Neuroendocrinological mechanisms underlying impulsive and compulsive behaviors in obesity: a narrative review of fMRI studies

Impulsivity and compulsivity are multidimensional constructs that are increasingly considered determinants of obesity. Studies using functional magnetic resonance imaging (fMRI) have provided insight on how differences in brain response during tasks exploring facets of impulsivity and compulsivity relate to the ingestive behaviors that support the etiology and maintenance of obesity. In this narrative review, we provide an overview of neuroimaging studies exploring impulsivity and compulsivity factors as they relate to weight status. Special focus will be placed on studies examining the impulsivity-related dimensions of attentional bias, delayed gratification and emotion regulation. Discussions of compulsivity within the context of obesity will be restricted to fMRI studies investigating habit formation and response flexibility under shifting contingencies. Further, we will highlight neuroimaging research demonstrating how alterations in neuroendocrine functioning are linked to excessive food intake and may serve as a driver of the impulsive and compulsive behaviors observed in obesity. Research on the associations between brain response with neuroendocrine factors, such as insulin, peptide YY (PYY), leptin, ghrelin and glucagon-like peptide 1 (GLP-1), will be reviewed.

Compulsivity and impulsivity traits linked to attenuated developmental frontostriatal myelination trajectories

The transition from adolescence to adulthood is a period when ongoing brain development coincides with a substantially increased risk of psychiatric disorders. The developmental brain changes accounting for this emergent psychiatric symptomatology remain obscure. Capitalizing on a unique longitudinal dataset that includes in vivo myelin-sensitive magnetization transfer (MT) MRI scans, we show that this developmental period is characterized by brain-wide growth in MT trajectories within both gray matter and adjacent juxtacortical white matter. In this healthy population, the expression of common developmental traits, namely compulsivity and impulsivity, is tied to a reduced growth of these MT trajectories in frontostriatal regions. This reduction is most marked in dorsomedial and dorsolateral prefrontal regions for compulsivity and in lateral and medial prefrontal regions for impulsivity. These findings highlight that psychiatric traits of compulsivity and impulsivity are linked to regionally specific reductions in myelin-related growth in late adolescent brain development.

Median and Dorsal Raphe Serotonergic Neurons Control Moderate Versus Compulsive Cocaine Intake

BACKGROUND

Reduced expression of the serotonin transporter (SERT) promotes anxiety and cocaine intake in both humans and rats. We tested the hypothesis that median raphe nucleus (MRN) and dorsal raphe nucleus (DRN) serotonergic projections differentially mediate these phenotypes.

METHODS

We used virally mediated RNA interference to locally downregulate SERT expression and compared the results with those of constitutive SERT knockout. Rats were allowed either short access (ShA) (1 hour) or long access (LgA) (6 hours) to cocaine self-administration to model moderate versus compulsive-like cocaine taking.

RESULTS

SERT knockdown in the MRN increased cocaine intake selectively under ShA conditions and, like ShA cocaine self-administration, reduced corticotropin-releasing factor (CRF) immunodensity in the paraventricular nucleus of the hypothalamus. In contrast, SERT knockdown in the DRN increased cocaine intake selectively under LgA conditions and, like LgA cocaine self-administration, reduced CRF immunodensity in the central nucleus of the amygdala. SERT knockdown in the MRN or DRN produced anxiety-like behavior, as did withdrawal from ShA or LgA cocaine self-administration. The phenotype of SERT knockout rats was a summation of the phenotypes generated by MRN- and DRN-specific SERT knockdown.

CONCLUSIONS

Our results highlight a differential role of serotonergic projections arising from the MRN and DRN in the regulation of cocaine intake. We propose that a cocaine-induced shift from MRN-driven serotonergic control of CRF levels in the hypothalamus to DRN-driven serotonergic control of CRF levels in the amygdala may contribute to the transition from moderate to compulsive intake of cocaine.

Can we predict development of impulsive-compulsive behaviours in Parkinson's disease?

OBJECTIVE

To determine clinical and structural imaging predictors of impulsive-compulsive behaviour (ICB) in de novo Parkinson's disease (PD).

METHODS

From a cohort of 1116 subjects from the Parkinson's Progression Marker Initiative database, we created a subcohort of 42 de novo PD without ICB at baseline with available 3T MRI and who developed ICB during follow-up. PD-ICB were matched for age, gender and disease duration to 42 patients with PD without ICB over follow-up (PD-no-ICB) and 42 healthy controls (HCs). Baseline demographic and clinical predictors of ICB were analysed. For the longitudinal neuroimaging analysis, we selected 27 patients with PD-ICB with available neuroimaging after ICB onset, who were matched with 32 PD-no-ICB and 35 HCs. Baseline and longitudinal structural differences were compared using voxel-based morphometry and voxel-based quantification.

RESULTS

People who went on to develop ICB had more severe anxiety, worse autonomic and global cognitive functions and were more likely to have rapid eye movement sleep behaviour disorder. Logistic regression confirmed that worse autonomic and cognitive functions were predictors of ICB. We could not find any morphological feature on baseline MRI that predicted later onset of ICB. When comparing PD groups at follow-up, a small region of increased atrophy in the anterior limb of the left internal capsule adjacent to the head of the left caudate nucleus was found in PD-ICB, but not surviving correction for multiple comparisons.

CONCLUSIONS

Worse autonomic and cognitive functions predict development of ICB at the time of PD diagnosis. Structural imaging fails to identify morphological features associated with the development of ICB.

Putamen volume correlates with obsessive compulsive characteristics in healthy population

Obsessions and compulsions (OCs) are frequent in healthy subjects; however neural backgrounds of the subclinical OCs were largely unknown. Results from recent studies suggested involvement of the putamen in the OC traits. To investigate this issue, 49 healthy subjects were assessed using structural magnetic resonance imaging (MRI) and the Maudsley Obsessive Compulsive Inventory (MOCI). Anatomical delineation on MRI yielded the global volume and local shape of the putamen. Other striatal structures (the caudate nucleus and globus pallidus) were also examined for exploratory purpose. The relationship between volume/shape of each structures and MOCI measure was analyzed, with sex, age, state anxiety, trait anxiety, and full-scale Intelligence Quotient regressed out. The volume analysis revealed a positive relationship between the MOCI total score and the bilateral putamen volumes. The shape analysis demonstrated associations between the higher MOCI total score and hypertrophy of the anterior putamen in both hemispheres. The present study firstly revealed that the volume changes of the putamen correlated with the manifestation of subclinical OC traits. The dysfunctional cortico-anterior striatum networks seemed to be one of the neuronal subsystems underlying the subclinical OC traits.

Abnormal gray matter and white matter volume in 'Internet gaming addicts'

Internet gaming addiction (IGA) is usually defined as the inability of an individual to control his/her use of the Internet with serious negative consequences. It is becoming a prevalent mental health concern around the world. To understand whether Internet gaming addiction contributes to cerebral structural changes, the present study examined the brain gray matter density and white matter density changes in participants suffering IGA using voxel-based morphometric analysis. Compared with the healthy controls (N=36, 22.2 ± 3.13 years), IGA participants (N=35, 22.28 ± 2.54 years) showed significant lower gray matter density in the bilateral inferior frontal gyrus, left cingulate gyrus, insula, right precuneus, and right hippocampus (all p<0.05). IGA participants also showed significant lower white matter density in the inferior frontal gyrus, insula, amygdala, and anterior cingulate than healthy controls (all p<0.05). Previous studies suggest that these brain regions are involved in decision-making, behavioral inhibition and emotional regulation. Current findings might provide insight in understanding the biological underpinnings of IGA.

Neural correlates of sexual cue reactivity in individuals with and without compulsive sexual behaviours

Although compulsive sexual behaviour (CSB) has been conceptualized as a "behavioural" addiction and common or overlapping neural circuits may govern the processing of natural and drug rewards, little is known regarding the responses to sexually explicit materials in individuals with and without CSB. Here, the processing of cues of varying sexual content was assessed in individuals with and without CSB, focusing on neural regions identified in prior studies of drug-cue reactivity. 19 CSB subjects and 19 healthy volunteers were assessed using functional MRI comparing sexually explicit videos with non-sexual exciting videos. Ratings of sexual desire and liking were obtained. Relative to healthy volunteers, CSB subjects had greater desire but similar liking scores in response to the sexually explicit videos. Exposure to sexually explicit cues in CSB compared to non-CSB subjects was associated with activation of the dorsal anterior cingulate, ventral striatum and amygdala. Functional connectivity of the dorsal anterior cingulate-ventral striatum-amygdala network was associated with subjective sexual desire (but not liking) to a greater degree in CSB relative to non-CSB subjects. The dissociation between desire or wanting and liking is consistent with theories of incentive motivation underlying CSB as in drug addictions. Neural differences in the processing of sexual-cue reactivity were identified in CSB subjects in regions previously implicated in drug-cue reactivity studies. The greater engagement of corticostriatal limbic circuitry in CSB following exposure to sexual cues suggests neural mechanisms underlying CSB and potential biological targets for interventions.

A phenotypic structure and neural correlates of compulsive behaviors in adolescents

BACKGROUND

A compulsivity spectrum has been hypothesized to exist across Obsessive-Compulsive disorder (OCD), Eating Disorders (ED), substance abuse (SA) and binge-drinking (BD). The objective was to examine the validity of this compulsivity spectrum, and differentiate it from an externalizing behaviors dimension, but also to look at hypothesized personality and neural correlates.

METHOD

A community-sample of adolescents (N=1938; mean age 14.5 years), and their parents were recruited via high-schools in 8 European study sites. Data on adolescents' psychiatric symptoms, DSM diagnoses (DAWBA) and substance use behaviors (AUDIT and ESPAD) were collected through adolescent- and parent-reported questionnaires and interviews. The phenotypic structure of compulsive behaviors was then tested using structural equation modeling. The model was validated using personality variables (NEO-FFI and TCI), and Voxel-Based Morphometry (VBM) analysis.

RESULTS

Compulsivity symptoms best fit a higher-order two factor model, with ED and OCD loading onto a compulsivity factor, and BD and SA loading onto an externalizing factor, composed also of ADHD and conduct disorder symptoms. The compulsivity construct correlated with neuroticism (r=0.638; p ≤ 0.001), conscientiousness (r=0.171; p ≤ 0.001), and brain gray matter volume in left and right orbitofrontal cortex, right ventral striatum and right dorsolateral prefrontal cortex. The externalizing factor correlated with extraversion (r=0.201; p ≤ 0.001), novelty-seeking (r=0.451; p ≤ 0.001), and negatively with gray matter volume in the left inferior and middle frontal gyri.

CONCLUSIONS

Results suggest that a compulsivity spectrum exists in an adolescent, preclinical sample and accounts for variance in both OCD and ED, but not substance-related behaviors, and can be differentiated from an externalizing spectrum.

White matter abnormalities in skin picking disorder: a diffusion tensor imaging study

Skin picking disorder (SPD) is characterized by the repetitive and compulsive picking of skin, resulting in tissue damage. Neurocognitive findings in SPD implicate difficulty with response inhibition (suppression of pre-potent motor responses). This function is dependent on the integrity of the right frontal gyrus and the anterior cingulate cortices, and white-matter tracts connecting such neural nodes. It was hypothesized that SPD would be associated with reduced fractional anisotropy in regions implicated in top-down response suppression, particularly white-matter tracts in proximity of the bilateral anterior cingulate and right frontal (especially orbitofrontal and inferior frontal) cortices. 13-subjects meeting proposed SPD criteria for DSM-5 free from other current psychiatric comorbidities, and 12 healthy comparison subjects underwent MRI with a 3-T system. Between-group comparisons of imaging data underwent voxelwise analysis with permutation modeling and cluster correction. Fractional anisotropy (measured using diffusion tensor imaging) was the primary outcome measure. Subjects with SPD exhibited significantly reduced fractional anisotropy in tracts distributed bilaterally, which included the anterior cingulate cortices. Fractional anisotropy did not correlate significantly with SPD disease severity, or depressive or anxiety scores. These findings implicate disorganization of white-matter tracts involved in motor generation and suppression in the pathophysiology of SPD, findings remarkably similar to those previously reported in trichotillomania. This study adds considerable support to the notion that-in addition to the phenomenological and comorbid overlap between SPD and trichotillomania-these disorders likely share overlapping neurobiology.

A case of semantic variant primary progressive aphasia with severe insular atrophy

Insular degeneration has been linked to symptoms of frontotemporal dementia (FTD). Presented in this case is a patient exhibiting semantic variant primary progressive aphasia, behavioral disturbance. Upon autopsy, he was found to have severe insular atrophy. In addition, selective serotonin reuptake inhibitors were ineffective in reducing symptoms of obsessive-compulsive behaviors or emotional blunting. This case suggests that Seeley et al.'s (2007 , Alzheimer Disease & Associated Disorders, 21, S50) hypothesis that von Economo neurons and fork cell-rich brain regions, particularly in the insula, are targeted in additional subtypes of FTD beyond the behavioral variant.

Neuroanatomical and cellular substrates of hypergrooming induced by microinjection of oxytocin in central nucleus of amygdala, an experimental model of compulsive behavior

Oxytocin (OT) is a neurosecretory nonapeptide synthesized in hypothalamic cells that project to the neurohypophysis as well as to widely distributed sites in the central nervous system. Central OT microinjections induce a variety of cognitive, sexual, reproductive, grooming and affiliative behaviors in animals. Obsessive-compulsive disorder (OCD) includes a range of cognitive and behavioral symptoms that bear some relationship with OT. Here, we study the neuroanatomical and cellular substrates of the hypergrooming induced by administration of OT in the central nucleus of amygdala (CeA). In this context, this hypergrooming is considered as a model of compulsive behavior. Our data suggest a link between the CeA and the hypothalamic grooming area (HGA). The HGA includes parts of the paraventricular nucleus and the dorsal hypothalamic area. Our data on colocalization of OT (immunohistochemistry for peptide), OT receptor (binding assay) and its retrogradely labeled cells after Fluoro-Gold injection in the CeA suggest that CeA and connections are important substrates of the circuit underlying this OT-dependent compulsive behavioral pattern.

The natural history of temporal variant frontotemporal dementia

BACKGROUND

The temporal variant of frontotemporal dementia (tvFTD) features asymmetric anterior temporal/amygdala degeneration as well as ventromedial frontal, insular, and inferoposterior temporal involvement. Left temporal atrophy has been linked to loss of semantic knowledge, whereas behavioral symptoms dominate the right temporal variant.

OBJECTIVE

To investigate the first symptoms and the timing of subsequent symptoms in patients with left versus right tvFTD.

METHODS

Twenty-six patients with tvFTD were identified. Six had right > left temporal atrophy (right temporal lobe variant [RTLV]) and were matched with six having comparable left > right temporal atrophy (left temporal lobe variant [LTLV]). Clinical records were reviewed to generate individualized symptom chronologies.

RESULTS

In all patients, first symptoms involved semantics (4/6 LTLV, 1/6 RTLV), behavior (4/6 RTLV, 1/6 LTLV), or both (1 LTLV, 1 RTLV). Semantic loss began with anomia, word-finding difficulties, and repetitive speech, whereas the early behavioral syndrome was characterized by emotional distance, irritability, and disruption of physiologic drives (sleep, appetite, libido). After an average of 3 years, patients developed whichever of the two initial syndromes--semantic or behavioral--that they lacked at onset. A third stage, 5 to 7 years from onset, saw the emergence of disinhibition, compulsions, impaired face recognition, altered food preference, and weight gain. Compulsions in LTLV were directed toward visual, nonverbal stimuli, whereas patients with RTLV were drawn to games with words and symbols.

CONCLUSIONS

The temporal variant of frontotemporal dementia follows a characteristic cognitive and behavioral progression that suggests early spread from one anterior temporal lobe to the other. Later symptoms implicate ventromedial frontal, insular, and inferoposterior temporal regions, but their precise anatomic correlates await confirmation.

Striatal volume on magnetic resonance imaging and repetitive behaviors in autism

BACKGROUND

The repetitive behaviors seen in autism phenotypically resemble those seen in obsessive-compulsive disorder (OCD) and Tourette Syndrome (TS), disorders in which structural and functional abnormalities of the basal ganglia (BG) are present and correspond to the severity of repetitive behaviors.

METHODS

Seventeen subjects with autism by DSM-IV and Autism Diagnostic Interview (ADI) and 17 matched controls completed a 1.5 T magnetic resonance image (MRI) of the brain. Two blinded researchers, with good inter-rater reliability, outlined the right and left caudate and putamen. Autistic and control BG volumes covaried for total brain volume were compared using analysis of covariance. BG volumes within the autistic group were correlated with the ADI Repetitive Behavior scores (ADI-C domain).

RESULTS

Right caudate volume controlled for total brain volume was significantly larger in autistic subjects than in controls. In addition, right caudate and total putamen volumes correlated positively with repetitive behavior scores on the ADI-C domain, particularly the higher order OCD-like repetitive behaviors.

CONCLUSIONS

Increased right caudate volume in autism is of interest, since this has also been observed in OCD patients. Increased volume of the right caudate and total putamen positively correlated with greater repetitive behaviors, supporting the hypothesis of BG dysfunction associated with repetitive behaviors in autistic adults.

Utilization behavior as a white matter disconnection syndrome

We report a case of utilization behavior that was examined neuropathologically. A 72-year-old right-handed male patient, who was admitted with a complaint of transient loss of consciousness, displayed utilization behavior several times. He used daily objects that were placed in front of him, such as a teacup and a toothbrush, without instructions to do so. If the examiner asked the patient not to use the objects, the patient did not use them. MRI revealed acute infarction of the left superior frontal gyrus, where decreased blood flow was revealed by SPECT. The patient died of an acute worsening of dilated cardiomyopathy. Neuropathological examination demonstrated an acute phase infarction of the subcortical white matter of the left superior frontal lobe, which correlated well with neuroradiological findings. Utilization behavior has been thought a "frontal lobe symptom". However, we propose that utilization behavior might be considered a white matter disconnection syndrome.

The neuropsychological basis of addictive behaviour

The argument advanced in this review is that drug addiction can be understood in terms of normal learning and memory systems of the brain which, through the actions of chronically self-administered drugs, are pathologically subverted, thereby leading to the establishment of compulsive drug-seeking habits, strengthened by the motivational impact of drug-associated stimuli and occurring at the expense of other sources of reinforcement. We review data from our studies that have utilized procedures which reveal the various influences of pavlovian stimuli on goal-directed behaviour, namely discriminated approach, pavlovian-to-instrumental transfer and conditioned reinforcement, in order to demonstrate their overlapping and also unique neural bases. These fundamental studies are also reviewed in the context of the neural and psychological mechanisms underlying drug-seeking behaviour that is under the control of drug-associated environmental stimuli. The ways in which such drug-seeking behaviour becomes compulsive and habitual, as well as the propensity for relapse to drug-seeking even after long periods of relapse, are discussed in terms of the aberrant learning set in train by the effects of self-administered drugs on plastic processes in limbic cortical-ventral striatal systems.

Addiction, a disease of compulsion and drive: involvement of the orbitofrontal cortex

Understanding the changes in the brain which occur in the transition from normal to addictive behavior has major implications in public health. Here we postulate that while reward circuits (nucleus accumbens, amygdala), which have been central to theories of drug addiction, may be crucial to initiate drug self-administration, the addictive state also involves disruption of circuits involved with compulsive behaviors and with drive. We postulate that intermittent dopaminergic activation of reward circuits secondary to drug self-administration leads to dysfunction of the orbitofrontal cortex via the striato-thalamo-orbitofrontal circuit. This is supported by imaging studies showing that in drug abusers studied during protracted withdrawal, the orbitofrontal cortex is hypoactive in proportion to the levels of dopamine D2 receptors in the striatum. In contrast, when drug abusers are tested shortly after last cocaine use or during drug-induced craving, the orbitofrontal cortex is hypermetabolic in proportion to the intensity of the craving. Because the orbitofrontal cortex is involved with drive and with compulsive repetitive behaviors, its abnormal activation in the addicted subject could explain why compulsive drug self-administration occurs even with tolerance to the pleasurable drug effects and in the presence of adverse reactions. This model implies that pleasure per se is not enough to maintain compulsive drug administration in the drugaddicted subject and that drugs that could interfere with the activation of the striato-thalamo-orbitofrontal circuit could be beneficial in the treatment of drug addiction.

Repetitive and compulsive behavior in frontal lobe degenerations

The authors review the relationship of repetitive behaviors to frontal lobe degenerations and report the repetitive and compulsive behaviors, radiologic imaging findings, and neuropathology of 3 patients with dementia secondary to frontal lobe degeneration. These 3 patients and 78% of 46 proven pathologic cases of frontal lobe degeneration described in the literature demonstrate repetitive behaviors ranging from motor stereotypies to complex obsessive-compulsive disorder. This review suggests that combined damage to the frontal lobe, caudate nucleus, and globus pallidus may account for the repetitive behaviors seen in frontal lobe degenerations, idiopathic obsessive-compulsive disorder, and other neuropsychiatric diseases.

A compulsive movement disorder with cavitation of caudate nucleus

Images

[Transcortical aphasia and echolalia; problems of speech initiative]

Transcortical aphasia accompanied by echolalia occurs with malacias involving the postero-median part of the frontal lobe which includes the supplementary motor field of Penfield and is nourished by the anterior cerebral artery. The syndrome manifests itself in such cases even in fine detials in the same form as does in Pick's atrophy. The same also holds true for cases in which a tumour involves the region mentioned. Sentences or fragments of sentences are echolalised; tendency to perseveration is very marked. It is hardly, if at all, possible to evaluate the verbal understanding of these patients. Analysis of their behaviour supports the assumption that they have not lost the adaptation to some situations. Echolalia is often associated with forced grasping and other compulsory phenomena. Therefore, it may be interpreted as a sign of disinhibition of the acusticomotor reflex present during the development of the speech. Competition between the intentionality and the appearance of compulsory phenomena greatly depends on the general condition of the patient, particularly on the clarity of consciousness. The integrity of the postero-median part of the frontal lobe is indespensable for a normal reaction by speech to stimuli received from the sensory areas. The influence of the supplementary motor field on speech intention seems to be linked to the dominant hemisphere. In case lesions of the territory of the anterior cerebral artery and the cortico-bulbar neuron system are coexisting in the dominant hemisphere, the speech disturbance shifts to complete motor aphasia. In such cases the pathomechanism is analogous to that of the syndrome of Liepmann, i.e., right-sided hemiparesis with left-sided apraxia. So-called transcortical motor aphasia without echolalia can be caused by loss of stimuli from the sensory fields.