Reproducibility of 3D 1H MR spectroscopic imaging of the prostate at 1.5T.

PURPOSE: To determine the reproducibility of 3D proton magnetic resonance spectroscopic imaging ((1)H-MRSI) of the human prostate in a multicenter setting at 1.5T. MATERIALS AND METHODS: Fourteen subjects were measured twice with 3D point-resolved spectroscopy (PRESS) (1)H-MRSI using an endorectal coil. MRSI voxels were selected in the peripheral zone and combined central gland at the same location in the prostate in both measurements. Voxels with approved spectral quality were included to calculate Bland-Altman parameters for reproducibility from the choline plus creatine to citrate ratio (CC/C). The repeated spectroscopic data were also evaluated with a standardized clinical scoring system. RESULTS: A total of 74 voxels were included for reproducibility analysis. The complete range of biologically interesting CC/C ratios was covered. The overall within-voxel standard deviation (SD) of the CC/C ratio of the repeated measurements was 0.13. This value is equal to the between-subject SD of noncancer prostate tissue. In >90% of the voxels the standardized clinical score did not differ relevantly between the measurements. CONCLUSION: Repeated measurements of in vivo 3D (1)H-MRSI of the complete prostate at 1.5T produce equal and quantitative results. The reproducibility of the technique is high enough to provide it as a reliable tool in assessing tumor presence in the prostate.

Discriminating cancer from noncancer tissue in the prostate by 3-dimensional proton magnetic resonance spectroscopic imaging: a prospective multicenter validation study.

OBJECTIVES: A prospective multicenter validation of the ability of 1H magnetic resonance spectroscopic imaging (MRSI) to distinguish cancer from noncancer tissues throughout the prostate with histopathology of the resected organ as the standard of reference. MATERIALS AND METHODS: Institutional review board approval was obtained for all centers and all participating patients and volunteers provided written informed consent. Ninety-nine patients and 10 age-matched volunteers from 8 participating centers underwent magnetic resonance imaging and 3-dimensional MRSI with an endorectal coil at 1.5 T. Selected MRSI voxels were assigned to the peripheral zone (PZ), the central gland (CG), the periurethral area, and cancer tissue. Signal ratios of choline + creatine to citrate (CC/C) in spectra of these voxels were automatically calculated. Receiver operating characteristic curves were constructed to assess the accuracy by which this ratio can discriminate cancer from noncancer tissue. RESULTS: A total of 70% of voxels in noncancer tissue and 90% of voxels in cancer tissue passed the quality check of the automatically fitted spectra. The median CC/C was significantly different between any noncancer and cancer tissue (P < 0.0001), but not between the different contributing centers. CC/C increased with cancer focus size (P =0.0008) and certainty of voxel mapping to histopathologic cancer site (P 0.0001). The area under the receiver operating characteristic curve for discriminating voxels of cancer tissue from noncancer tissue was 0.88 (confidence interval: 0.84-0.92) in the PZ and 0.76 (confidence interval: 0.71- 0.81) in the CG.

Matrix-binding vascular endothelial growth factor (VEGF) isoforms guide granule cell migration in the cerebellum via VEGF receptor Flk1.

Vascular endothelial growth factor (VEGF) regulates angiogenesis, but also has important, yet poorly characterized roles in neuronal wiring. Using several genetic and in vitro approaches, we discovered a novel role for VEGF in the control of cerebellar granule cell (GC) migration from the external granule cell layer (EGL) toward the Purkinje cell layer (PCL). GCs express the VEGF receptor Flk1, and are chemoattracted by VEGF, whose levels are higher in the PCL than EGL. Lowering VEGF levels in mice in vivo or ectopic VEGF expression in the EGL ex vivo perturbs GC migration. Using GC-specific Flk1 knock-out mice, we provide for the first time in vivo evidence for a direct chemoattractive effect of VEGF on neurons via Flk1 signaling. Finally, using knock-in mice expressing single VEGF isoforms, we show that pericellular deposition of matrix-bound VEGF isoforms around PC dendrites is necessary for proper GC migration in vivo. These findings identify a previously unknown role for VEGF in neuronal migration.

Anterior cruciate ligament deficiency causes brain plasticity: a functional MRI study.

BACKGROUND: The mechanoreceptors located in anterior cruciate ligament (ACL) constitute an afferent source of information toward the central nervous system. It has been proposed that ACL deficiency causes a disturbance in neuromuscular control, affects central programs and consequently the motor response resulting in serious dysfunction of the injured limb. PURPOSE: The objective of this study was to investigate whether chronic anterior cruciate ligament injury causes plastic changes in brain activation patterns. STUDY DESIGN: Case control study; Level of evidence, 3. METHODS: Seventeen right leg-dominant male participants with chronic anterior cruciate ligament deficiency and 18 matched healthy male participants with no special sport or habitual physical activity participated in this study. Patient selection criteria comprised a complete right unilateral anterior cruciate ligament rupture > or = 6 months before testing. Brain activation was examined by using functional magnetic resonance imaging technique (1.5-T scanner). RESULTS: Results show that patients with anterior cruciate ligament deficiency had diminished activation in several sensorimotor cortical areas and increased activation in 3 areas compared with controls: presupplementary motor area, posterior secondary somatosensory area, and posterior inferior temporal gyrus. CONCLUSION: The current study reveals that anterior cruciate ligament deficiency can cause reorganization of the central nervous system, suggesting that such an injury might be regarded as a neurophysiologic dysfunction, not a simple peripheral musculoskeletal injury. This evidence could explain clinical symptoms that accompany this type of injury and lead to severe dysfunction. Understanding the pattern of brain activation after a peripheral joint injury such as anterior cruciate ligament injury lead to new standards in rehabilitation and motor control learning with a wide application in a number of clinical and research areas (eg, surgical procedures, patient re-education, athletic training, etc).

Deficiency or inhibition of oxygen sensor Phd1 induces hypoxia tolerance by reprogramming basal metabolism.

HIF prolyl hydroxylases (PHD1-3) are oxygen sensors that regulate the stability of the hypoxia-inducible factors (HIFs) in an oxygen-dependent manner. Here, we show that loss of Phd1 lowers oxygen consumption in skeletal muscle by reprogramming glucose metabolism from oxidative to more anaerobic ATP production through activation of a Pparalpha pathway. This metabolic adaptation to oxygen conservation impairs oxidative muscle performance in healthy conditions, but it provides acute protection of myofibers against lethal ischemia. Hypoxia tolerance is not due to HIF-dependent angiogenesis, erythropoiesis or vasodilation, but rather to reduced generation of oxidative stress, which allows Phd1-deficient myofibers to preserve mitochondrial respiration. Hypoxia tolerance relies primarily on Hif-2alpha and was not observed in heterozygous Phd2-deficient or homozygous Phd3-deficient mice. Of medical importance, conditional knockdown of Phd1 also rapidly induces hypoxia tolerance. These findings delineate a new role of Phd1 in hypoxia tolerance and offer new treatment perspectives for disorders characterized by oxidative stress.

Lateralization of functional magnetic resonance imaging (fMRI) activation in the auditory pathway of patients with lateralized tinnitus.

INTRODUCTION: Tinnitus is hypothesized to be an auditory phantom phenomenon resulting from spontaneous neuronal activity somewhere along the auditory pathway. We performed fMRI of the entire auditory pathway, including the inferior colliculus (IC), the medial geniculate body (MGB) and the auditory cortex (AC), in 42 patients with tinnitus and 10 healthy volunteers to assess lateralization of fMRI activation. METHODS: Subjects were scanned on a 3T MRI scanner. A T2*-weighted EPI silent gap sequence was used during the stimulation paradigm, which consisted of a blocked design of 12 epochs in which music presented binaurally through headphones, which was switched on and off for periods of 50 s. Using SPM2 software, single subject and group statistical parametric maps were calculated. Lateralization of activation was assessed qualitatively and quantitatively. RESULTS: Tinnitus was lateralized in 35 patients (83%, 13 right-sided and 22 left-sided). Significant signal change (P(corrected) < 0.05) was found bilaterally in the primary and secondary AC, the IC and the MGB. Signal change was symmetrical in patients with bilateral tinnitus. In patients with lateralized tinnitus, fMRI activation was lateralized towards the side of perceived tinnitus in the primary AC and IC in patients with right-sided tinnitus, and in the MGB in patients with left-sided tinnitus. In healthy volunteers, activation in the primary AC was left-lateralized. CONCLUSION: Our paradigm adequately visualized the auditory pathways in tinnitus patients. In lateralized tinnitus fMRI activation was also lateralized, supporting the hypothesis that tinnitus is an auditory phantom phenomenon.

Lower limb sensorimotor network: issues of somatotopy and overlap.

Functional magnetic resonance imaging (fMRI) was used (1) to describe the pattern of whole brain activity during motion of isolated joints of the lower limb, (2) to examine the somatotopic organization of lower limb joint representations in the primary sensorimotor cortex and the anterior lobe of the cerebellum and 3) to quantify the degree of overlap between these lower limb joint activations. Eighteen healthy, right leg dominant volunteers participated in a motor block-design study, performing repetitive knee, ankle and toes flexion/extension movements. In order to relate lower limb joints activation to the well-described patterns of finger movement, serial finger-to-thumb opposition was also assessed. All movements were auditory paced at 72 beats/min (1.2 Hz). Isolated lower limb joints movement activated a distributed sensorimotor network, including primary and non-primary sensorimotor areas. Although a large overlap was evident in primary sensorimotor cortex (SM1) and cerebellum representations of the three lower limb joints, a somatotopic arrangement was recognizable with reference to center of mass coordinates of each individual joint in the above areas. Detection of active brain regions during movement of the lower limb joints is feasible with fMRI although a carefully optimized methodology protocol is required.

Frequency-selective quantitation of short-echo time 1H magnetic resonance spectra.

Accurate and efficient filtering techniques are required to suppress large nuisance components present in short-echo time magnetic resonance (MR) spectra. This paper discusses two powerful filtering techniques used in long-echo time MR spectral quantitation, the maximum-phase FIR filter (MP-FIR) and the Hankel-Lanczos Singular Value Decomposition with Partial ReOrthogonalization (HLSVD-PRO), and shows that they can be applied to their more complex short-echo time spectral counterparts. Both filters are validated and compared through extensive simulations. Their properties are discussed. In particular, the capability of MP-FIR for dealing with macromolecular components is emphasized. Although this property does not make a large difference for long-echo time MR spectra, it can be important when quantifying short-echo time spectra.

Word reading and posterior temporal dysfunction in amnestic mild cognitive impairment.

Patient studies that combine functional magnetic resonance imaging with chronometric analysis of language dysfunction may reveal the critical contribution of brain areas to language processes as well as shed light on disease pathogenesis. In amnestic mild cognitive impairment (MCI), a prodromal stage of Alzheimer's disease, we examined whether the brain system for associative-semantic judgments with words or with pictures is affected and how this relates to off-line chronometric analysis of word reading and picture naming. A consecutive memory clinic-based series of 13 amnestic MCI patients as well as 13 matched controls participated. One area, the lower bank of the posterior third of the left superior temporal sulcus (STS), showed a significant group-by-task interaction: In controls, it was activated during the associative-semantic condition with words compared with the visuoperceptual control condition but not when the same tasks were compared with pictures as input. In MCI, this word-specific activation was significantly reduced. Response amplitude correlated (r = 0.90) with the steepness of the slope of the time-accuracy curve for word reading. Our data provide converging evidence for a critical contribution of the lower bank of the left posterior STS to mapping word form onto word meaning (lexical-semantic retrieval).

A 3 T event-related functional magnetic resonance imaging (fMRI) study of primary and secondary gustatory cortex localization using natural tastants.

INTRODUCTION: It is known that taste is centrally represented in the insula, frontal and parietal operculum, as well as in the orbitofrontal cortex (secondary gustatory cortex). In functional MRI (fMRI) experiments activation in the insula has been confirmed, but activation in the orbitofrontal cortex is only infrequently found, especially at higher field strengths (3 T). Due to large susceptibility artefacts, the orbitofrontal cortex is a difficult region to examine with fMRI. Our aim was to localize taste in the human cortex at 3 T, specifically in the orbitofrontal cortex as well as in the primary gustatory cortex. METHODS: Event-related fMRI was performed at 3 T in seven healthy volunteers. Taste stimuli consisted of lemon juice and chocolate. To visualize activation in the orbitofrontal cortex a dedicated 3D SENSE EPI fMRI sequence was used, in addition to a 2D SENSE EPI fMRI sequence for imaging the entire brain. Data were analyzed using a perception-based model. RESULTS: The dedicated 3D SENSE EPI sequence successfully reduced susceptibility artefacts in the orbitofrontal area. Significant taste-related activation was found in the orbitofrontal and insular cortices. CONCLUSION: fMRI of the orbitofrontal cortex is feasible at 3 T, using a dedicated sequence. Our results corroborate findings from previous studies.

Lateralization of brain activity during lower limb joints movement. An fMRI study.

Studies of unilateral finger movement in right-handed subjects have shown asymmetrical patterns of activation in primary motor cortex and subcortical regions. In order to investigate the existence of an analogous pattern during lower limb joints movements, functional magnetic resonance imaging (fMRI) was used. Eighteen healthy, right leg dominant volunteers participated in a motor block design study, performing unilateral right and left repetitive knee, ankle and toes flexion/extension movements. Aiming to relate lower limb joints activation to the well-described patterns of finger movement, serial finger-to-thumb opposition was also assessed. All movements were auditory paced at 72 beats/min (1.2 Hz). Brain activation during movement of the nondominant joints was more bilateral than during the same movement performed with the dominant joints. Finger movement had a stronger lateralized pattern of activation in comparison with lower limb joints, implying a different functional specialization. Differences were also evident between the joints of the lower limb. Ankle and toes movements elicited the same extend of MR signal change in the majority of the examined brain regions, whereas knee joint movement was associated with a different pattern. Finally, lateralization index in primary sensorimotor cortex and basal ganglia was significantly affected by the main effect of dominance, whereas the lateralization index in cerebellum was significantly affected by the joint main effect, demonstrating a lateralization index increase from proximal to distal joints.

Magnetization transfer imaging in chronic schizophrenia.

BACKGROUND: It has recently been suggested that new imaging methods such as magnetization transfer imaging (MTI) may play an important role in detecting subtle gray- and white-matter abnormalities in schizophrenia. The aim of the study was to investigate whether MTI, analyzed on a voxel-by-voxel basis, could identify areas of abnormal magnetization transfer ratio (MTR) in patients with schizophrenia. MATERIAL/METHODS: Twenty schizophrenic patients and 23 healthy controls matched for handedness and demographic variables underwent MTI and T1-weighted structural MRI in a 3-tesla scanner. Post-processing was performed with SPM99 and included co-registration of the MT-weighted and non-MT-weighted images, calculation of the MTR maps, spatial normalization, and smoothing. Differences in the MTR maps between groups were assessed using two-sample t-tests. Significant changes in MTR were detected at an individual voxel threshold of p < 0.05. RESULTS: Group comparisons revealed no significant MTR changes, although there was a trend towards MTR reduction in the left superior temporal gyrus, in the right occipital cortex, and left periventricular white matter in patients compared with controls prior to correction for multiple comparisons (p < 0.001, uncorrected). CONCLUSIONS: MTI and voxel-by-voxel statistical analysis used in the study failed to identify regions of significant MTR reductions in schizophrenic patients. Our results disagree with findings of widespread MTR abnormalities reported in recent literature.

Liver tumor model with implanted rhabdomyosarcoma in rats: MR imaging, microangiography, and histopathologic analysis.

In compliance with institutional regulations for care and use of laboratory animals, the aim of this study was to establish and characterize a rodent liver tumor model to provide a platform for preclinical assessment of new diagnostic and therapeutic strategies. A rhabdomyosarcoma tumor was implanted in the right and left liver lobes of 20 rats, for a total of 40 tumors. T1- and T2-weighted magnetic resonance (MR) images, diffusion-weighted images, and dynamic susceptibility contrast agent-enhanced perfusion-weighted images were obtained up to 16 days after tumor implantation and were compared with postmortem three-dimensional computed tomographic (CT) images, digital microangiograms, and histopathologic findings. Fifteen tumors were examined with proton ((1)H) MR spectroscopy. All tumors grew, with a mean volume doubling time of 2.2 days +/- 0.9 (standard deviation) and a final size of 591 mm(3)+/- 124. The rhabdomyosarcoma tumor showed hypervascularity at MR imaging, three-dimensional CT, microangiography, and histologic analysis. On dynamic susceptibility contrast-enhanced perfusion-weighted images, the maximum signal intensity decrease differed in time and extent between the tumor and the liver, with a significantly (P < .001) higher relative blood volume, relative blood flow, and permeability value in the tumor than in the liver. With (1)H MR spectroscopy, the rhabdomyosarcoma tumor and the liver featured significant (P < .001) choline and lipid peaks, respectively. Implantation of a rhabdomyosarcoma tumor in the livers of rats is feasible and reproducible, and this animal model seems promising for future testing of new diagnostic and therapeutic strategies.

Activation of cortical and subcortical auditory structures at 3 T by means of a functional magnetic resonance imaging paradigm suitable for clinical use.

OBJECTIVES: Visualization of functional magnetic resonance imaging (fMRI) activation of subcortical auditory structures remains challenging because of the cardiac-related pulsatile movement of both the brainstem and the cerebrospinal fluid and involved, until now, special scanning, pre- and postprocessing techniques, which are not convenient in clinical settings. The aim of this study is to examine the activation in both cortical and subcortical auditory structures by means of an fMRI paradigm, which is suitable for clinical use. MATERIALS AND METHODS: Twenty subjects (13 volunteers and 7 patients) were examined on a 3 T imaging system with binaural musical stimulation. RESULTS: Both cortical and subcortical auditory structures are successfully visualized in volunteers and patients. CONCLUSIONS: Activation of both the cortical and subcortical auditory structures can be visualized by means of an appropriate fMRI setup at 3 T. This paradigm can easily be used in patients with tumors and/or hearing disorders.

Mapping multiple visual areas in the human brain with a short fMRI sequence.

It is a fundamental insight of neuroscience that the cerebral cortex is divided into spatially separated and functionally distinct areas. In this study, we tried to map a large number of visual areas in individual subjects passively viewing a simple stimulus sequence during functional magnetic resonance imaging (fMRI) at 1.5 T. The blocked stimulus sequence contrasted static object photographs with video takes of movement through natural indoor and outdoor scenes, alternated with a control fixation task. Two runs of the 5-min sequence sufficed to invoke 29 distinguishable activations, 16 (13 bilateral) of which were observed in all 10 participants. At the ventral side, object responsive activations were organized along the lateral occipital-temporal surface and near the collateral and occipital-temporal sulci. The latter activations, corresponding to the lateral occipital complex, showed a different activation profile from those near the collateral sulcus, most likely corresponding to the color constancy areas V4/V8-V4alpha. A potentially new fusiform object area was seen in 6 subjects, even more anterior than the parahippocampal place area. At the dorsal side, consistent activations were mainly related to motion stimuli and included the well-known areas V3a, VIPS, POIPS, hV5+, STS and the cingulate sulcus. There was consistent activation in the parietal-occipital sulcus, containing the areas V6a and V6. In addition, all subjects showed activation in the superior-anterior precuneus. Thus, the short stimulus sequence robustly invoked multiple visual areas and can be used to map the organization of the visual system in normal and brain-damaged individuals.

Tissue segmentation and classification of MRSI data using canonical correlation analysis.

In this article an accurate and efficient technique for tissue typing is presented. The proposed technique is based on Canonical Correlation Analysis, a statistical method able to simultaneously exploit the spectral and spatial information characterizing the Magnetic Resonance Spectroscopic Imaging (MRSI) data. Recently, Canonical Correlation Analysis has been successfully applied to other types of biomedical data, such as functional MRI data. Here, Canonical Correlation Analysis is adapted for MRSI data processing in order to retrieve in an accurate and efficient way the possible tissue types that characterize the organ under investigation. The potential and limitations of the new technique have been investigated by using simulated as well as in vivo prostate MRSI data, and extensive studies demonstrate a high accuracy, robustness, and efficiency. Moreover, the performance of Canonical Correlation Analysis has been compared to that of ordinary correlation analysis. The test results show that Canonical Correlation Analysis performs best in terms of accuracy and robustness.

Anterior temporal laterality in primary progressive aphasia shifts to the right.

In aphasia due to stroke, language-related activity shifts not only to undamaged cortex within the dominant hemisphere but also toward right-sided areas homotopical to the left-sided lesion. We examined whether a rightward shift takes place in primary progressive aphasia (PPA). Nineteen PPA patients participated, 19 healthy subjects and 14 patients with amnestic mild cognitive impairment who served as controls. Subjects underwent neuropsychological assessment, structural magnetic resonance imaging (MRI), and a functional MRI with a factorial design: words versus pictures and associative-semantic versus visuoperceptual task. Measures of neuropsychological performance were entered as regressors into a multiple linear regression analysis, with response amplitude during the associative-semantic versus control conditions as outcome variable. Language competence correlated negatively with responses in the right anterior temporal cortex and positively with volume and responses in the left-sided homotope. In normal subjects, anterior temporal activation was more extensive to the left than the right (laterality index [LI], +0.64; standard error [SE], 0.11). Laterality was inverted in PPA with word comprehension deficit (LI, - 0.34; SE, 0.19), with an intermediate pattern in PPA without comprehension deficit (LI, +0.23; SE, 0.14). The rightward laterality shift previously reported in aphasic stroke extends to PPA, in particular, when comprehension is deficient.

Quantitative diffusion tensor imaging in cerebral palsy due to periventricular white matter injury.

Periventricular white matter injury (PWI) is a major form of brain injury observed in congenital hemiparesis. The aim of this study is to determine the usefulness of diffusion tensor imaging (DTI) and fibre tracking in delineating the primary and secondary degenerative changes in cerebral white matter and deep grey matter in patients with spastic cerebral palsy due to PWI and to look for any possible reorganization of the axonal architecture. Five hemiparetic cerebral palsy patients (median age 14 years) with known PWI were prospectively studied with DTI of the brain at 1.5T and quantitatively compared with five age and sex matched controls. Fibre tracts for various corticofugal, thalamocortical and association tracts were generated and analysed for the DTI fibre count and for diffusion parameters. A region of interest based analysis was performed for the directionally averaged mean diffusivity (D(av)) and fractional anisotropy (FA) values in various white matter locations in the brain and the brainstem and in the deep grey matter nuclei. Group statistics were performed for these parameters using Mann-Whitney U-test comparing the affected sides in patients with either side in controls and the unaffected side in hemiparetics. There was significant reduction in DTI fibre count on the lesional side involving corticospinal tract (CST), corticobulbar tract (CBT) and superior thalamic radiation in the patient group compared with controls. Also there was an increase in DTI fibre count in the unaffected side of the hemiparetic patients in CST and CBT, which reached statistical significance only in CBT. The corpus callosum, cingulum, superior longitudinal fasciculus and middle cerebellar peduncle failed to show any significant change. ROI measurements on the primary site of white matter lesion and the thalamus revealed a significant increase in D(av) and decrease in FA, suggesting primary degeneration. The CST in the brainstem, the body of corpus callosum and the head of caudate and lentiform nuclei showed features of secondary degeneration on the affected side. The CST on the unaffected side of hemiparetics was found to have a significant decrease in D(av) and an increase in FA. Thus the degeneration of various motor and sensory pathways, as well as deep grey matter structures, appears to be important in determining the pathophysiological mechanisms in patients with congenital PWI. Also evidence suggesting the reorganization of sensorimotor tracts in the unaffected side of spastic hemiparetic patients was noted.

Passive somatosensory discrimination tasks in healthy volunteers: differential networks involved in familiar versus unfamiliar shape and length discrimination.

Somatosensory discrimination of unseen objects relies on processing of proprioceptive and tactile information to detect spatial features, such as shape or length, as acquired by exploratory finger movements. This ability can be impaired after stroke, because of somatosensory-motor deficits. Passive somatosensory discrimination tasks are therefore used in therapy to improve motor function. Whereas the neural correlates of active discrimination have been addressed repeatedly, little is known about the neural networks activated during passive discrimination of somatosensory information. In the present study, we applied functional magnetic resonance imaging (fMRI) while the right index finger of ten healthy subjects was passively moved along various shapes and lengths by an fMRI compatible robot. Comparing discriminating versus non-discriminating passive movements, we identified a bilateral parieto-frontal network, including the precuneus, superior parietal gyrus, rostral intraparietal sulcus, and supramarginal gyrus as well as the supplementary motor area (SMA), dorsal premotor (PMd), and ventral premotor (PMv) areas. Additionally, we compared the discrimination of different spatial features, i.e., discrimination of length versus familiar (rectangles or triangles) and unfamiliar geometric shapes (arbitrary quadrilaterals). Length discrimination activated mainly medially located superior parietal and PMd circuits whereas discrimination of familiar geometric shapes activated more laterally located inferior parietal and PMv regions. These differential parieto-frontal circuits provide new insights into the neural basis of extracting spatial features from somatosensory input and suggest that different passive discrimination tasks could be used for lesion-specific training following stroke.

Parieto-premotor areas mediate directional interference during bimanual movements.

In bimanual movements, interference emerges when limbs are moved simultaneously along incompatible directions. The neural substrate and mechanisms underlying this phenomenon are largely unknown. We used functional magnetic resonance imaging to compare brain activation during directional incompatible versus compatible bimanual movements. Our main results were that directional interference emerges primarily within superior parietal, intraparietal and dorsal premotor areas of the right hemisphere. The same areas were also activated when the unimanual subtasks were executed in isolation. In light of previous findings in monkeys and humans, we conclude that directional interference activates a parieto-premotor circuit that is involved in the control of goal-directed movements under somatosensory guidance. Moreover, our data suggest that the parietal cortex might represent an important locus for integrating spatial aspects of the limbs' movements into a common action. It is hypothesized to be the candidate structure from where interference arises when directionally incompatible movements are performed. We discuss the possibility that interference emerges when computational resources in these parietal areas are insufficient to code two incompatible movement directions independently from each other.