Three-dimensional maximum probability atlas of the human brain, with particular reference to the temporal lobe

Astrocytosis measured by ¹¹C-deprenyl PET correlates with decrease in gray matter density in the parahippocampus of prodromal Alzheimer's patients

PURPOSE

The Alzheimer's disease (AD) pathology is characterized by fibrillar amyloid deposits and neurofibrillary tangles, as well as the activation of astrocytosis, microglia activation, atrophy, dysfunctional synapse, and cognitive impairments. The aim of this study was to test the hypothesis that astrocytosis is correlated with reduced gray matter density in prodromal AD.

METHODS

Twenty patients with AD or mild cognitive impairment (MCI) underwent multi-tracer positron emission tomography (PET) studies with (11)C-Pittsburgh compound B ((11)C-PIB), (18) F-Fluorodeoxyglucose ((18) F-FDG), and (11)C-deuterium-L-deprenyl ((11)C-DED) PET imaging, as well as magnetic resonance imaging (MRI) scanning, cerebrospinal fluid (CSF) biomarker analysis, and neuropsychological assessments. The parahippocampus was selected as a region of interest, and each value was calculated for four different imaging modalities. Correlation analysis was applied between DED slope values and gray matter (GM) densities by MRI. To further explore possible relationships, correlation analyses were performed between the different variables, including the CSF biomarker.

RESULTS

A significant negative correlation was obtained between DED slope values and GM density in the parahippocampus in PIB-positive (PIB + ve) MCI patients (p = 0.025) (prodromal AD). Furthermore, in exploratory analyses, a positive correlation was observed between PIB-PET retention and DED binding in AD patients (p = 0.014), and a negative correlation was observed between PIB retention and CSF Aβ42 levels in MCI patients (p = 0.021), while the GM density and CSF total tau levels were negatively correlated in both PIB + ve MCI (p = 0.002) and MCI patients (p = 0.001). No significant correlation was observed with FDG-PET and with any of the other PET, MRI, or CSF biomarkers.

CONCLUSIONS

High astrocytosis levels in the parahippocampus of PIB + ve MCI (prodromal AD) patients suggest an early preclinical influence on cellular tissue loss. The lack of correlation between astrocytosis and CSF tau levels, and a positive correlation between astrocytosis and fibrillar amyloid deposition in clinical demented AD together indicate that parahippocampal astrocytosis might have some causality within the amyloid pathology.

Abnormal functional connectivity of the medial cortex in euthymic bipolar II disorder

This project utilized functional MRI (fMRI) and a motor activation paradigm to investigate neural circuitry in euthymic bipolar II disorder. We hypothesized that circuitry involving the cortical midline structures (CMS) would demonstrate abnormal functional connectivity. Nineteen subjects with recurrent bipolar disorder and 18 controls were studied using fMRI and a motor activation paradigm. We used functional connectivity analyses to identify circuits with aberrant connectivity. We found increased functional connectivity among bipolar subjects compared to healthy controls in two CMS circuits. One circuit included the medial aspect of the left superior frontal gyrus and the dorsolateral region of the left superior frontal gyrus. The other included the medial aspect of the right superior frontal gyrus, the dorsolateral region of the left superior frontal gyrus and the right medial frontal gyrus and surrounding region. Our results indicate that CMS circuit dysfunction persists in the euthymic state and thus may represent trait pathology. Future studies should address whether these circuits contribute to relapse of illness. Our results also suggest the possibility that aberrations of superior frontal circuitry may impact default mode network and cognitive processes.

Switching brain serotonin with oxytocin

Serotonin (5-HT) and oxytocin (OXT) are two neuromodulators involved in human affect and sociality and in disorders like depression and autism. We asked whether these chemical messengers interact in the regulation of emotion-based behavior by administering OXT or placebo to 24 healthy subjects and mapping cerebral 5-HT system by using 2'-methoxyphenyl-(N-2'-pyridinyl)-p-[(18)F]fluoro-benzamidoethylpiperazine ([(18)F]MPPF), an antagonist of 5-HT1A receptors. OXT increased [(18)F]MPPF nondisplaceable binding potential (BPND) in the dorsal raphe nucleus (DRN), the core area of 5-HT synthesis, and in the amygdala/hippocampal complex, insula, and orbitofrontal cortex. Importantly, the amygdala appears central in the regulation of 5-HT by OXT: [(18)F]MPPF BPND changes in the DRN correlated with changes in right amygdala, which were in turn correlated with changes in hippocampus, insula, subgenual, and orbitofrontal cortex, a circuit implicated in the control of stress, mood, and social behaviors. OXT administration is known to inhibit amygdala activity and results in a decrease of anxiety, whereas high amygdala activity and 5-HT dysregulation have been associated with increased anxiety. The present study reveals a previously unidentified form of interaction between these two systems in the human brain, i.e., the role of OXT in the inhibitory regulation of 5-HT signaling, which could lead to novel therapeutic strategies for mental disorders.

Acute increases in synaptic GABA detectable in the living human brain: a [¹¹C]Ro15-4513 PET study

The inhibitory γ-aminobutyric acid (GABA) neurotransmitter system is associated with the regulation of normal cognitive functions and dysregulation has been reported in a number of neuropsychiatric disorders including anxiety disorders, schizophrenia and addictions. Investigating the role of GABA in both health and disease has been constrained by difficulties in measuring acute changes in synaptic GABA using neurochemical imaging. The aim of this study was to investigate whether acute increases in synaptic GABA are detectable in the living human brain using the inverse agonist GABA-benzodiazepine receptor (GABA-BZR) positron emission tomography (PET) tracer, [(11)C]Ro15-4513. We examined the effect of 15 mg oral tiagabine, which increases synaptic GABA by inhibiting the GAT1 GABA uptake transporter, on [(11)C]Ro15-4513 binding in 12 male participants using a paired, double blind, placebo-controlled protocol. Spectral analysis was used to examine synaptic α1 and extrasynaptic α5 GABA-BZR subtype availability in brain regions with high levels of [(11)C]Ro15-4513 binding. We also examined the test-retest reliability of α1 and a5-specific [(11)C]Ro15-4513 binding in a separate cohort of 4 participants using the same spectral analysis protocol. Tiagabine administration produced significant reductions in hippocampal, parahippocampal, amygdala and anterior cingulate synaptic α1 [(11)C]Ro15-4513 binding, and a trend significance reduction in the nucleus accumbens. These reductions were greater than test-retest reliability, indicating that they are not the result of chance observations. Our results suggest that acute increases in endogenous synaptic GABA are detectable in the living human brain using [(11)C]Ro15-4513 PET. These findings have potentially major implications for the investigation of GABA function in brain disorders and in the development of new treatments targeting this neurotransmitter system.

A common currency for the computation of motivational values in the human striatum

Reward comparison in the brain is thought to be achieved through the use of a 'common currency', implying that reward value representations are computed on a unique scale in the same brain regions regardless of the reward type. Although such a mechanism has been identified in the ventro-medial prefrontal cortex and ventral striatum in the context of decision-making, it is less clear whether it similarly applies to non-choice situations. To answer this question, we scanned 38 participants with fMRI while they were presented with single cues predicting either monetary or erotic rewards, without the need to make a decision. The ventral striatum was the main brain structure to respond to both cues while showing increasing activity with increasing expected reward intensity. Most importantly, the relative response of the striatum to monetary vs erotic cues was correlated with the relative motivational value of these rewards as inferred from reaction times. Similar correlations were observed in a fronto-parietal network known to be involved in attentional focus and motor readiness. Together, our results suggest that striatal reward value signals not only obey to a common currency mechanism in the absence of choice but may also serve as an input to adjust motivated behaviour accordingly.

Multi-contrast multi-atlas parcellation of diffusion tensor imaging of the human brain

In this paper, we propose a novel method for parcellating the human brain into 193 anatomical structures based on diffusion tensor images (DTIs). This was accomplished in the setting of multi-contrast diffeomorphic likelihood fusion using multiple DTI atlases. DTI images are modeled as high dimensional fields, with each voxel exhibiting a vector valued feature comprising of mean diffusivity (MD), fractional anisotropy (FA), and fiber angle. For each structure, the probability distribution of each element in the feature vector is modeled as a mixture of Gaussians, the parameters of which are estimated from the labeled atlases. The structure-specific feature vector is then used to parcellate the test image. For each atlas, a likelihood is iteratively computed based on the structure-specific vector feature. The likelihoods from multiple atlases are then fused. The updating and fusing of the likelihoods is achieved based on the expectation-maximization (EM) algorithm for maximum a posteriori (MAP) estimation problems. We first demonstrate the performance of the algorithm by examining the parcellation accuracy of 18 structures from 25 subjects with a varying degree of structural abnormality. Dice values ranging 0.8-0.9 were obtained. In addition, strong correlation was found between the volume size of the automated and the manual parcellation. Then, we present scan-rescan reproducibility based on another dataset of 16 DTI images - an average of 3.73%, 1.91%, and 1.79% for volume, mean FA, and mean MD respectively. Finally, the range of anatomical variability in the normal population was quantified for each structure.

The predictive power of brain mRNA mappings for in vivo protein density: a positron emission tomography correlation study

Substantial efforts are being spent on postmortem mRNA transcription mapping on the assumption that in vivo protein distribution can be predicted from such data. We tested this assumption by comparing mRNA transcription maps from the Allen Human Brain Atlas with reference protein concentration maps acquired with positron emission tomography (PET) in two representative systems of neurotransmission (opioid and serotoninergic). We found a tight correlation between mRNA expression and specific binding with 5-HT1A receptors measured with PET, but for opioid receptors, the correlation was weak. The discrepancy can be explained by differences in expression regulation between the two systems: transcriptional mechanisms dominate the regulation in the serotoninergic system, whereas in the opioid system proteins are further modulated after transcription. We conclude that mRNA information can be exploited for systems where translational mechanisms predominantly regulate expression. Where posttranscriptional mechanisms are important, mRNA data have to be interpreted with caution. The methodology developed here can be used for probing assumptions about the relationship of mRNA and protein in multiple neurotransmission systems.

Subcortical and Deep Cortical Atrophy in Frontotemporal Dementia due to Granulin Mutations

BACKGROUND/AIMS

Parkinsonism is often associated with symptoms of frontotemporal dementia (FTD), but its pathogenesis has been largely neglected. In genetic inherited FTD-related granulin (GRN) mutations, parkinsonism is an early sign, and it is more common than in sporadic disorders. Our aim was to study grey matter (GM) volume changes in subcortical and deep cortical regions in GRN-related FTD.

METHODS

A total of 33 FTD patients (13 carriers of the GRN mutation, GRN+, and 20 non-carriers, GRN-) and 12 healthy controls (HC) were included in the study. Each subject underwent an MRI examination (1) for voxel-based morphometry to study GM differences in cortical and subcortical regions, and (2) for a region of interest approach using a probabilistic atlas of subcortical regions (caudate nucleus, putamen, thalamus and amygdala) to assess the regional differences.

RESULTS

The GRN+ group showed greater damage in frontotemporal regions than the GRN- group. The FTD patients had greater GM atrophy in the caudate nucleus and in the thalamus bilaterally than the HC. Damage to these subcortical and deep cortical regions was greater in the GRN+ than in the GRN- patients.

DISCUSSION

Subcortical and deep cortical involvement is a key feature of FTD, and more pronounced in GRN-related disease. Damage to the caudate region in GRN+ patients may explain the parkinsonism frequently associated since the early stages of the disease.

Test-retest reproducibility of cannabinoid-receptor type 1 availability quantified with the PET ligand [¹¹C]MePPEP

Background

Endocannabinoids are involved in normal cognition, and dysfunction in cannabinoid-receptor-mediated neurotransmission has been suggested in a variety of neurological and psychiatric pathologies. The type 1 cannabinoid receptor (CB₁) is widely expressed in the human central nervous system. The objective of this study was to quantify the test–retest reproducibility of measures of the PET ligand [¹¹C]MePPEP in order to assess the stability of CB₁-receptor quantification in humans in vivo.

Methods

Fifteen healthy subjects (eight females; median age 32 years, range 25 to 65 years) had a 90-minute PET scan on two occasions after injection of a median dose of [¹¹C]MePPEP of 364 MBq. Metabolite-corrected arterial plasma input functions were obtained for all scans. Eight ROIs, reflecting different levels of receptor densities/concentrations, were defined automatically: hippocampus, anterior cingulate gyrus, inferior frontal gyrus, caudate nucleus, globus pallidus, nucleus accumbens, thalamus, and pons. We used seven quantification methods: reversible compartmental models with one and two tissue classes, two and four rate constants, and a variable blood volume term (2kbv; 4kbv); model-free (spectral) analyses with and without regularisation, including one with voxel-wise quantification; the simplified reference tissue model (SRTM) with pons as a pseudo-reference region; and modified standard uptake values (mSUVs) calculated for the period of ~ 30–60 min after injection. Percentage test–retest change and between-subject variability were both assessed, and test–retest reliability was quantified by the intraclass correlation coefficient (ICC). The ratio of binding estimates pallidum:pons served as an indicator of a method's ability to reflect binding heterogeneity.

Results

Neither the SRTM nor the 4kbv model produced reliable measures, with ICCs around zero. Very good (> 0.75) or excellent (> 0.80) ICCs were obtained with the other methods. The most reliable were spectral analysis parametric maps (average across regions ± standard deviation 0.83 ± 0.03), rank shaping regularised spectral analysis (0.82 ± 0.05), and the 2kbv model (0.82 ± 0.09), but mSUVs were also reliable for most regions (0.79 ± 0.13). Mean test–retest changes among the five well-performing methods ranged from 12 ± 10% for mSUVs to 16% for 2kbv. Intersubject variability was high, with mean between-subject coefficients of variation ranging from 32 ± 13% for mSUVs to 45% for 2kbv. The highest pallidum:pons ratios of binding estimates were achieved by mSUV (4.2), spectral analysis-derived parametric maps (3.6), and 2kbv (3.6).

Conclusion

Quantification of CB₁ receptor availability using [¹¹C]MePPEP shows good to excellent reproducibility with several kinetic models and model-free analyses, whether applied on a region-of-interest or voxelwise basis. Simple mSUV measures were also reliable for most regions, but do not allow fully quantitative interpretation. [¹¹C]MePPEP PET is well placed as a tool to investigate CB₁-receptor mediated neurotransmission in health and disease.

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[11C]MePPEP is a PET tracer for cannabinoid receptors (CB1R).

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Extensive evaluation of [11C]MePPEP data quantification strategies in large sample

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We highlight successful methods to quantify CB1R in regions of interest.

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Highly reliable parametric maps (ICC 0.83 ± 0.03) allow whole-brain surveys.

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Modified standard uptake values also reliable, without arterial input functions

Assessment of biofeedback rehabilitation in post-stroke patients combining fMRI and gait analysis: a case study

BACKGROUND

The ability to walk independently is a primary goal for rehabilitation after stroke. Gait analysis provides a great amount of valuable information, while functional magnetic resonance imaging (fMRI) offers a powerful approach to define networks involved in motor control. The present study reports a new methodology based on both fMRI and gait analysis outcomes in order to investigate the ability of fMRI to reflect the phases of motor learning before/after electromyographic biofeedback treatment: the preliminary fMRI results of a post stroke subject's brain activation, during passive and active ankle dorsal/plantarflexion, before and after biofeedback (BFB) rehabilitation are reported and their correlation with gait analysis data investigated.

METHODS

A control subject and a post-stroke patient with chronic hemiparesis were studied. Functional magnetic resonance images were acquired during a block-design protocol on both subjects while performing passive and active ankle dorsal/plantarflexion. fMRI and gait analysis were assessed on the patient before and after electromyographic biofeedback rehabilitation treatment during gait activities. Lower limb three-dimensional kinematics, kinetics and surface electromyography were evaluated. Correlation between fMRI and gait analysis categorical variables was assessed: agreement/disagreement was assigned to each variable if the value was in/outside the normative range (gait analysis), or for presence of normal/diffuse/no activation of motor area (fMRI).

RESULTS

Altered fMRI activity was found on the post-stroke patient before biofeedback rehabilitation with respect to the control one. Meanwhile the patient showed a diffuse, but more limited brain activation after treatment (less voxels). The post-stroke gait data showed a trend towards the normal range: speed, stride length, ankle power, and ankle positive work increased. Preliminary correlation analysis revealed that consistent changes were observed both for the fMRI data, and the gait analysis data after treatment (R > 0.89): this could be related to the possible effects BFB might have on the central as well as on the peripheral nervous system.

CONCLUSIONS

Our findings showed that this methodology allows evaluation of the relationship between alterations in gait and brain activation of a post-stroke patient. Such methodology, if applied on a larger sample subjects, could provide information about the specific motor area involved in a rehabilitation treatment.

ITK: enabling reproducible research and open science

Reproducibility verification is essential to the practice of the scientific method. Researchers report their findings, which are strengthened as other independent groups in the scientific community share similar outcomes. In the many scientific fields where software has become a fundamental tool for capturing and analyzing data, this requirement of reproducibility implies that reliable and comprehensive software platforms and tools should be made available to the scientific community. The tools will empower them and the public to verify, through practice, the reproducibility of observations that are reported in the scientific literature. Medical image analysis is one of the fields in which the use of computational resources, both software and hardware, are an essential platform for performing experimental work. In this arena, the introduction of the Insight Toolkit (ITK) in 1999 has transformed the field and facilitates its progress by accelerating the rate at which algorithmic implementations are developed, tested, disseminated and improved. By building on the efficiency and quality of open source methodologies, ITK has provided the medical image community with an effective platform on which to build a daily workflow that incorporates the true scientific practices of reproducibility verification. This article describes the multiple tools, methodologies, and practices that the ITK community has adopted, refined, and followed during the past decade, in order to become one of the research communities with the most modern reproducibility verification infrastructure. For example, 207 contributors have created over 2400 unit tests that provide over 84% code line test coverage. The Insight Journal, an open publication journal associated with the toolkit, has seen over 360,000 publication downloads. The median normalized closeness centrality, a measure of knowledge flow, resulting from the distributed peer code review system was high, 0.46.

Initial evaluation of 18F-GE-179, a putative PET Tracer for activated N-methyl D-aspartate receptors

N-methyl D-aspartate (NMDA) ion channels play a key role in a wide range of physiologic (e.g., memory and learning tasks) and pathologic processes (e.g., excitotoxicity). To date, suitable PET markers of NMDA ion channel activity have not been available. (18)F-GE-179 is a novel radioligand that selectively binds to the open/active state of the NMDA receptor ion channel, displacing the binding of (3)H-tenocyclidine from the intrachannel binding site with an affinity of 2.4 nM. No significant binding was observed with 10 nM GE-179 at 60 other neuroreceptors, channels, or transporters. We describe the kinetic behavior of the radioligand in vivo in humans.

METHODS

Nine healthy participants (6 men, 3 women; median age, 37 y) each underwent a 90-min PET scan after an intravenous injection of (18)F-GE-179. Continuous arterial blood sampling over the first 15 min was followed by discrete blood sampling over the duration of the scan. Brain radioactivity (KBq/mL) was measured in summation images created from the attenuation- and motion-corrected dynamic images. Metabolite-corrected parent plasma input functions were generated. We assessed the abilities of 1-, 2-, and 3-compartment models to kinetically describe cerebral time-activity curves using 6 bilateral regions of interest. Parametric volume-of-distribution (V(T)) images were generated by voxelwise rank-shaping regularization of exponential spectral analysis (RS-ESA).

RESULTS

A 2-brain-compartment, 4-rate-constant model best described the radioligand's kinetics in normal gray matter of subjects at rest. At 30 min after injection, 37% of plasma radioactivity represented unmetabolized (18)F-GE-179. The highest mean levels of gray matter radioactivity were seen in the putamina and peaked at 7.5 min. A significant positive correlation was observed between K1 and V(T) (Spearman ρ = 0.398; P = 0.003). Between-subject coefficients of variation of V(T) ranged between 12% and 16%. Voxelwise RS-ESA yielded similar V(T)s and coefficients of variation.

CONCLUSION

(18)F-GE-179 exhibits high and rapid brain extraction, with a relatively homogeneous distribution in gray matter and acceptable between-subject variability. Despite its rapid peripheral metabolism, quantification of (18)F-GE-179 VT is feasible both within regions of interest and at the voxel level. The specificity of (18)F-GE-179 binding, however, requires further characterization with in vivo studies using activation and disease models.

A perfusion fMRI investigation of thematic and categorical context effects in the spoken production of object names

The context in which objects are presented influences the speed at which they are named. We employed the blocked cyclic naming paradigm and perfusion functional magnetic resonance imaging (fMRI) to investigate the mechanisms responsible for interference effects reported for thematically and categorically related compared to unrelated contexts. Naming objects in categorically homogeneous contexts induced a significant interference effect that accumulated from the second cycle onwards. This interference effect was associated with significant perfusion signal decreases in left middle and posterior lateral temporal cortex and the hippocampus. By contrast, thematically homogeneous contexts facilitated naming latencies significantly in the first cycle and did not differ from heterogeneous contexts thereafter, nor were they associated with any perfusion signal changes compared to heterogeneous contexts. These results are interpreted as being consistent with an account in which the interference effect both originates and has its locus at the lexical level, with an incremental learning mechanism adapting the activation levels of target lexical representations following access. We discuss the implications of these findings for accounts that assume thematic relations can be active lexical competitors or assume mandatory involvement of top-down control mechanisms in interference effects during naming.

Automatic structural parcellation of mouse brain MRI using multi-atlas label fusion

Multi-atlas segmentation propagation has evolved quickly in recent years, becoming a state-of-the-art methodology for automatic parcellation of structural images. However, few studies have applied these methods to preclinical research. In this study, we present a fully automatic framework for mouse brain MRI structural parcellation using multi-atlas segmentation propagation. The framework adopts the similarity and truth estimation for propagated segmentations (STEPS) algorithm, which utilises a locally normalised cross correlation similarity metric for atlas selection and an extended simultaneous truth and performance level estimation (STAPLE) framework for multi-label fusion. The segmentation accuracy of the multi-atlas framework was evaluated using publicly available mouse brain atlas databases with pre-segmented manually labelled anatomical structures as the gold standard, and optimised parameters were obtained for the STEPS algorithm in the label fusion to achieve the best segmentation accuracy. We showed that our multi-atlas framework resulted in significantly higher segmentation accuracy compared to single-atlas based segmentation, as well as to the original STAPLE framework.

Comparison of PET template-based and MRI-based image processing in the quantitative analysis of C11-raclopride PET

Background

Quantitative measures of ¹¹C-raclopride receptor binding can be used as a correlate of postsynaptic D₂ receptor density in the striatum, allowing ¹¹C-raclopride positron emission tomography (PET) to be used for the differentiation of Parkinson’s disease from atypical parkinsonian syndromes. Comparison with reference values is recommended to establish a reliable diagnosis. A PET template specific to raclopride may facilitate direct computation of parametric maps without the need for an additional MR scan, aiding automated image analysis.

Methods

Sixteen healthy volunteers underwent a dynamic ¹¹C-raclopride PET and a high-resolution T1-weighted MR scan of the brain. PET data from eight healthy subjects was processed to generate a raclopride-specific PET template normalized to standard space. Subsequently, the data processing based on the PET template was validated against the standard magnetic resonance imaging (MRI)-based method in 8 healthy subjects and 20 patients with suspected parkinsonian syndrome. Semi-quantitative image analysis was performed in Montreal Neurological Institute (MNI) and in original image space (OIS) using VOIs derived from a probabilistic brain atlas previously validated by Hammers et al. (Hum Brain Mapp, 15:165–174, 2002).

Results

The striatal-to-cerebellar ratio (SCR) of ¹¹C-raclopride uptake obtained using the PET template was in good agreement with the MRI-based image processing method, yielding a Lin’s concordance coefficient of 0.87. Bland-Altman analysis showed that all measurements were within the ±1.96 standard deviation range. In all 20 patients, the PET template-based processing was successful and manual volume of interest optimization had no further impact on the diagnosis of PD in this patient group. A maximal difference of <5% was found between the measured SCR in MNI space and OIS.

Conclusions

The PET template-based method for automated quantification of postsynaptic D₂ receptor density is simple to implement and facilitates rapid, robust and reliable image analysis. There was no significant difference between the SCR values obtained with either PET- or MRI-based image processing. The method presented alleviates the clinical workflow and facilitates automated image analysis.

Fast parallel image registration on CPU and GPU for diagnostic classification of Alzheimer's disease

Nonrigid image registration is an important, but time-consuming task in medical image analysis. In typical neuroimaging studies, multiple image registrations are performed, i.e., for atlas-based segmentation or template construction. Faster image registration routines would therefore be beneficial. In this paper we explore acceleration of the image registration package elastix by a combination of several techniques: (i) parallelization on the CPU, to speed up the cost function derivative calculation; (ii) parallelization on the GPU building on and extending the OpenCL framework from ITKv4, to speed up the Gaussian pyramid computation and the image resampling step; (iii) exploitation of certain properties of the B-spline transformation model; (iv) further software optimizations. The accelerated registration tool is employed in a study on diagnostic classification of Alzheimer's disease and cognitively normal controls based on T1-weighted MRI. We selected 299 participants from the publicly available Alzheimer's Disease Neuroimaging Initiative database. Classification is performed with a support vector machine based on gray matter volumes as a marker for atrophy. We evaluated two types of strategies (voxel-wise and region-wise) that heavily rely on nonrigid image registration. Parallelization and optimization resulted in an acceleration factor of 4-5x on an 8-core machine. Using OpenCL a speedup factor of 2 was realized for computation of the Gaussian pyramids, and 15-60 for the resampling step, for larger images. The voxel-wise and the region-wise classification methods had an area under the receiver operator characteristic curve of 88 and 90%, respectively, both for standard and accelerated registration. We conclude that the image registration package elastix was substantially accelerated, with nearly identical results to the non-optimized version. The new functionality will become available in the next release of elastix as open source under the BSD license.

Enhanced orbitofrontal cortex function and lack of attentional bias to cocaine cues in recreational stimulant users

BACKGROUND

Although cocaine is known to be a highly addictive drug, there appears to be a select subset of individuals who are able to use the substance recreationally without developing dependence. These individuals do not report experiencing feelings of craving for cocaine, an important distinction from dependent users. However, no prior studies have compared attentional bias with cocaine cues between these groups to confirm this difference. Additionally, previous investigations into cognitive abilities in these individuals have been conflicting, and no research has been conducted on the neurobiological processes underlying cognitive functioning in this group.

METHODS

This study administered the emotional cocaine-word Stroop to 27 recreational cocaine users, 50 stimulant-dependent individuals, and 52 healthy control participants during functional magnetic resonance imaging scanning. Behavioral and functional imaging results were compared between groups to assess attentional bias and cognitive effort to resist salient cocaine stimuli.

RESULTS

Recreational users did not exhibit attentional bias to the cocaine words and did not differ from control subjects on task performance. Conversely, stimulant-dependent individuals were significantly more impaired on the task. Recreational participants also displayed a unique pattern of activation during performance, with significant underactivation in the orbitofrontal and anterior cingulate cortices compared with both dependent users and control subjects.

CONCLUSIONS

The absence of bias to cocaine-related stimuli in recreational users indicates they do not share attentional preference for these words with dependent users. Their distinct pattern of activation suggests a decreased need for cognitive control due to diminished desire for the drug, potentially serving as a resilience factor against dependence.

MR-less surface-based amyloid assessment based on 11C PiB PET

Background

β-amyloid (Aβ) plaques in brain's grey matter (GM) are one of the pathological hallmarks of Alzheimer's disease (AD), and can be imaged in vivo using Positron Emission Tomography (PET) with ¹¹C or ¹⁸F radiotracers. Estimating Aβ burden in cortical GM has been shown to improve diagnosis and monitoring of AD. However, lacking structural information in PET images requires such assessments to be performed with anatomical MRI scans, which may not be available at different clinical settings or being contraindicated for particular reasons. This study aimed to develop an MR-less Aβ imaging quantification method that requires only PET images for reliable Aβ burden estimations.

Materials and Methods

The proposed method has been developed using a multi-atlas based approach on ¹¹C-PiB scans from 143 subjects (75 PiB+ and 68 PiB- subjects) in AIBL study. A subset of 20 subjects (PET and MRI) were used as atlases: 1) MRI images were co-registered with tissue segmentation; 2) 3D surface at the GM-WM interfacing was extracted and registered to a canonical space; 3) Mean PiB retention within GM was estimated and mapped to the surface. For other participants, each atlas PET image (and surface) was registered to the subject's PET image for PiB estimation within GM. The results are combined by subject-specific atlas selection and Bayesian fusion to generate estimated surface values.

Results

All PiB+ subjects (N = 75) were highly correlated between the MR-dependent and the PET-only methods with Intraclass Correlation (ICC) of 0.94, and an average relative difference error of 13% (or 0.23 SUVR) per surface vertex. All PiB- subjects (N = 68) revealed visually akin patterns with a relative difference error of 16% (or 0.19 SUVR) per surface vertex.

Conclusion

The demonstrated accuracy suggests that the proposed method could be an effective clinical inspection tool for Aβ imaging scans when MRI images are unavailable.

Complex visual search in children and adolescents: effects of age and performance on fMRI activation

Complex visuospatial processing relies on distributed neural networks involving occipital, parietal and frontal brain regions. Effects of physiological maturation (during normal brain development) and proficiency on tasks requiring complex visuospatial processing have not yet been studied extensively, as they are almost invariably interrelated. We therefore aimed at dissociating the effects of age and performance on functional MRI (fMRI) activation in a complex visual search task. In our cross-sectional study, healthy children and adolescents (n = 43, 19 females, 7-17 years) performed a complex visual search task during fMRI. Resulting activation was analysed with regard to the differential effects of age and performance. Our results are compatible with an increase in the neural network's efficacy with age: within occipital and parietal cortex, the core regions of the visual exploration network, activation increased with age, and more so in the right than in the left hemisphere. Further, activation outside the visual search network decreased with age, mainly in left inferior frontal, middle temporal, and inferior parietal cortex. High-performers had stronger activation in right superior parietal cortex, suggesting a more mature visual search network. We could not see effects of age or performance in frontal cortex. Our results show that effects of physiological maturation and effects of performance, while usually intertwined, can be successfully disentangled and investigated using fMRI in children and adolescents.

Quantitative cerebral perfusion imaging in children and young adults with Moyamoya disease: comparison of arterial spin-labeling-MRI and H(2)[(15)O]-PET

BACKGROUND AND PURPOSE

Cerebral perfusion assessment is important in the preoperative evaluation and postoperative follow-up of patients with Moyamoya disease. The objective of this study was to evaluate the correlation of quantitative CBF measurements performed with arterial spin-labeling-MR imaging and H2[(15)O]-PET in children and young adults with Moyamoya disease.

MATERIALS AND METHODS

Thirteen children and young adults (8 female patients; age, 9.7 ± 7.1 years; range, 1-23 years) with Moyamoya disease underwent cerebral perfusion imaging with H2[(15)O]-PET (Discovery STE PET/CT, 3D Fourier rebinning filtered back-projection, 128 × 128 × 47 matrix, 2.34 × 2.34 × 3.27 mm(3) voxel spacing) and arterial spin-labeling (3T scanner, 3D pulsed continuous arterial spin-labeling sequence, 32 axial sections, TR = 5.5 seconds, TE = 25 ms, FOV = 24 cm, 128 × 128 matrix, 1.875 × 1.875 × 5 mm(3) voxel spacing) within less than 2 weeks of each other. Perfusion of left and right anterior cerebral artery, MCA, and posterior cerebral artery territories was qualitatively assessed for arterial spin-labeling-MR imaging and H2[(15)O]-PET by 2 independent readers by use of a 3-point-Likert scale. Quantitative correlation of relative CBF with cerebellar normalization between arterial spin-labeling-MR imaging and H2[(15)O]-PET was evaluated in a volume-based approach for each vascular territory after 3D image coregistration.

RESULTS

Interreader agreement was good (κ = 0.67-0.69), and strong and significant correlations were found between arterial spin-labeling-MR imaging and H2[(15)O]-PET for both qualitative perfusion scoring (ρ = 0.77; P < .001) and quantitative perfusion assessment of relative CBF with cerebellar normalization (r = 0.67, P < .001).

CONCLUSIONS

In children and young adults with Moyamoya disease, quantitative evaluation of CBF is possible with the use of arterial spin-labeling-MR imaging without ionizing radiation or contrast injection with a good correlation to H2[(15)O]-PET after cerebellar normalization.

Neural and behavioral correlates of aberrant salience in individuals at risk for psychosis

The "aberrant salience" model proposes that psychotic symptoms first emerge when chaotic brain dopamine transmission leads to the attribution of significance to stimuli that would normally be considered irrelevant. This is thought to occur during the prodromal phase of psychotic disorders, but this prediction has not been tested previously. In the present study, we tested this model in 18 healthy volunteers and 18 unmedicated individuals at ultra-high risk of psychosis. Subjects performed the Salience Attribution Test, which provides behavioral measures of adaptive and aberrant motivational salience, during functional magnetic resonance imaging to assess neural responses to relevant and irrelevant stimulus features. On a separate occasion, the same subjects were also studied with [(18)F]fluorodopa positron emission tomography to measure dopamine synthesis capacity. Individuals at ultra-high risk of psychosis were more likely to attribute motivational salience to irrelevant stimulus features (t(26.7) = 2.8, P = .008), and this bias was related to the severity of their delusion-like symptoms (r = .62, P = .008). Ventral striatal responses to irrelevant stimulus features were also correlated with delusion-like symptoms in the ultra-high risk group (r = .59, P = .017). Striatal dopamine synthesis capacity correlated negatively with hippocampal responses to irrelevant stimulus features in ultra-high risk individuals, but this relationship was positive in controls. These data are consistent with the hypothesis that aberrant salience processing underlies psychotic symptoms and involves functional alterations in the striatum, hippocampus, and the subcortical dopamine system.

Cholinergic basal forebrain atrophy predicts amyloid burden in Alzheimer's disease

We compared accuracy of hippocampus and basal forebrain cholinergic system (BFCS) atrophy to predict cortical amyloid burden in 179 cognitively normal subjects (CN), 269 subjects with early stages of mild cognitive impairment (MCI), 136 subjects with late stages of MCI, and 86 subjects with Alzheimer's disease (AD) dementia retrieved from the Alzheimer's Disease Neuroimaging Initiative database. Hippocampus and BFCS volumes were determined from structural magnetic resonance imaging scans at 3 Tesla, and cortical amyloid load from AV45 (florbetapir) positron emission tomography scans. In receiver operating characteristics analyses, BFCS volume provided significantly more accurate classification into amyloid-negative and -positive categories than hippocampus volume. In contrast, hippocampus volume more accurately identified the diagnostic categories of AD, late and early MCI, and CN compared with whole and anterior BFCS volume, whereas posterior BFCS and hippocampus volumes yielded similar diagnostic accuracy. In logistic regression analysis, hippocampus and posterior BFCS volumes contributed significantly to discriminate MCI and AD from CN, but only BFCS volume predicted amyloid status. Our findings suggest that BFCS atrophy is more closely associated with cortical amyloid burden than hippocampus atrophy in predementia AD.

Hippocampal volume loss following childhood convulsive status epilepticus is not limited to prolonged febrile seizures

Purpose

Childhood convulsive status epilepticus (CSE), in particular prolonged febrile seizures (PFS), has been linked with mesial temporal sclerosis (MTS). Previous studies have shown that hippocampal injury occurs in the acute phase immediately following CSE, but little is known about the longer term evolution of such injury. This study aimed to investigate the longer term outcome of childhood CSE with sequential magnetic resonance imaging (MRI) looking for progressive hippocampal injury during the first year post-CSE.

Methods

Eighty children (0.18–15.5 years) underwent brain MRI 1 month post-CSE, 50 with a repeat MRI at 6 months and 46 with repeat MRI at 12 months post-CSE. Thirty-one control subjects without neurologic problems had a single brain MRI for comparison. Hippocampal volumes were measured from each MRI scan by two independent observers, and hippocampal growth rates were estimated in each patient with suitable imaging.

Key Findings

Hippocampal volume loss was found in 20–30% of patients and was not associated with the etiology or clinical features of CSE, including seizure duration or focality. A borderline association was found between a history of previous seizures (p = 0.063) and the number of previous febrile seizures (p = 0.051), suggesting that multiple insults may be important in the pathogenesis of progressive hippocampal injury.

Significance

It is apparent that progressive hippocampal damage can occur after CSE of any etiology and is not limited to PFS. Repeated seizures may play an important role, but further follow-up is needed to determine any other risk factors and proportion of children showing initial volume loss progress to clinical MTS and temporal lobe epilepsy.

Extensive left temporal pole damage does not impact on theory of mind abilities

The temporal poles (TPs) are among the brain regions that are often considered as the brain network sustaining our ability to understand other people's mental states or "Theory of Mind" (ToM). However, so far the functional role of the left and right TPs in ToM is still debated, and it is even not clear yet whether these regions are necessary for ToM. In this study, we tested whether the left TP is necessary for ToM by assessing the mentalizing abilities of a patient (C.M.) diagnosed with semantic dementia. Converging evidence from detailed MRI and (18)F-fluoro-2-deoxy-d-glucose PET examinations showed a massive atrophy of the left TP with the right TP being relatively unaffected. Furthermore, C.M.'s atrophy encompassed most regions of the left TP usually activated in neuroimaging studies investigating ToM. Given C.M.'s language impairments, we used a battery of entirely nonverbal ToM tasks. Across five tasks encompassing 100 trials, which probed the patient's ability to attribute various mental states (intentions, knowledge, and beliefs), C.M. showed a totally spared performance. This finding suggests that, despite its consistently observed activation in neuroimaging studies involving ToM tasks, the left TP is not necessary for ToM reasoning, at least in nonverbal conditions and as long as its right counterpart is preserved. Implications for understanding the social abilities of patients with semantic dementia are discussed.

individual variation in sleep quality and duration is related to cerebral mu opioid receptor binding potential during tonic laboratory pain in healthy subjects

OBJECTIVE

Although poor sleep is a consequence of pain, sleep disturbance reciprocally induces hyperalgesia and exacerbates clinical pain. Conceptual models of chronic pain implicate dysfunctional supraspinal pain processing mechanisms, mediated in part by endogenous opioid peptides. Our preliminary work indicates that sleep disruption impairs psychophysical measures of descending pain modulation, but few studies have investigated whether insufficient sleep may be associated with alterations in endogenous opioid systems. This preliminary, exploratory investigation sought to examine the relationship between sleep and functioning of the cerebral mu opioid system during the experience of pain in healthy participants.

SUBJECTS AND DESIGN

Twelve healthy volunteers participated in a 90-minute positron emission tomography imaging scan using [11C]Carfentanil, a mu opioid receptors agonist. During the session, pain responses to a 10% topical capsaicin cream were continuously rated on a 0-100 scale. Participants also completed the Pittsburgh Sleep Quality Index (PSQI).

RESULTS

Poor sleep quality (PSQI) was positively and significantly associated with greater binding potential (BP) in regions within the frontal lobes. In addition, sleep duration was negatively associated with BP in these areas as well as the temporal lobe and anterior cingulate.

CONCLUSIONS

These findings suggest that poor sleep quality and short sleep duration are associated with endogenous opioid activity in these brain regions during the application of a noxious stimulus. Elucidating the role of the endogenous opioid system in mediating some of the associations between sleep and pain could significantly improve our understanding of the pathophysiology of chronic pain and might advance clinical practice by suggesting interventions that could buffer the adverse effects of poor sleep on pain.

Differences in functional connectivity in major depression versus bipolar II depression

BACKGROUND

Objective methods of differentiating unipolar versus bipolar depression would enhance our ability to treat these disorders by providing more accurate diagnoses. One first step towards developing diagnostic methodology is determining whether brain function as assessed by functional MRI (fMRI) and functional connectivity analyses might differentiate the two disorders.

METHODS

Fourteen subjects with bipolar II depression and 26 subjects with recurrent unipolar depression were studied using fMRI and functional connectivity analyses.

RESULTS

The first key finding of this study was that functional connectivity of the right posterior cingulate cortex differentiates bipolar II and unipolar depression. Additionally, results suggest that functional connectivity of this region is associated with suicidal ideation and depression severity in unipolar but not bipolar II depression.

LIMITATIONS

The primary limitation is the relatively small sample size, particularly for the correlational analyses.

CONCLUSIONS

The functional connectivity of right posterior cingulate cortex may differential unipolar from bipolar II depression. Further, connectivity of this region may be associated with depression severity and suicide risk in unipolar but not bipolar depression.

Periventricular [(11)C]flumazenil binding for predicting postoperative outcome in individual patients with temporal lobe epilepsy and hippocampal sclerosis

A third of patients with intractable temporal lobe epilepsy and hippocampal sclerosis (HS) are not seizure free (NSF) after surgery. Increased periventricular [¹¹C]flumazenil (FMZ) binding, reflecting heterotopic neuron concentration, has been described as one predictor of NSF outcome at the group level. We aimed to replicate this finding in an independent larger cohort and investigated whether NSF outcome can be predicted in individuals.

Preoperative [¹¹C]FMZ summed radioactivity images were available for 16 patients with HS and 41 controls. Images were analyzed using SPM8, explicitly including the white matter, and correction for global radioactivity via group-specific ANCOVA. Periventricular increases were assessed with a mask and different cutoffs for distinguishing NSF and seizure free (SF) patients.

NSF patients had increased [¹¹C]FMZ binding around the posterior horn of the ventricles ipsilaterally (z = 2.53) and contralaterally (z = 4.44) to the seizure focus compared with SF patients. Compared with controls, SF patients had fewer periventricular increases (two clusters, total volume 0.87 cm³, z_max = 3.8) than NSF patients (two ipsilateral and three contralateral clusters, 6.15 cm³, z_max = 4.8). In individuals and at optimized cutoffs, five (63%) of eight NSF patients and one (13%) of eight SF patients showed periventricular increases compared with controls (accuracy 75%). Only one (2%) of the 41 controls had increases at the same cutoff.

The association between periventricular [¹¹C]FMZ increases and NSF outcome after temporal lobe resection for HS has been confirmed in an independent cohort on simple summed activity images. [¹¹C]FMZ-PET may be useful for individual preoperative counseling with clinically relevant accuracy.

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[¹¹C]FMZ periventricular WM binding for predicting surgery outcome in mTLE-HS.

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Summed radioactivity images allowed replicating a prior study at the group level.

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Blood sampling constraint removed in comparison to the previous study.

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Periventricular abnormalities may allow predicting surgery outcome in individuals.

Magnetic resonance volumetry reveals focal brain atrophy in transient epileptic amnesia

Transient epileptic amnesia (TEA) is a recently described epilepsy syndrome characterized by recurrent episodes of isolated memory loss. It is associated with two unusual forms of interictal memory impairment: accelerated long-term forgetting (ALF) and autobiographical amnesia. We investigated the neural basis of TEA using manual volumetry and automated multi-atlas-based segmentation of whole-brain magnetic resonance imaging data from 40 patients with TEA and 20 healthy controls. Both methods confirmed the presence of subtle, bilateral hippocampal atrophy. Additional atrophy was revealed in perirhinal and orbitofrontal cortices. The volumes of these regions correlated with anterograde memory performance. No structural correlates were found for ALF or autobiographical amnesia. The results support the hypothesis that TEA is a focal medial temporal lobe epilepsy syndrome but reveal additional pathology in connected brain regions. The unusual interictal memory deficits of TEA remain unexplained by structural pathology and may reflect physiological disruption of memory networks by subclinical epileptiform activity.

Associations between children's socioeconomic status and prefrontal cortical thickness

Childhood socioeconomic status (SES) predicts executive function performance and measures of prefrontal cortical function, but little is known about its anatomical correlates. Structural MRI and demographic data from a sample of 283 healthy children from the NIH MRI Study of Normal Brain Development were used to investigate the relationship between SES and prefrontal cortical thickness. Specifically, we assessed the association between two principal measures of childhood SES, family income and parental education, and gray matter thickness in specific subregions of prefrontal cortex and on the asymmetry of these areas. After correcting for multiple comparisons and controlling for potentially confounding variables, parental education significantly predicted cortical thickness in the right anterior cingulate gyrus and left superior frontal gyrus. These results suggest that brain structure in frontal regions may provide a meaningful link between SES and cognitive function among healthy, typically developing children.

Neurological features of epilepsy, ataxia, sensorineural deafness, tubulopathy syndrome

AIM

Recently, we reported a previously unrecognized symptom constellation comprising epilepsy, ataxia, sensorineural deafness, and tubulopathy (EAST syndrome) associated with recessive mutations in the KCNJ10 gene. Here, we provide a detailed characterization of the clinical features of the syndrome to aid patient management with respect to diagnosis, prognostic counselling, and identification of best treatment modalities.

METHOD

We conducted a retrospective review of the detailed neurological and neuroradiological features of nine children (four females, five males; age range at last examination 6-20y) with genetically proven EAST syndrome.

RESULTS

All children presented with tonic-clonic seizures in infancy. Later, non-progressive, cerebellar ataxia and hearing loss were noted. Whilst seizures mostly responded well to treatment, ataxia proved to be the most debilitating feature, with three patients non-ambulant. All available magnetic resonance imaging (MRI) revealed subtle symmetrical signal changes in the cerebellar dentate nuclei. Moreover, four patients had a small corpus callosum and brainstem hypoplasia, and three had a small spinal cord. Regional quantitative volumetric analysis of the images confirmed the corpus callosum and brainstem hypoplasia and showed further patterns of variation from the norm.

INTERPRETATION

The neurological features of EAST syndrome appear to be non-progressive, which is important for prognostic counselling. The spectrum of EAST syndrome includes consistent abnormalities on brain MRI, which may aid diagnosis. Further longitudinal documentation is required to determine the true natural history of the disorder.

[¹¹C]-(R)PK11195 tracer kinetics in the brain of glioma patients and a comparison of two referencing approaches

PURPOSE

Translocator protein (TSPO) is a biomarker of neuroinflammation that can be imaged by PET using [¹¹C]-(R)PK11195. We sought to characterize the [¹¹C]-(R)PK11195 kinetics in gliomas of different histotypes and grades, and to compare two reference tissue input functions (supervised cluster analysis versus cerebellar grey matter) for the estimation of [¹¹C]-(R)PK11195 binding in gliomas and surrounding brain structures.

METHODS

Twenty-three glioma patients and ten age-matched controls underwent structural MRI and dynamic [¹¹C]-(R)PK11195 PET scans. Tissue time-activity curves (TACs) were extracted from tumour regions as well as grey matter (GM) and white matter (WM) of the brains. Parametric maps of binding potential (BPND) were generated with the simplified reference tissue model using the two input functions, and were compared with each other. TSPO expression was assessed in tumour tissue sections by immunohistochemistry.

RESULTS

Three types of regional kinetics were observed in individual tumour TACs: GM-like kinetics (n=6, clearance of the tracer similar to that in cerebellar GM), WM-like kinetics (n=8, clearance of the tracer similar to that in cerebral WM) and a form of mixed kinetics (n=9, intermediate rate of clearance). Such kinetic patterns differed between low-grade astrocytomas (WM-like kinetics) and oligodendrogliomas (GM-like and mixed kinetics), but were independent of tumour grade. There was good agreement between parametric maps of BPND derived from the two input functions in all controls and 10 of 23 glioma patients. In 13 of the 23 patients, BPND values derived from the supervised cluster input were systematically smaller than those using the cerebellar input. Immunohistochemistry confirmed that TSPO expression increased with tumour grade.

CONCLUSION

The three types of [¹¹C]-(R)PK11195 kinetics in gliomas are determined in part by tracer delivery, and indicated that kinetic analysis is a valuable tool in the study of gliomas with the potential for in vivo discrimination between low-grade astrocytomas and oligodendrogliomas. Supervised cluster and cerebellar input functions produced consistent BPND estimates in approximately half of the gliomas investigated, but had a systematic difference in the remainder. The cerebellar input is preferred based on theoretical and practical considerations.

What MEG can reveal about inference making: the case of if...then sentences

Characterizing the neural substrate of reasoning has been investigated with regularity over the last 10 years or so while relying on measures that come primarily from positron emission tomography and functional magnetic resonance imaging. To some extent, these techniques—as well as those from electroencephalography—have shown that time course is equally worthwhile for revealing the way reasoning processes work in the brain. In this work, we employ magnetoencephalography while investigating Modus Ponens (If P then Q; P//Therefore, Q) in order to simultaneously derive time course and the source of this fundamental logical inference. The present results show that conditional reasoning involves several successive cognitive processes, each of which engages a distinct cerebral network over the course of inference making, and as soon as a conditional sentence is processed.

Distinctive personality traits and neural correlates associated with stimulant drug use versus familial risk of stimulant dependence

BACKGROUND

Stimulant drugs such as cocaine and amphetamine have a high abuse liability, but not everyone who uses them develops dependence. However, the risk for dependence is increased for individuals with a family history of addiction. We hypothesized that individuals without a family history of dependence who have been using cocaine recreationally for several years but have not made the transition to dependence will differ in terms of personality traits and brain structure from individuals who are either dependent on stimulants or at risk for dependence.

METHODS

We compared 27 individuals without a familial risk of dependence who had been using cocaine recreationally with 50 adults with stimulant dependence, their nondependent siblings (n = 50), and unrelated healthy volunteers (n = 52) who had neither a personal nor a family history of dependence. All participants underwent a magnetic resonance imaging brain scan and completed a selection of personality measures that have been associated with substance abuse.

RESULTS

Increased sensation-seeking traits and abnormal orbitofrontal and parahippocampal volume were shared by individuals who were dependent on stimulant drugs or used cocaine recreationally. By contrast, increased levels of impulsive and compulsive personality traits and limbic-striatal enlargement were shared by stimulant-dependent individuals and their unaffected siblings.

CONCLUSIONS

We provide evidence for distinct neurobiological phenotypes that are either associated with familial vulnerability for dependence or with regular stimulant drug use. Our findings further suggest that some individuals with high sensation-seeking traits but no familial vulnerability for dependence are likely to use cocaine but may have relatively low risk for developing dependence.

Presynaptic striatal dopamine dysfunction in people at ultra-high risk for psychosis: findings in a second cohort

BACKGROUND

Using positron emission tomography (PET), we previously observed increases in 3,4-dihydroxy-6-[(18)F]fluoro-L-phenylalanine ((18)F-DOPA) uptake in the striatum of subjects at ultra-high risk (UHR) for psychosis, indicating elevated presynaptic dopamine synthesis capacity. The purpose of this study was to test if this finding would be replicated in a second UHR cohort.

METHODS

(18)F-DOPA PET was used to estimate dopamine synthesis capacity in the striatum of an entirely new cohort of 26 individuals at UHR for psychosis (14 males, mean±SD age = 22.7±4.7 years) and 20 healthy volunteers matched for age and gender (11 males, mean±SD age = 24.5±4.5 years).

RESULTS

Dopamine synthesis capacity was elevated in the whole [t(44) = 2.6; p = .01, effect size = .81] and associative striatum [t(44) = 2.6; p = .01, effect size = .73] of UHR compared with control subjects. When the two samples were combined to give a final sample of 32 control and 50 UHR subjects, the higher levels of dopamine synthesis capacity in the UHR group reached significance across the whole [F(1,81) = 11.0; p = .001], associative [F(1,81) = 12.7; p = .001], and sensorimotor [F(1,81) = 4.7; p = .03], but not the limbic [F(1,81) = 2.1; p = .2], striatum.

CONCLUSIONS

The findings indicate that elevated dopamine synthesis capacity in the dorsal striatum is a robust feature of individuals at UHR for psychosis and provide further evidence that dopaminergic abnormalities precede the onset of psychosis.

Interaction of 11C-tariquidar and 11C-elacridar with P-glycoprotein and breast cancer resistance protein at the human blood-brain barrier

The adenosine triphosphate-binding cassette transporters P-glycoprotein (Pgp) and breast cancer resistance protein (BCRP) are 2 major gatekeepers at the blood-brain barrier (BBB) that restrict brain distribution of several clinically used drugs. In this study, we investigated the suitability of the radiolabeled Pgp/BCRP inhibitors (11)C-tariquidar and (11)C-elacridar to assess Pgp density in the human brain with PET.

METHODS

Healthy subjects underwent a first PET scan of 120-min duration with either (11)C-tariquidar (n = 6) or (11)C-elacridar (n = 5) followed by a second PET scan of 60-min duration with (R)-(11)C-verapamil. During scan 1 (at 60 min after radiotracer injection), unlabeled tariquidar (3 mg/kg) was intravenously administered. Data were analyzed using 1-tissue 2-rate-constant (1T2K) and 2-tissue 4-rate-constant (2T4K) compartment models and either metabolite-corrected or uncorrected arterial input functions.

RESULTS

After injection of (11)C-tariquidar or (11)C-elacridar, the brain PET signal corrected for radioactivity in the vasculature was low (~0.1 standardized uptake value), with slow washout. In response to tariquidar injection, a moderate but statistically significant rise in brain PET signal was observed for (11)C-tariquidar (+27% ± 15%, P = 0.014, paired t test) and (11)C-elacridar (+21% ± 15%, P = 0.014) without changes in plasma activity concentrations. Low levels of radiolabeled metabolites (<25%) were detected in plasma up to 60 min after injection of (11)C-tariquidar or (11)C-elacridar. The 2T4K model provided better data fits than the 1T2K model. Model outcome parameters were similar when metabolite-corrected or uncorrected input functions were used. There was no significant correlation between distribution volumes of (11)C-tariquidar or (11)C-elacridar and distribution volumes of (R)-(11)C-verapamil in different brain regions.

CONCLUSION

The in vivo behavior of (11)C-tariquidar and (11)C-elacridar was consistent with that of dual Pgp/BCRP substrates. Both tracers were unable to visualize cerebral Pgp density, most likely because of insufficiently high binding affinities in relation to the low density of Pgp in human brain (∼1.3 nM). Despite their inability to visualize Pgp density, (11)C-tariquidar and (11)C-elacridar may find use as a new class of radiotracers to study the interplay of Pgp and BCRP at the human BBB in limiting brain uptake of dual substrates.

Cortical sources of ERP in prosaccade and antisaccade eye movements using realistic source models

The cortical sources of event-related-potentials (ERP) using realistic source models were examined in a prosaccade and antisaccade procedure. College-age participants were presented with a preparatory interval and a target that indicated the direction of the eye movement that was to be made. In some blocks a cue was given in the peripheral location where the target was to be presented and in other blocks no cue was given. In Experiment 1 the prosaccade and antisaccade trials were presented randomly within a block; in Experiment 2 procedures were compared in which either prosaccade and antisaccade trials were mixed in the same block, or trials were presented in separate blocks with only one type of eye movement. There was a central negative slow wave occurring prior to the target, a slow positive wave over the parietal scalp prior to the saccade, and a parietal spike potential immediately prior to saccade onset. Cortical source analysis of these ERP components showed a common set of sources in the ventral anterior cingulate and orbital frontal gyrus for the presaccadic positive slow wave and the spike potential. In Experiment 2 the same cued- and non-cued blocks were used, but prosaccade and antisaccade trials were presented in separate blocks. This resulted in a smaller difference in reaction time between prosaccade and antisaccade trials. Unlike the first experiment, the central negative slow wave was larger on antisaccade than on prosaccade trials, and this effect on the ERP component had its cortical source primarily in the parietal and mid-central cortical areas contralateral to the direction of the eye movement. These results suggest that blocked prosaccade and antisaccade trials results in preparatory or set effects that decreases reaction time, eliminates some cueing effects, and is based on contralateral parietal-central brain areas.

Dopaminergic function in the psychosis spectrum: an [18F]-DOPA imaging study in healthy individuals with auditory hallucinations

BACKGROUND

The psychosis phenotype appears to exist in the population as a continuum, but it is not clear if subclinical psychotic symptoms and psychotic disorders share the same neurobiology. We investigated whether the dopaminergic dysfunction seen in psychotic disorders is also present in healthy, well-functioning people with hallucinations.

METHODS

We compared dopamine synthesis capacity (using 6-[(18)F]fluoro-L-DOPA [[(18)F]-DOPA] positron emission tomography imaging) in 16 healthy individuals with frequent persistent auditory verbal hallucinations (hallucinating group) with that in 16 matched controls.

RESULTS

There was no significant difference in dopamine synthesis capacity in the striatum, or its functional subdivisions, between groups and no relationship between subclinical psychotic symptom severity or schizotypal traits and dopamine synthesis capacity in the hallucinating group.

CONCLUSIONS

Altered dopamine synthesis capacity is unlikely to underlie subclinical hallucinations, suggesting that although there may be a phenomenological psychosis continuum, there are distinctions at the neurobiological level.

Partial volume correction using structural-functional synergistic resolution recovery: comparison with geometric transfer matrix method

We validated the use of a novel image-based method for partial volume correction (PVC), structural-functional synergistic resolution recovery (SFS-RR) for the accurate quantification of dopamine synthesis capacity measured using [(18)F]DOPA positron emission tomography. The bias and reliability of SFS-RR were compared with the geometric transfer matrix (GTM) method. Both methodologies were applied to the parametric maps of [(18)F]DOPA utilization rates (ki(cer)). Validation was first performed by measuring repeatability on test-retest scans. The precision of the methodologies instead was quantified using simulated [(18)F]DOPA images. The sensitivity to the misspecification of the full-width-half-maximum (FWHM) of the scanner point-spread-function on both approaches was also assessed. In the in-vivo data, the ki(cer) was significantly increased by application of both PVC procedures while the reliability remained high (intraclass correlation coefficients >0.85). The variability was not significantly affected by either PVC approach (<10% variability in both cases). The corrected ki(cer) was significantly influenced by the FWHM applied in both the acquired and simulated data. This study shows that SFS-RR can effectively correct for partial volume effects to a comparable degree to GTM but with the added advantage that it enables voxelwise analyses, and that the FWHM used can affect the PVC result indicating the importance of accurately calibrating the FWHM used in the recovery model.

Cognitive control dysfunction and abnormal frontal cortex activation in stimulant drug users and their biological siblings

Cognitive and neural abnormalities are known to accompany chronic drug abuse, with impairments in cognition and changes in cortical structure seen in stimulant-dependent individuals. However, premorbid differences have also been observed in the brains and behavior of individuals at risk for substance abuse, before they develop dependence. Endophenotype research has emerged as a useful method for assessing preclinical traits that may be risk factors for pathology by studying patient populations and their undiagnosed first-degree relatives. This study used the color-word Stroop task to assess executive functioning in stimulant-dependent individuals, their unaffected biological siblings and unrelated healthy control volunteers using a functional magnetic resonance imaging paradigm. Both the stimulant-dependent and sibling participants demonstrated impairments in cognitive control and processing speed on the task, registering significantly longer response latencies. However, the two groups generated very different neural responses, with the sibling participants exhibiting a significant decrease in activation in the inferior frontal gyrus compared with both stimulant-dependent individuals and control participants. Both target groups also demonstrated a decrease in hemispheric laterality throughout the task, exhibiting a disproportionate increase in right hemispheric activation, which was associated with their behavioral inefficiencies. These findings not only suggest a possible risk factor for stimulant abuse of poor inhibitory control and cortical inefficiency but they also demonstrate possible adaptations in the brains of stimulant users.

Microglia, amyloid, and glucose metabolism in Parkinson's disease with and without dementia

[(11)C](R)PK11195-PET measures upregulation of translocator protein, which is associated with microglial activation, [(11)C]PIB-PET is a marker of amyloid, while [(18)F]FDG-PET measures cerebral glucose metabolism (rCMRGlc). We hypothesize that microglial activation is an early event in the Parkinson's disease (PD) spectrum and is independent of the amyloid pathology. The aim of this study is to evaluate in vivo the relationship between microglial activation, amyloid deposition, and glucose metabolism in Parkinson's disease dementia (PDD) and PD subjects without dementia. Here, we evaluated 11 PDD subjects, 8 PD subjects without dementia, and 24 control subjects. Subjects underwent T1 and T2 MRI, [(11)C](R)PK11195, [(18)F]FDG, and [(11)C]PIB PET scans. Parametric maps of [(11)C](R)PK11195 binding potential, rCMRGlc, and [(11)C]PIB uptake were interrogated using region of interest and SPM (statistical parametric mapping) analysis. The PDD patients showed a significant increase of microglial activation in anterior and posterior cingulate, striatum, frontal, temporal, parietal, and occipital cortical regions compared with the controls. The PD subjects also showed a statistically significant increase in microglial activation in temporal, parietal, and occipital regions. [(11)C]PIB uptake was marginally increased in PDD and PD. There was a significant reduction in glucose metabolism in PDD and PD. We have also demonstrated pixel-by-pixel correlation between mini-mental state examination (MMSE) score and microglial activation, and MMSE score and rCMRGlc. In conclusion, we have demonstrated that cortical microglial activation and reduced glucose metabolism can be detected early on in this disease spectrum. Significant microglial activation may be a factor in driving the disease process in PDD. Given this, agents that affect microglial activation could have an influence on disease progression.

Magnetic resonance imaging evidence for presymptomatic change in thalamus and caudate in familial Alzheimer's disease

Amyloid imaging studies of presymptomatic familial Alzheimer's disease have revealed the striatum and thalamus to be the earliest sites of amyloid deposition. This study aimed to investigate whether there are associated volume and diffusivity changes in these subcortical structures during the presymptomatic and symptomatic stages of familial Alzheimer's disease. As the thalamus and striatum are involved in neural networks subserving complex cognitive and behavioural functions, we also examined the diffusion characteristics in connecting white matter tracts. A cohort of 20 presenilin 1 mutation carriers underwent volumetric and diffusion tensor magnetic resonance imaging, neuropsychological and clinical assessments; 10 were symptomatic, 10 were presymptomatic and on average 5.6 years younger than their expected age at onset; 20 healthy control subjects were also studied. We conducted region of interest analyses of volume and diffusivity changes in the thalamus, caudate, putamen and hippocampus and examined diffusion behaviour in the white matter tracts of interest (fornix, cingulum and corpus callosum). Voxel-based morphometry and tract-based spatial statistics were also used to provide unbiased whole-brain analyses of group differences in volume and diffusion indices, respectively. We found that reduced volumes of the left thalamus and bilateral caudate were evident at a presymptomatic stage, together with increased fractional anisotropy of bilateral thalamus and left caudate. Although no significant hippocampal volume loss was evident presymptomatically, reduced mean diffusivity was observed in the right hippocampus and reduced mean and axial diffusivity in the right cingulum. In contrast, symptomatic mutation carriers showed increased mean, axial and in particular radial diffusivity, with reduced fractional anisotropy, in all of the white matter tracts of interest. The symptomatic group also showed atrophy and increased mean diffusivity in all of the subcortical grey matter regions of interest, with increased fractional anisotropy in bilateral putamen. We propose that axonal injury may be an early event in presymptomatic Alzheimer's disease, causing an initial fall in axial and mean diffusivity, which then increases with loss of axonal density. The selective degeneration of long-coursing white matter tracts, with relative preservation of short interneurons, may account for the increase in fractional anisotropy that is seen in the thalamus and caudate presymptomatically. It may be owing to their dense connectivity that imaging changes are seen first in the thalamus and striatum, which then progress to involve other regions in a vulnerable neuronal network.