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

A psychological and neuroanatomical model of obsessive-compulsive disorder

Imaging, surgical, and lesion studies suggest that the prefrontal cortex (orbitofrontal and anterior cingulate cortexes), basal ganglia, and thalamus are involved in the pathogenesis of obsessive-compulsive disorder (OCD). On the basis of these findings several models of OCD have been developed, but have had difficulty fully integrating the psychological and neuroanatomical findings of OCD. Recent research in the field of cognitive neuroscience on the normal function of these brain areas demonstrates the role of the orbitofrontal cortex in reward, the anterior cingulate cortex in error detection, the basal ganglia in affecting the threshold for activation of motor and behavioral programs, and the prefrontal cortex in storing memories of behavioral sequences (called "structured event complexes" or SECs). The authors propose that the initiation of these SECs can be accompanied by anxiety that is relieved with completion of the SEC, and that a deficit in this process could be responsible for many of the symptoms of OCD. Specifically, the anxiety can form the basis of an obsession, and a compulsion can be an attempt to receive relief from the anxiety by repeating parts of, or an entire, SEC. The authors discuss empiric support for, and specific experimental predictions of, this model. The authors believe that this model explains the specific symptoms, and integrates the psychology and neuroanatomy of OCD better than previous models.

Voxel based morphometry reveals specific gray matter changes in primary dystonia

The present study assessed patterns of brain tissue alterations in different types of primary dystonia using voxel-based morphometry (VBM). Nine patients with primary generalized dystonia (GD), 11 patients with primary cervical dystonia (CD), and 11 patients with primary focal hand dystonia (FHD) as well as 31 age and gender-matched controls were included. When compared with healthy controls, patients with primary dystonia (n=31) showed gray matter volume increase bilaterally in the globus pallidus internus, nucleus accumbens, prefrontal cortex, as well as unilaterally in the left inferior parietal lobe. This is the first study using VBM in patients with different types of primary dystonia, showing a common pattern of gray matter changes.

Structural brain abnormalities in the frontostriatal system and cerebellum in pedophilia

Even though previous neuropsychological studies and clinical case reports have suggested an association between pedophilia and frontocortical dysfunction, our knowledge about the neurobiological mechanisms underlying pedophilia is still fragmentary. Specifically, the brain morphology of such disorders has not yet been investigated using MR imaging techniques. Whole brain structural T1-weighted MR images from 18 pedophile patients (9 attracted to males, 9 attracted to females) and 24 healthy age-matched control subjects (12 hetero- and 12 homosexual) from a comparable socioeconomic stratum were processed by using optimized automated voxel-based morphometry within multiple linear regression analyses. Compared to the homosexual and heterosexual control subjects, pedophiles showed decreased gray matter volume in the ventral striatum (also extending into the nucl. accumbens), the orbitofrontal cortex and the cerebellum. These observations further indicate an association between frontostriatal morphometric abnormalities and pedophilia. In this respect these findings may support the hypothesis that there is a shared etiopathological mechanism in all obsessive-compulsive spectrum disorders.

Cortical thinning in obsessive compulsive disorder

Although studies of obsessive-compulsive disorder (OCD) over the last 20 years have suggested abnormalities in frontal-subcortical circuitry, evidences of structural abnormalities in those areas are still imperfect and contradictory. With recent advances in neuroimaging technology, it is now possible to study cortical thickness based on cortical surfaces, which offers a direct quantitative index of cortical mass. Using the constrained Laplacian-based automated segmentation with proximities (CLASP) algorithm, we measured cortical thickness of 55 patients with OCD (33 men and 22 women) and 52 age- and sex-matched healthy volunteers (32 men and 20 women). We found multiple regions of cortical thinning in OCD patients compared to the normal control group. Patients with OCD had thinner left inferior frontal, left middle frontal, left precentral, left superior temporal, left parahippocampal, left orbitofrontal, and left lingual cortices. Most thinned regions were located in the left ventral cortex system, providing a new perspective that this ventral cortical system may be involved in the pathophysiology of OCD.

Integrating evidence from neuroimaging and neuropsychological studies of obsessive-compulsive disorder: the orbitofronto-striatal model revisited

Obsessive-compulsive disorder (OCD) is a common, heritable and disabling neuropsychiatric disorder. Theoretical models suggest that OCD is underpinned by functional and structural abnormalities in orbitofronto-striatal circuits. Evidence from cognitive and neuroimaging studies (functional and structural magnetic resonance imaging (MRI) and positron emission tomography (PET)) have generally been taken to be supportive of these theoretical models; however, results from these studies have not been entirely congruent with each other. With the advent of whole brain-based structural imaging techniques, such as voxel-based morphometry and multivoxel analyses, we consider it timely to assess neuroimaging findings to date, and to examine their compatibility with cognitive studies and orbitofronto-striatal models. As part of this assessment, we performed a quantitative, voxel-level meta-analysis of functional MRI findings, which revealed consistent abnormalities in orbitofronto-striatal and other additional areas in OCD. This review also considers the evidence for involvement of other brain areas outside orbitofronto-striatal regions in OCD, the limitations of current imaging techniques, and how future developments in imaging may aid our understanding of OCD.

Neurocognitive endophenotypes of obsessive-compulsive disorder

Endophenotypes (intermediate phenotypes) are objective, heritable, quantitative traits hypothesized to represent genetic risk for polygenic disorders at more biologically tractable levels than distal behavioural and clinical phenotypes. It is theorized that endophenotype models of disease will help to clarify both diagnostic classification and aetiological understanding of complex brain disorders such as obsessive-compulsive disorder (OCD). To investigate endophenotypes in OCD, we measured brain structure using magnetic resonance imaging (MRI), and behavioural performance on a response inhibition task (Stop-Signal) in 31 OCD patients, 31 of their unaffected first-degree relatives, and 31 unrelated matched controls. Both patients and relatives had delayed response inhibition on the Stop-Signal task compared with healthy controls. We used a multivoxel analysis method (partial least squares) to identify large-scale brain systems in which anatomical variation was associated with variation in performance on the response inhibition task. Behavioural impairment on the Stop-Signal task, occurring predominantly in patients and relatives, was significantly associated with reduced grey matter in orbitofrontal and right inferior frontal regions and increased grey matter in cingulate, parietal and striatal regions. A novel permutation test indicated significant familial effects on variation of the MRI markers of inhibitory processing, supporting the candidacy of these brain structural systems as endophenotypes of OCD. In summary, structural variation in large-scale brain systems related to motor inhibitory control may mediate genetic risk for OCD, representing the first evidence for a neurocognitive endophenotype of OCD.

Pediatric OCD structural brain deficits in conflict monitoring circuits: A voxel-based morphometry study

The aim of this study is to use a voxel-based morphometry protocol to compare the brains of 18 children with obsessive-compulsive disorder (OCD) with those of a healthy group matched for gender and handedness. Images were acquired with a 1.5-T MRI scanner, spatially normalized, and segmented with an optimized voxel-based morphometry protocol. OCD children presented a 5.93% reduction of gray matter (GM) total volume in comparison with control brains. We identified OCD brain volume reductions in regions that have been extensively related to action monitoring and error signaling processes. Specifically, we found decreased bilateral GM in frontal (significant after Family Wise Error (FEW), multiple comparisons correction) and cingulate regions as well as decreased white matter (WM) in bilateral frontal and right parietal (p<0.001 uncorrected). Additionally, we found a negative correlation between symptom severity and bilateral hippocampal GM-volume (p<0.001uncorrected) as well as a positive correlation between age and GM left caudate volume (p=0.037 FWE small volume corrected) in the OCD group. As a conclusion, our results point to conflict monitoring structural brain regions as primary deficits in pediatric OCD, and to striatal abnormalities as age-related deficits.

Neurobiologie bei Tic- und Zwangsstörungen

Zusammenfassung. Erst in den letzten Jahren wird auch in der Forschung vermehrtes Augenmerk auf die Überschneidung von Tic- und Zwangsstörungen gerichtet. Während in Übersichtsarbeiten zum gemeinsamen Auftreten von Tic- und Zwangsstörungen die zahlreichen Befunde zu Phänomenologie, begleitender Psychopathologie, Epidemiologie und daraus resultierenden Therapieimplikationen breiten Raum einnehmen, sind die Untersuchungsergebnisse hinsichtlich ätiologischer und pathophysiologischer Gemeinsamkeiten in entsprechenden Arbeiten unterrepräsentiert. Daher wird mit dieser Arbeit ein Überblick über den aktuellen neurobiologischen Forschungsstand zu den Gemeinsamkeiten und Unterschieden von Tic- und Zwangsstörungen gegeben.

Toward a better understanding of the pathophysiology of OCD SSRI responders: QEEG source localization

OBJECTIVE

To demonstrate the utility of three-dimensional source localization of the scalp-recorded electroencephalogram (EEG) for the identification of the most probable underlying brain dysfunction in patients with obsessive-compulsive disorder (OCD).

METHOD

Eyes-closed resting EEG data was recorded from the scalp locations of the International 10/20 System. Variable resolution electromagnetic tomography (VARETA) was applied to artifact-free EEG data. This mathematical algorithm estimates the source generators of EEG recorded from the scalp.

RESULTS

An excess in the alpha range was found with sources in the corpus striatum, in the orbito-frontal and temporo-frontal regions in untreated OCD patients. This abnormality was seen to decrease following successful treatment with paroxetine.

CONCLUSION

The VARETA findings of an activation/deactivation pattern in cortical and subcortical structures in paroxetine-responsive patients are in good accordance with data obtained in previously published positron emission tomography studies related to current hypotheses of a thalamo-striatal-frontal feedback loop being relevant for understanding the pathophysiology of OCD.

Volumetric MRI study of key brain regions implicated in obsessive-compulsive disorder

Neuroanatomic abnormalities have been implicated in the pathophysiology of obsessive-compulsive disorder (OCD). To date, no study has measured the orbito-frontal cortex (OFC), anterior cingulate, caudate nucleus, and thalamus concurrently in first-episode patients. Thus, we performed a volumetric MRI study in patients who were treatment-naive and healthy controls focusing on the in vivo neuroanatomy of the whole brain, total gray and white matter volume, thalamus, caudate nucleus, anterior cingulate cortex, and OFC concurrently. The volumes of thalamus, caudate nucleus, anterior cingulate cortex, and OFC were measured in 12 OCD patients who were treatment-naive and 12 healthy control subjects. Anterior cingulate and OFC volumes included both white and gray matters. Volumetric measurements were made with T1-weighted coronal MRI images, with 1.5-mm-thick slices, at 1.5 T. The patients had increased white matter volume than healthy controls. The patient group had significantly smaller left and right OFC volumes and significantly greater left and right thalamus volumes compared with healthy controls. Anterior cingulate exhibited a near-significant difference between the patients and healthy controls on left side. Significant correlations were found between Y-BOCS scores and left OFC, and right OFC, and between Y-BOCS and left thalamus volumes in the patient group. In conclusion, our findings suggest that abnormalities in these areas may play an important role in the pathophysiology of OCD.

Identifying patients with obsessive-compulsive disorder using whole-brain anatomy

Structural neuroimaging studies have reported a variety of brain alterations between groups of obsessive-compulsive disorder (OCD) patients and healthy controls. However, the large heterogeneity in discrete anatomical measures that exists among patients prevents a clear discrimination of single patients from healthy subjects. This reduces the potential clinical applicability of structural neuroimaging studies. In the present study we assessed the feasibility of identifying OCD patients on the basis of whole-brain anatomical alterations. Whole-brain magnetic resonance images were collected from two consecutive samples of OCD outpatients (n=72 and n=30), and control subjects (n=72 and n=30). We computed the whole-brain (voxel-wise) pattern of structural difference between OCD patients and control subjects at the group level. A single expression value of this difference pattern was calculated for each subject, expressing their degree of 'OCD-like' anatomical alteration. Accuracy of patient classification based on these expression values was assessed using two validation approaches. Firstly, using a cross-validation method, we obtained a high classification accuracy (average of the sensitivity and specificity indices) of 93.1%. In a second assessment, which classified new groups of OCD patients and control subjects, overall accuracy was lower at 76.6%. Individual expression values for OCD patients were significantly correlated with overall symptom severity as measured by the Y-BOCS scale. Our results suggest that OCD patients can be identified on the basis of whole-brain structural alterations, although the accuracy of our approach may be limited by the inherent variability of psychiatric populations. Nevertheless, the anatomical characterization of individual patients may ultimately provide the psychiatrist with relevant biological information.

The experience of emotion

Experiences of emotion are content-rich events that emerge at the level of psychological description, but must be causally constituted by neurobiological processes. This chapter outlines an emerging scientific agenda for understanding what these experiences feel like and how they arise. We review the available answers to what is felt (i.e., the content that makes up an experience of emotion) and how neurobiological processes instantiate these properties of experience. These answers are then integrated into a broad framework that describes, in psychological terms, how the experience of emotion emerges from more basic processes. We then discuss the role of such experiences in the economy of the mind and behavior.

Relationships between plasma leptin concentrations and human brain structure: a voxel-based morphometric study

We have previously demonstrated that obese people have reduced grey matter (GM) in several brain areas, including regions implicated in the regulation of taste (i.e., inferior frontal operculum and postcentral gyrus), reward (i.e., putamen), and behavioural processing (i.e., middle frontal gyrus), compared with their lean counterparts. It is well established that the brain may serve as a direct target for adiposity signals, one of the most important being leptin. We investigated the relationships between fasting plasma leptin concentrations and brain tissue composition in a group of 32 young adult Caucasians (12M/20F, age 32+/-1 years, body fat 29+/-1%, mean+/-S.E.) with normal glucose tolerance by using voxel-based morphometry of magnetic resonance imaging scans. Fasting plasma leptin concentrations were positively correlated with GM volumes of the left cerebellum and left inferior temporal gyrus and negatively associated with GM volumes of the left inferior frontal operculum, left postcentral gyrus, and right putamen (P<0.001, uncorrected for multiple comparisons) after adjustment for sex, percent body fat, age, fasting plasma insulin concentrations (i.e., the major determinants of plasma leptin), and global GM volume (thus allowing for an assessment of regional effects only). This study showed an independent, negative correlation between fasting plasma leptin concentrations, which are increased in obesity, and the volumes of GM in brain areas where obese people have reduced GM compared to their lean counterparts. These relationships may explain some of the abnormalities in brain morphology recently found to be associated with excess body fatness.

The influence of sulcal variability on morphometry of the human anterior cingulate and paracingulate cortex

Human anterior cingulate (ACC) and paracingulate (PaC) cortices play an important role in cognitive and affective regulation and have been implicated in numerous psychiatric and neurological conditions. The region they comprise displays marked inter-individual variability in sulcal and gyral architecture, and although recent evidence suggests that this variability has functional significance, it is often ignored in automated and region-of-interest (ROI) morphometric investigations. This has lead to confounded interpretation of results and inconsistent findings across a number of studies and in a variety of clinical populations. In this paper, we present a reliable method for parcellating the dorsal, ventral, and subcallosal ACC and PaC that accounts for individual variation in the local cortical folding pattern. We also investigated the effect of one well characterized morphological variation, the incidence of the paracingulate sulcus (PCS), on regional volumes in 24 (12 male, 12 female) healthy participants. The presence of a PCS was shown to affect both ACC and PaC volumes, such that it was associated with an 88% increase in paracingulate cortex and a concomitant 39% decrease in cingulate cortex. These findings illustrate the potential confounds inherent in morphometric approaches that ignore or attempt to minimize inter-individual variations in sulcal and gyral anatomy and underscore the need to consider this variability when attempting to understand disease processes or characterize brain structure-function relationships.

What is the optimal way to subdivide obsessive-compulsive disorder?

The clinical presentation of obsessive-compulsive disorder (OCD) varies not only across patients but over the course of the disorder. This diversity indicates that OCD is a heterogeneous disorder, which may have an important impact on psychopathological, longitudinal, genetic, and treatment research. To better understand OCD heterogeneity, more homogeneous phenotypic descriptions are necessary to delimiting clinically meaningful subgroups of patients. Besides phenotypic descriptions, another method of delimiting OCD patient subgroups includes the search for endophenotypes (extended phenotypes) based on neurophysiological, immunological, genetic, neuropsychological, or neuroanatomic (neuroimaging) paradigms. This article will describe some strategies that deal with OCD heterogeneity, including the identification of more homogeneous phenotypical categories, an improved understanding of obsessive-compulsive symptom dimensions and how to use them as quantitative traits, and broadening the diagnostic boundaries of OCD to include other related conditions. The relevance and limitations of each approach are also discussed. Since the etiological mechanisms associated with the expressions of OCD are unknown, there is probably not one but several heuristic strategies to search for more homogeneous OCD subgroup, that combined may provide the most fruitful results.

Parietal white matter abnormalities in obsessive-compulsive disorder: a magnetic resonance spectroscopy study at 3-Tesla

OBJECTIVE

To identify a neurochemical basis for the hypothesis that an aberrant cortico-subcortical circuit underlies obsessive-compulsive disorder (OCD). The white matter was also investigated because of recent research which suggests the altered connectivity of axons.

METHOD

Using 3-Tesla magnetic resonance spectroscopy, the relative concentrations of N-acetylaspartate (NAA) and choline-containing compounds (Cho) to creatine/phosphocreatine (Cr) were measured in the anterior cingulate, basal ganglia, thalamus, frontal and parietal white matter of 12 OCD patients, and 32 control subjects.

RESULTS

The mean concentration of Cho/Cr was significantly higher in the patients than in the controls, but only in the parietal white matter, while no significant group differences in NAA/Cr were observed in any of the brain regions. Parietal Cho/Cr correlated positively with the severity of OCD symptoms.

CONCLUSION

This finding provides indirect evidence for the parietal white matter involvement in OCD, thus suggesting a change in the phospholipids of myelinated axons and/or glia cells.

Brain abnormalities in human obesity: A voxel-based morphometric study

Obesity is accompanied by damage to several tissues. Overweight is a risk factor for Alzheimer's disease and other neurodegenerative disorders. Whether structural abnormalities associated with excess body fat may also occur in the brain is unknown. We sought to determine to what extent excess body fat is associated with regional alterations in brain structure using voxel-based morphometry (VBM), a whole-brain unbiased technique based upon high-definition 3D magnetic resonance imaging (MRI) scans normalized into a common standard space and allowing for an objective assessment of neuroanatomical differences throughout the brain. We studied 24 obese (11 male, 13 female; age: 32 +/- 8 years; body mass index [BMI]: 39.4 +/- 4.7 kg/m2) and 36 lean (25 male, 11 female; mean age: 33 +/- 9 years; BMI: 22.7 +/- 2.2 kg/m2) non-diabetic Caucasians. In comparison with the group of lean subjects, the group of obese individuals had significantly lower gray matter density in the post-central gyrus, frontal operculum, putamen, and middle frontal gyrus (P < 0.01 after adjustment for sex, age, handedness, global tissue density, and multiple comparisons). BMI was negatively associated with GM density of the left post-central gyrus in obese but not lean subjects. This study identified structural brain differences in human obesity in several brain areas previously involved in the regulation of taste, reward, and behavioral control. These alterations may either precede obesity, representing a neural marker of increased propensity to gaining weight, or occur as a consequence of obesity, indicating that also the brain is affected by increased adiposity.