OBJECTIVE

To compare use of standard enteral formula versus enteric formula with prebiotic content in terms of nutrition therapy related outcomes among neurocritical care patients.

METHODS

A total of 46 adult neurocritical care patients who received nutrition therapy with standard enteral formula (SEF group; n = 23) or enteral formula with prebiotic content (EFPC group; n = 23) during their hospitalization in intensive care unit (ICU) were included in this prospective randomized controlled study. Data on patient demographics (age, gender), diagnosis, co-morbid diseases, anthropometrics, length of stay (LOS) in hospital and ICU, Nutritional Risk Screening (NRS-2002) score, and Acute Physiology and Chronic Health (APACHE-II) score were recorded at enrollment. Data on daily nutritional intake [total energy (kcal/day), carbohydrate (g/day), protein (g/day), lipid (g/day), FOS (g/day), enteral volume (ml/day), fluid in enteral product (ml/day) and fluid intake (ml/day)], achievement of target dose [total fluid intake in enteral product (ml)/20 h], laboratory findings (blood biochemistry and complete blood count), complications and drug treatments were recorded on Day 1, Day 4, Day 7, Day 14 and Day 21 of nutrition therapy in SEF and EFPC groups.

RESULTS

Use of EFPC compared to SEF was associated with significantly higher total energy, carbohydrate, protein, lipid, enteral volume and fluid intake (p values ranged from <0.05 to <0.001) on each day of nutrition therapy. Target dose was achieved by majority of patients (86.9%) and at day 4 of nutrition therapy in most of patients (71.7%) in the overall study population. Patients in the EFPC group had a non-significant tendency for higher rate (95.7% vs. 78.3%) and earlier (87.0% vs. 56.5% on day 4) achievement of target dose, lower rate (8.7% vs. 56.5%) and faster amelioration (none vs. 52.2% were diarrheic on day 7) of diarrhea and lesser need for insulin (56.5% vs. 13.0%, p = 0.002). Nutrition therapy was associated with significant decrease in prealbumin (Day 14 vs. Day 1, p < 0.05 for both), albumin (Day 14 vs. day 1, p < 0.01 for SEF, p < 0.05 for PEF), hemoglobin (Day 14 and Day 21 vs. Day 1and Day 14 vs. Day 4, p < 0.001 for each for SEF, Day 7, Day 14 and Day 21 vs. Day 1, p < 0.01 for each for PEF) and hematocrit (Day 14 and Day 21 vs. Day 1, p < 0.001 for each for both) levels in both SEF and EFPC groups.

CONCLUSIONS

In conclusion, our findings revealed achievement of target nutritional intake in majority of neurocritical care patients via nutrition therapy, whereas EFPC was associated with a non-significant tendency for more frequent and earlier achievement of target dose along with significantly lower rate and faster amelioration of diarrhea as compared with SEF group. Prealbumin and albumin levels remained below the normal range, whereas C reactive protein (CRP) and white blood cell (WBC) were over the normal range throughout the nutrition period in both groups, while creatinine and urea levels were higher in EFPC than in SEF group. Hence, our findings seem to emphasize the importance of avoiding protein debt in provision of nutrition therapy and the likelihood of deterioration of nutritional status in elderly neurocritical care patients despite provision of early enteral nutrition support due to complex and deleterious inflammatory and metabolic changes during critical illness.

Somatosensory evoked magnetic fields (SEFs) following painful electrical stimulation of the finger were investigated in 5 normal subjects. Equivalent current dipoles (ECDs) of deflections shorter than 100 msec in latency were located in the primary sensory cortex (SI) in the hemisphere contralateral to the stimulated finger following either non-painful or painful stimulation. Two main deflections, N100m-P100m and N250m-P250m, were independently identified following painful stimulation, although they were not found in SEFs following non-painful weak stimulation. ECDs of the N100m-P100m were considered to be located in the bilateral second sensory cortices (SII). ECDs of the N250m-P250m were identified in the bilateral cingulate cortices and SII, but the intersubject difference was large. Therefore, we considered that contralateral SI and bilateral SII were initially activated by painful noxious stimulation, and then multiple areas including bilateral SII and cingulate cortices were activated. In EEG recordings (evoked potentials), no potential corresponding to N100m-P100m was found, probably because it was difficult to record activation in SII by EEG recordings. The P250 potential which corresponded to the N250m-P250m was clearly identified, probably because activation of multiple areas generated large long-duration EEG potentials which were maximal around the vertex, unlike MEG recordings.

OBJECTIVE

We have evaluated left ventricular ejection fraction (LVEF) at rest (REF) and after stress (SEF) with dual-isotope gated myocardial perfusion SPECT (GMPS) with 201Tl injected at rest and 99mTc sestamibi (99mTc-MIBI) injected at peak stress, to assess the occurrence of post-stress stunning.

METHODS

Two hundred and thirty-six consecutive patients had GMPS at rest and post-stress. The summed stress and rest scores and the summed difference score (SDS) were calculated using a 17-segment model analysis of GMPS. An SDS >3 indicated significant ischaemia. The REF and SEF were automatically generated and the DEF (SEF-REF) was calculated.

RESULTS

Significant stress induced ischaemia was observed in 103 patients (44%). REF was 54.72%+/-15.75% and SEF was 55.69%+/-16.65% (P<0.0015). DEF was -2.25+/-5.36 and 3.42+/-5.25 in patients with and without ischaemia, respectively (P<0.001). Post-stress stunning (>5% decrease in LVEF) was present in 68 patients (29%) and in 58/103 (56%) patients with ischaemia, after treadmill exercise or dipyridamole infusion and was more common in patients with severe ischaemia. The single significant predictor of DEF in univariate analysis and of stunning using logistic binary regression was stress induced ischaemia (P<0.0001).

CONCLUSIONS

LVEF increases post-stress in patients with no ischaemia and may decrease in 56% of patients with ischaemia, possibly due to stunning. The best predictor of post-stress stunning is stress induced ischaemia and its occurrence is related to the degree of ischaemia.

Value-based decisions could rely either on the selection of desired economic goods or on the selection of the actions that will obtain the goods. We investigated this question by recording from the supplementary eye field (SEF) of monkeys during a gambling task that allowed us to distinguish chosen good from chosen action signals. Analysis of the individual neuron activity, as well as of the population state-space dynamic, showed that SEF encodes first the chosen gamble option (the desired economic good) and only ~100 ms later the saccade that will obtain it (the chosen action). The action selection is likely driven by inhibitory interactions between different SEF neurons. Our results suggest that during value-based decisions, the selection of economic goods precedes and guides the selection of actions. The two selection steps serve different functions and can therefore not compensate for each other, even when information guiding both processes is given simultaneously.

We present all-dielectric gallium phosphide (GaP) nanoantennas as an efficient nanophotonic platform for surface-enhanced second harmonic generation (SHG) and fluorescence (SEF), showing negligible losses in the visible range. Employing single GaP nanodisks, we observe an increase of more than 3 orders of magnitude in the SHG conversion signal in comparison with the bulk. This constitutes an SHG efficiency as large as 0.0002%, which is to the best of our knowledge the highest yet achieved value for a single nano-object in the optical region. Furthermore, we show that GaP dimers with 35 nm gap can enhance up to 3600 times the fluorescence emission of dyes located in the gap of the nanoantenna. This is accomplished by a fluorescence lifetime reduction of at least 22 times, accompanied by a high-intensity field confinement in the gap region. These results open new avenues for low-loss nanophotonics in the optical regime.

Vegetative phase change in Arabidopsis thaliana is mediated by a decrease in the level of MIR156A and MIR156C, resulting in an increase in the expression of their targets, SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) genes. Changes in chromatin structure are required for the downregulation of MIR156A and MIR156C, but whether chromatin structure contributes to their initial elevated expression is unknown. We found that mutations in components of the SWR1 complex (ARP6, SEF) and in genes encoding H2A.Z (HTA9 and HTA11) reduce the expression of MIR156A and MIR156C, and accelerate vegetative phase change, indicating that H2A.Z promotes juvenile vegetative identity. However, arp6 and sef did not accelerate the temporal decline in miR156, and the downregulation of MIR156A and MIR156C was not accompanied by significant change in the level of H2A.Z at these loci. We conclude that H2A.Z contributes to the high expression of MIR156A/MIR156C early in shoot development, but does not regulate the timing of vegetative phase change. Our results also suggest that H2A.Z promotes the expression of MIR156A/MIR156C by facilitating the deposition of H3K4me3, rather than by decreasing nucleosome occupancy.

The medial frontal cortex has been suggested to play a role in the control, monitoring, and selection of behavior. The supplementary eye field (SEF) is a cortical area within medial frontal cortex that is involved in the regulation of eye movements. Neurophysiological studies in the SEF of macaque monkeys have systematically investigated the role of SEF in various behavioral control and monitoring functions. Inhibitory control studies indicate that SEF neurons do not directly participate in the initiation of eye movements. Instead, recent value-based decision making studies suggest that the SEF participates in the control of eye movements by representing the context-dependent action values of all currently possible oculomotor behaviors. These action value signals in SEF would be useful in directing the activity distribution in more primary oculomotor areas, to guide decisions towards behaviorally optimal choices. SEF also does not participate in the fast, inhibitory control of eye movements in response to sudden changes in the task requirements. Instead, it participates in the long-term regulation of oculomotor excitability to adjust the speed-accuracy tradeoff. The context-dependent control signals found in SEF (including the action value signals) have to be learned and continuously adjusted in response to changes in the environment. This is likely the function of the large number of different response monitoring and evaluation signals in SEF. In conclusion, the overall function of SEF in goal-directed behavior seems to be the learning of context-dependent rules that allow predicting the likely consequences of different eye movements. This map of action value signals could be used so that eye movements are selected that best fulfill the current long-term goal of the agent.

Tongue movements contribute to oral functions including swallowing, vocalizing, and breathing. Fine tongue movements are regulated through efferent and afferent connections between the cortex and tongue. It has been demonstrated that cortico-muscular coherence (CMC) is reflected at two frequency bands during isometric tongue protrusions: the beta (β) band at 15-35Hz and the low-frequency band at 2-10Hz. The CMC at the β band (β-CMC) reflects motor commands from the primary motor cortex (M1) to the tongue muscles through hypoglossal motoneuron pools. However, the generator mechanism of the CMC at the low-frequency band (low-CMC) remains unknown. Here, we evaluated the mechanism of low-CMC during isometric tongue protrusion using magnetoencephalography (MEG). Somatosensory evoked fields (SEFs) were also recorded following electrical tongue stimulation. Significant low-CMC and β-CMC were observed over both hemispheres for each side of the tongue. Time-domain analysis showed that the MEG signal followed the electromyography signal for low-CMC, which was contrary to the finding that the MEG signal preceded the electromyography signal for β-CMC. The mean conduction time from the tongue to the cortex was not significantly different between the low-CMC (mean, 80.9ms) and SEFs (mean, 71.1ms). The cortical sources of low-CMC were located significantly posterior (mean, 10.1mm) to the sources of β-CMC in M1, but were in the same area as tongue SEFs in the primary somatosensory cortex (S1). These results reveal that the low-CMC may be driven by proprioceptive afferents from the tongue muscles to S1, and that the oscillatory interaction was derived from each side of the tongue to both hemispheres. Oscillatory proprioceptive feedback from the tongue muscles may aid in the coordination of sophisticated tongue movements in humans.

The aim of the study was to assess the impact of selection for residual feed intake (RFI) on the behavioural activity of lines divergently selected for RFI during seven generations. In all, six successive batches from the seventh generation of selection were raised in collective pens equipped with a single-place electronic feeder (SEF) from 10 weeks of age to 100 kg BW. Each batch included four groups of 12 pigs: high RFI (RFI+) castrated males, RFI+ females, low RFI (RFI-) castrated males, RFI- females. At 17 weeks of age, health criteria were evaluated using a gradient scale for increased severity of lameness, body lesions, bursae and tail biting. Individual behavioural activities were recorded by 24-h video tape on the day after health evaluation. The investigative motivation towards unfamiliar objects was quantified at 18 weeks of age. The daily individual feeding patterns were computed from SEF records during the 4 weeks surrounding 12, 17 and 22 weeks of age. All pigs spent significantly most of their time lying in diurnal (80% of total scan) and nocturnal (>89%) periods. The RFI- pigs showed a lower proportion of health problems (P<0.01) than RFI+ pigs. The RFI- pigs used the SEF less than the RFI+ pigs, in diurnal (5.3% v. 6.4% of video scans, P<0.05) and nocturnal periods (3.6% v. 4.5% of video scans, P<0.05). This was confirmed by a significantly lower daily number and duration of visits to the SEF computed from the SEF data. The feeding activity measured from the video recording was significantly correlated (R>0.34; P<0.05) with feeding patterns computed from the SEF. The RFI- pigs spent less time standing over the 24-h period (9.7% v. 12.2% of scans, i.e. 35 min/day, P<0.05). In terms of energy costs, this amounted to 14% of the line difference in terms of daily metabolizable energy intake. The castrated males used the SEF more than females, especially at night (4.7% v. 3.4% of total scans, P<0.05), whereas females displayed greater investigation of their environment (7.7±0.3% v. 6.6±0.2% of total scans, P<0.05) and the novel objects (10.7% v. 4.9% of total scans, P<0.05). In conclusion, the lower physical activity associated with reduced energy expenditure in RFI- pigs compared with RFI+ pigs contributed significantly to their improved efficiency and was not related to worsened health scores.

Low intensity transcranial ultrasonic stimulation (TUS) has been demonstrated to non-invasively and transiently stimulate the nervous system. Although US neuromodulation has appeared robust in rodent studies, the effects of US in large mammals and humans have been modest at best. In addition, there is a lack of direct recordings from the stimulated neurons in response to US. Our study investigates the magnitude of the US effects on neuronal discharge in awake behaving monkeys and thus fills the void on both fronts.

In this study, we demonstrate the feasibility of recording action potentials in the supplementary eye field (SEF) as TUS is applied simultaneously to the frontal eye field (FEF) in macaques performing an antisaccade task.

We show that compared to a control stimulation in the visual cortex, SEF activity is significantly modulated shortly after TUS onset. Among all cell types 40% of neurons significantly changed their activity after TUS. Half of the neurons showed a transient increase of activity induced by TUS.

Our study demonstrates that the neuromodulatory effects of non-invasive focused ultrasound can be assessed in real time in awake behaving monkeys by recording discharge activity from a brain region reciprocally connected with the stimulated region. The study opens the door for further parametric studies for fine-tuning the ultrasonic parameters. The ultrasonic effect could indeed be quantified based on the direct measurement of the intensity of the modulation induced on a single neuron in a freely performing animal. The technique should be readily reproducible in other primate laboratories studying brain function, both for exploratory and therapeutic purposes and to facilitate the development of future clinical TUS devices.

Low-grade fibromyxoid sarcoma (LGFMS) is a bland spindle cell neoplasm that typically arises in the deep soft tissues of the proximal extremities or trunk of young adults. The majority of LGFMS are characterized by a recurrent (7;16)(q34;p11) translocation, resulting in the FUS-CREB3L2 fusion gene, which generates a chimeric protein with transcriptional regulatory activity. Small numbers harbor a FUS-CREB3L1 fusion resulting from t(11;16)(p11;p11), whilst rare cases harbor the EWSR1-CREB3L1 fusion. LGFMS is of low to moderate cellularity and consists of bland spindle cells with small, angulated nuclei and scant, wispy cytoplasm, arranged in a whorled growth pattern and typically showing abrupt transition from myxoid to fibrous areas. Immunohistochemical expression of MUC4 is a consistent finding. Hyalinized spindle cell tumor with giant rosettes (HSCTGR) is a morphological variant of LGFMS that shares the same balanced translocation, and is also immunoreactive for MUC4. A potential relationship between LGFMS and sclerosing epithelioid fibrosarcoma (SEF), a rare fibroblastic neoplasm that most commonly arises in the deep soft tissues of the lower extremities, limb girdles or trunk, has also been suggested. SEF is classically composed of nests and cords of epithelioid cells with clear or eosinophilic cytoplasm embedded within densely sclerotic stroma. In some cases, areas indistinguishable from LGFMS are present, and these have been shown to contain FUS-CREB3L2 fusion transcripts. The majority of pure SEF tumors harbor EWSR1 rearrangements, with EWSR1-CREB3L1 and more rarely EWSR1-CREB3L2 gene fusions more common than those involving FUS. MUC4 immunoreactivity is also seen in approximately 70% of SEF. Surgical resection of these tumors with clear margins is the treatment of choice. Correct diagnosis is important because of the significant potential for recurrence and late metastatic spread. We review LGFMS and SEF, discussing morphology and immunohistochemistry, genetics and molecular findings, and the differential diagnosis.

Since the environment is in constant flux, decision-making capabilities of the brain must be rapid and flexible. Yet in sensory motion processing pathways of the primate brain where decision making has been extensively studied, the flexibility of neurons is limited by inherent selectivity to motion direction and speed. The supplementary eye field (SEF), an area involved in decision making on moving stimuli, is not strictly a sensory or motor structure, and hence may not suffer such limitations. Here we test whether neurons in the SEF can flexibly interpret the rule of a go/nogo task when the decision boundary in the task changes with each trial. The task rule specified that the animal pursue a moving target with its eyes if and when the target entered a visible zone. The size of the zone was changed from trial to trial in order to shift the decision boundary, and thereby assign different go/nogo significance to the same motion trajectories. Individual SEF neurons interpreted the rule appropriately, signaling go or nogo in compliance with the rule and not the direction of motion. The results provide the first evidence that individual neurons in frontal cortex can flexibly interpret a rule that governs the decision to act.

The purpose of this study was to study the relationship between interictal spike sources and somatosensory cortices in benign rolandic epilepsy of childhood (BREC) using a whole-scalp neuromagnetometer. We recorded spontaneous magnetoencephalography (MEG) and EEG signals and cortical somatosensory-evoked magnetic fields (SEFs) to electric stimulation of the median nerve in 9 children with BREC. Interictal rolandic discharges (RDs) and SEFs were analyzed by equivalent current dipole (ECD) modeling. Based on the orientation and locations of corresponding ECDs, we compared generators of RDs with primary (SI) and second somatosensory cortices (SII). Our results showed that RDs and SII responses had similar ECD orientation on the magnetic field maps. The ECDs of RDs were localized 15.3 +/- 1.9 and 12.2 +/- 2.8 mm anterior to SI and SII, respectively. The spatial distance on average from the location of RDs to SII (21.9 +/- 1.6 mm) cortex was significantly shorter than to SI cortex (29.7 +/- 1.7 mm) (P<0.01, Wilcoxon signed-rank test). In conclusion, the cortical generators for RDs in patients with BREC are localized in the precentral motor cortex, closer to hand SII than to SI cortex.

OBJECTIVE

Patients must remain immobile for magnetoencephalography (MEG) and MRI recordings to allow precise localization of brain function for pre-surgical functional mapping. In young children with epilepsy, this is accomplished with recordings during sleep or with anesthesia. This paper demonstrates that MEG can detect, characterize and localize somatosensory-evoked fields (SEF) in infants younger than 4 years of age with or without total intravenous anesthesia (TIVA).

METHODS

We investigated the latency, amplitude, residual error (RE) and location of the N20m of the SEF in 26 infants (mean age=2.6 years). Seventeen patients underwent TIVA and 9 patients were tested while asleep, without TIVA.

RESULTS

MEG detected 44 reliable SEFs (77%) in 52 median nerve stimulations. We found 27 reliable SEFs (79%) with TIVA and 13 reliable SEFs (72%) without TIVA. TIVA effects included longer latencies (p<0.001) and lower RE (p<0.05) compared to those without TIVA. Older patients and larger head circumferences also showed significantly shorter latencies (p<0.01).

CONCLUSIONS

TIVA resulted in reliable SEFs with lower RE and longer latencies.

CONCLUSIONS

MEG can detect reliable SEFs in infants younger than 4 years old. When infants require TIVA for MEG and MRI acquisition, SEFs can still be reliably observed.

This study was undertaken to investigate immunopathologic mechanism of Enterococcus faecalis in relation to persistent apical periodontitis. We monitored the expression levels of alpha4 integrin in human polymorphonuclear neutophils (PMNs) after stimulated with sonicated extracts of E. faecalis (SEF) and compared with lipopolycaccarides (LPS) of Escherichia coli for various incubation time. Venous blood was collected from healthy volunteers and then PMNs were isolated and cultured with various concentrations of SEF for different periods of time. The levels of alpha4 integrin were measured by flow cytometry analysis. E. coli LPS group was used as a positive control and untreated PMNs as a negative control. Results showed that the expressions levels of alpha4 integrin were increased in human PMNs stimulated with E. coli LPS in comparison with unstimulated control cells (p < 0.05). In case of SEF stimulated group, the expression levels were decreased in time-dependent manner in comparison to E. coli LPS group (p < 0.05). Notably, after 12 h for incubation with SEF, the expression of alpha4 integrin was decreased in dose-dependent manner (p < 0.05). These findings suggest that E. faecalis seem to suppress PMNs recruiting activity by down-regulating alpha4 integrin expression, providing the possible mechanism that E. faecalis may play a crucial role in persistent apical periodontitis.

Subcellular compartmentalization has become an important theme in cell signaling. In particular, the Golgi apparatus (GA) plays a prominent role in compartmentalizing signaling cascades that originate at the plasma membrane or other organelles. To precisely regulate this process, cells have evolved a unique class of organizer proteins, termed "scaffold proteins". Sef, PAQR3, PAQR10 and PAQR11 are scaffold proteins that have recently been identified on the GA and are referred to as Golgi scaffolds. The major cell growth signaling pathways, such as Ras/MAPK, PI3K/AKT, insulin and VEGF (vascular endothelial growth factor), are tightly regulated spatially and temporally by these Golgi scaffolds to ensure a physiologically appropriate outcome. Here, we discuss the subcellular localization and characterization of the topology and functional domains of these Golgi scaffolds and summarize their roles in the compartmentalization of cell signaling. We also highlight the physiological and pathological roles of these Golgi scaffolds in tumorigenesis and developmental disorders.

Twenty-three patients undergoing intensive therapy had continuous EEG recording in an attempt to assess depth of sedation using spectral analysis. Median power frequency (MPF) and spectral edge frequency (SEF) were calculated and correlated with the clinical sedation score and blood concentration of sedative drug. Fifteen patients received isoflurane and eight midazolam. There was no correlation between MPF or SEF and sedation score or blood concentration of drug. These results suggest that no simple measure of the EEG is likely to correlate with depth of sedation in critically ill patients.

A 39-year-old woman with multiple sclerosis (MS) at exacerbation stage underwent dilatation and curettage. MS is characterized by chronic inflammation, demyelination, and gliosis in the central nervous system. Surgical stress often induces exacerbation of MS symptoms. Therefore, deep anesthesia is required for anesthetic management in cases of MS. We monitored electroencephalograph (EEG), spectral edge frequency 90 (SEF 90), spectral median frequency (SMF) and delta-amplitude for depth of anesthesia using pEEG (Dräger, Germany). In this case, anesthesia was induced with sevoflurane and gradually increased to 5% in oxygen 4 l.min-1 and maintained with sevoflurane 2-3% in 2 nitrous oxide l.min-1 and 2 l.min-1 oxygen. Surgery was completed and no spike wave was observed by pEEG monitoring during surgery. In conclusion, sevoflurane anesthesia was useful for a patient with MS during exacerbation stage.

Ultrastructure reports have described that liver sinusoidal endothelial cell (LSEC)s contain a cytoskeletal framework of filamentous actin. Small G protein has emerged as an important regulator of the actin cytoskeleton, and consequently, of cell morphology and motility. We investigated actin filaments in relation to SEF in LSECs using a heavy meromyosin-decorated reaction and thereby elucidated the roles of small G protein and actin cytoskeleton in the morphological and functional alterations of SEF. Caveolin-1 expression has also been found in fenestrations with many characteristics of liver sinusoidal endothelial cells. Currently, fenestral studies and human disease are revealing ways to increase the liver sieve's porosity, which is reduced through pathological mechanisms. Hepatic sinusoidal endothelial dysfunction, which is known to impair endothelium-dependent relaxation in the liver microcirculation, contributes to increased intrahepatic vascular resistance.

Abdominal aortic aneurysm (AAA) is a cardiovascular disease with high incidence among elderly population. Biomechanical computational analyses can provide fundamental insights into AAA pathogenesis and clinical management, but modeling should be sufficiently accurate. Several constitutive models of the AAA wall are present in the literature, and some of them seem to well describe the experimental behavior of the aneurysmatic human aorta. In this work we compare a two (2FF) and a four (4FF) fiber families constitutive models of the AAA wall. Both these models satisfactorily fit literature data from biaxial tests on the aneurysmatic tissue. To investigate the peculiar characteristics of these models, we considered the problem of AAA inflation, and solved it by implementing the constitutive equations in a finite element code. A 20% axial stretch was imposed to the aneurysm ends, to simulate the physiological condition. Although fitted on the same dataset, the two material models lead to considerably different outcomes. In particular, adopting a 4FF strain energy function (SEF), an increase of the circumferential stress values can be observed, while higher axial stresses are recorded for the 2FF model. These differences can be attributed to the intrinsic characteristics of the SEFs and to the effective stress field, with respect to the one experienced in biaxial experimental tests on which the fitting is based. In fact the two SEFs appear similar within the region of the stress-strain experimental data, but become different outside it, as in case of aneurysms, due to the effects of the data extrapolation process. It is suggested that experimental data should be obtained for conditions similar to those of the application for which they are intended.

OBJECTIVE

Brain responses to auditory and visual stimuli have been previously shown to depend on the level of spontaneous brain activity in the 8-13 Hz range. Our aim was to determine whether somatosensory evoked responses are influenced by ongoing rhythmic activity in the 8-13 Hz frequency range originating in the sensorimotor cortex (mu rhythm).

METHODS

We used a whole-head 122 channel magnetoencephalography (MEG) system to record somatosensory evoked fields (SEFs) in response to median nerve stimulation in 11 subjects. Spontaneous oscillations in the 8-13 Hz band over the contralateral sensorimotor cortex were evaluated in 3 different pre-stimulus time intervals using wavelet analysis.

RESULTS

The N20m SEF deflection did not depend on pre-stimulus activity, while the amplitude of the P35m deflection, and to a lesser extent that of the P60m deflection, showed a small positive correlation with the amplitude of the pre-stimulus mu rhythm. Although the amplitude of the mu rhythm varied by a factor of 2.3-5, the maximum variations in P35m and P60m amplitude were only 21 and 12%, respectively. The latencies of the peaks were not affected by the strength of the pre-stimulus mu rhythm.

CONCLUSIONS

It appears that the first excitatory cortical response (N20m) is independent of the oscillatory state (8-13 Hz frequency range) of the sensorimotor cortex. Later parts of the response (P35m and P60m) are also relatively stable compared with the large variations in mu rhythm.

Sources of the somatosensory evoked fields (SEF) for one subject were estimated using constraints from the magnetic resonance images (MRI) of the same subject. A realistic volume conductor model was shaped corresponding to the inside of the skull. Sources were restricted to a dipole patch riding on the surface of the cortex, reconstructed from the individual MRI. Such a patch can be considered as a uniformly activated cortical area giving rise to distributed currents which flow perpendicular to the cortical surface. Source locations obtained for the SEF in response to separate stimulations of lower lip, first and fifth digit, and collarbone followed the course of the contralateral central sulcus. The order of the estimated source locations was in agreement with the somatosensory homunculus of Penfield and Rasmussen. Similar results were obtained with the simple model of a current dipole in a homogeneous sphere. In contrast, combining a current dipole model with a realistic volume conductor model was rather problematic as it overestimates the radial dipole component by an order of magnitude.

MEG recordings visualized non-invasively a serial mediolateral activation of the human somatosensory 3b area followed by a stationary activation of area 1 after median nerve stimulation. Somatosensory evoked fields (SEFs) were recorded over the hand area contralateral to the right median nerve stimulation at the wrist in six normal subjects. A newly developed MEG vector beamformer technique applied to the SEFs revealed two distinct sources (areas 3b and 1) in the primary somatosensory cortex (SI) during the primary N20m-P22m response in all subjects. The first source was located in area 3b, which started to move sequentially toward mediolateral direction 0.7 ms prior to the peak of N20m and ended its movement 1.4 ms after the peak with a total distance of 11.2 mm. We speculate that the movement reflects a sequential mediolateral activation of the pyramidal cells in area 3b, which is mediated by horizontal connections running parallel to the cortical surface. The second source in area 1, located 5.6 mm medial and 4.2 mm posterior to the first source, was active 1.0 ms after the N20m peak. Then, the first source became inactive and the second source was dominant. In sharp contrast with the first source, the second source was stationary. The different behavior of these two components (moving vs stationary) indicates independent parallel inputs to area 3b and area 1 from the thalamus.

OBJECTIVE

An iterative k-space trajectory and radiofrequency (RF) pulse design method is proposed for excitation using nonlinear gradient magnetic fields.

METHODS

The spatial encoding functions (SEFs) generated by nonlinear gradient fields are linearly dependent in Cartesian coordinates. Left uncorrected, this may lead to flip angle variations in excitation profiles. In the proposed method, SEFs (k-space samples) are selected using a matching pursuit algorithm, and the RF pulse is designed using a conjugate gradient algorithm. Three variants of the proposed approach are given: the full algorithm, a computationally cheaper version, and a third version for designing spoke-based trajectories. The method is demonstrated for various target excitation profiles using simulations and phantom experiments.

RESULTS

The method is compared with other iterative (matching pursuit and conjugate gradient) and noniterative (coordinate-transformation and Jacobian-based) pulse design methods as well as uniform density spiral and EPI trajectories. The results show that the proposed method can increase excitation fidelity.

CONCLUSIONS

An iterative method for designing k-space trajectories and RF pulses using nonlinear gradient fields is proposed. The method can either be used for selecting the SEFs individually to guide trajectory design, or can be adapted to design and optimize specific trajectories of interest.