Active Voxels Research Articles

Participation of the Default Mode Network in the Cortical Control of Volitional Swallowing

Background & Aim: Early studies using functional MRI (fMRI) have demonstrated that volitional swallow is associated with activation of a number of cortical areas (middle cingulate gyrus, ventrolateral prefrontal cortex, ventrolateral sensory/motor cortices andmiddle insula), which collectively represent the “cortical swallowing network” (CSN). Although the activation of these regions has been reported in the literature, the reproducibility of these activations has not been systematically studied. The aim of our study is to investigate the reproducibility of the CSN across different fMRI sessions. Methods: We studied 16 young right-handed healthy volunteers utilizing a standard paradigm driven fMRI protocol and analyzed with an event-related analysis technique. Echo-planar images were obtained during two identical nine minute scans across different sessions while twenty-one dry swallows were performed by visual cues in random intervals. Physiologic circulatory and respiratory-related signal changes were removed retrospectively. Functional images were then aligned, registered (12 degrees of freedom), and mapped stereotaxically to the standard coordinate system. Generalized linear model was then used to remove undesirable signal changes correlated with motion, white matter and cerebrospinal fluid. Finally, the second order group random mixed-effect multilevel analysis was performed to identify active cortical regions. Clusters with p<0.01 corrected for multiple comparisons were considered significant. The number of activated voxels (3.75x3.75x4 mm3) along with their average and peak percent signal change within each cluster was reported and compared between the two study sessions in order to determine the correlation co-efficient. Results: All subjects showed significant and clustered activity within the deglutition network during both scans. Activity within the right precuneus and supplementary area were not reproducible. Overall, the percent fMRI signal change and the number of activated voxels were similar between the two studies with correlation co-efficients r=0.88 and r=0.86, respectively (p<0.0001). Activity within the right precuneus and supplementary area were not reproducible. Within the remaining 20 regions of interest (ROI), the overlap of activity maps across both sessions showed that the center of the activated clusters was within 6.3±4.8 mm (less than two voxels). The difference in maximum activated voxel activity was 9.7±5.9 mm. Conclusions: fMRI activity maps as well as percent signal change and number of voxels activated by volitional swallow in the CSN are reproducible between studies.

Reliability and Reproducibility of FMRI Activity in the Cortical Swallowing Network

Background & Aim: Early studies using functional MRI (fMRI) have demonstrated that volitional swallow is associated with activation of a number of cortical areas (middle cingulate gyrus, ventrolateral prefrontal cortex, ventrolateral sensory/motor cortices andmiddle insula), which collectively represent the “cortical swallowing network” (CSN). Although the activation of these regions has been reported in the literature, the reproducibility of these activations has not been systematically studied. The aim of our study is to investigate the reproducibility of the CSN across different fMRI sessions. Methods: We studied 16 young right-handed healthy volunteers utilizing a standard paradigm driven fMRI protocol and analyzed with an event-related analysis technique. Echo-planar images were obtained during two identical nine minute scans across different sessions while twenty-one dry swallows were performed by visual cues in random intervals. Physiologic circulatory and respiratory-related signal changes were removed retrospectively. Functional images were then aligned, registered (12 degrees of freedom), and mapped stereotaxically to the standard coordinate system. Generalized linear model was then used to remove undesirable signal changes correlated with motion, white matter and cerebrospinal fluid. Finally, the second order group random mixed-effect multilevel analysis was performed to identify active cortical regions. Clusters with p<0.01 corrected for multiple comparisons were considered significant. The number of activated voxels (3.75x3.75x4 mm3) along with their average and peak percent signal change within each cluster was reported and compared between the two study sessions in order to determine the correlation co-efficient. Results: All subjects showed significant and clustered activity within the deglutition network during both scans. Activity within the right precuneus and supplementary area were not reproducible. Overall, the percent fMRI signal change and the number of activated voxels were similar between the two studies with correlation co-efficients r=0.88 and r=0.86, respectively (p<0.0001). Activity within the right precuneus and supplementary area were not reproducible. Within the remaining 20 regions of interest (ROI), the overlap of activity maps across both sessions showed that the center of the activated clusters was within 6.3±4.8 mm (less than two voxels). The difference in maximum activated voxel activity was 9.7±5.9 mm. Conclusions: fMRI activity maps as well as percent signal change and number of voxels activated by volitional swallow in the CSN are reproducible between studies.

Does Biofeedback Therapy Modulate Anorectal (Gut)-Brain Axis in Patients With Dyssynergic Defecation?

Background & Aim: Early studies using functional MRI (fMRI) have demonstrated that volitional swallow is associated with activation of a number of cortical areas (middle cingulate gyrus, ventrolateral prefrontal cortex, ventrolateral sensory/motor cortices andmiddle insula), which collectively represent the “cortical swallowing network” (CSN). Although the activation of these regions has been reported in the literature, the reproducibility of these activations has not been systematically studied. The aim of our study is to investigate the reproducibility of the CSN across different fMRI sessions. Methods: We studied 16 young right-handed healthy volunteers utilizing a standard paradigm driven fMRI protocol and analyzed with an event-related analysis technique. Echo-planar images were obtained during two identical nine minute scans across different sessions while twenty-one dry swallows were performed by visual cues in random intervals. Physiologic circulatory and respiratory-related signal changes were removed retrospectively. Functional images were then aligned, registered (12 degrees of freedom), and mapped stereotaxically to the standard coordinate system. Generalized linear model was then used to remove undesirable signal changes correlated with motion, white matter and cerebrospinal fluid. Finally, the second order group random mixed-effect multilevel analysis was performed to identify active cortical regions. Clusters with p<0.01 corrected for multiple comparisons were considered significant. The number of activated voxels (3.75x3.75x4 mm3) along with their average and peak percent signal change within each cluster was reported and compared between the two study sessions in order to determine the correlation co-efficient. Results: All subjects showed significant and clustered activity within the deglutition network during both scans. Activity within the right precuneus and supplementary area were not reproducible. Overall, the percent fMRI signal change and the number of activated voxels were similar between the two studies with correlation co-efficients r=0.88 and r=0.86, respectively (p<0.0001). Activity within the right precuneus and supplementary area were not reproducible. Within the remaining 20 regions of interest (ROI), the overlap of activity maps across both sessions showed that the center of the activated clusters was within 6.3±4.8 mm (less than two voxels). The difference in maximum activated voxel activity was 9.7±5.9 mm. Conclusions: fMRI activity maps as well as percent signal change and number of voxels activated by volitional swallow in the CSN are reproducible between studies.

Language-invariant verb processing regions in Spanish-English bilinguals.

Nouns and verbs are fundamental grammatical building blocks of all languages. Studies of brain-damaged patients and healthy individuals have demonstrated that verb processing can be dissociated from noun processing at a neuroanatomical level. In cases where bilingual patients have a noun or verb deficit, the deficit has been observed in both languages. This suggests that the noun-verb distinction may be based on neural components that are common across languages. Here we investigated the cortical organization of grammatical categories in healthy, early Spanish-English bilinguals using functional magnetic resonance imaging (fMRI) in a morphophonological alternation task. Four regions showed greater activity for verbs than for nouns in both languages: left posterior middle temporal gyrus (LMTG), left middle frontal gyrus (LMFG), pre-supplementary motor area (pre-SMA), and right middle occipital gyrus (RMOG); no regions showed greater activation for nouns. Multi-voxel pattern analysis within verb-specific regions showed indistinguishable activity patterns for English and Spanish, indicating language-invariant bilingual processing. In LMTG and LMFG, patterns were more similar within than across grammatical category, both within and across languages, indicating language-invariant grammatical class information. These results suggest that the neural substrates underlying verb-specific processing are largely independent of language in bilinguals, both at the macroscopic neuroanatomical level and at the level of voxel activity patterns.

Cerebral lateralization of praxis in right‐ and left‐handedness: Same pattern, different strength

We aimed to investigate the effect of hand effector and handedness on the cerebral lateralization of pantomiming learned movements. Fourteen right-handed and 14 left-handed volunteers performed unimanual and bimanual tool-use pantomimes with their dominant or nondominant hand during fMRI. A left hemispheric lateralization was observed in the right- and left-handed group regardless of which hand(s) performed the task. Asymmetry was most marked in the dorsolateral prefrontal cortex (DLPFC), premotor cortex (PMC), and superior and inferior parietal lobules (SPL and IPL). Unimanual pantomimes did not reveal any significant differences in asymmetric cerebral activation patterns between left- and right-handers. Bimanual pantomimes showed increased left premotor and posterior parietal activation in left- and right-handers. Lateralization indices (LI) of the 10% most active voxels in DLPFC, PMC, SPL, and IPL were calculated for each individual in a contrast that compared all tool versus all control conditions. Left-handers showed a significantly reduced overall LI compared with right-handers. This was mainly due to diminished asymmetry in the IPL and SPL. We conclude that the recollection and pantomiming of learned gestures recruits a similar left lateralized activation pattern in right and left-handed individuals. Handedness only influences the strength (not the side) of the lateralization, with left-handers showing a reduced degree of asymmetry that is most readily observed over the posterior parietal region. Together with similar findings in language and visual processing, these results point to a lesser hemispheric specialization in left-handers that may be considered in the cost/benefit assessment to explain the disproportionate handedness polymorphism in humans.

A mutual information‐based metric for evaluation of fMRI data‐processing approaches

We propose a novel approach for evaluating the performance of activation detection in real (experimental) datasets using a new mutual information (MI)-based metric and compare its sensitivity to several existing performance metrics in both simulated and real datasets. The proposed approach is based on measuring the approximate MI between the fMRI time-series of a validation dataset and a calculated activation map (thresholded label map or continuous map) from an independent training dataset. The MI metric is used to measure the amount of information preserved during the extraction of an activation map from experimentally related fMRI time-series. The processing method that preserves maximal information between the maps and related time-series is proposed to be superior. The results on simulation datasets for multiple analysis models are consistent with the results of ROC curves, but are shown to have lower information content than for real datasets, limiting their generalizability. In real datasets for group analyses using the general linear model (GLM; FSL4 and SPM5), we show that MI values are (1) larger for groups of 15 versus 10 subjects and (2) more sensitive measures than reproducibility (for continuous maps) or Jaccard overlap metrics (for thresholded maps). We also show that (1) for an increasing fraction of nominally active voxels, both MI and false discovery rate (FDR) increase, and (2) at a fixed FDR, GLM using FSL4 tends to extract more voxels and more information than SPM5 using the default processing techniques in each package.

Refractive surgery in anisometropic adult patients induce plastic changes in primary visual cortex

To prospectively study the effect of refractive surgery in the primary visual cortex of adult anisometropic and isometropic myopic patients. Two anisometropic and two isometropic myopic patients were examined with multifocal functional magnetic resonance imaging technique (mffMRI) before refractive surgery and at 3, 6, 9 and 12 months postoperatively. Two controls without refractive surgery were also examined with mffMRI in the beginning and in the end of the study. Anisometropic patients had only their more myopic eye operated to correct the anisometropia. The myopic isometropic patients had their both eyes operated. Operated anisometropic eyes showed 65% reduced amount of active voxels in foveal data at 12 months postoperatively compared with the preoperative situation. In unoperated anisometropic eyes, the corresponding value was 86% and in myopic patients and controls 31% and 1%, respectively. To confirm this finding, the number of activated voxels representing the innermost ring of the stimulus was also calculated, and an exactly similar phenomenon was encountered in the anisometropic patients. Both anisometropic patients improved the best-spectacle-corrected visual acuity in the operated eye after refractive surgery. Our results suggest that plastic changes may take place in the primary visual cortex of anisometropic adult patients after refractive surgery.

Evidence of Left Inferior Frontal–Premotor Structural and Functional Connectivity Deficits in Adults Who Stutter

The neurophysiological basis for stuttering may involve deficits that affect dynamic interactions among neural structures supporting fluid speech processing. Here, we examined functional and structural connectivity within corticocortical and thalamocortical loops in adults who stutter. For functional connectivity, we placed seeds in the left and right inferior frontal Brodmann area 44 (BA44) and in the ventral lateral nucleus (VLN) of the thalamus. Subject-specific seeds were based on peak activation voxels captured during speech and nonspeech tasks using functional magnetic resonance imaging. Psychophysiological interaction (PPI) was used to find brain regions with heightened functional connectivity with these cortical and subcortical seeds during speech and nonspeech tasks. Probabilistic tractography was used to track white matter tracts in each hemisphere using the same seeds. Both PPI and tractrography supported connectivity deficits between the left BA44 and the left premotor regions, while connectivity among homologous right hemisphere structures was significantly increased in the stuttering group. No functional connectivity differences between BA44 and auditory regions were found between groups. The functional connectivity results derived from the VLN seeds were less definitive and were not supported by the tractography results. Our data provide strongest support for deficient left hemisphere inferior frontal to premotor connectivity as a neural correlate of stuttering.

Full-brain auto-regressive modeling (FARM) using fMRI

In order to fully uncover the information potentially available in the fMRI signal, we model it as a multivariate auto-regressive process. To infer the model, we do not apply any form of clustering or dimensionality reduction, and solve the problem of under-determinacy using sparse regression. We find that only a few small clusters (with average size of 3-4 voxels) are useful in predicting the activity of other voxels, and demonstrate remarkable consistency within a subject as well as across multiple subjects. Moreover, we find that: (a) the areas that can predict activity of other voxels are consistent with previous results related to networks activated by the specific somatosensory task, as well as networks related to the default mode activity; (b) there is a global dynamical state dominated by two prominent (although not unique) streams, originating in the posterior parietal cortex and the posterior cingulate/precuneus cortex; (c) these streams span default mode and task-specific networks, and interact in several regions, notably the insula; and (d) the posterior cingulate is a central node of the default mode network, in terms of its ability to determine the future evolution of the rest of the nodes.

The effect of patient positioning aids on PET quantification in PET/MR imaging

Clinical PET/MR requires the use of patient positioning aids to immobilize and support patients for the duration of the combined examination. Ancillary immobilization devices contribute to overall attenuation of the PET signal, but are not detected with conventional MR sequences and, hence, are ignored in standard MR-based attenuation correction (MR-AC). We report on the quantitative effect of not accounting for the attenuation of patient positioning aids in combined PET/MR imaging. We used phantom and patient data acquired with positioning aids on a PET/CT scanner (Biograph 16, HI-REZ) to mimic PET/MR imaging conditions. Reference CT-based attenuation maps were generated from measured (original) CT transmission images (origCT-AC). We also created MR-like attenuation maps by following the same conversion procedure of the attenuation values except for the prior delineation and subtraction of the positioning aids from the CT images (modCT-AC). First, a uniform (68)Ge cylinder was positioned centrally in the PET/CT scanner and fixed with a vacuum mattress (10cm thick) and, in a repeat examination, with MR positioning foam pads. Second, 16 patient datasets were selected for subsequent processing. All patients were regionally immobilized with positioning aids: a vacuum mattress for head/neck imaging (nine patients) and a foam mattress for imaging of the lower extremities (seven patients). PET images were reconstructed following CT-based attenuation and scatter correction using the original and modified (MR-like) CT images: PET(origCT-AC) and PET(modCT-AC), respectively. PET images following origCT-AC and modCT-AC were compared visually and in terms of mean differences of voxels with a standardized uptake value of at least 1.0. In addition, we report maximum activity concentration in lesions for selected patients. In the phantom study employing the vacuum mattress the average voxel activity in PET(modCT-AC) was underestimated by 6.4% compared to PET(origCT-AC), with 3.4% of the PET voxels being underestimated by 10% or more. When the MR foam pads were not accounted for during AC, PET(modCT-AC) was underestimated by 1.1% on average, with none of the PET voxels being underestimated by 10% or more. Evaluation of the head/neck patient data showed a decrease of 8.4% ([(68)Ga]DOTATOC) and 7.4% ([(18)F]FDG) when patient positioning aids were not accounted for during AC, while the corresponding decrease was insignificant for the lower extremities. Depending on the size and density of the positioning aids used, a regionally variable underestimation of PET activity following AC is observed when positioning aids are not accounted for. This underestimation may become relevant in combined PET/MR imaging of patients with neuropsychiatric indications, but appears to be of no clinical relevance in imaging the extremities.

Dynamic Spatial Discrimination Maps of Discriminative Activation between Different Tasks Based on Support Vector Machines

As a set of supervised pattern recognition methods, support vector machines (SVMs) have been successfully applied to functional magnetic resonance imaging (fMRI) field, but few studies have focused on visualizing discriminative regions of whole brain between different cognitive tasks dynamically. This paper presents a SVM-based method for visualizing dynamically discriminative activation of whole-brain voxels between two kinds of tasks without any contrast. Our method provides a series of dynamic spatial discrimination maps (DSDMs), representing the temporal evolution of discriminative brain activation during a duty cycle and describing how the discriminating information changes over the duty cycle. The proposed method was applied to investigate discriminative brain functional activations of whole brain voxels dynamically based on a hand-motor task experiment. A set of DSDMs between left hand movement and right hand movement were reached. Our results demonstrated not only where but also when the discriminative activations of whole brain voxels occurred between left hand movement and right hand movement during one duty cycle.

Functional MRI study: passive motor paradigm in the assessment of sensorimotor system

The fMRI study of 7 healthy volunteers was performed to evaluate the neuron networks of sensorimotor system during active and passive movements of the left and right index fingers. While performing all the tasks, the predominant activation of primary sensorimotor, premotor, supplementary motor areas, secondary sensory zones were shown on the contralateral side, as well as ipsilateral cerebellar activation. It was demonstrated that brain activation areas in both types of paradigm were corresponding, as well as the activation clusters size, amplitude and voxel coordinates, with the maximum values in the primary motor and sensory cortex. These results allow recommending the paradigm of passive index finger movements in given rate for the evaluation of sensorimotor system in patients with movement disorders.

Assessment of Cortical Visual Impairment in Infants with Periventricular Leukomalacia: a Pilot Event-Related fMRI Study

ObjectiveWe wanted to investigate the usefulness of event-related (ER) functional MRI (fMRI) for the assessment of cortical visual impairment in infants with periventricular leukomalacia (PVL).Materials and MethodsFMRI data were collected from 24 infants who suffered from PVL and from 12 age-matched normal controls. Slow ER fMRI was performed using a 3.0T MR scanner while visual stimuli were being presented. Data analysis was performed using Statistical Parametric Mapping software (SPM2), the SPM toolbox MarsBar was used to analyze the region of interest data, and the time to peak (TTP) of hemodynamic response functions (HRFs) was estimated for the surviving voxels. The number of activated voxels and the TTP values of HRFs were compared. Pearson correlation analysis was performed to compare visual impairment evaluated by using Teller Acuity Cards (TAC) with the number of activated voxels in the occipital lobes in all patients.ResultsIn all 12 control infants, the blood oxygenation level-dependent (BOLD) signal was negative and the maximum response was located in the anterior and superior part of the calcarine fissure, and this might correspond to the anterior region of the primary visual cortex (PVC). In contrast, for the 24 cases of PVL, there were no activated pixels in the PVC in four subjects, small and weak activations in six subjects, deviated activations in seven subjects and both small and deviated activations in three subjects. The number of active voxels in the occipital lobe was significantly correlated with the TAC-evaluated visual impairment (p < 0.001). The mean TTP of the HRFs was significantly delayed in the cases of PVL as compared with that of the normal controls.ConclusionDetermining the characteristics of both the BOLD response and the ER fMRI activation may play an important role in the cortical visual assessment of infants with PVL.

Cognitive processing and functional interactions within hippocampal-neocortical networks during a spatial working memory task in humans

Cognitive processing and functional interactions within hippocampal-neocortical networks during a spatial working memory task in humans

Reconstruction of emission tomography data using origin ensembles.

A new statistical reconstruction method based on origin ensembles (OE) for emission tomography (ET) is examined. Using a probability density function (pdf) derived from first principles, an ensemble expectation of numbers of detected event origins per voxel is determined. These numbers divided by sensitivities of voxels and acquisition time provide OE estimates of the voxel activities. The OE expectations are shown to be the same as expectations calculated using the complete-data space. The properties of the OE estimate are examined. It is shown that OE estimate approximates maximum likelihood (ML) estimate for conditions usually achieved in practical applications in emission tomography. Three numerical experiments with increasing complexity are used to validate theoretical findings and demonstrate similarities of ML and OE estimates. Recommendations for achieving improved accuracy and speed of OE reconstructions are provided.

Aggregated wavelet estimation and its application to ultra-fast fMRI

The methodology of aggregation of known nonparametric regression estimators into a single better estimator has received increasing attention in statistical literature. Traditional aggregation means that a linear or convex combination of several estimators is considered. Wavelet regression estimation, due to its multiresolution nature, presents another opportunity for aggregation – using different estimation procedures on different resolution scales. Such an opportunity becomes attractive if known wavelet estimators have desired complementary properties on different frequencies. The difficulty of such an aggregation is that the assignment of scales depends on an underlying regression function and regression errors. This paper proposes a data-driven aggregation of two wavelet estimators – SureBlock of Cai and Zhou [(2009), ‘A Data-driven Block Thresholding Approach to Wavelet Estimation’, Annals of Statistics, 37, 569–595] and Universal of Efromovich [(1999a,b), Nonparametric Curve Estimation: Methods, Theory and Applications, New York: Springer; ‘Quasi-linear Wavelet Estimation’, Journal of the American Statistical Association, 94, 189–204] – to achieve a better quality of estimation, better data-compression, and better visualisation of functions with different smoothness characteristics on low and high frequencies. The proposed estimator is motivated by an applied problem of denoising and compression of ultra-fast (UF) functional magnetic resonance imaging (fMRI) – the new magnetic resonance technology that screens the activity of brain voxels every 50 ms with the purpose of understanding human brain activity. The proposed aggregated wavelet estimator is supported by the asymptotic theory, tested via intensive numerical simulations and UF fMRI applications, and it is expected to be useful in similar applications.

Natural scene categorization by global scene properties: Evidence from patterns of fMRI activity

Human scene categorization is remarkably rapid and accurate, but little is known about the neural representation mediating this feat. While previous studies on neural representation of scenes have focused on basic level scene categories, here we examined whether the neural representation of scenes reflect global properties of scene structure, such as openness of a space, or properties of surfaces and contents within a space, such as naturalness. In an fMRI study, human participants performed a one-back task on blocks of images of four scene groups: Open Natural images, Closed Natural images, Open Urban images, Closed Urban images. Each image group included multiple basic level categories. For example, Open Natural images included open views of fields, oceans and deserts; while Open Urban images included open views of highways, parking lots, and airports. For each participant, we defined regions of interest (ROIs) of the parahippocampal place area (PPA), the fusiform face area (FFA), lateral occipital complex (LOC) and V1. Multivariate pattern analysis was applied to voxels within each ROIs, and split-half pattern correlation and Euclidian distances across voxel activations were calculated (Haxby et al., 2001). We observed high identification accuracy in the PPA and V1, but not in the FFA and LOC. Most interestingly, when the correct identification failed in the PPA, the confusion was between images with the same layout rather than between images with the same content. For example, Open Natural images were often highly correlated with Open Urban images, but rarely with Closed Natural images. These results suggest that a critical component of scene representation in the brain is the coding of global properties of spatial layout.

Robustly measuring vascular reactivity differences with breath-hold: Normalising stimulus-evoked and resting state BOLD fMRI data

Inter-subject differences in local cerebral blood flow (CBF) and cerebral blood volume (CBV) contribute to differences in BOLD signal reactivity and, therefore, unmodelled variance in group level fMRI analyses. A simple way of elevating blood CO2 concentrations to characterise subject differences in vascular reactivity is through breath-holds but two aspects of this measure are often neglected: (1) breath-holds are usually modelled as blocks even though CO2 accumulates over time and (2) increases in CO2 differ between subjects. This study demonstrates that the BOLD breath-hold response is best modelled by convolving the end-tidal CO2 trace with a standard haemodynamic response function and including its temporal derivative. Inclusion of the BOLD breath-hold response as a voxel-dependent covariate in a group level analysis increases the spatial extent of activation in stimulus evoked and resting state datasets. By expressing the BOLD breath-hold response as a percentage signal increase with respect to an absolute change in the partial pressure of CO2 (expressed in mmHg), the spatial extent of stimulus-evoked activation is further improved. This demonstrates that individual end-tidal CO2 increases to breath-hold should be accounted for to provide an accurate measure of vascular reactivity resulting in more statistically active voxels in group level analyses.

Partial Least Squares (PLS) methods for neuroimaging: A tutorial and review

Partial Least Squares (PLS) methods are particularly suited to the analysis of relationships between measures of brain activity and of behavior or experimental design. In neuroimaging, PLS refers to two related methods: (1) symmetric PLS or Partial Least Squares Correlation (PLSC), and (2) asymmetric PLS or Partial Least Squares Regression (PLSR). The most popular (by far) version of PLS for neuroimaging is PLSC. It exists in several varieties based on the type of data that are related to brain activity: behavior PLSC analyzes the relationship between brain activity and behavioral data, task PLSC analyzes how brain activity relates to pre-defined categories or experimental design, seed PLSC analyzes the pattern of connectivity between brain regions, and multi-block or multi-table PLSC integrates one or more of these varieties in a common analysis. PLSR, in contrast to PLSC, is a predictive technique which, typically, predicts behavior (or design) from brain activity. For both PLS methods, statistical inferences are implemented using cross-validation techniques to identify significant patterns of voxel activation. This paper presents both PLS methods and illustrates them with small numerical examples and typical applications in neuroimaging.

Attention deficits in schizophrenia — Preliminary evidence of dissociable transient and sustained deficits

Attention deficits are considered to be fundamental in patients with schizophrenia. During attention tasks, patients with schizophrenia have been shown to display increased brain activity in some neuroimaging studies but reduced brain activity in others. These conflicting findings may be due to some study designs primarily eliciting transient engagement of attention and other study designs primarily eliciting sustained engagement of attention.In the present study, ten males with schizophrenia and fourteen age-matched, male controls performed a visual selective attention task. A mixed block/event-related fMRI design was used, allowing for separate analysis of transient and sustained phases of attention.Results revealed that the schizophrenia group made significantly fewer correct responses and displayed a significantly slower mean response time than the control group. Voxel-wise random effects analyses revealed that both groups displayed activation in regions considered to constitute a core attentional network including the anterior cingulate gyrus, dorsolateral prefrontal cortex, insula and inferior parietal sulcus. Region of Interest (ROI) analyses revealed that across the entire sequence of task and non-task blocks, the schizophrenia group displayed a greater percentage of active voxels than controls in many ROIs. However, during transient periods most pertinent to task performance, the schizophrenia group displayed a lower percentage of active voxels than controls.These results help to explain contrasting findings across previous studies and suggest that attention deficits displayed by patients with schizophrenia are more likely to reflect deficits in modulating brain activity in response to variations in transient, attention demanding stimuli, rather than deficits in sustained attention.