Detecting activations in PET and fMRI: levels of inference and power

Emotional conflict in interpersonal interactions

Facial displays of emotions can help to infer the mental states of other individuals. However, the expectations we generate on the basis of people's emotions can mismatch their actual behaviour in certain circumstances, which generates conflict. In the present study, we explored the neural mechanisms of emotional conflict during interpersonal interactions. Participants had to accept or reject economic offers made by several partners who displayed emotional expressions. On every trial, a cue informed participants of whether they could trust the emotion of their partner or not. Trustworthy (low-conflict) partners with happy facial expressions were cooperative and those with angry expressions did not cooperate. Untrustworthy (high-conflict) partners, on the other hand, cooperated when their expression was angry and did not cooperate when they displayed a happy emotion. Behavioural responses were faster for trustworthy than for untrustworty partners. High-conflict partners activated the anterior cingulate and the anterior insula. In turn, trustworthy partners were associated with activations in the left precuneus. Our results suggest that the emotion displayed by another person affects our decision-making in social contexts. When emotional expressions are linked to their natural consequences, they engage ToM processes. In contrast, untrustworthy emotional expressions engage conflict-related brain regions.

Long-term changes in cerebellar activation during functional recovery from transient peripheral motor paralysis

Localized altered cerebellar cortical activity can be associated with short-term changes in motor learning that take place in the course of hours, but it is unknown whether it can be correlated to long-term recovery from transient peripheral motor diseases, and if so, whether it occurs concomitantly in related brain regions. Here we show in a longitudinal fMRI study of patients with unilateral Bell's palsy that increases in ipsilateral cerebellar activity follow the recovery course of facial motor functions over at least one and a half years. These findings hold true for changes in brain activity related to both oral and peri-orbital activation, even though these processes are differentially mediated by unilateral and bilateral brain connectivities, respectively. Activation of non-facial musculature, which was studied for control, does not show any change in cerebellar activity over time. The localized changes in cerebellar activities following activation of facial functions occur concomitantly with increases in activity of the facial region in the contralateral primary motor cortex suggesting that the cerebellum acts together with the cerebral cortex in long-term adaptation to transient pathological sensorimotor processing.

With time on our side? Task-dependent compensatory processes in graceful aging

Graceful aging has been associated with frontal hyperactivations in working- and episodic long-term memory tasks, a compensatory process, according to some, that allows the best normal elders to perform these tasks at a juvenile level, in spite of natural cortical impoverishment. In this study, 24 young and 24 healthy elderly participants were compared. Graceful aging was explored by investigating domains where most healthy elders perform like youngers (e.g. lexical-semantic knowledge) and tasks that are typically more challenging, like episodic long-term recognition memory tasks. With voxel-based morphometry, we also studied to what extent changes of fMRI activation were consistent with the pattern of brain atrophy. We found that hyperactivations and hypoactivations of the elders were not restricted to the frontal lobes, rather they presented with task-dependent patterns. Only hypoactivations and normal levels of activation systematically overlapped with regional atrophy. We conclude that compensatory processes associated with graceful aging may not necessarily be a sign of early saturation of executive resources, if this was to be represented by a systematic frontal hyperactivation, but rather they may represent the ability of recruiting new cognitive strategies. We discuss two possible approaches to further test this hypothesis.

Impact of the HTR3A gene with early life trauma on emotional brain networks and depressed mood

BACKGROUND

The risk for mental illnesses such as depression is increasingly conceptualized as the product of gene-environment interactions and their impact on brain structure and function. The role of serotonin 3A receptor gene (HTR3A -42C>T polymorphism) and its interaction with early life stress (ELS) was investigated in view of the receptor's localization to brain regions central to emotion processing.

METHODS

Fronto-limbic grey matter (GM) loss was measured using magnetic resonance imaging and assessed using voxel-based morphometry analysis in 397 nonclinical individuals from the Brain Resource International Database. Negative mood symptoms were also assessed.

RESULTS

The HTR3A CC genotype group, compared to the T carriers, demonstrated comparative loss to GM in hippocampal structures, which extended to the frontal cortices for those CC genotype individuals also exposed to ELS. Elevations in depressed mood were also evident.

CONCLUSIONS

These findings suggest that the HTR3A CC genotype may be associated with alterations in brain structures central to emotion processing, particularly when exposed to stress, and further highlight the potential role of the serotonin system in the pathophysiology of affective disorders. In contrast, those individuals with the T allele, in particular the TT genotype, may be more protected from such alterations combined with minimal exposure to ELS events.

A statistical method (cross-validation) for bone loss region detection after spaceflight

Astronauts experience bone loss after the long spaceflight missions. Identifying specific regions that undergo the greatest losses (e.g. the proximal femur) could reveal information about the processes of bone loss in disuse and disease. Methods for detecting such regions, however, remains an open problem. This paper focuses on statistical methods to detect such regions. We perform statistical parametric mapping to get t-maps of changes in images, and propose a new cross-validation method to select an optimum suprathreshold for forming clusters of pixels. Once these candidate clusters are formed, we use permutation testing of longitudinal labels to derive significant changes.

Brain activation due to postoperative pain from the right hand measured with regional cerebral blood flow using positron emission tomography

Background Brain activation resulting from acute postoperative pain has to our knowledge not previously been studied using positron emission tomography, except from one case study. The aim of this study was to monitor activation in brain sensory pathways during acute pain after surgery of the hand. A secondary aim was to compare brain activation in clinical postoperative pain to that previously reported, by the same research group, for a model of experimental pain from the same body area. Increase in regional cerebral blood flow (rCBF) is presumed to indicate neuronal activation and decrease in blood flow decreased neuronal firing. An increase in blood flow in a brain region may represent stimulatory activity as well as inhibitory. Methods Brain activity was measured during clinical postoperative pain and a pain free state in six patients with positron emission tomography (PET) as changes in regional cerebral blood flow (rCBF). rCBF during pain from surgery of the right thumb base was compared with a pain free state achieved by regional anaesthesia of the painful area. Results In postoperative pain, patients had a significantly higher CBF in the contralateral/primary and secondary somatosensory cortices as well as in the contralateral motor cortex compared to the pain free stat during local regional anaesthesia. Relatively lower rCBF during the pain state was observed in clusters in the contralateral tertiary sensory cortex, ipsilateral and contralateral secondary visual cortex, prelimbic cortex, ipsilateral prefrontal as well as anterior cingulate cortex and contralateral secondary somatosensory cortex. The increased rCBF in primary and somatosensory cortices probably correspond to pain localizing processing. We also compared the findings in cerebral activation patterns of the postoperative pain state as described above, with the results from a previously published study by the same research group, using an experimental pain model when pain was inflicted with application of mustard oil in the same location, the thumb base region of the right hand. Since no formal statistical analysis was carried out between the two studies, the data are not very strong, but the differences reported were obvious when comparing the two situations. The comparison gave the following outcome: Digit activation occurred in identical sensory brain areas, i.e. primary and secondary somatosensory cortices, as compared to the changes in this study, supporting that pain localization processes use similar sensory pathways in a nociceptive acute experimental pain model, and in clinical acute postoperative nociceptive pain. Dissimilarities were observed between the models in activation of brain areas coding of the emotional pain qualities, indicating some differences between the experimental and "real" acute nociceptive pain. Conclusion We have reported a distinct cerebral activation pattern produced by acute postoperative pain following hand surgery. The findings were compared to data obtained in a previously published report of the cerebral activation pattern from an acute experimental pain model in volunteers. We found similarities as well as some differences in the activation pattern between the two situations.

Add a picture for suspense: neural correlates of the interaction between language and visual information in the perception of fear

We investigated how visual and linguistic information interact in the perception of emotion. We borrowed a phenomenon from film theory which states that presentation of an as such neutral visual scene intensifies the percept of fear or suspense induced by a different channel of information, such as language. Our main aim was to investigate how neutral visual scenes can enhance responses to fearful language content in parts of the brain involved in the perception of emotion. Healthy participants' brain activity was measured (using functional magnetic resonance imaging) while they read fearful and less fearful sentences presented with or without a neutral visual scene. The main idea is that the visual scenes intensify the fearful content of the language by subtly implying and concretizing what is described in the sentence. Activation levels in the right anterior temporal pole were selectively increased when a neutral visual scene was paired with a fearful sentence, compared to reading the sentence alone, as well as to reading of non-fearful sentences presented with the same neutral scene. We conclude that the right anterior temporal pole serves a binding function of emotional information across domains such as visual and linguistic information.

Adjusting the neuroimaging statistical inferences for nonstationarity

In neuroimaging cluster-based inference has generally been found to be more powerful than voxel-wise inference. However standard cluster-based methods assume stationarity (constant smoothness), while under nonstationarity clusters are larger in smooth regions just by chance, making false positive risk spatially variant. Hayasaka et al. proposed a Random Field Theory (RFT) based nonstationarity adjustment for cluster inference and validated the method in terms of controlling the overall family-wise false positive rate. The RFT-based methods, however, have never been directly assessed in terms of homogeneity of local false positive risk. In this work we propose a new cluster size adjustment that accounts for local smoothness, based on local empirical cluster size distributions and a two-pass permutation method. We also propose a new approach to measure homogeneity of local false positive risk, and use this method to compare the RFT-based and our new empirical adjustment methods. We apply these techniques to both cluster-based and a related inference, threshold-free cluster enhancement (TFCE). Using simulated and real data we confirm the expected heterogeneity in false positive risk with unadjusted cluster inference but find that RFT-based adjustment does not fully eliminate heterogeneity; we also observe that our proposed empirical adjustment dramatically increases the homogeneity and TFCE inference is generally quite robust to nonstationarity.

Multinomial inference on distributed responses in SPM

In this work, we propose statistical methods to perform inference on the spatial distribution of topological features (e.g. maxima or clusters) in statistical parametric maps (SPMs). This contrasts with local inference on the features per se (e.g., height or extent), which is well-studied (e.g. Friston et al., 1991, 1994; Worsley et al., 1992, 2003, 2004). We present a Bayesian approach to detecting experimentally-induced patterns of distributed responses in SPMs with anisotropic, non-stationary noise and arbitrary geometry. We extend the framework to accommodate fixed- and random-effects analyses at the within and between-subject levels respectively. We illustrate the method by characterising the anatomy of language at different scales of functional segregation.

Animated brain: a functional neuroimaging study on animacy experience

Previous research used animated geometric figures to investigate social cognitive processes involved in ascribing mental states to others (e.g. mentalizing). The relationship between animacy perception and brain areas commonly involved in social cognition, as well as the influence of particular motion patterns on animacy experience, however, remains to be further elucidated. We used a recently introduced paradigm for the systematic variation of motion properties, and employed functional magnetic resonance imaging to identify the neural mechanisms underlying animacy experience. Based on individual ratings of increased animacy experience the following brain regions of the "social neural network" (SNN), known to be involved in social cognitive processes, were recruited: insula, superior temporal gyrus, fusiform gyrus, parahippocampal gyrus and the ventromedial prefrontal cortex bilaterally. Decreased animacy experience was associated with increased neural activity in the inferior parietal and inferior frontal gyrus, key constituents of the human "mirror neuron system" (hMNS). These findings were corroborated when analyses were based on movement patterns alone, irrespective of subjective experience. Additionally to the areas found for increased animacy experience, an increase in interactive movements elicited activity in the amygdala and the temporal pole. In conclusion, the results suggest that the hMNS is recruited during a low-level stage of animacy judgment representing a basic disposition to detect the salience of movements, whereas the SNN appears to be a high-level processing component serving evaluation in social and mental inference.

Amygdalar modulation of frontotemporal connectivity during the inkblot test

Unique and unusual responses to inkblot stimuli evoked by emotionally vulnerable psychiatric patients have been considered as examples of interference of emotion with perceptual processes. However, few studies have investigated the interaction between emotion-related and perception-related neural circuits during performance of the inkblot test. In our recent studies using the inkblot stimuli, enlargement of the amygdala was revealed in association with frequent production of unique responses to the inkblot stimuli. Additionally, our studies demonstrated right temporopolar activation associated with the production of unique responses, as well as left anterior prefrontal and bilateral occipitotemporal activation associated with the production of typical responses. On the basis of these results, we hypothesized that the amygdala is involved in modulation of the connectivity among the frontotemporal regions identified in the activation analysis. To address this issue, we performed a functional connectivity analysis of functional magnetic resonance imaging data, using physiophysiological interaction implemented in Statistical Parametric Mapping 2 (SPM2). This analysis revealed that the amygdala imposed a positive modulation on the connection from the anterior prefrontal region to the temporopolar region, and a negative modulation on the connection from the temporopolar region to the occipitotemporal regions. These results suggest that interference of emotion affects perception during the inkblot test.

Effective connectivity of cortical and subcortical regions during unification of sentence structure

In a recent fMRI study we showed that left posterior middle temporal gyrus (LpMTG) subserves the retrieval of a word's lexical-syntactic properties from the mental lexicon (long-term memory), while left posterior inferior frontal gyrus (LpIFG) is involved in unifying (on-line integration of) this information into a sentence structure (Snijders et al., 2009). In addition, the right IFG, right MTG, and the right striatum were involved in the unification process. Here we report results from a psychophysical interactions (PPI) analysis in which we investigated the effective connectivity between LpIFG and LpMTG during unification, and how the right hemisphere areas and the striatum are functionally connected to the unification network. LpIFG and LpMTG both showed enhanced connectivity during the unification process with a region slightly superior to our previously reported LpMTG. Right IFG better predicted right temporal activity when unification processes were more strongly engaged, just as LpIFG better predicted left temporal activity. Furthermore, the striatum showed enhanced coupling to LpIFG and LpMTG during unification. We conclude that bilateral inferior frontal and posterior temporal regions are functionally connected during sentence-level unification. Cortico-subcortical connectivity patterns suggest cooperation between inferior frontal and striatal regions in performing unification operations on lexical-syntactic representations retrieved from LpMTG.

Exposure to parental verbal abuse is associated with increased gray matter volume in superior temporal gyrus

OBJECTIVE

Exposure to parental verbal aggression (PVA) during childhood increases risk for the development of psychopathology, particularly mood and anxiety disorders. Other forms of childhood abuse have been found to be associated with alterations in brain structure. The aim of this study was to ascertain whether exposure to PVA was associated with discernible effects on brain morphology.

METHODS

Optimized voxel-based morphometry was performed on 21 unmedicated, right-handed subjects (18-25 years) with histories of PVA and 19 psychiatrically healthy controls of comparable age and gender. Group differences in gray matter volume (GMV)--covaried by age, gender, parental education, financial stress, and total GMV--were assessed using high-resolution, T1-weighted, volumetric MRI data sets (Siemens 3T trio scanner).

RESULTS

GMV was increased by 14.1% in the left superior temporal gyrus (STG, BA 22) (P=0.004, corrected cluster level). GMV in this cluster was associated most strongly with levels of maternal (ß=0.544, P<0.0001) and paternal (ß=0.300, P<0.02) verbal aggression and inversely associated with parental education (ß=-0.577, P<0.0001).

CONCLUSION

Previous studies have demonstrated an increase in STG GMV in children with abuse histories, and found a reduction in fractional anisotropy in the arcuate fasciculus connecting Wernicke's and frontal areas in young adults exposed to PVA. These findings and the present results suggest that the development of auditory association cortex involved in language processing may be affected by exposure to early stress and/or emotionally abusive language.

Statistical Parametric Mapping reveals ligand and region-specific activation of G-proteins by CB1 receptors and non-CB1 sites in the 3D reconstructed mouse brain

CB(1) receptors mediate the CNS effects of Delta(9)-tetrahydrocannabinol and synthetic cannabinoids. Previous studies have investigated cannabinoid-mediated G-protein activity in a subset of brain regions thought to mediate the behavioral effects of cannabinoids, but a detailed regional comparison of the effects of multiple ligands has not been conducted. This study used a novel approach, Statistical Parametric Mapping (SPM), to analyze 3D reconstructed brain images derived from agonist-stimulated [(35)S]GTPgammaS autoradiography in a whole-brain unbiased manner. SPM analysis demonstrated regional differences in the relative efficacies of cannabinoid agonists methanandamide (M-AEA), CP55,940 (CP) and WIN55,212-2 (WIN) in CB(1)(+/+) mouse brains. To assess the potential contribution of novel cannabinoid binding sites, experiments were performed in CB(1)(-/-) mouse brains. SPM analysis revealed that the aminoalkylindole WIN, but not the bicyclic cannabinoid CP or the endocannabinoid analogue M-AEA, stimulated [(35)S]GTPgammaS binding in cortex, hippocampus, hypothalamus, amygdala, cerebellum and certain brainstem areas (dorsal tegmental complex and locus coeruleus). No differences between WIN-stimulated G-protein activity and basal activity were found in basal ganglia. Pharmacological experiments using the CB(1) antagonist SR141716A in CB(1)(+/+) mice showed that SR141716A blocked WIN-stimulated G-protein activity in all brain regions, suggesting that it binds to both CB(1) and putative non-CB(1) sites. These studies show ligand and region-specific cannabinoid-mediated G-protein activity at both CB(1) and non-CB(1) sites and demonstrate that SPM is a powerful approach for the analysis of reconstructed brain imaging data derived from agonist-stimulated [(35)S]GTPgammaS autoradiography.

Training of working memory impacts structural connectivity

Working memory is the limited capacity storage system involved in the maintenance and manipulation of information over short periods of time. Individual capacity of working memory is associated with the integrity of white matter in the frontoparietal regions. It is unknown to what extent the integrity of white matter underlying the working memory system is plastic. Using voxel-based analysis (VBA) of fractional anisotropy (FA) measures of fiber tracts, we investigated the effect of working memory training on structural connectivity in an interventional study. The amount of working memory training correlated with increased FA in the white matter regions adjacent to the intraparietal sulcus and the anterior part of the body of the corpus callosum after training. These results showed training-induced plasticity in regions that are thought to be critical in working memory. As changes in myelination lead to FA changes in diffusion tensor imaging, a possible mechanism for the observed FA change is increased myelination after training. Observed structural changes may underlie previously reported improvement of working memory capacity, improvement of other cognitive functions, and altered functional activity following working memory training.

On entropy rate for the complex domain

We derive the entropy rate formula for a complex Gaussian random process by using a widely linear model. The resulting expression is general and applicable to both circular and noncircular Gaussian processes, since any second-order stationary process can be modeled as the output of a widely linear system driven by a circular white noise. Furthermore, we demonstrate application of the derived formula to an order selection problem. We extend a scheme for independent and identically distributed (i.i.d.) sampling to the complex domain to improve the estimation performance of information-theoretic criteria when samples are correlated. We show the effectiveness of the approach for order selection for simulated and actual functional magnetic resonance imaging (fMRI) data that are inherently complex valued.

Interleaved transcranial magnetic stimulation and fMRI suggests that lamotrigine and valproic acid have different effects on corticolimbic activity

RATIONALE

Combined transcranial magnetic stimulation (TMS) and functional magnetic resonance imaging (fMRI) can be used to study anticonvulsant drugs. A previous study showed that lamotrigine (LTG) inhibited brain activation induced when TMS was applied over motor cortex, whereas it increased activation induced by TMS applied over prefrontal cortex.

OBJECTIVES

The present double-blind, placebo-controlled, crossover study in 30 healthy subjects again combined TMS and fMRI to test whether the effects seen previously with LTG would be confirmed and to compare these with a second anticonvulsant drug, valproic acid (VPA).

RESULTS

Statistical parametric mapping analysis showed that both LTG and VPA, compared to placebo, inhibited TMS-induced activation of the motor cortex. In contrast, when TMS was applied over prefrontal cortex, LTG increased the activation of limbic regions, confirming previous results; VPA had no effect.

CONCLUSION

We conclude that LTG and VPA have similar inhibitory effects on motor circuits, but differing effects on the prefrontal corticolimbic system. The study demonstrates that a combination of TMS and fMRI techniques may be useful in the study of the effects of neuroactive drugs on specific brain circuits.

Morphological characteristics of brain tumors causing seizures

OBJECTIVE

To quantify size and localization differences between tumors presenting with seizures vs nonseizure neurological symptoms.

DESIGN

Retrospective imaging survey. We performed magnetic resonance imaging-based morphometric analysis and nonparametric mapping in patients with brain tumors.

SETTING

University-affiliated teaching hospital.

PATIENTS OR OTHER PARTICIPANTS

One hundred twenty-four patients with newly diagnosed supratentorial glial tumors.

MAIN OUTCOME MEASURES

Volumetric and mapping methods were used to evaluate differences in size and location of the tumors in patients who presented with seizures as compared with patients who presented with other symptoms.

RESULTS

In high-grade gliomas, tumors presenting with seizures were smaller than tumors presenting with other neurological symptoms, whereas in low-grade gliomas, tumors presenting with seizures were larger. Tumor location maps revealed that in high-grade gliomas, deep-seated tumors in the pericallosal regions were more likely to present with nonseizure neurological symptoms. In low-grade gliomas, tumors of the temporal lobe as well as the insular region were more likely to present with seizures.

CONCLUSIONS

The influence of size and location of the tumors on their propensity to cause seizures varies with the grade of the tumor. In high-grade gliomas, rapidly growing tumors, particularly those situated in deeper structures, present with non-seizure-related symptoms. In low-grade gliomas, lesions in the temporal lobe or the insula grow large without other symptoms and eventually cause seizures. Quantitative image analysis allows for the mapping of regions in each group that are more or less susceptible to seizures.

Working memory fMRI activation in cocaine-dependent subjects: association with treatment response

Functional magnetic resonance imaging (fMRI) studies of early abstinence cocaine users offer information about the state of the brain when most cocaine users seek treatment. This study examined the relationship between pretreatment brain function and subsequent treatment response in 19 treatment-seeking early abstinence cocaine-dependent (CD) subjects. These subjects and 14 non-drug-using control subjects underwent fMRI while performing a working memory task with three levels of difficulty. CD subjects were then randomized to treatment studies. Results showed CD subjects had significantly lower (random effects, corrected for multiple comparisons) brain activation in caudate, putamen, cingulate gyrus, middle and superior frontal gyri, inferior frontal gyrus pars triangularis and pars opercularis, precentral gyrus, and thalamus compared with non-drug-using controls. Within CD subjects, thalamic activation significantly correlated with treatment response. This study shows CD subjects in early abstinence have alterations of brain function in frontal, striatal, and thalamic brain regions known to be part of a circuit associated with motor control, reward, and cognition. Subjects with pretreatment thalamic deactivation showed the poorest treatment response, possibly related to thalamic involvement in mesocortical and mesolimbic dopamine projections.

Source-based morphometry of gray matter volume in men with first-episode schizophrenia

OBJECTIVES

There is a lot of variability between the results of studies reporting the pattern of gray matter volume changes in schizophrenia. Methodological issues may play an important role in this heterogeneity. The aim of the present study was to replicate the better performance of multivariate "source-based morphometry" (SBM) over the mass-univariate approach.

EXPERIMENTAL DESIGN

Voxel-based morphometry of Jacobian-modulated gray matter volume images, using voxel and cluster level inference, and SBM were performed in a group of first-episode schizophrenia patients (N = 49) and healthy controls (N = 127).

RESULTS

Using SBM we were able to find a significant reduction of gray matter volume in fronto-temporo-cerebellar areas whereas no significant results were obtained using voxel-based morphometry.

CONCLUSION

Multivariate analysis of gray matter volume seems to be a suitable method for characterization of the pattern of changes at the beginning of the illness in schizophrenia subjects.

Comparing isotropic and anisotropic smoothing for voxel-based DTI analyses: A simulation study

Voxel-based analysis (VBA) methods are increasingly being used to compare diffusion tensor image (DTI) properties across different populations of subjects. Although VBA has many advantages, its results are highly dependent on several parameter settings, such as those from the coregistration technique applied to align the data, the smoothing kernel, the statistics, and the post-hoc analyses. In particular, to increase the signal-to-noise ratio and to mitigate the adverse effect of residual image misalignments, DTI data are often smoothed before VBA with an isotropic Gaussian kernel with a full width half maximum up to 16 x 16 x 16 mm(3). However, using isotropic smoothing kernels can significantly partial volume or voxel averaging artifacts, adversely affecting the true diffusion properties of the underlying fiber tissue. In this work, we compared VBA results between the isotropic and an anisotropic Gaussian filtering method using a simulated framework. Our results clearly demonstrate an increased sensitivity and specificity of detecting a predefined simulated pathology when the anisotropic smoothing kernel was used.

Improving fMRI sensitivity by normalization of basal physiologic state

The power of fMRI in assessing neural activities is hampered by inter-subject variations in basal physiologic parameters, which may not be related to neural activation but has a modulatory effect on fMRI signals. Therefore, normalization of fMRI signals with these parameters is useful in reducing variations and improving sensitivity of this important technique. Recently, we have shown that basal venous oxygenation is a significant modulator of fMRI signals and individuals with higher venous oxygenation tend to have lower fMRI signals. In this study, we aim to test the utility of venous oxygenation normalization in distinguishing subject groups. A "model" condition was used in which two visual stimuli with different flashing frequencies were used to stimulate two subject groups, respectively, thereby simulating the situation of control and patient groups. It was found that visual-evoked BOLD signal is significantly correlated with baseline venous T2 (P = 0.0003) and inclusion of physiologic modulator in the regression analysis can substantially reduce P values of group-level statistical tests. When applied to voxel-wise analysis, the normalization process can allow the detection of more significant voxels. The utility of other basal parameters, including blood pressure, heart rate, arterial oxygenation, and end-tidal CO(2), in BOLD normalization was also assessed and it was found that the improvement was less significant. Time-to-peak of the BOLD responses was also studied and it was found that subjects with higher basal venous oxygenation tend to slower BOLD responses.

The interactive effects of ketamine and nicotine on human cerebral blood flow

AIM

The purpose of this study was to determine if acute nicotine attenuated ketamine-induced regional cerebral blood flow (rCBF).

METHOD

Following 2-4 h of nicotine abstinence, healthy chronic smokers participated in four sets of rCBF studies, H2(15)O positron emission tomography, during a simple sensory motor control task. The four drug conditions studied were placebo, ketamine alone, nicotine alone, and ketamine + nicotine.

RESULTS

Intravenous ketamine increased rCBF in frontal, orbital-frontal, and anterior cingulate areas. Nicotine alone induced marked rCBF elevations in the lateral occipital cortex and rCBF suppressions in the basal ganglia and anterior cingulate cortex. Nicotine added to ketamine attenuated the ketamine-induced elevated rCBF in the anterior cingulate cortex but caused a marked rCBF increase in the orbital frontal region.

CONCLUSION

This study illustrates the interactive effects of ketamine, an NMDA receptor antagonist, and nicotine in multiple brain regions. Nicotine substantially ameliorated the effects of ketamine on anterior cingulate rCBF and, when given alone, markedly suppressed anterior cingulate rCBF. The enhanced, synergistic orbitofrontal effects observed with ketamine and nicotine together suggest a marked increase in excitatory neurotransmission in a brain region often linked to psychosis, reward, and addictive behaviors.

Meta-analysis of neuroimaging data

As the number of neuroimaging studies that investigate psychological phenomena grows, it becomes increasingly difficult to integrate the knowledge that has accrued across studies. Meta-analyses are designed to serve this purpose, as they allow the synthesis of findings not only across studies but also across laboratories and task variants. Meta-analyses are uniquely suited to answer questions about whether brain regions or networks are consistently associated with particular psychological domains, including broad categories such as working memory or more specific categories such as conditioned fear. Meta-analysis can also address questions of specificity, which pertains to whether activation of regions or networks is unique to a particular psychological domain, or is a feature of multiple types of tasks. This review discusses several techniques that have been used to test consistency and specificity in published neuroimaging data, including the kernel density analysis (KDA), activation likelihood estimate (ALE), and the recently developed multilevel kernel density analysis (MKDA). We discuss these techniques in light of current and future directions in the field. Copyright © 2010 John Wiley & Sons, Ltd. This article is categorized under: Neuroscience > Cognition.

Cerebral oxygen and glucose metabolism in patients with mitochondrial m.3243A>G mutation

The m.3243A>G mutation is the most common pathogenic mutation in mitochondrial DNA. It leads to defective oxidative phosphorylation, decreased oxygen consumption and increased glucose utilization and lactate production in vitro. However, oxygen and glucose metabolism has not been studied in the brain of patients harbouring the m.3243A>G mutation. Therefore, 14 patients with the m.3243A>G mutation, not experiencing acute stroke-like episodes and 14 age-matched controls underwent positron emission tomography using 2-[(18)F]fluoro-2-deoxyglucose, [(15)O]H(2)O and [(15)O]O(2) as the tracers during normoglycaemia. The metabolic rate of oxygen and glucose were determined using a quantitative region of interest analysis. Metabolites in unaffected periventricular tissue were measured using magnetic resonance spectroscopy. We found that the cerebral metabolic rate of oxygen was decreased by 26% (range 18%-29%) in the grey as well as the white matter of patients with the m.3243A>G mutation. A decrease in the metabolic rate of glucose was found with predilection to the posterior part of the brain. No major changes were detected in cerebral blood flow or the number of white matter lesions. Our results show that the m.3243A>G mutation leads to a global decrease in oxygen consumption in the grey matter including areas where no other signs of disease were present.

Catechol-o-methyltransferase valine(158)methionine genotype and resting regional cerebral blood flow in medication-free patients with schizophrenia

BACKGROUND

A valine(158)methionine (val(158)met) polymorphism in catechol-O-methyltransferase (COMT) modulates cortical dopaminergic catabolism and has been associated with schizophrenia. Consistent with schizophrenia itself, during cognitive tasks, the risk (val) allele predicts less efficient prefrontal cortex (PFC) physiology and worse performance, while during aversive stimuli viewing, this allele predicts less limbic activation. Task-independent effects of this polymorphism in schizophrenia have not yet been characterized.

METHODS

Twenty-five medication-free patients (28 +/- 6 years; 19 male patients) and 47 healthy individuals (29 +/- 8 years; 33 male individuals) were genotyped for the COMT val(158)met polymorphism and underwent two 60-second radiolabeled water ([(15)O]H(2)O) regional cerebral blood flow (rCBF) positron emission tomography scans (10 mCi/scan) during rest. Data were analyzed with a random-effects general linear model using COMT genotype as a covariate.

RESULTS

In patients, but not healthy individuals, val (risk) allele load predicted less regional cerebral blood flow in the right dorsolateral PFC, right superior temporal gyrus, and left precuneus, but greater rCBF in the amygdala and parahippocampal gyrus.

CONCLUSIONS

In schizophrenia, brain structures important for executive and affective processing show activity that is differentially predicted by COMT allelic variation in an opposing manner even at rest, providing evidence for the salience of prefrontal dopaminergic tone in task-independent, basal-level neural activity.

Smaller insula and inferior frontal volumes in young adults with pervasive developmental disorders

Enlarged head circumference and increased brain weight have been reported in infants with pervasive developmental disorders (PDD), and volumetric studies suggest that children with PDD have abnormally enlarged brain volumes. However, little is known about brain volume abnormalities in young adults with PDD. We explored gray matter (GM) volume in young adults with PDD. T1-weighted volumetric images were acquired with a 3-T magnetic resonance scanner from 32 males with high-functioning PDD (23.8+/-4.2 years; Full Scale Intelligence Quotient [FSIQ]=101.6+/-15.6) and 40 age-matched normal male control subjects (22.5+/-4.3 years; FSIQ=109.7+/-7.9). Regional GM volumes were compared between the two groups using voxel-based morphometry (VBM) with the Diffeomorphic Anatomical Registration using Exponentiated Lie algebra (DARTEL). Compared with the control group, the high-functioning PDD group showed significantly less GM in the right insula, the right inferior frontal gyrus, and the right inferior parietal lobule. A conservative threshold confirmed considerably smaller volumes in the right insula and inferior frontal gyrus. In these areas, negative correlations were found between Autism Spectrum Quotient scores and GM volume, although no significant correlations were found between each subject's FSIQ and GM volume. No regions showed greater GM volumes in the high-functioning PDD group. The insular cortex, which works as a relay area for multiple neurocognitive systems, may be one of the key regions underlying the complex clinical features of PDD. These smaller GM volumes in high-functioning PDD subjects may reflect the clinical features of PDD itself, rather than FSIQ.

Stimulation of the subthalamic nucleus and impulsivity: release your horses

OBJECTIVE

In Parkinson disease (PD) patients, deep brain stimulation (DBS) of the subthalamic nucleus (STN) may contribute to certain impulsive behavior during high-conflict decisions. A neurocomputational model of the basal ganglia has recently been proposed that suggests this behavioral aspect may be related to the role played by the STN in relaying a "hold your horses" signal intended to allow more time to settle on the best option. The aim of the present study was 2-fold: 1) to extend these observations by providing evidence that the STN may influence and prevent the execution of any response even during low-conflict decisions; and 2) to identify the neural correlates of this effect.

METHODS

We measured regional cerebral blood flow during a Go/NoGo and a control (Go) task to study the motor improvement and response inhibition deficits associated with STN-DBS in patients with PD.

RESULTS

Although it improved Unified Parkinson Disease Rating Scale motor ratings and induced a global decrease in reaction time during task performance, STN-DBS impaired response inhibition, as revealed by an increase in commission errors in NoGo trials. These behavioral effects were accompanied by changes in synaptic activity consisting of a reduced activation in the cortical networks responsible for reactive and proactive response inhibition.

INTERPRETATION

The present results suggest that although it improves motor functions in PD patients, modulation of STN hyperactivity with DBS may tend at the same time to favor the appearance of impulsive behavior by acting on the gating mechanism involved in response initiation.

Neural correlates of high-level adaptation-related aftereffects

Prolonged exposure to complex stimuli, such as faces, biases perceptual decisions toward nonadapted, dissimilar stimuli, leading to contrastive aftereffects. Here we tested the neural correlates of this perceptual bias using a functional magnetic resonance imaging adaptation (fMRIa) paradigm. Adaptation to a face or hand stimulus led to aftereffects by biasing the categorization of subsequent ambiguous face/hand composite stimuli away from the adaptor category. The simultaneously observed fMRIa in the face-sensitive fusiform face area (FFA) and in the body-part-sensitive extrastriate body area (EBA) depended on the behavioral response of the subjects: adaptation to the preferred stimulus of the given area led to larger signal reduction during trials when it biased perception than during trials when it was less effective. Activity in two frontal areas correlated positively with the activity patterns in FFA and EBA. Based on our novel adaptation paradigm, the results suggest that the adaptation-induced aftereffects are mediated by the relative activity of category-sensitive areas of the human brain as demonstrated by fMRI.

Three stages and four neural systems in time estimation

Gibbon's scalar expectancy theory assumes three processing stages in time estimation: a collating level in which event durations are automatically tracked, a counting level that reads out the time-tracking system, and a comparing level in which event durations are matched to abstract temporal references. Pöppel's theory, however, postulates a dual system for perception of durations below and above 2 s. By testing the neurophysiological plausibility of Gibbon's proposal using functional magnetic resonance imaging, we validate a three-staged model of time estimation and further show that the collating process is duplicated. Although the motor system automatically tracks durations below 2 s, mesial brain regions of the so-called "default mode network" keep track of longer events. Our results further support unique counting and comparing systems, involving prefrontal and parietal cortices in collators' readout, and the temporal cortex in contextual time estimation. These findings provide a coherent neuroanatomical framework for two theories of time perception.

The neural basis of agency: an fMRI study

Agency, a feeling that the self is the cause of action, has a strong relationship to the processing of discrepancies between the predicted multi-sensory feedback from one's intended action and its actual outcome (hereafter, agency error). Although previous studies have explored the neural basis of agency by assessing the brain's response to agency error, the effects found are confounded by two types of error irrelevant to agency: a mismatch between different sensory inputs in general (sensory mismatch, SM error) and a basic response to any type of prediction error (oddball error). In this functional magnetic resonance imaging study, we identified the neural response specific to agency error by dissociating it from responses to SM and oddball errors. Subjects played a game in which they controlled an on-screen character. Neural responses to rare events of violated control and congruency between types of audio-visual feedback were compared to dissociate agency from SM error. In a separate session, subjects viewed repetitive motions of the character, and neural responses to rare events of unpredictable change in movement were identified as related to oddball error. Agency-error-specific activation was observed in the supplementary motor area (SMA), left cerebellum, right posterior parietal cortex (PPC), and right extrastriate body area (EBA). Oddball errors also activated areas near the PPC and EBA peaks. SM errors activated the pre-SMA and the right posterior superior temporal sulcus. Our results suggest that the SMA, cerebellum, and some parts of the PPC and EBA serve as the neural bases of agency.

A dissociation between linguistic and communicative abilities in the human brain

Although language is an effective vehicle for communication, it is unclear how linguistic and communicative abilities relate to each other. Some researchers have argued that communicative message generation involves perspective taking (mentalizing), and-crucially-that mentalizing depends on language. We employed a verbal communication paradigm to directly test whether the generation of a communicative action relies on mentalizing and whether the cerebral bases of communicative message generation are distinct from parts of cortex sensitive to linguistic variables. We found that dorsomedial prefrontal cortex, a brain area consistently associated with mentalizing, was sensitive to the communicative intent of utterances, irrespective of linguistic difficulty. In contrast, left inferior frontal cortex, an area known to be involved in language, was sensitive to the linguistic demands of utterances, but not to communicative intent. These findings show that communicative and linguistic abilities rely on cerebrally (and computationally) distinct mechanisms.

Neuroanatomical correlates of cognitive self-appraisal in neurodegenerative disease

Self-appraisal is a critical cognitive function, which helps us to choose tasks based on an accurate assessment of our abilities. The neural mechanisms of self-appraisal are incompletely understood, although a growing body of literature suggests that several frontal and subcortical regions are important for self-related processing. Anosognosia, or lack of awareness of one's deficits, is common in neurodegenerative dementias, offering an important window onto the brain systems involved in self-appraisal. We examined the neuroanatomical basis of self-appraisal in a mixed group of 39 individuals, including 35 with cognitive impairment due to one of several probable neurodegenerative diseases, using voxel-based morphometry and an objective, neuropsychologically-based measure of self-appraisal accuracy. Self-appraisal accuracy was correlated with tissue content in the right ventromedial prefrontal cortex (vmPFC). We hypothesize that emotional/physiological processing carried out by vmPFC is an important factor mediating self-appraisal accuracy in dementia.

Modulation of limbic circuitry predicts treatment response to antipsychotic medication: a functional imaging study in schizophrenia

The regional neuronal changes taking place in the early and late stages of antipsychotic treatment are still not well characterized in humans. In addition, it is not known whether these regional changes are predictive of or are correlated with treatment response. Using PET with 15O, we evaluated the time course of regional cerebral blood flow (rCBF) patterns generated by a first (haloperidol) and a second (olanzapine) generation antipsychotic drug in patients with schizophrenia during a 6-week treatment trial. Patients were initially scanned after withdrawal of all psychotropic medication (2 weeks), and then blindly randomized to treatment with haloperidol (n=12) or olanzapine (n=17) for a period of 6 weeks. Patients were scanned again after 1 and 6 weeks of treatment. All assessments, including scanning sessions, were obtained in a double-blind manner. As hypothesized, we observed rCBF changes that were common to both the drugs, implicating cortico-subcortical and limbic neuronal networks in antipsychotic action. In addition, in these regions, some patterns seen at weeks 1 and 6 were distinctive, indexing neuronal changes related to an early (ventral striatum, hippocampus) and consolidated (anterior cingulate/medial frontal cortex) stage of drug response. Finally, both after 1 and 6 weeks of treatment, we observed differential patterns of rCBF activation between good and poor responders. After 1 week of treatment, greater rCBF increase in the ventral striatum and greater decrease in the hippocampus were associated with good response.

Elucidating a magnetic resonance imaging-based neuroanatomic biomarker for psychosis: classification analysis using probabilistic brain atlas and machine learning algorithms

BACKGROUND

No objective diagnostic biomarkers or laboratory tests have yet been developed for psychotic illness. Magnetic resonance imaging (MRI) studies consistently find significant abnormalities in multiple brain structures in psychotic patients relative to healthy control subjects, but these abnormalities show substantial overlap with anatomic variation that is in the normal range and therefore nondiagnostic. Recently, efforts have been made to discriminate psychotic patients from healthy individuals using machine-learning-based pattern classification methods on MRI data.

METHODS

Three-dimensional cortical gray matter density (GMD) maps were generated for 36 patients with recent-onset psychosis and 36 sex- and age-matched control subjects using a cortical pattern matching method. Between-group differences in GMD were evaluated. Second, the sparse multinomial logistic regression classifier included in the Multivariate Pattern Analysis in Python machine-learning package was applied to the cortical GMD maps to discriminate psychotic patients from control subjects.

RESULTS

Patients showed significantly lower GMD, particularly in prefrontal, cingulate, and lateral temporal brain regions. Pattern classification analysis achieved 86.1% accuracy in discriminating patients from controls using leave-one-out cross-validation.

CONCLUSIONS

These results suggest that even at the early stage of illness, psychotic patients present distinct patterns of regional cortical gray matter changes that can be discriminated from the normal pattern. These findings indicate that we can detect complex patterns of brain abnormality in early stages of psychotic illness, which has critical implications for early identification and intervention in individuals at ultra-high risk for developing psychosis/schizophrenia.

Topological FDR for neuroimaging

In this technical note, we describe and validate a topological false discovery rate (FDR) procedure for statistical parametric mapping. This procedure is designed to deal with signal that is continuous and has, in principle, unbounded spatial support. We therefore infer on topological features of the signal, such as the existence of local maxima or peaks above some threshold. Using results from random field theory, we assign a p-value to each maximum in an SPM and identify an adaptive threshold that controls false discovery rate, using the Benjamini and Hochberg (BH) procedure (1995). This provides a natural complement to conventional family wise error (FWE) control on local maxima. We use simulations to contrast these procedures; both in terms of their relative number of discoveries and their spatial accuracy (via the distribution of the Euclidian distance between true and discovered activations). We also assessed two other procedures: cluster-wise and voxel-wise FDR procedures. Our results suggest that (a) FDR control of maxima or peaks is more sensitive than FWE control of peaks with minimal cost in terms of false-positives, (b) voxel-wise FDR is substantially less accurate than topological FWE or FDR control. Finally, we present an illustrative application using an fMRI study of visual attention.

Sustained attention in patients receiving and abstinent following methadone maintenance treatment for opiate dependence: performance and neuroimaging results

OBJECTIVE

Impairments in the function of attention exacerbate the course of opiate dependence and may play a role in the relapsing nature of the disorder. This study used clinical measures and positron emission tomography (PET) to assess the functioning of sustained attention in subjects with a history of opiate dependence.

METHODS

A test of auditory sustained attention was administered to 10 subjects receiving methadone maintenance treatment, 13 formerly opiate-dependent subjects in protracted abstinence, and 14 healthy Comparison subjects. Simultaneous measurement of regional glucose metabolism was made by [(18)F] flourodeoxyglucose PET. Subjects groups were compared on the measures of sustained attention and regional cerebral glucose metabolism.

RESULTS

Healthy Comparison subjects scored significantly better than either methadone-maintained or abstinent former opiate addicts on measures of sustained attention. Formerly opiate-dependent subjects in protracted abstinence scored better than methadone-maintained subjects on sustained attention. Methadone-maintained subjects demonstrated a relative reduction in regional cerebral glucose metabolism in the right supramarginal gyrus, and the thalamus bilaterally. The Comparison subjects without a history of opiate dependence demonstrated a relative increase in regional cerebral glucose metabolism in the right anterior cingulate gyrus, the right medial superior frontal gyrus and the thalamus bilaterally.

CONCLUSIONS

Subjects with a history of opiate dependence have impairments in the functioning of sustained attention, and abnormalities in brain regions identified as important in attention processing. Impairments in attention performance persist in subjects who enjoy prolonged abstinence from opiates.