compulsive disorder (OCD) is a common neuropsychiatric disorder that is characterized by recurrent intrusive thoughts, ideas or images and repetitive ritualistic behaviours. Although focal structural and functional abnormalities in specific brain regions have been widely studied in populations with OCD, changes in the functional relations among them remain poorly understood. This study examined OCD–related alterations in functional connectivity patterns in the brain’s top–down control network.

Methods

We applied resting-state functional magnetic resonance imaging to investigate the correlation patterns of intrinsic or spontaneous blood oxygen level–dependent signal fluctuations in 18 patients with OCD and 16 healthy controls. The brain control networks were first constructed by thresholding temporal correlation matrices of 39 brain regions associated with top–down control and then analyzed using graph theory-based approaches.

Results

Compared with healthy controls, the patients with OCD showed decreased functional connectivity in the posterior temporal regions and increased connectivity in various control regions such as the cingulate, precuneus, thalamus and cerebellum. Furthermore, the brain’s control networks in the healthy controls showed small-world architecture (high clustering coefficients and short path lengths), suggesting an optimal balance between modularized and distributed information processing. In contrast, the patients with OCD showed significantly higher local clustering, implying abnormal functional organization in the control network. Further analysis revealed that the changes in network properties occurred in regions of increased functional connectivity strength in patients with OCD.

Limitations

The patient group in the present study was heterogeneous in terms of symptom clusters, and most of the patients with OCD were medicated.

Conclusion

Our preliminary results suggest that the organizational patterns of intrinsic brain activity in the control networks are altered in patients with OCD and thus provide empirical evidence for aberrant functional connectivity in the large-scale brain systems in people with this disorder.     

Orbital frontal cortex in treatment-naïve pediatric obsessive–compulsive disorder

The orbital frontal cortex (OFC) has been implicated in obsessive–compulsive disorder (OCD). Participants comprised 28 treatment-naïve pediatric OCD patients and 21 controls, who were examined using magnetic resonance imaging. OCD patients had larger right but not left OFC white matter volume than controls. This is fresh evidence implicating white matter in OCD.     

Neuroimaging of cognitive brain function in paediatric obsessive compulsive disorder: a review of literature and preliminary meta-analysis

Obsessive compulsive disorder (OCD) is a frequent psychiatric disorder with a prevalence of 1–3?%, and it places an enormous burden on patients and their relatives. Up to 50?% of all cases suffer from onset in childhood or adolescence, and the disorder often takes a chronic course with a poor long-term prognosis. Paediatric OCD, with its high familiality, is often referred to as a distinct OCD subtype that coincides with a developmental period in which the prefrontal cortex exhibits extensive structural and functional maturation. In the present review, we included all studies examining cognitive brain activation in children and/or adolescents with OCD. We conducted extensive literature searches for relevant articles (Pubmed, ScienceDirect) and summarize, tabulate, and discuss their results. For the eight activation studies using functional magnetic resonance imaging, we also performed preliminary meta-analyses to assess the most consistent hypo- and hyperactivation in paediatric OCD patients during cognitive task performance. The review of literature as well as our preliminary meta-analyses of paediatric studies indicated altered functional activation in the same brain regions of affective and cognitive cortico-striatal-thalamic (CST) circuits as for adult OCD patients despite some variations in the direction of activation difference. The still small number of studies that examined brain activation in paediatric OCD patients thereby largely converged with previous findings in adult patients and with the established neurobiological models of CST circuit dysfunction in OCD.     

White matter abnormalities of fronto-striato-thalamic circuitry in obsessive-compulsive disorder: A study using diffusion spectrum imaging tractography

Previous studies have reported white matter abnormalities in patients with obsessive-compulsive disorder (OCD). This study aimed to further explore white matter abnormalities in OCD patients through diffusion spectrum imaging (DSI) and tractography of the two white matter tracts which most probably play an important role in OCD neuropathology: the anterior segment of cingulum bundles (ACB) and the anterior thalamic radiations (ATR). Twelve right-handed, medicated adult patients with OCD and 12 matched controls underwent DSI on a 3 tesla magnetic resonance imaging (MRI) system. Tractography based on DSI data was reconstructed to define the ACB and ATR. Mean generalized fractional anisotropy (GFA) was calculated for each targeted tract and was used to analyze local changes in microstructural integrity along individual tracts. There was a significantly lower mean GFA in both the right ATR and left ACB in OCD subjects compared to controls. OCD subjects also demonstrated decreased left-lateralized asymmetry of the ACB when compared to controls. Furthermore, the mean GFA of the left ACB positively correlated with OCD subjects’ obsessive subscores on the Yale-Brown Obsessive-Compulsive scale. This study supports the white matter abnormalities in the ACB and ATR of OCD subjects, which corroborates neurobiological models that posit a defect in fronto-striato-thalamic circuitry in OCD.     

Investigating SAPAP3 variants in the etiology of obsessive-compulsive disorder and trichotillomania in the South African white population

Background

Obsessive-compulsive disorder (OCD) is a debilitating psychiatric disorder characterized by repeated obsessions and compulsions. Trichotillomania (TTM), a psychiatric disorder characterized by repetitive hairpulling, is presently classified as an impulse control disorder, but has also been viewed as an obsessive-compulsive spectrum disorder. Both conditions are complex disorders, with evidence from family and twin studies indicating that their etiology includes a genetic component. Results from a recent knockout animal model suggest that SAP90/PSD95-associated protein 3 (SAPAP3) may be involved in the pathophysiology of both disorders.

Methods

Seven polymorphic variants distributed across the gene encoding SAPAP3 were genotyped in South African white OCD (n = 172), TTM (n = 45), and control (n = 153) subjects. Single-locus and haplotype analyses were conducted to determine association between genetic variants and subjects with OCD, TTM, and controls.

Results

Although single-locus analysis revealed a significant association between rs11583978 in SAPAP3 and TTM, this association was nonsignificant after correction for multiple testing. In the OCD group, a significant association was observed between earlier age at onset and the A-T-A-T (rs11583978-rs7541937-rs6662980-rs4652867) haplotype compared with the C-G-G-G haplotype.

Conclusions

This study generated preliminary evidence to link SAPAP3 variants to the development of earlier onset OCD. Future studies should concentrate on locating the susceptibility variant(s) by focusing on functional polymorphisms within SAPAP3.     

Regional gray matter abnormalities in obsessive-compulsive disorder: a voxel-based morphometry study.

BACKGROUND: Several structural magnetic resonance imaging (MRI) studies have investigated the presence of brain abnormalities in obsessive-compulsive disorder (OCD) but have not produced consistent findings. This might be partly related to their use of a regions-of-interest approach. We assessed gray matter volumes in 19 OCD subjects and 15 healthy volunteers, using voxel-based morphometry (VBM). METHODS: Images were acquired with a 1.5-T MRI scanner, spatially normalized, and segmented with optimized VBM. Statistical comparisons were performed with the general linear model. RESULTS: Significant findings were detected in regions predicted a priori to be implicated in OCD, including increased gray matter in OCD subjects relative to control subjects in posterior orbitofrontal and parahippocampal regions; decreased gray matter in OCD patients in the left anterior cingulate cortex; and inverse correlations between obsessive-compulsive symptom severity and gray matter in the medial thalamus (p < .001, uncorrected for multiple comparisons). Also, an unpredicted site of gray matter reduction in OCD patients in the right parietal associative cortex approached significance (p = .052, corrected for multiple comparisons). CONCLUSIONS: Our findings are consistent with previous studies implicating dysfunction of orbitofrontal, cingulate, thalamic, and temporolimbic regions in OCD and suggest that the involvement of the parietal cortex in the pathophysiology of OCD warrants further investigation.     

Combined analysis of grey matter voxel-based morphometry and white matter tract-based spatial statistics in late-life bipolar disorder

Background

Previous magnetic resonance imaging (MRI) studies in young patients with bipolar disorder indicated the presence of grey matter concentration changes as well as microstructural alterations in white matter in various neocortical areas and the corpus callosum. Whether these structural changes are also present in elderly patients with bipolar disorder with long-lasting clinical evolution remains unclear.

Methods

We performed a prospective MRI study of consecutive elderly, euthymic patients with bipolar disorder and healthy, elderly controls. We conducted a voxel-based morphometry (VBM) analysis and a tract-based spatial statistics (TBSS) analysis to assess fractional anisotropy and longitudinal, radial and mean diffusivity derived by diffusion tensor imaging (DTI).

Results

We included 19 patients with bipolar disorder and 47 controls in our study. Fractional anisotropy was the most sensitive DTI marker and decreased significantly in the ventral part of the corpus callosum in patients with bipolar disorder. Longitudinal, radial and mean diffusivity showed no significant between-group differences. Grey matter concentration was reduced in patients with bipolar disorder in the right anterior insula, head of the caudate nucleus, nucleus accumbens, ventral putamen and frontal orbital cortex. Conversely, there was no grey matter concentration or fractional anisotropy increase in any brain region in patients with bipolar disorder compared with controls.

Limitations

The major limitation of our study is the small number of patients with bipolar disorder.

Conclusion

Our data document the concomitant presence of grey matter concentration decreases in the anterior limbic areas and the reduced fibre tract coherence in the corpus callosum of elderly patients with long-lasting bipolar disorder.     

Functional magnetic resonance imaging study of regional brain activation during implicit sequence learning in obsessive-compulsive disorder.

BACKGROUND: Corticostriatal circuitry has been implicated in the pathophysiology of obsessive-compulsive disorder (OCD). The serial reaction time (SRT) task, a paradigm that tests implicit sequence learning, has been used with imaging to probe striatal function. Initial studies have indicated that OCD patients exhibit deficient striatal activation and aberrant hippocampal recruitment compared with healthy control (HC) subjects. Here, we used the SRT and functional magnetic resonance imaging (fMRI) to replicate prior results in a larger sample and to test for relationships between regional activation and OCD symptom dimensions. METHODS: Using SPM99, fMRI-SRT data from 12 OCD and 12 matched HC subjects were analyzed. Symptom dimensions followed a four-factor model scored on a 0- to 10-point scale. RESULTS: For the implicit learning versus random contrast, group by condition interactions revealed aberrant recruitment within the hippocampus as well as orbitofrontal cortex (OCD > HC) but no striatal group differences. However, an inverse correlation was found between striatal activation and specific symptom factors. CONCLUSIONS: These results replicate previous smaller studies showing aberrant hippocampal recruitment in OCD during SRT performance. Although findings of deficient striatal activation in OCD were not replicated, correlation results suggest that this inconsistency may be attributable to differences among OCD symptom dimensions.     

Error Processing and Inhibitory Control in Obsessive-Compulsive Disorder: A Meta-analysis Using Statistical Parametric Maps

Background

Error processing and inhibitory control enable the adjustment of behaviors to meet task demands. Functional magnetic resonance imaging studies report brain activation abnormalities in patients with obsessive-compulsive disorder (OCD) during both processes. However, conclusions are limited by inconsistencies in the literature and small sample sizes. Therefore, the aim here was to perform a meta-analysis of the existing literature using unthresholded statistical maps from previous studies.

Brain structural imaging correlates of olfactory dysfunction in obsessive–compulsive disorder

Olfactory dysfunction has been described in obsessive–compulsive disorder (OCD). Brain regions involved in smell processing partially overlap with structures included in the neurobiological models of OCD, although no previous studies have analyzed the neuroanatomical correlates of olfactory dysfunction in this disorder. The aim of our study was to examine the association between regional gray matter volume, as assessed by a voxel-based morphometry analysis of magnetic resonance images (MRI), and olfactory function, as assessed by the Sniffin’ Sticks test (SST). Olfactory function was assessed in 19 OCD patients and 19 healthy volunteers. All participants were also scanned in a 1.5-T magnet to obtain T1-weighted anatomical MRIs, which were pre-processed and analyzed with SPM8. Three different correlation models were used to study the association between regional gray matter volumes and olfactory function in the domains assessed by the SST: detection threshold, discrimination, and identification. OCD patients showed a significant impairment in all the domains assessed by the SST. Voxel-based mapping revealed a positive association in healthy controls between detection threshold and the gray matter content of a left anterior cingulate cortex cluster. In OCD patients, a positive correlation was observed between identification errors and the gray matter volume of the left medial orbital gyrus. In a post hoc analysis, these two gray matter regions were shown to be enlarged in OCD patients. Our findings support the idea that olfactory dysfunction in OCD is associated with volumetric changes in brain areas typically implicated in the neurobiology of the disorder.     

A manual and automated MRI study of anterior cingulate and orbito-frontal cortices, and caudate nucleus in obsessive-compulsive disorder: comparison with healthy controls and patients with schizophrenia

Functional imaging and neuropsychological data suggest that interconnected brain structures including the orbito-frontal cortex (OFC), anterior cingulate cortex (ACC) and caudate nucleus (CN) are involved in the pathophysiology of obsessive-compulsive disorder (OCD), but structural imaging studies investigating these regions have yielded inconclusive results. This may be due to inconsistencies in the identification of anatomical boundaries and methodologies utilised (i.e. automated vs. manual tracing). This magnetic resonance imaging study used manual tracing to measure volumes of selected brain regions (OFC, ACC and CN) in OCD patients and compared them with samples of healthy (HC) and psychiatric (schizophrenia; SCZ) controls (n=18 in each group). Concurrently, automated voxel-based analysis was also used to detect subtle differences in cerebral grey and white matter. For the OCD vs. HC comparison, there were no significant volumetric differences detected using the manual or the automated method (although the latter revealed a deficit in the subcortical white matter of the right temporal region). A direct comparison of the two patient groups showed no significant differences using the manual method. However, a moderate effect size was detected for OFC grey matter (reduced in SCZ), which was supported by findings of reduced OFC volume in the automated analysis. Automated analyses also showed reduced volumes in the dorsal (white matter) and ventral ACC (grey and white matter), as well as the left posterior cingulate (grey and white matter) in SCZ. The findings suggest that in contrast to findings in SCZ, there are very few (if any) gross structural anomalies in OCD.