Clusters Of Voxels Research Articles

Plant Phenotyping: An Active Vision Cell for Three-Dimensional Plant Shoot Reconstruction.

Three-dimensional (3D) computer-generated models of plants are urgently needed to support both phenotyping and simulation-based studies such as photosynthesis modeling. However, the construction of accurate 3D plant models is challenging, as plants are complex objects with an intricate leaf structure, often consisting of thin and highly reflective surfaces that vary in shape and size, forming dense, complex, crowded scenes. We address these issues within an image-based method by taking an active vision approach, one that investigates the scene to intelligently capture images, to image acquisition. Rather than use the same camera positions for all plants, our technique is to acquire the images needed to reconstruct the target plant, tuning camera placement to match the plant's individual structure. Our method also combines volumetric- and surface-based reconstruction methods and determines the necessary images based on the analysis of voxel clusters. We describe a fully automatic plant modeling/phenotyping cell (or module) comprising a six-axis robot and a high-precision turntable. By using a standard color camera, we overcome the difficulties associated with laser-based plant reconstruction methods. The 3D models produced are compared with those obtained from fixed cameras and evaluated by comparison with data obtained by x-ray microcomputed tomography across different plant structures. Our results show that our method is successful in improving the accuracy and quality of data obtained from a variety of plant types.

OA046] Visualizing sites of increased cellularity and high permeability in soft tissue sarcomas

Purpose Radiological evaluation of tumor aggressiveness is very frequently based on diffusion and/or perfusion imaging findings and conclusions are used to guide biopsy. The present work describes a post processing process that highlights areas of increased cellularity (low ADC) and also increased vascular transendothelial permeability (high K trans ), two of the most significant markers of malignancy, at the early stage of imaging. Preliminary results tested on 5 patients with soft tissue sarcomas are presented. Methods Quantitative ADC maps were generated from MR data by pixelwise mono-exponential fitting of multi-b (8b, 0–1500) DW images with custom-built tools written in Python. Similarly, K trans map was calculated based on the Extended Tofts Model from T1-w GRE data (temporal resolution 7 s, 45 time points). All pixel values assigned as tumor volume (3D ROI) were used as input for the initial whole tumor ADC and K trans histograms. As a next step, only pixels with values lower than the mean of ADC histogram and K trans values greater than the mean K trans were located and visualized in order to examine if a voxel cluster with adequate size is discriminated after thresholding. Patient population (5 male, mean age 60) comprised 3 dedifferentiated liposarcomas and 2 pleomorphic liposarcomas. Results Whole tumor pixel percentages with ADC value below the mean ADC value of the same ROI (used as histogram threshold) for the five high grade liposarcomas were: 58.7, 82.5, 52.1, 65.7, and 78.8%. Ktrans pixel percentages above the mean K trans (threshold) were: 11.8, 23.4, 4.3, 62.9, 39.9% respectively. The percentage of pixels meeting both criteria for low ADC and high K trans were: 4.2, 14.2, 0.6, 20.1, 15.3% respectively. Conclusion For 4 out of 5 patients visualization of a pixel cluster with adequate size that can be proposed as suitable site for preoperative needle biopsy was possible. Further appropriate ADC/ K trans thresholding can be used to increase disease conspicuity under certain criteria, depending on the special characteristics of each tumor subtype.

Classification of Alzheimer's Disease Stages: An Approach Using PCA-Based Algorithm.

Early diagnosis of Alzheimer's disease (AD) allows individuals and their health managers to manage healthier medication. We proposed an approach for classification of AD stages, with respect to principal component analysis (PCA)-based algorithm. The PCA has been extensively applied as the most auspicious face-recognition algorithm. For the proposed algorithm, 100 images of 10 children were transformed for feature extraction and covariance matrix was constructed to obtain eigenvalues. The eigenvector provided a useful framework for face recognition. For the classification of AD stages, magnetic resonance imaging (MRI) and functional magnetic resonance imaging (fMRI) data were obtained from Alzheimer's Disease Neuroimaging Initiative database. Hippocampus is one of the most affected regions by AD. Thus, we selected clusters of voxels from the "hippocampus" of AD screening stage (mild cognitive impairment), AD stage 1, AD stage 2, and AD stage 3. By using eigenvectors corresponding to maximum eigenvalues of fMRI data, the purposed algorithm classified the voxels of AD stages effectively.

Resting-state connectivity and spontaneous activity of ventromedial prefrontal cortex predict depressive symptomology and peripheral inflammation in HIV.

Depression and chronic inflammation are common in persons infected with the human immunodeficiency virus (HIV+). Although depression and response to inflammatory challenge are shown to reflect activity in common neural networks, little is known regarding sub-clinical presentation in persons chronically infected with HIV. The relationship of resting-state functional connectivity (rsFC) between the subgenual anterior cingulate cortex (sgACC) and bilateral amygdala to Beck Depression Inventory-1 (BDI) scores were compared within a group of 23 HIV+ and 23 HIV-negative comparison adults. An interaction was found wherein lower rsFC between the sgACC and both right and left amygdala was associated with higher BDI scores in HIV+ individuals. Total BDI scores and plasma levels of IL-6, IL-8, TNF-α, and IL-10 made available from 10 of the HIV+ patients were regressed upon an index of spontaneous whole-brain activity at rest; i.e., the amplitude of low-frequency fluctuations (ALFFs). Elevated levels of depression and IL-6 were associated with increased ALFF in a cluster of voxels on the medial portion of the ventral surface of the frontal lobe (Brodmann Area 11). Within this sampleof HIV+ individuals lowerrsFC of the sgACC with subcortical limbic regions predictsgreater burden of depressive symptomology whereaselevated activity in the adjacent BA 11 may reflect sickness, indexed by elevated IL-6,and associated depressive behaviors.

Effects of lesion extent and location on upper limb function following hemispheric stroke

A large proportion of stroke survivors present spastic paresis of the upper limb (UL). Therapeutic interventions result in large variance in the response of patients to the same treatment protocols, possibly stemming from differences in lesion characteristics, among other factors. Here we concentrated on the impact of lesion size and location on UL function following stroke, comparing the effect of right hemisphere damage (RHD) to that of left hemisphere damage (LHD). Clinical and lesion data for the current study were collected as part of a multicenter randomized, controlled trial (ENHANCE project; ClinicalTrials.gov, ID: NCT02725853 ). Two groups of patients with subacute stroke were compared: those with right hemisphere ( n = 8) and left hemisphere damage ( n = 15). Voxel-based lesion symptom mapping (VLSM) was employed to identify voxel clusters in the normalized brain where damage exerts a significant impact on the functioning of the hemiparetic UL, as revealed by the Functional Ability Scale of the short (streamlined) version of the Wolf Motor Function Test. Motor function of the hemiparetic UL was affected in LHD patients by damage to voxel clusters involving (a) cortical areas of the superior temporal regions and the insula, (b) white matter tracts, notably the superior and inferior fronto-occipital fascicles, the corona radiata and the internal capsule, and (c) the basal ganglia and thalamus. In the RHD group, VLSM analysis showed a different pattern where UL function was affected almost exclusively by damage to subcortical structures of the corona radiata, the capsular-putaminal region, the superior longitudinal fasciculus and the external capsule. Motor function of the hemiparetic upper limb in patients with subacute stroke was affected differently by damage to homologous structures in the left and right cerebral hemispheres.

Effects of lesion extent and location on upper limb spasticity following hemispheric stroke

Spasticity of the hemiparetic upper limb (UL) leading to difficulty performing activities of daily living is a major concern in stroke rehabilitation. Spasticity results from impaired control of motoneuronal activation thresholds exerted by descending direct and indirect pathways. This is reflected by pathological alteration of the specific muscle length/joint angle at which the stretch reflex and other proprioceptive reflexes begin to act (tonic stretch reflex threshold, TSRT). The relationship between lesion location and the appearance of spasticity is poorly understood. We investigated the relationship between lesion characteristics and elbow-flexor (biceps) TSRT in the hemiparetic UL, as part of an international multicenter RCT (ENHANCE project; ClinicalTrials.gov, ID: NCT02725853 ). Elbow-flexor TSRT (°) was examined in 8 right-hemisphere damaged (RHD) and 15 left hemisphere damaged (LHD) stroke patients using the Montreal Stretch Reflex Threshold device. Normalized lesion data were used for voxel-based lesion-symptom mapping (VLSM) analyses of lesion impact on biceps spasticity. Application of VLSM using 10 continuous affected voxels as a minimum for consideration, showed in the LHD group, a cluster localized in the superior part of the corona radiata, where damage affected the level of spasticity in the biceps as revealed by its TSRT (smaller clusters were recognized in the external capsule and insula). In the RHD group, VLSM failed to reveal voxel clusters where damage affected the biceps TSRT. The paucity of hemispheric voxels where damage is related to increased spasticity levels may indicate that impaired regulation of motoneuronal activation threshold after stroke is attributed to the sum effect of various brainstem control substrates (which cannot be analyzed using VLSM), rather than to direct corticospinal control.

Image-based Data Mining to Probe Dosimetric Correlates of Radiation-induced Trismus

To identify imaged regions in which dose is associated with radiation-induced trismus after head and neck cancer radiation therapy (HNRT) using a novel image-based data mining (IBDM) framework. A cohort of 86 HNRT patients were analyzed for region identification. Trismus was characterized as a continuous variable by the maximum incisor-to-incisor opening distance (MID) at 6 months after radiation therapy. Patient anatomies and dose distributions were spatially normalized to a common frame of reference using deformable image registration. IBDM was used to identify clusters of voxels associated with MID (P ≤ .05 based on permutation testing). The result was externally tested on a cohort of 35 patients with head and neck cancer. Internally, we also performed a dose-volume histogram-based analysis by comparing the magnitude of the correlation between MID and the mean dose for the IBDM-identified cluster in comparison with 5 delineated masticatory structures. A single cluster was identified with the IBDM approach (P < .01), partially overlapping with the ipsilateral masseter. The dose-volume histogram-based analysis confirmed that the IBDM cluster had the strongest association with MID, followed by the ipsilateral masseter and the ipsilateral medial pterygoid (Spearman's rank correlation coefficients: Rs = -0.36, -0.35, -0.32; P = .001, .001, .002, respectively). External validation confirmed an association between mean dose to the IBDM cluster and MID (Rs = -0.45; P = .007). IBDM bypasses the common assumption that dose patterns within structures are unimportant. Our novel IBDM approach for continuous outcome variables successfully identified a cluster of voxels that are highly associated with trismus, overlapping partially with the ipsilateral masseter. Tests on an external validation cohort showed an even stronger correlation with trismus. These results support use of the region in HNRT treatment planning to potentially reduce trismus.

Localization and Functional Characterization of an Occipital Visual Word form Sensitive Area

In human occipitotemporal cortex, category-specific processing for visual objects seems to involve pairs of cortical regions, often with one located in the occipital cortex and another more anteriorly. We investigated whether such an arrangement might be the case for visual word processing. In addition to the Visual Word Form Area (VWFA) located in the occipitotemporal sulcus, we observed that another region in occipital lobe with robust responses to written words (Chinese characters). The current fMRI study investigated this area’s precise location and its functional selectivity using Chinese characters and other categories of visual images (cars, chairs and insects). In all the 13 subjects we could identify a cluster of voxels near the inferior occipital gyrus or middle occipital gyrus with stronger responses to Chinese characters than scrambled objects. We tentatively label this area as the Occipital Word Form Sensitive Area (OWA). The OWA’s response amplitudes showed similar preference to written words as the VWFA, with the VWFA showing a higher degree of word selectivity, which was confirmed by the result from spatial patterns of response. These results indicate that the OWA, together with the VWFA, are critical parts of the network for processing and representing the category information for word.

F162. MORE EFFORT, BUT LESS EFFICIENCY - WORKING MEMORY IN SCHIZOPHRENIA: AN INVESTIGATION INTO CAUSE FOR DIVERGENT RESULTS

BackgroundFunctional brain imaging studies of working memory in people with schizophrenia have reported divergent reports with some studies reporting hypofrontal activation while report hypofrontal activation. The inconsistencies in the literature have been postulated to be related to task requirements or poor task performance in schizophrenia. An alternative hypothesis proposed is that different regions within the PFC show either hypo or hyperactivity, depending on their location. In view of the inconsistencies in previous research, the aim of the current research is to examine abnormalities in a cohort of partially remitted people with schizophrenia and matched controlsMethodsTwenty people with schizophrenia and 20 matched healthy controls (matched on age, gender and parental social and economic status) were selected from the Nottingham area to undergo a functional magnetic resonance imaging (fMRI) scan while undergoing two levels of the visual n-back task (zeroback and two back). The behavioural results (latency and accuracy) on the nback task was compared using repeated measures analysis. The MR images were reoriented, realigned, co-registered to the T1-weighted anatomical image, and normalised to the MNI space. Normalised images were resliced to a voxel size of 3 mm3, smoothed with an 8 mm full-width half-maximum Gaussian kernel using SPM 5. The GLM approach implemented in SPM 5 was utilized for fMRI data modeling and analyses. Each epoch type (zero-back, two-back and rest) was modeled in a boxcar design, using a canonical hemodynamic response function and its temporal derivative. The single group second level analysis consisted of voxelwise one-sample t-tests with significance threshold set at voxel level p < .05, false discovery rate (FDR) corrected for multiple comparisons across the entire brain.The between-group comparison employed voxelwise two sample t-tests with the significance criterion based on the spatial extent of suprathreshold voxel clusters, a method proposed by (Friston et al., 1994). The criterion for inclusion of a voxel in a cluster was set at p < .05 (uncorrected) and a cluster was considered as significant at level of p < .05 (corrected).ResultsPatients exhibited relatively high general function and mild symptoms, but had significantly longer reaction time and decline in performance. Both controls and patients activated similar set of brain regions similar to Central executive network and deactivated brain areas comprising the default mode network. Most noteworthy, we did not find evidence for hypofrontality (reduced activity in DLPFC in patients compared to controls) in this study. Compared to controls, patients showed areas of greater activation in left postcentral gyrus, anterior and posterior medial frontal gyrus and left superior temporal gyrus.DiscussionBoth controls and patients showed activation in widespread brain areas consistent with the CEN, and deactivation in areas consistent with DMN regions. There was no evidence of hypofrontality in this sample of remitted people with schizophrenia. Patients showed activation patterns on the zeroback task similar to the activation patterns for controls on the two back task, suggesting that patients showed increased brain activation on a task with lesser requirements, though behavioural results suggest inefficiency despite the increased effort.

The site of stimulation moderates neuropsychiatric symptoms after subthalamic deep brain stimulation for Parkinson's disease.

Deep brain stimulation of the subthalamic nucleus for Parkinson's disease is an established advanced therapy that addresses motor symptoms and improves quality of life. However, it has also been associated with neuropsychiatric symptoms such as impulsivity and hypomania. When significant, these symptoms can be distressing, necessitating psychiatric intervention. However, a comprehensive analysis of neurocognitive and neuropsychiatric outcomes with reference to the site of subthalamic stimulation has not been undertaken. We examined this matter in a consecutive sample of 64 persons with Parkinson's disease undertaking subthalamic deep brain stimulation. Participants were assessed with a battery of neuropsychiatric instruments at baseline and at repeated postoperative intervals. A psychiatrist identified patients with emergent, clinically-significant symptoms due to stimulation. The site of the active electrode contact and a simulated volume of activated tissue were evaluated with reference to putative limbic, associative and motor subregions of the subthalamic nucleus. We studied anatomical correlates of longitudinal neuropsychiatric change and delineated specific subthalamic regions associated with neuropsychiatric impairment. We tested the ability of these data to predict clinically-significant symptoms. Subthalamic stimulation within the right associative subregion was associated with inhibitory errors on the Excluded Letter Fluency task at 6-weeks (p = 0.023) and 13-weeks postoperatively (p = 0.0017). A cluster of subthalamic voxels associated with inhibitory errors was identified in the right associative and motor subregions. At 6-weeks, clinically-significant neuropsychiatric symptoms were associated with the distance of the active contact to the right associative subregion (p = 0.0026) and stimulation within the right associative subregion (p = 0.0009). At 13-weeks, clinically-significant symptoms were associated with the distance to the right (p = 0.0027) and left (p = 0.0084) associative subregions and stimulation within the right associative subregion (p = 0.0026). Discrete clusters of subthalamic voxels associated with high and low likelihood of postoperative neuropsychiatric symptoms were identified in ventromedial and dorsolateral zones, respectively. When a classifier was trained on these data, clinically-significant symptoms were predicted with an accuracy of 79%. These data underscore the importance of accurate electrode targeting, contact selection and device programming to reduce postoperative neuropsychiatric impairment. The ability to predict neuropsychiatric symptoms based on subthalamic data may permit anticipation and prevention of these occurrences, improving safety and tolerability.

Multi-Table Differential Correlation Analysis of Neuroanatomical and Cognitive Interactions in Turner Syndrome.

Girls and women with Turner syndrome (TS) have a completely or partially missing X chromosome. Extensive studies on the impact of TS on neuroanatomy and cognition have been conducted. The integration of neuroanatomical and cognitive information into one consistent analysis through multi-table methods is difficult and most standard tests are underpowered. We propose a new two-sample testing procedure that compares associations between two tables in two groups. The procedure combines multi-table methods with permutation tests. In particular, we construct cluster size test statistics that incorporate spatial dependencies. We apply our new procedure to a newly collected dataset comprising of structural brain scans and cognitive test scores from girls with TS and healthy control participants (age and sex matched). We measure neuroanatomy with Tensor-Based Morphometry (TBM) and cognitive function with Wechsler IQ and NEuroPSYchological tests (NEPSY-II). We compare our multi-table testing procedure to a single-table analysis. Our new procedure reports differential correlations between two voxel clusters and a wide range of cognitive tests whereas the single-table analysis reports no differences. Our findings are consistent with the hypothesis that girls with TS have a different brain-cognition association structure than healthy controls.

Sex differences in white matter alterations following repetitive subconcussive head impacts in collegiate ice hockey players.

ObjectiveRepetitive subconcussive head impacts (RSHI) may lead to structural, functional, and metabolic alterations of the brain. While differences between males and females have already been suggested following a concussion, whether there are sex differences following exposure to RSHI remains unknown. The aim of this study was to identify and to characterize sex differences following exposure to RSHI.MethodsTwenty-five collegiate ice hockey players (14 males and 11 females, 20.6 ± 2.0 years), all part of the Hockey Concussion Education Project (HCEP), underwent diffusion-weighted magnetic resonance imaging (dMRI) before and after the Canadian Interuniversity Sports (CIS) ice hockey season 2011–2012 and did not experience a concussion during the season. Whole-brain tract-based spatial statistics (TBSS) were used to compare pre- and postseason imaging in both sexes for fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD). Pre- and postseason neurocognitive performance were assessed by the Immediate Post-Concussion Assessment and Cognitive Test (ImPACT).ResultsSignificant differences between the sexes were primarily located within the superior longitudinal fasciculus (SLF), the internal capsule (IC), and the corona radiata (CR) of the right hemisphere (RH). In significant voxel clusters (p < 0.05), decreases in FA (absolute difference pre- vs. postseason: 0.0268) and increases in MD (0.0002), AD (0.00008), and RD (0.00005) were observed in females whereas males showed no significant changes. There was no significant correlation between the change in diffusion scalar measures over the course of the season and neurocognitive performance as evidenced from postseason ImPACT scores.ConclusionsThe results of this study suggest sex differences in structural alterations following exposure to RSHI. Future studies need to investigate further the underlying mechanisms and association with exposure and clinical outcomes.

Conservatism and the neural circuitry of threat: economic conservatism predicts greater amygdala-BNST connectivity during periods of threat vs safety.

Political conservatism is associated with an increased negativity bias, including increased attention and reactivity toward negative and threatening stimuli. Although the human amygdala has been implicated in the response to threatening stimuli, no studies to date have investigated whether conservatism is associated with altered amygdala function toward threat. Furthermore, although an influential theory posits that connectivity between the amygdala and bed nucleus of the stria terminalis (BNST) is important in initiating the response to sustained or uncertain threat, whether individual differences in conservatism modulate this connectivity is unknown. To test whether conservatism is associated with increased reactivity in neural threat circuitry, we measured participants’ self-reported social and economic conservatism and asked them to complete high-resolution fMRI scans while under threat of an unpredictable shock and while safe. We found that economic conservatism predicted greater connectivity between the BNST and a cluster of voxels in the left amygdala during threat vs safety. These results suggest that increased amygdala–BNST connectivity during threat may be a key neural correlate of the enhanced negativity bias found in conservatism.

Microstructural cerebral lesions are associated with the severity of central sleep apnea with Cheyne-Stokes-respiration in heart failure and are modified by PAP-therapy

This study investigated the association of microstructural cerebral lesions with central sleep apnea with Cheyne-Stokes-respiration (CSA-CSR) in heart failure (HF) patients and the effect of positive airway pressure therapy (PAP) of CSA-CSR on these lesions.PAP-therapy was initiated in patients with HF with midrange and with reduced ejection fraction (NYHA≥II; left ventricular ejection fraction <50%) and proven CSA-CSR.Cerebral magnetic resonance imaging (MRI) scans at 3T including diffusion tensor imaging were obtained before and after 4 months of PAP-therapy.Cerebral MRI scans revealed microstructural lesions in all 11 patients with HF with midrange or reduced ejection fraction and CSA-CSR (64±8years, 82% male, left ventricular ejection fraction 37±11%) that were focussed on the brainstem and frontal cerebral regions.This microstructural damage correlated with the severity of CSA-CSR and 4 months of PAP-therapy lead to voxel clusters of altered fiber integrity in these lesions.Microstructural cerebral lesions might contribute to the pathophysiology of CSA-CSR in HF. In these patients PAP-therapy induces neuronal plasticity.

Regional Dose Differences Associated with Radiation-Induced Acute Severe Dysphagia

To apply a voxel-based analysis (VBA) to explore possible correlation between radiation-induced acute dysphagia (RIAD) and local dose release in a cohort of patients treated for head and neck (H&N) tumor with RT. In a cohort 42 H&N patients treated with definitive RT (35 fractions of 2 Gy) and no previous surgery, 9 subjects developed severe RIAD (CTCAE v 4.0 grade ≥3). Each planning CT was registered to a common coordinate system (CCS) via a log-diffeomorphic approach. The obtained deformation fields were used to map the dose of each patient into the CCS. The dose warping accuracy was evaluated by Dice, modified Hausdorff distance (MHD) and dose-organ overlap (DOO) scores. A preliminary significance analysis of the dose differences was performed according to the normalized maximum dose difference (Tmax). Then, a statistical mapping scheme for nonparametric multiple permutation inference on dose maps with threshold-free cluster enhancement (TFCE) was applied, and the corresponding P < 0.05 subregions (S.05) were generated. A ROC-based test was performed on the mean dose extracted from S.05. The registration process resulted in a geometrically robust and accurate dose warping. In Table, pre- and post-registration scores are reported along with the significance of accuracy improvement. A significantly higher dose was delivered to RIAD patients (Tmax statistic: P = .038) in two voxel clusters (overall volume of 5.1 cm3 according to TFCE) located in correspondence of Cricopharyngeus Muscle (CM) and Cervical Esophagus, as shown in Table 1. The ROC-AUC from the mean dose on S.05 was .81.Tabled 1Abstract 106; Table 1PrePostP-valueMedianRangeMedianRangeDice.67.03-.83.80.59-.82<10-5MHD (mm)2.31.53-24.131.22.78-4.46<10-6DOO.59.32-.78.87.74-.92<10-4Non-RIADRIADS.05 Mean Dose (Gy)3310-574838-58.003 Open table in a new tab In this study, a method for the dosimetric VBA was applied to a cohort of H&N patients. To the best of our knowledge this represents the first attempt to go beyond the organ-based philosophy in normal-tissue complication probability modeling in the H&N region and to explore a correlation between radiation-induced toxicity and local dose differences. Compared to other districts, H&N poses serious difficulties in terms of registration accuracy, due to the high motility of the structures and considerable inter-patient anatomical variability. Notably, the adopted registration strategy succeeded in a sharp normalization of patients' doses to a CCS and the following statistical analysis was able to highlight dose differences between RIAD and non-RIAD subjects in very elusive structures, such as the CM. The TFCE approach pointed out a higher dose release in regions that are likely associated with swallowing function, and the good ability of the mean dose on S.05 to predict the dysphagia outcome is confirmed by a relatively high AUC. We believe that the VBA may provide new insights into spatial signature of radiation sensitivity in a highly composite region such as the H&N district.

Matching corresponding visual areas with fMRI and MEG

fMRI and MEG have complementary strengths. fMRI offers high spatial resolution, MEG offers high temporal resolution. The challenge is combining information from the two technologies. We recorded BOLD while observers watched a 25min clip of the Skyfall film in a 3T MRI scanner. We used ICA to segment the visually responsive areas of the cortex into clusters of voxels with similar timecourses (and hence tuning for visual features). The timecourse of each cluster (ICA component) was extracted. Observers watched the same film clip in a MEG scanner. Using SAM, we projected the sensor data into synthetic voxels in an anatomical coordinate frame to match the fMRI data. For each voxel, for each frequency band, from delta to ultra gamma, at a temporal resolution of 2 seconds (to match the fMRI data acquisition), we calculated the power (magnitude of the Hilbert envelope). We then cleaned the MEG data and convolved it with a BOLD haemodynamic response function. Using a standard GLM analysis we searched for MEG voxels with timecourses that correlated with the timecourses of a selection of the fMRI-ICA components. From the fMRI data we chose candidate components on the lateral and medial surface of occipital lobe. We found activation in comparable anatomical locations in the MEG data. The use of extended (~20min) broadband visual stimuli (film clips) that impose a temporal structure, coupled with ICA, is a promising way to segment the visually responsive cortex and match across imaging modalities. Meeting abstract presented at VSS 2017

Letter re: Practice guideline summary: Use of fMRI in the presurgical evaluation of patients with epilepsy: Report of the Guideline Development, Dissemination, and Implementation Subcommittee of the American Academy of Neurology.

The American Academy of Neurology (AAN) endorsement for the use of fMRI evaluation of hemispheric dominance for language in epilepsy surgery candidates1 appears as an odd and disconcerting sequel to the article by Eckland et al.,2 which reported that the clustering approach in functional MRI (fMRI) data processing may be responsible for an excessively high rate of false-positive findings. The latter report implied that up to 70% of the significant fMRI effects reported in approximately 40,000 peer-reviewed publications could represent no brain physiology facts, but type I statistical errors to the degree that they employed clustering of activated voxels.2 Consequently, it is fitting to suggest users of these popular fMRI software packages (SPM, FSL, AFNI) reconsider conclusions based on differences in activation levels of voxel clusters between task conditions. This raises the question of whether those who use the clustering procedure for the purpose of assessing hemisphere dominance for language should be alarmed for having made incorrect assessments in the past and refrain from using them for the same purpose in the future. Our answer is no, since language laterality judgments are typically made on the basis of laterality indices (i.e., the relative degree of activation defined as the ratio of left- and right-hemisphere activated voxels that are equally likely or unlikely to be activated). However, depending on how users of these automated software packages derive estimates of localization of the language network hubs (a practice not endorsed by the AAN),1 they may need to exercise more caution now that the shortcomings of these data reduction and analysis procedures were directly demonstrated and made widely known.

Voxel-based analysis unveils regional dose differences associated with radiation-induced morbidity in head and neck cancer patients

The risk of radiation-induced toxicity in patients treated for head and neck (HN) cancer with radiation therapy (RT) is traditionally estimated by condensing the 3D dose distribution into a monodimensional cumulative dose-volume histogram which disregards information on dose localization. We hypothesized that a voxel-based approach would identify correlations between radiation-induced morbidity and local dose release, thus providing a new insight into spatial signature of radiation sensitivity in composite regions like the HN district. This methodology was applied to a cohort of HN cancer patients treated with RT at risk of radiation-induced acute dysphagia (RIAD). We implemented an inter-patient elastic image registration framework that proved robust enough to match even the most elusive HN structures and to provide accurate dose warping. A voxel-based statistical analysis was then performed to test regional dosimetric differences between patients with and without RIAD. We identified a significantly higher dose delivered to RIAD patients in two voxel clusters in correspondence of the cricopharyngeus muscle and cervical esophagus. Our study goes beyond the well-established organ-based philosophy exploring the relationship between radiation-induced morbidity and local dose differences in the HN region. This approach is generally applicable to different HN toxicity endpoints and is not specific to RIAD.

Brain changes following four weeks of unimanual motor training: Evidence from behavior, neural stimulation, cortical thickness, and functional MRI.

Although different aspects of neuroplasticity can be quantified with behavioral probes, brain stimulation, and brain imaging assessments, no study to date has combined all these approaches into one comprehensive assessment of brain plasticity. Here, 24 healthy right-handed participants practiced a sequence of finger-thumb opposition movements for 10 min each day with their left hand. After 4weeks, performance for the practiced sequence improved significantly (P < 0.05 FWE) relative to a matched control sequence, with both the left (mean increase: 53.0% practiced, 6.5% control) and right (21.0%; 15.8%) hands. Training also induced significant (cluster p-FWE < 0.001) reductions in functional MRI activation for execution of the trained sequence, relative to the control sequence. These changes were observed as clusters in the premotor and supplementary motor cortices (right hemisphere, 301 voxel cluster; left hemisphere 700 voxel cluster), and sensorimotor cortices and superior parietal lobules (right hemisphere 864 voxel cluster; left hemisphere, 1947 voxel cluster). Transcranial magnetic stimulation over the right ("trained") primary motor cortex yielded a 58.6% mean increase in a measure of motor evoked potential amplitude, as recorded at the left abductor pollicis brevis muscle. Cortical thickness analyses based on structural MRI suggested changes in the right precentral gyrus, right post central gyrus, right dorsolateral prefrontal cortex, and potentially the right supplementary motor area. Such findings are consistent with LTP-like neuroplastic changes in areas that were already responsible for finger sequence execution, rather than improved recruitment of previously nonutilized tissue. Hum Brain Mapp 38:4773-4787, 2017. © 2017 Wiley Periodicals, Inc.

The pulvinar nucleus is associated with the presence of dysarthria in patients with basal ganglia hemorrhage.

Dysarthria is a frequent symptom in patients with stroke. The anatomical structures responsible for dysarthria have been reported in patients with lacunar infarcts, but the related lesions in patients with basal ganglia hemorrhage (BGH) have not been investigated. The aim of this study was to identify associations between the lesion location and the presence/absence of dysarthria in patients with BGH using voxel-based lesion symptom mapping (VLSM) analyses. A retrospective analysis was conducted on 26 patients with acute BGH (mean age, 54.0 years; men:women, 14:12) who underwent conservative management. The patients were classified into groups based on the presence or absence of dysarthria at the time of admission, which was determined by reviewing the patients' medical records. Brain lesions were traced on magnetic resonance images that were acquired within the first 3 weeks after BGH onset, and then separate high-resolution region-of-interest images were generated. Associations between dysarthria and the lesion location were determined with the VLSM analyses. The average volume of the delimited lesions was 7.38±5.75cm3. The VLSM analyses identified several voxel clusters, mainly in the pulvinar nucleus of the left thalamus, that were significantly related to the presence of dysarthria at admission. These findings suggest that patients with BGH extending into the left pulvinar nucleus should be monitored for dysarthria.