Stress and reward processing in bipolar disorder: a functional magnetic resonance imaging study.

OBJECTIVES: A link between negative life stress and the onset of mood episodes in bipolar disorder (BD) has been established, but processes underlying such a link remain unclear. Growing evidence suggests that stress can negatively affect reward processing and related neurobiological substrates, indicating that a dysregulated reward system may provide a partial explanation. The aim of this study was to test the impact of stress on reward-related neural functioning in BD. METHODS: Thirteen euthymic or mildly depressed individuals with BD and 15 controls performed a Monetary Incentive Delay (MID) task while undergoing functional magnetic resonance imaging during no-stress and stress (negative psychosocial stressor involving poor performance feedback and threat of monetary deductions) conditions. RESULTS: In hypothesis-driven region-of-interest analyses, a significant group-by-condition interaction emerged in the amygdala during reward anticipation. Relative to controls, while anticipating a potential reward, subjects with BD were characterized by amygdalar hyperactivation in the no-stress condition but hypoactivation during stress. Moreover, relative to controls, subjects with BD had significantly larger amygdala volumes. After controlling for structural differences, the effects of stress on amygdalar function remained, whereas groups no longer differed during the no-stress condition. During reward consumption, a group-by-condition interaction emerged in the putamen due to increased putamen activation in response to rewards in participants with BD during stress, but an opposite pattern in controls. CONCLUSIONS: Overall, findings highlight possible impairments in using reward-predicting cues to adaptively engage in goal-directed actions in BD, combined with stress-induced hypersensitivity to reward consumption. Potential clinical implications are discussed.

Neuronal dysfunction and disconnection of cortical hubs in non-demented subjects with elevated amyloid burden.

Disruption of functional connectivity between brain regions may represent an early functional consequence of ß-amyloid pathology prior to clinical Alzheimer's disease. We aimed to investigate if non-demented older individuals with increased amyloid burden demonstrate disruptions of functional whole-brain connectivity in cortical hubs (brain regions typically highly connected to multiple other brain areas) and if these disruptions are associated with neuronal dysfunction as measured with fluorodeoxyglucose-positron emission tomography. In healthy subjects without cognitive symptoms and patients with mild cognitive impairment, we used positron emission tomography to assess amyloid burden and cerebral glucose metabolism, structural magnetic resonance imaging to quantify atrophy and novel resting state functional magnetic resonance imaging processing methods to calculate whole-brain connectivity. Significant disruptions of whole-brain connectivity were found in amyloid-positive patients with mild cognitive impairment in typical cortical hubs (posterior cingulate cortex/precuneus), strongly overlapping with regional hypometabolism. Subtle connectivity disruptions and hypometabolism were already present in amyloid-positive asymptomatic subjects. Voxel-based morphometry measures indicate that these findings were not solely a consequence of regional atrophy. Whole-brain connectivity values and metabolism showed a positive correlation with each other and a negative correlation with amyloid burden. These results indicate that disruption of functional connectivity and hypometabolism may represent early functional consequences of emerging molecular Alzheimer's disease pathology, evolving prior to clinical onset of dementia. The spatial overlap between hypometabolism and disruption of connectivity in cortical hubs points to a particular susceptibility of these regions to early Alzheimer's-type neurodegeneration and may reflect a link between synaptic dysfunction and functional disconnection.

Reliability of functional magnetic resonance imaging associative encoding memory paradigms in non-demented elderly adults.

Functional magnetic resonance imaging (fMRI) holds significant potential to aid in the development of early interventions to improve memory function, and to assess longitudinal change in memory systems in aging and early Alzheimer's disease (AD). However, the test-retest reliability of hippocampal activation and of "beneficial" deactivation in the precuneus has yet to be fully established during memory encoding tasks in older subjects. Using a mixed block and event-related face-name associative encoding paradigm, we assessed the reliability of hippocampal activation and default network deactivation over a 4- to 6-week interscan interval in 27 older individuals who were cognitively normal [Clinical Dementia Rating (CDR) Scale = 0; n = 18] or mildly impaired (CDR = 0.5; n = 9). Reliability was assessed in whole brain maps and regions of interest using both a full-task paradigm of six functional runs as well as an abbreviated paradigm of the first two functional runs, which would be advantageous for use in clinical trials. We found reliable hippocampal signal response across both block- and event-related designs in the right hippocampus. Comparable reliability in hippocampal activation was found in the full and the abbreviated paradigm. Similar reliability in hippocampal activation was observed across both CDR groups overall, but the CDR 0.5 group was more variable in left hippocampal activity. Task-related deactivation in the precuneus demonstrated much greater variability than hippocampal activation in all analyses. Overall, these results are encouraging for the utility of fMRI in "Proof of Concept" clinical trials investigating the efficacy of potentially therapeutic agents for treatment of age-related memory changes, cognitive impairment, and early AD.

Minute effects of sex on the aging brain: a multisample magnetic resonance imaging study of healthy aging and Alzheimer's disease.

Age is associated with substantial macrostructural brain changes. While some recent magnetic resonance imaging studies have reported larger age effects in men than women, others find no sex differences. As brain morphometry is a potentially important tool in diagnosis and monitoring of age-related neurological diseases, e.g., Alzheimer's disease (AD), it is important to know whether sex influences brain aging. We analyzed cross-sectional magnetic resonance scans from 1143 healthy participants from seven subsamples provided by four independent research groups. In addition, 96 patients with mild AD were included. Estimates of cortical thickness continuously across the brain surface, as well as volume of 17 subcortical structures, were obtained by use of automated segmentation tools (FreeSurfer). In the healthy participants, no differences in aging slopes between women and men were found in any part of the cortex. Pallidum corrected for intracranial volume showed slightly higher age correlations for men. The analyses were repeated in each of the seven subsamples, and the lack of age x sex interactions was largely replicated. Analyses of the AD sample showed no interactions between sex and age for any brain region. We conclude that sex has negligible effects on the age slope of brain volumes both in healthy participants and in AD.

High consistency of regional cortical thinning in aging across multiple samples.

Cross-sectional magnetic resonance imaging (MRI) studies of cortical thickness and volume have shown age effects on large areas, but there are substantial discrepancies across studies regarding the localization and magnitude of effects. These discrepancies hinder understanding of effects of aging on brain morphometry, and limit the potential usefulness of MR in research on healthy and pathological age-related brain changes. The present study was undertaken to overcome this problem by assessing the consistency of age effects on cortical thickness across 6 different samples with a total of 883 participants. A surface-based segmentation procedure (FreeSurfer) was used to calculate cortical thickness continuously across the brain surface. The results showed consistent age effects across samples in the superior, middle, and inferior frontal gyri, superior and middle temporal gyri, precuneus, inferior and superior parietal cortices, fusiform and lingual gyri, and the temporo-parietal junction. The strongest effects were seen in the superior and inferior frontal gyri, as well as superior parts of the temporal lobe. The inferior temporal lobe and anterior cingulate cortices were relatively less affected by age. The results are discussed in relation to leading theories of cognitive aging.

Brain-performance correlates of working memory retrieval in schizophrenia: a cognitive modeling approach.

Correlations of cognitive functioning with brain activation during a sternberg item recognition paradigm (SIRP) were investigated in patients with schizophrenia and in healthy controls studied at 8 sites. To measure memory scanning times, 4 response time models were fit to SIRP data. The best fitting model assumed exhaustive serial memory scanning followed by self-terminating memory search and involved one intercept parameter to represent SIRP processes not contributing directly to memory scanning. Patients displayed significantly longer response times with increasing memory load and differed on the memory scanning, memory search, and intercept parameters of the best fitting probability model. Groups differed in the correlation between the memory scanning parameter and linear brain response to increasing memory load within left inferior and left middle frontal gyrus, bilateral caudate, and right precuneus. The pattern of findings in these regions indicated that high scanning capacity was associated with high neural capacity among healthy subjects but that scanning speed was uncoupled from brain response to increasing memory load among schizophrenia patients. Group differences in correlation of the best fitting model's scanning parameter with a quadratic trend in brain response to increasing memory load suggested inefficient or disordered patterns of neural inhibition among individuals with schizophrenia, especially in the left perirhinal and entorhinal cortices. The results show at both cognitive and neural levels that disordered memory scanning contributes to deficient SIRP performance among schizophrenia patients.

Cerebral cortex and the clinical expression of Huntington's disease: complexity and heterogeneity.

The clinical phenotype of Huntington's disease (HD) is far more complex and variable than depictions of it as a progressive movement disorder dominated by neostriatal pathology represent. The availability of novel neuro-imaging methods has enabled us to evaluate cerebral cortical changes in HD, which we have found to occur early and to be topographically selective. What is less clear, however, is how these changes influence the clinical expression of the disease. In this study, we used a high-resolution surface based analysis of in vivo MRI data to measure cortical thickness in 33 individuals with HD, spanning the spectrum of disease and 22 age- and sex-matched controls. We found close relationships between specific functional and cognitive measures and topologically specific cortical regions. We also found that distinct motor phenotypes were associated with discrete patterns of cortical thinning. The selective topographical associations of cortical thinning with clinical features of HD suggest that we are not simply correlating global worsening with global cortical degeneration. Our results indicate that cortical involvement contributes to important symptoms, including those that have been ascribed primarily to the striatum, and that topologically selective changes in the cortex might explain much of the clinical heterogeneity found in HD. Additionally, a significant association between regional cortical thinning and total functional capacity, currently the leading primary outcome measure used in neuroprotection trials for HD, establishes cortical MRI morphometry as a potential biomarker of disease progression.

The relationship between diffusion tensor imaging and volumetry as measures of white matter properties.

There is still limited knowledge about the relationship between different structural brain parameters, despite huge progress in analysis of neuroimaging data. The aim of the present study was to test the relationship between fractional anisotropy (FA) from diffusion tensor imaging (DTI) and regional white matter (WM) volume. As WM volume has been shown to develop until middle age, the focus was on changes in WM properties in the age range of 40 to 60 years. 100 participants were scanned with magnetic resonance imaging (MRI). Each hemisphere was parcellated into 35 WM regions, and volume, FA, axial, and radial diffusion in each region were calculated. The relationships between age and the regional measures of FA and WM volume were tested, and then FA and WM volume were correlated, corrected for intracranial volume, age, and sex. WM volume was weakly related to age, while FA correlated negatively with age in 26 of 70 regions, caused by a mix of reduced axial and increased radial diffusion with age. 23 relationships between FA and WM volume were found, with seven being positive and sixteen negative. The positive correlations were mainly caused by increased radial diffusion. It is concluded that FA is more sensitive than volume to changes in WM integrity during middle age, and that FA-age correlations probably are related to reduced amount of myelin with increasing age. Further, FA and WM volume are moderately to weakly related and to a large extent sensitive to different characteristics of WM integrity.

Consistent neuroanatomical age-related volume differences across multiple samples.

Magnetic resonance imaging (MRI) is the principal method for studying structural age-related brain changes in vivo. However, previous research has yielded inconsistent results, precluding understanding of structural changes of the aging brain. This inconsistency is due to methodological differences and/or different aging patterns across samples. To overcome these problems, we tested age effects on 17 different neuroanatomical structures and total brain volume across five samples, of which one was split to further investigate consistency (883 participants). Widespread age-related volume differences were seen consistently across samples. In four of the five samples, all structures, except the brainstem, showed age-related volume differences. The strongest and most consistent effects were found for cerebral cortex, pallidum, putamen and accumbens volume. Total brain volume, cerebral white matter, caudate, hippocampus and the ventricles consistently showed non-linear age functions. Healthy aging appears associated with more widespread and consistent age-related neuroanatomical volume differences than previously believed.

Remifentanil administration reveals biphasic phMRI temporal responses in rat consistent with dynamic receptor regulation.

Many pharmacological stimuli influence multiple neurotransmitter systems in the brain, and the dynamics of the functional brain response can vary regionally. In this study, the temporal response of cerebral blood volume (CBV) was employed to spatially segment cerebral effects due to infusion of a potent mu-opioid receptor agonist. Repeated intravenous injection of 10 mug/kg remifentanil in rats caused reproducible regional positive, negative, and biphasic changes in CBV. Three temporal processes were identified in the cerebral response and analyzed within the framework of the general linear model. Firstly, a slow component identified CBV changes that were almost exclusively negative, and the spatial distribution was similar to the inhibition produced by morphine (200 microg/kg). The largest CBV reductions occurred in caudate, accumbens, ventral hippocampus, cingulate, and piriform cortex. Secondly, a more rapid temporal component corresponded primarily with a regional distribution of positive changes in CBV consistent with GABAergic inhibition of hippocampal interneurons and associated projections. Thirdly, a response with the dynamics of mean arterial blood pressure correlated positively with CBV changes in hypothalamus, consistent with a central mechanism for control of blood pressure. We propose that the dominant source of the temporal variance in signal is dynamic modulation of drug targets by receptor endocytosis, an established effect in vitro. These results suggest that the temporal response of fMRI signal reflects underlying neurobiological processes, so that temporal decomposition strategies may aid interpretation of pharmacological mechanisms by identifying interconnected regions or those associated with common neural targets and processes.

Fear fosters flight: a mechanism for fear contagion when perceiving emotion expressed by a whole body.

Darwin regarded emotions as predispositions to act adaptively, thereby suggesting that characteristic body movements are associated with each emotional state. To this date, investigations of emotional cognition have predominantly concentrated on processes associated with viewing facial expressions. However, expressive body movements may be just as important for understanding the neurobiology of emotional behavior. Here, we used functional MRI to clarify how the brain recognizes happiness or fear expressed by a whole body. Our results indicate that observing fearful body expressions produces increased activity in brain areas narrowly associated with emotional processes and that this emotion-related activity occurs together with activation of areas linked with representation of action and movement. The mechanism of fear contagion hereby suggested may automatically prepare the brain for action.

Vascular responses to syntactic processing: event-related fMRI study of relative clauses.

Event-related functional magnetic resonance imaging was used to investigate the localization of syntactic processing in sentence comprehension. Matched pairs of sentences containing identical lexical items were compared. One member of the pair consisted of a syntactically simpler sentence, containing a subject relativized clause. The second member of the pair consisted of a syntactically more complex sentence, containing an object relativized clause. Ten subjects made plausibility judgments about the sentences, which were presented one word at a time on a computer screen. There was an increase in BOLD hemodynamic signal in response to the presentation of all sentences compared to fixation in both right and left occipital cortex, the left perisylvian cortex, and the left premotor and motor areas. BOLD signal increased in the left angular gyrus when subjects processed the complex portion of syntactically more complex sentences. This study shows that a hemodynamic response associated with processing the syntactically complex portions of a sentence can be localized to one part of the dominant perisylvian association cortex.