A principal component network analysis of prefrontal-limbic functional magnetic resonance imaging time series in schizophrenia patients and healthy controls

We investigated neural regulation of emotional arousal. We hypothesized that the interactions between the components of the prefrontal-limbic system determine the global trajectories of the individual's brain activation, with the strengths and modulations of these interactions being potentially key components underlying the differences between healthy individuals and those with schizophrenia. Using affect-valent facial stimuli presented to 11 medicated schizophrenia patients and 65 healthy controls, we activated neural regions associated with the emotional arousal response during functional magnetic resonance imaging (fMRI). Performing first a random effects analysis of the fMRI data to identify activated regions, we obtained 352 data-point time series for six brain regions: bilateral amygdala, hippocampus and two prefrontal regions (Brodmann Areas 9 and 45). Since standard statistical methods are not designed to capture system features and evolution, we used principal component analyses on two types of pre-processed data: contrasts and group averages. We captured an important characteristic of the evolution of our six-dimensional brain network: all subject trajectories are almost embedded in a two-dimensional plane. Moreover, the direction of the largest principal component was a significant differentiator between the control and patient populations: the left and right amygdala coefficients were substantially higher in the case of patients, and the coefficients of Brodmann Area 9 were, to a lesser extent, higher in controls. These results are evidence that modulations between the regions of interest are the important determinant factors for the system's dynamical behavior. We place our results within the context of other principal component analyses used in neuroimaging, as well as of our existing theoretical model of prefrontal-limbic dysregulation.

Variation in orbitofrontal cortex volume: relation to sex, emotion regulation and affect

Sex differences in brain structure have been examined extensively but are not completely understood, especially in relation to possible functional correlates. Our two aims in this study were to investigate sex differences in brain structure, and to investigate a possible relation between orbitofrontal cortex subregions and affective individual differences. We used tensor-based morphometry to estimate local brain volume from MPRAGE images in 117 healthy right-handed adults (58 female), age 18-40 years. We entered estimates of local brain volume as the dependent variable in a GLM, controlling for age, intelligence and whole-brain volume. Men had larger left planum temporale. Women had larger ventromedial prefrontal cortex (vmPFC), right lateral orbitofrontal (rlOFC), cerebellum, and bilateral basal ganglia and nearby white matter. vmPFC but not rlOFC volume covaried with self-reported emotion regulation strategies (reappraisal, suppression), expressivity of positive emotions (but not of negative), strength of emotional impulses, and cognitive but not somatic anxiety. vmPFC volume statistically mediated sex differences in emotion suppression. The results confirm prior reports of sex differences in orbitofrontal cortex structure, and are the first to show that normal variation in vmPFC volume is systematically related to emotion regulation and affective individual differences.

Tracking the emergence of conceptual knowledge during human decision making

Concepts lie at the very heart of intelligence, providing organizing principles with which to comprehend the world. Surprisingly little, however, is understood about how we acquire and deploy concepts. Here, we show that a functionally coupled circuit involving the hippocampus and ventromedial prefrontal cortex (vMPFC) underpins the emergence of conceptual knowledge and its effect on choice behavior. Critically, the hippocampus alone supported the efficient transfer of knowledge to a perceptually novel setting. These findings provide compelling evidence that the hippocampus supports conceptual learning through the networking of discrete memories and reveal the nature of its interaction with downstream valuation modules such as the vMPFC. Our study offers neurobiological insights into the remarkable capacity of humans to discover the conceptual structure of related experiences and use this knowledge to solve exacting decision problems.

Developmental effects of aggressive behavior in male adolescents assessed with structural and functional brain imaging

Aggressive behavior is common during adolescence. Although aggression-related functional changes in the ventromedial prefrontal cortex (vmPFC) and frontopolar cortex (FPC) have been reported in adults, the neural correlates of aggressive behavior in adolescents, particularly in the context of structural neurodevelopment, are obscure. We used functional and structural magnetic resonance imaging (MRI) to measure the blood oxygenation level-depended signal and cortical thickness. In a block-designed experiment, 14-17-year old adolescents imagined aggressive and non-aggressive interactions with a peer. We show reduced vmPFC activation associated with imagined aggressive behavior as well as enhanced aggression-related activation and cortical thinning in the FPC with increasing age. Changes in FPC activation were also associated with judgments of the severity of aggressive acts. Reduced vmPFC activation was associated with greater aggression indicating its normal function is to exert inhibitory control over aggressive impulses. Concurrent FPC activation likely reflects foresight of harmful consequences that result from aggressive acts. The correlation of age-dependent activation changes and cortical thinning demonstrates ongoing maturation of the FPC during adolescence towards a refinement of social and cognitive information processing that can potentially facilitate mature social behavior in aggressive contexts.

Altered prefrontal lobe oxygenation in bipolar disorder: a study by near-infrared spectroscopy

BACKGROUND

Previous studies have reported prefrontal cortex (PFC) pathophysiology in bipolar disorder.

METHOD

We examined the hemodynamics of the PFC during resting and cognitive tasks in 29 patients with bipolar disorder and 27 healthy controls, matched for age, verbal abilities and education. The cognitive test battery consisted of letter and category fluency (LF and CF), Sets A and B of the Raven's Colored Progressive Matrices (RCPM-A and RCPM-B) and the letter cancellation test (LCT). The tissue oxygenation index (TOI), the ratio of oxygenated hemoglobin (HbO2) concentration to total hemoglobin concentration, was measured in the bilateral PFC by spatially resolved near-infrared spectroscopy. Changes in HbO2 concentration were also measured.

RESULTS

The bipolar group showed slight but significant impairment in performance for the non-verbal tasks (RCPM-A, RCPM-B and LCT), with no significant between-group differences for the two verbal tasks (LF and CF). A group x task x hemisphere analysis of variance (ANOVA) on the TOI revealed an abnormal pattern of prefrontal oxygenation across different types of cognitive processing in the bipolar group. Post hoc analyses following a group x task x hemisphere ANOVA on HbO2 concentration revealed that the bipolar group showed a greater increase in HbO2 concentration in the LCT and in RCPM-B, relative to controls.

CONCLUSIONS

Both indices of cortical activation (TOI and HbO2 concentration) indicated a discrepancy in the PFC function between verbal versus non-verbal processing, indicating task-specific abnormalities in the hemodynamic control of the PFC in bipolar disorder.

Illuminating the black box: investigating prefrontal cortical hemodynamics during exercise with near-infrared spectroscopy

Near-infrared spectroscopy (NIRS) presents an appealing option for investigating hemodynamic changes in the cerebral cortex during exercise. This review examines the physical basis of NIRS and the types of available instruments. Emphasis is placed on the physiological interpretation of NIRS signals. Theories from affective neuroscience and exercise psychobiology, including Davidson's prefrontal asymmetry hypothesis, Dietrich's transient hypofrontality hypothesis, and Ekkekakis's dual-mode model, are reviewed, highlighting the potential for designing NIRS-based tests in the context of exercise. Findings from 28 studies involving acute bouts of exercise are summarized. These studies suggest that the oxygenation of the prefrontal cortex increases during mild-to-moderate exercise and decreases during strenuous exercise, possibly proximally to the respiratory compensation threshold. Future studies designed to test hypotheses informed by psychological theories should help elucidate the significance of these changes for such important concepts as cognition, affect, exertion, and central fatigue.

Training improves multitasking performance by increasing the speed of information processing in human prefrontal cortex

Our ability to multitask is severely limited: task performance deteriorates when we attempt to undertake two or more tasks simultaneously. Remarkably, extensive training can greatly reduce such multitasking costs. While it is not known how training alters the brain to solve the multitasking problem, it likely involves the prefrontal cortex given this brain region's purported role in limiting multitasking performance. Here, we show that the reduction of multitasking interference with training is not achieved by diverting the flow of information processing away from the prefrontal cortex or by segregating prefrontal cells into independent task-specific neuronal ensembles, but rather by increasing the speed of information processing in this brain region, thereby allowing multiple tasks to be processed in rapid succession. These results not only reveal how training leads to efficient multitasking, they also provide a mechanistic account of multitasking limitations, namely the poor speed of information processing in human prefrontal cortex.

Changes after behavior therapy among responsive and nonresponsive patients with obsessive-compulsive disorder

Neuroimaging studies have suggested that behavior therapy (BT) might change abnormal activity in the frontal-subcortical circuits of the brain in patients with obsessive-compulsive disorder (OCD). However, the results of these studies have been rather inconsistent. The aim of the present study was to use statistical parametric mapping (SPM) analysis to explore the effects of successful BT on regional cerebral blood flow (rCBF) in patients with OCD. Forty-five OCD patients who were treatment-resistant to a single serotonin reuptake inhibitor (SRI) trial were examined. Single photon emission computed tomography (SPECT) using 99mTc-ECD was performed before and after the completion of 12 weeks of BT. Although no significant differences in pre-treatment rCBF were observed between responders and nonresponders to BT, the post-treatment rCBF values in the left medial prefrontal cortex (Brodmann area 10) and bilateral middle frontal gyri (Brodmann area 10) were significantly lower in the responders than in the nonresponders. Furthermore, the baseline rCBF in the bilateral orbitofrontal cortex (OFC) was significantly correlated with the change in the Y-BOCS score among the responders. Our results support the hypothesis that while the OFC may be associated with the BT response, BT may result in changes in rCBF in the medial and middle frontal cortex.

Comparing the bird in the hand with the ones in the bush

In this issue of Neuron, Boorman and colleagues shed new light on the roles of lateral frontopolar and ventromedial prefrontal cortices in task switching and decision making.

Hemispheric differences in frontal and parietal influences on human occipital cortex: direct confirmation with concurrent TMS-fMRI

We used concurrent TMS-fMRI to test directly for hemispheric differences in causal influences of the right or left fronto-parietal cortex on activity (BOLD signal) in the human occipital cortex. Clinical data and some behavioral TMS studies have been taken to suggest right-hemisphere specialization for top-down modulation of vision in humans, based on deficits such as spatial neglect or extinction in lesioned patients, or findings that TMS to right (vs. left) fronto-parietal structures can elicit stronger effects on visual performance. But prior to the recent advent of concurrent TMS and neuroimaging, it was not possible to directly examine the causal impact of one (stimulated) brain region upon others in humans. Here we stimulated the frontal or intraparietal cortex in the left or right hemisphere with TMS, inside an MR scanner, while measuring with fMRI any resulting BOLD signal changes in visual areas V1-V4 and V5/MT+. For both frontal and parietal stimulation, we found clear differences between effects of right- versus left-hemisphere TMS on activity in the visual cortex, with all differences significant in direct statistical comparisons. Frontal TMS over either hemisphere elicited similar BOLD decreases for central visual field representations in V1-V4, but only right frontal TMS led to BOLD increases for peripheral field representations in these regions. Hemispheric differences for effects of parietal TMS were even more marked: Right parietal TMS led to strong BOLD changes in V1-V4 and V5/MT+, but left parietal TMS did not. These data directly confirm that the human frontal and parietal cortex show right-hemisphere specialization for causal influences on the visual cortex.

Endogenous testosterone levels are associated with amygdala and ventromedial prefrontal cortex responses to anger faces in men but not women

Testosterone moderates behavioral and physiological responses to the emotion anger. However, little is known about the effects of testosterone in the human brain in the context of the perception of anger. We used fMRI to measure BOLD responses to anger faces in the amygdala and ventromedial prefrontal cortex (vmPFC) as a function of endogenous testosterone levels in 24 participants (10 men). In one task, participants passively viewed anger faces and neutral faces and in another task, participants engaged in an oddball task while viewing anger and neutral faces. Men's, but not women's, amygdala BOLD response to anger faces was negatively correlated with their endogenous testosterone levels in both tasks. Men's, but not women's, vmPFC BOLD response to anger faces was positively correlated with their endogenous testosterone levels in the passive-viewing task. In men, amygdala and vmPFC BOLD responses to anger faces were negatively associated. Our results extend past research by documenting associations between endogenous testosterone levels and BOLD responses to anger faces in the amygdala and vmPFC in men, and our results also support research that documents negative associations between amygdala and vmPFC activity.

Association between sigma-1 receptor gene polymorphism and prefrontal hemodynamic response induced by cognitive activation in schizophrenia

The molecular biological role of the sigma-1 receptor (Sig-1R) has attracted much attention. Evidence suggests that the Sig-1R engaged in modulating NMDA and dopamine receptors is involved in the pathophysiology of schizophrenia and the mechanism of psychotropic drug efficacy. However, whether the Sig-1R genotype affects brain function in schizophrenia in vivo remains unknown. We investigated the association between Sig-1R functional polymorphism (Gln2Pro) and brain function in schizophrenia. The subjects were 40 patients with schizophrenia and 60 healthy controls, all right-handed, who gave written informed consent to participate. Signals, detected from prefrontal regions by 52-channel near-infrared spectroscopy (NIRS) during cognitive activation, were compared between two Sig1-R genotype subgroups (Gln/Gln individuals and Pro carriers) matched for age, gender, premorbid IQ and task performance. The prefrontal hemodynamic response of healthy controls during the verbal fluency task was higher than that of patients with schizophrenia. For the patients with schizophrenia, even after controlling the effect of medication, the [oxy-Hb] increase in the prefrontal cortex of the Gln/Gln genotype group was significantly greater than that of the Pro carriers (false discovery rate corrected p<0.05). Clinical symptoms were not significantly different between the two Sig-1R genotype subgroups. These differences were not significant in the healthy controls. This is the first functional imaging genetics study that implicated the association between Sig-1R genotype and prefrontal cortical function in schizophrenia in vivo. Our findings also suggest that the prefrontal hemodynamic response assessed by noninvasive and less demanding NIRS is a useful intermediate phenotype for translational research in schizophrenia.

The neural correlates of third-party punishment

Legal decision-making in criminal contexts includes two essential functions performed by impartial "third parties:" assessing responsibility and determining an appropriate punishment. To explore the neural underpinnings of these processes, we scanned subjects with fMRI while they determined the appropriate punishment for crimes that varied in perpetrator responsibility and crime severity. Activity within regions linked to affective processing (amygdala, medial prefrontal and posterior cingulate cortex) predicted punishment magnitude for a range of criminal scenarios. By contrast, activity in right dorsolateral prefrontal cortex distinguished between scenarios on the basis of criminal responsibility, suggesting that it plays a key role in third-party punishment. The same prefrontal region has previously been shown to be involved in punishing unfair economic behavior in two-party interactions, raising the possibility that the cognitive processes supporting third-party legal decision-making and second-party economic norm enforcement may be supported by a common neural mechanism in human prefrontal cortex.

Increased hippocampal, thalamic, and prefrontal hemodynamic response to an urban noise stimulus in schizophrenia

OBJECTIVE

People with schizophrenia often have difficulty ignoring unimportant noises in the environment. While experimental measures of sensory gating have yielded insight into neurobiological mechanisms related to this deficit, the degree to which these measures reflect the real-world experience of people with schizophrenia is unknown. The goal of this study was to develop a clinically relevant sensory gating paradigm and to assess differences in brain hemodynamic responses during the task in schizophrenia.

METHOD

Thirty-five participants, including 18 outpatients with schizophrenia and 17 healthy comparison subjects, underwent scanning on a 3-T MR system while passively listening to an "urban white noise" stimulus, a mixture of common sounds simulating a busy urban setting, including multiple conversations and events recorded from a neighborhood gathering, music, and talk radio. P50 evoked responses from a typical paired-click sensory gating task also were measured.

RESULTS

Listening to the urban white noise stimulus produced robust activation of the auditory pathway in all participants. Activation was observed in the bilateral primary and secondary auditory cortices, medial geniculate nuclei, and inferior colliculus. Greater activation was observed in the schizophrenia patients relative to the comparison subjects in the hippocampus, thalamus, and prefrontal cortex. Higher P50 test/conditioning ratios also were observed in the schizophrenia patients. These evoked responses correlated with hemodynamic responses in the hippocampus and the prefrontal cortex.

CONCLUSIONS

The finding of greater activation of the hippocampus, thalamus, and prefrontal cortex during a sensory gating task with high face validity further supports the involvement of these brain regions in gating deficits in schizophrenia. This link is strengthened by the observed correlation between evoked responses in the paired-click paradigm and hemodynamic responses in a functional MRI sensory gating paradigm.

Re-evaluating dorsolateral prefrontal cortex activation during working memory in schizophrenia

Previous neuroimaging studies of working memory (WM) in schizophrenia have generated conflicting findings of hypo- and hyper-frontality, discrepancies potentially driven by differences in task difficulty and/or performance. This study proposes and tests a new model of the performance-activation relationship in schizophrenia by combining changes by load with overall individual differences in performance. Fourteen patients with recent-onset schizophrenia and eighteen controls underwent functional magnetic resonance imaging while performing a parametric verbal WM task. Group level differences followed a linear "cross-over" pattern, such that in controls, activation in the dorsolateral prefrontal cortex (DLPFC) increased as performance decreased, while patients showed the opposite. Overall, low performing patients were hypoactive and high performing patients hyperactive relative to controls. However, patients and controls showed similar functions of activation by load in which activation rises with task difficulty but levels off or slightly decreases at higher loads. Moreover, across all loads and at their own WM capacity, higher performing patients showed greater DLPFC activation than controls, while lower performing patients activated least. This study establishes a novel framework for predicting the relationship between functional activation and WM performance by combining changes of activation by WM load occurring within each subject with the overall differences in activation associated with general WM performance. Essentially, increasing task difficulty correlates asymptotically with increasing activation in all subjects, but depending on their behavioral performance, patients show overall hyper- versus hypofrontality, a pattern potentially derived from individual differences in underlying cellular changes that may relate to levels of functional disability.

An exploratory study of the neural mechanisms of decision making in compulsive hoarding

BACKGROUND

Prior studies have suggested unique patterns of neural activity associated with compulsive hoarding. However, to date no studies have examined the process of making actual decisions about whether to keep or discard possessions in patients with hoarding symptoms. An increasing body of clinical data and experimental psychopathology research suggests that hoarding is associated with impaired decision making; therefore, it is important to understand the neural underpinnings of decision-making abnormalities in hoarding patients.

METHOD

Twelve adult patients diagnosed with compulsive hoarding, 17% of whom also met criteria for obsessive-compulsive disorder (OCD), and 12 matched healthy controls underwent functional magnetic resonance imaging (fMRI) while making decisions about whether or not to discard personal paper items (e.g. junk mail) brought to the laboratory as well as control items that did not belong to them. Items were either saved or destroyed following each decision.

RESULTS

When deciding about whether to keep or discard personal possessions, compulsive hoarding participants displayed excessive hemodynamic activity in lateral orbitofrontal cortex and parahippocampal gyrus. Among hoarding participants, decisions to keep personal possessions were associated with greater activity in superior temporal gyrus, middle temporal gyrus, medial frontal gyrus, anterior cingulate cortex, precentral gyrus, and cerebellum than were decisions to discard personal possessions.

CONCLUSIONS

These results provide partial support for an emerging model of compulsive hoarding based on complications of the decision-making process. They also suggest that compulsive hoarding may be characterized by focal deficits in the processing of reward and changes in reward contingencies, particularly when these are perceived to be punishing.

An fMRI study of working memory in first-degree unaffected relatives of schizophrenia patients

Identifying intermediate phenotypes of genetically complex psychiatric illnesses such as schizophrenia is important. First-degree relatives of persons with schizophrenia have increased genetic risk for the disorder and tend to show deficits on working memory (WM) tasks. An open question is the relationship between such behavioral endophenotypes and the corresponding brain activation patterns revealed during functional imaging. We measured task performance during a Sternberg WM task and used functional magnetic resonance imaging (fMRI) to assess whether 23 non-affected first-degree relatives showed altered performance and functional activation compared to 43 matched healthy controls. We predicted that a significant proportion of unaffected first-degree relatives would show either aberrant task performance and/or abnormal related fMRI blood oxygen level dependent (BOLD) patterns. While task performance in the relatives was not different than that of controls they were significantly slower in responding to probes., Schizophrenia relatives displayed reduced activation, most markedly in bilateral dorsolateral/ventrolateral (DLPFC/VLPFC) prefrontal and posterior parietal cortex when encoding stimuli and in bilateral DLPFC and parietal areas during response selection. Additionally, fMRI differences in both conditions were modulated by load, with a parametric increase in between-group differences with load in several key regions during encoding and an opposite effect during response selection.

Deficit of pericapillary oligodendrocytes in the prefrontal cortex in schizophrenia

OBJECTIVE

Our previous studies have shown a significant decrease of numerical density of oligodendrocytes in the prefrontal cortex in postmortem schizophrenic brains. Deficit of oligodendrocytes was associated with loss of oligodendroglial satellites of pyramidal neurons. In this study we tested the hypothesis that there might be a deficit and loss of pericapillary oligodendrocytes in the prefrontal cortex in schizophrenia.

METHOD

Autopsy samples from the prefrontal cortex (BA 10) were obtained from 12 normal controls and 12 chronic schizophrenic cases. Capillaries and oligodendrocytes were viewed in paraffin sections stained with a Luxol-fast blue and cresyl violet. Electron microscopy was applied to study the ultrastructure of oligodendrocytes. For morphometric analysis, an average of 100 rectilinear capillary segments from layer V was sampled for each individual. The number of oligodendrocytes visible along rectilinear segments was expressed as the number of oligodendrocytes per 0.01 mm of capillary length.

RESULTS

Subjects with schizophrenia had a significantly lower (-23%; P < 0.005) number of pericapillary oligodendrocytes compared to controls. Prominent ultrastructural dystrophic and degenerative alterations of pericapillary oligodendrocytes have been revealed in schizophrenic brains.

CONCLUSION

The present study provides evidence that there is a prominent reduction, damage and loss of pericapillary oligodendrocytes in the prefrontal cortex in schizophrenia. These changes may contribute to the pathophysiological basis for altered blood-brain barrier and lowered metabolic rates in subjects with schizophrenia.

Changes in regional cerebral blood flow following mood challenge in drug-free, remitted patients with unipolar depression

Studies of mood provocation in remitted patients with depression have enabled the description of specific brain changes relevant to depression relapse vulnerability. Because patients in these studies were also receiving maintenance pharmacotherapy, the ability to subtract out the drug effect from the changes observed is reduced. Our study addresses this concern. Changes in regional cerebral blood flow (rCBF) among 11 medication-free, remitted patients with unipolar depression relative to baseline state were assessed with [(15)O]H(2)O positron emission tomography (PET) following provocation of sadness. Participants showed decreased activation in prefrontal cortex similar to those reported for remitted, medicated patients undergoing mood challenge, as well as for acutely depressed patients who were medication free. Previously reported mediofrontal changes in remitted patients are unlikely to be a consequence of maintenance medication and more likely are evidence of relapse vulnerability.

Genetic variation in MAOA modulates ventromedial prefrontal circuitry mediating individual differences in human personality

Little is known about neural mechanisms underlying human personality and temperament, despite their considerable importance as highly heritable risk mediators for somatic and psychiatric disorders. To identify these circuits, we used a combined genetic and imaging approach focused on Monoamine Oxidase A (MAOA), encoding a key enzyme for monoamine metabolism previously associated with temperament and antisocial behavior. Male carriers of a low-expressing genetic variant exhibited dysregulated amygdala activation and increased functional coupling with ventromedial prefrontal cortex (vmPFC). Stronger coupling predicted increased harm avoidance and decreased reward dependence scores, suggesting that this circuitry mediates a part of the association of MAOA with these traits. We utilized path analysis to parse the effective connectivity within this system, and provide evidence that vmPFC regulates amygdala indirectly by influencing rostral cingulate cortex function. Our data implicate a neural circuit for variation in human personality under genetic control, provide an anatomically consistent mechanism for vmPFC-amygdala interactions underlying this variation, and suggest a role for vmPFC as a superordinate regulatory area for emotional arousal and social behavior.

Cingulate-precuneus interactions: a new locus of dysfunction in adult attention-deficit/hyperactivity disorder

BACKGROUND

Pathophysiologic models of attention-deficit/hyperactivity disorder (ADHD) have focused on frontal-striatal circuitry with alternative hypotheses relatively unexplored. On the basis of evidence that negative interactions between frontal foci involved in cognitive control and the non-goal-directed "default-mode" network prevent attentional lapses, we hypothesized abnormalities in functional connectivity of these circuits in ADHD.

METHODS

Resting-state blood oxygen level-dependent functional magnetic resonance imaging (fMRI) scans were obtained at 3.0-Tesla in 20 adults with ADHD and 20 age- and sex-matched healthy volunteers.

RESULTS

Examination of healthy control subjects verified presence of an antiphasic or negative relationship between activity in dorsal anterior cingulate cortex (centered at x = 8, y = 7, z = 38) and in default-mode network components. Group analyses revealed ADHD-related compromises in this relationship, with decreases in the functional connectivity between the anterior cingulate and precuneus/posterior cingulate cortex regions (p < .0004, corrected). Secondary analyses revealed an extensive pattern of ADHD-related decreases in connectivity between precuneus and other default-mode network components, including ventromedial prefrontal cortex (p < 3 x 10(-11), corrected) and portions of posterior cingulate (p < .02, corrected).

CONCLUSIONS

Together with prior unbiased anatomic evidence of posterior volumetric abnormalities, our findings suggest that the long-range connections linking dorsal anterior cingulate to posterior cingulate and precuneus should be considered as a candidate locus of dysfunction in ADHD.

Opposing influences of emotional and non-emotional distracters upon sustained prefrontal cortex activity during a delayed-response working memory task

Performance in delayed-response working memory (WM) tasks is typically associated with sustained activation in the dorsolateral prefrontal cortex (dlPFC) that spans the delay between the memoranda and the memory probe. Recent studies have demonstrated that novel distracters presented during the delay interval both affect sustained activation and impair WM performance. However, the effect of the performance-impairing distracters upon sustained dlPFC delay activity was related to the characteristics of the distracters: memoranda-confusable distracters increased delay activity, whereas memoranda-nonconfusable emotional distracters decreased delay activity. Because these different effects were observed in different studies, it is possible that different dlPFC regions were involved and the paradox is more apparent than real. To investigate this possibility, event-related fMRI data were recorded while subjects performed a WM task for faces with memoranda-confusable (novel faces) and memoranda-nonconfusable emotional (novel scenes) distracters presented during the delay interval. Consistent with previous findings, confusable face distracters increased dlPFC delay activity, while nonconfusable emotional distracters decreased dlPFC delay activity, and these opposing effects modulated activity in the same dlPFC regions. These results provide direct evidence that specific regions of the dlPFC are generally involved in mediating the effects of distraction, while showing sensitivity to the nature of distraction. These findings are relevant for understanding alterations in the neural mechanisms associated with both general impairment of cognitive control and with specific impairment in the ability to control emotional distraction, such as those observed in aging and affective disorders, respectively.

Influence of vigilance and learning on prefrontal activation in schizophrenia

BACKGROUND

Executive functions, which are neuroanatomically associated with the frontal lobe, are known to be impaired in schizophrenia. It is, however, still unclear whether the underlying functional disturbance is due to a hyper- or a hypoactivation of the dorsolateral prefrontal cortex (DLPFC) or neither.

METHODS

To address this question, we examined the brain activation of 21 schizophrenic patients on atypical antipsychotic medication and 21 healthy control subjects during a mental maze task by means of fMRI.

RESULTS

We found no significant overall difference in cerebral activation between the groups, but differences in the change in DLPFC activation from the first to the second half of the experiment. In the maze compared to the control task, there was a decrease in activation in the DLPFC in the patients and an almost significant increase in the controls. The change in activation in the patient group correlated with a change in subjective sleepiness, while the increase in activation in the controls could be attributed to learning processes.

CONCLUSION

We hypothesized that differential temporal influences on brain activation could lead to either hyper- or hypoactivation of the DLPFC in schizophrenia.

Functional Magnetic Resonance Imaging Evidence for a Hierarchical Organization of the Prefrontal Cortex

The prefrontal cortex (PFC) is central to flexible and organized action. Recent theoretical and empirical results suggest that the rostro-caudal axis of the frontal lobes may reflect a hierarchical organization of control. Here, we test whether the rostro-caudal axis of the PFC is organized hierarchically, based on the level of abstraction at which multiple representations compete to guide selection of action. Four functional magnetic resonance imaging (fMRI) experiments parametrically manipulated the set of task-relevant (a) responses, (b) features, (c) dimensions, and (d) overlapping cue-to-dimension mappings. A systematic posterior to anterior gradient was evident within the PFC depending on the manipulated level of representation. Furthermore, across four fMRI experiments, activation in PFC subregions was consistent with the sub- and superordinate relationships that define an abstract representational hierarchy. In addition to providing further support for a representational hierarchy account of the rostro-caudal gradient in the PFC, these data provide important empirical constraints on current theorizing about control hierarchies and the PFC.