bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of immobilization support, water activity, and enzyme ionization state on cutinase activity and enantioselectivity in organic media
Authors: Vidinha Pedro , Harper Neil , Micaelo Nuno M. , Lourenco Nuno M.T. , Gomes da Silva Marco D.R. , Cabral Joaquim M.S. , Afonso Carlos A.M. , Soares Claudio M. , Barreiros Susana
Published: January 2004

We studied the reaction between vinyl butyrate and 2‐phenyl‐1‐propanol in acetonitrile catalyzed by Fusarium solani pisi cutinase immobilized on zeolites NaA and NaY and on Accurel PA‐6. The choice of 2‐phenyl‐1‐propanol was based on modeling studies that suggested moderate cutinase enantioselectivity towards this substrate. With all the supports, initial rates of transesterification were higher at a water activity (aw) of 0.2 than at aw = 0.7, and the reverse was true for initial rates of hydrolysis. By providing acid–base control in the medium through the use of solid‐state buffers that control the parameter pH‐pNa, which we monitored using an organo‐soluble chromoionophoric indicator, we were able, in some cases, to completely eliminate dissolved butyric acid. However, none of the buffers used were able to improve the rates of transesterification relative to the blanks (no added buffer) when the enzyme was immobilized at an optimum pH of 8.5. When the enzyme was immobilized at pH 5 and exhibited only marginal activity, however, even a relatively acidic buffer with a pKa of 4.3 was able to restore catalytic activity to about 20% of that displayed for a pH of immobilization of 8.5, at otherwise identical conditions. As aw was increased from 0.2 to 0.7, rates of transesterification first increased slightly and then decreased. Rates of hydrolysis showed a steady increase in that aw range, and so did total initial reaction rates. The presence or absence of the buffers did not impact on the competition between transesterification and hydrolysis, regardless of whether the butyric acid formed remained as such in the reaction medium or was eliminated from the microenvironment of the enzyme through conversion into an insoluble salt. Cutinase enantioselectivity towards 2‐phenyl‐1‐propanol was indeed low and was not affected by differences in immobilization support, enzyme protonation state, or aw. © 2004 Wiley Periodicals, Inc.
Online detection of feed demand in high cell density cultures of Escherichia coli by measurement of changes in dissolved oxygen transients in complex media
Authors: Whiffin Victoria S. , Cooney Michael J. , Cord‐Ruwisch Ralf
Published: January 2004

A starvation‐based dissolved oxygen (DO) transient controller was developed to supply growth‐limiting substrate to high cell density fed‐batch cultures of recombinant Escherichia coli. The algorithm adjusted a preexisting feed rate in proportion to the culture's oxygen demand, which was estimated from transients in the DO concentration after short periods of feed interruption. In this manner, the addition of glucose feed was precisely controlled at a rate that did not exceed the acetate production threshold, thus preventing acetate accumulation. In comparison to exponential feed algorithms commonly used in industry, the implementation of the new feeding strategy increased the final cell density from 32 to 44 g (dry cell weight).L−1, with less than 16 mM acetate accumulated, producing an ideal culture for subsequent induction. Despite a constant starvation level and relatively low levels of acetate, experimental cultivations still tended to produce acetate towards the end of the process. The use of a simple Monod model provided an explanation as to why this may occur in high cell density cultivations and suggests how it may be overcome. © 2004 Wiley Periodicals, Inc.
Analyzing and modeling of photobioreactors by combining first principles of physiology and hydrodynamics
Authors: Luo Hu‐Ping , Al‐Dahhan Muthanna H.
Published: January 2004

Mixing in photobioreactors is known to enhance biomass productivity considerably, and flow dynamics play a significant role in the reactor's performance, as they determine the mixing and the cells' movement. In this work we focus on analyzing the effects of mixing and flow dynamics on the photobioreactor performance. Based on hydrodynamic findings from the CARPT(Computer Automated Radioactive Particle Tracking) technique, a possible mechanism for the interaction between the mixing and the physiology of photosynthesis is presented, and the effects of flow dynamics on light availability and light intensity fluctuation are discussed and quantitatively characterized. Furthermore, a dynamic modeling approach is developed for photobioreactor performance evaluation, which integrates first principles of photosynthesis, hydrodynamics, and irradiance distribution within the reactor. The results demonstrate the reliability and the possible applicability of this approach to commercially interesting microalgae/cyanobacteria culture systems. © 2004 Wiley Periodicals, Inc.
Biocatalytic scrubbing of gaseous acrylonitrile using Rhodococcus ruber immobilized in synthetic silicone polymer (ImmobaSil™) rings
Authors: Roach P.C.J. , Ramsden D.K. , Hughes J. , Williams P.
Published: January 2004

Microbial detoxification of acrylonitrile vapor was performed using Rhodococcus ruber immobilized into rings of a synthetic silicone polymer (ImmobaSil™) sponge. The immobilization matrix was used as both the cell support material and also as the trickle‐bed column packing. The elimination capacity of the biocatalytic scrubber was determined for different influent concentrations of gaseous acrylonitrile. The working life of the nongrowing biocatalyst was also examined under test conditions and was found to be at least 70 days before biocatalyst replacement was required. An elimination capacity of 4.0 kg m−3 h−1 was achieved with a 95% removal efficiency, and an elimination capacity of over 7.2 kg m−3 h−1 acrylonitrile was achieved with a removal efficiency of 90%. This elimination capacity is 10 times that previously published in the literature. © 2003 Wiley Periodicals, Inc.
Salt‐activation of nonhydrolase enzymes for use in organic solvents
Authors: Morgan John A. , Clark Douglas S.
Published: January 2004

Enzymatic reactions are important for the synthesis of chiral molecules. One factor limiting synthetic applications of enzymes is the poor aqueous solubility of numerous substrates. To overcome this limitation, enzymes can be used directly in organic solvents; however, in nonaqueous media enzymes usually exhibit only a fraction of their aqueous‐level activity. Salt‐activation, a technique previously demonstrated to substantially increase the transesterification activity of hydrolytic enzymes in organic solvents, was applied to horse liver alcohol dehydrogenase, soybean peroxidase, galactose oxidase, and xanthine oxidase, which are oxidoreductase and oxygenase enzymes. Assays of the lyophilized enzyme preparations demonstrated that the presence of salt protected enzymes from irreversible inactivation. In organic solvents, there were significant increases in activity for the salt‐activated enzymes compared to nonsalt‐activated controls for every enzyme tested. The increased enzymatic activity in organic solvents was shown to result from a combination of protection against inactivation during the freeze‐drying process and other as‐yet undetermined factors. © 2004 Wiley Periodicals, Inc.
Characterization of the cellular uptake and metabolic conversion of acetylated N‐acetylmannosamine (ManNAc) analogues to sialic acids
Authors: Jones Mark B. , Teng Howard , Rhee Jun Kyu , Lahar Nicholas , Baskaran Gautam , Yarema Kevin J.
Published: January 2004

“Sialic acid engineering” refers to the strategy where cell surface carbohydrates are modified by the biosynthetic incorporation of metabolic intermediates, such as non‐natural N‐acetylmannosamine (ManNAc) analogues, into cellular glycoconjugates. While this technology has promising research, biomedical, and biotechnological applications due to its ability to endow the cell surface with novel physical and chemical properties, its adoption on a large scale is hindered by the inefficient metabolic utilization of ManNAc analogues. We address this limitation by proposing the use of acetylated ManNAc analogues for sialic acid engineering applications. In this paper, the metabolic flux of these “second‐generation” compounds into a cell, and, subsequently, into the target sialic acid biosynthetic pathway is characterized in detail. We show that acetylated ManNAc analogues are metabolized up to 900‐fold more efficiently than their natural counterparts. The acetylated compounds, however, decrease cell viability under certain culture conditions. To determine if these toxic side effects can be avoided, we developed an assay to measure the cellular uptake of acetylated ManNAc from the culture medium and its subsequent flux into sialic acid biosynthetic pathway. This assay shows that the majority ( > 80%) of acetylated ManNAc is stored in a cellular “reservoir” capable of safely sequestering this analogue. These results provide conditions that, from a practical perspective, enable the acetylated analogues to be used safely and efficaciously and therefore offer a general strategy to facilitate metabolic substrate‐based carbohydrate engineering efforts. In addition, these results provide fundamental new insights into the metabolic processing of non‐natural monosaccharides. © 2004 Wiley Periodicals, Inc.
Resonance energy transfer for assessing the molecular integrity of proteins for local delivery
Authors: Wu David , Edelman Elazer R.
Published: January 2004

It remains unclear whether the limitations to the therapeutic potential of angiogenic growth factors stem from pharmacokinetic concerns related to inadequate delivery or from a reduced sensitivity of target tissues. Here, we report a novel method using resonance energy transfer to assess the molecular integrity of proteins after local delivery. As an example, we labeled fibroblast growth factor‐2 with a fluorescent donor and nonfluorescent acceptor pair, tetramethylrhodamine and QSY‐7, and demonstrate in an ex vivo bovine carotid artery model that this growth factor is not limited by proteolytic constraints imposed by the tissue. Our data indicate that FGF‐2 is unlikely to be degraded within the arterial wall and suggest that pharmacokinetic limitations alone cannot fully explain the muted response seen thus far in therapeutic angiogenesis. In general, resonance energy transfer may serve as a novel approach to assess the molecular integrity of protein‐based therapies in local delivery. © 2004 Wiley Periodicals, Inc.
Effect of initial moisture content and chip size on the bioconversion efficiency of softwood lignocellulosics
Authors: Cullis Ian F. , Saddler John N. , Mansfield Shawn D.
Published: January 2004

Previous optimization strategies for the bioconversion of lignocellulosics by steam explosion technologies have focused on the effects of temperature, pH, and treatment time, but have not accounted for changes in severity brought about by properties inherent in the starting feedstock. Consequently, this study evaluated the effects of chip properties, feedstock size (40‐mesh, 1.5 × 1.5 cm, 5 × 5 cm), and moisture content (12% and 30%) on the overall bioconversion process, and more specifically on the efficacy of removal of recalcitrant lignin from the lignocellulosic substrates following steam explosion. Increasing chip size resulted in an improvement in the solids recovery, with concurrent increases in the water soluble, hemicellulose‐derived sugar recovery (7.5%). This increased recovery is a result of a decrease in the “relative severity” of the pretreatment as chip size increases. Additionally, the decreased relative severity minimized the condensation of the recalcitrant residual lignin and therefore increased the efficacy of peroxide fractionation, where a 60% improvement in lignin removal was possible with chips of larger initial size. Similarly, increased initial moisture content reduced the relative severity of the pretreatment, generating improved solids and hemicellulose‐derived carbohydrate recovery. Both increased chip size and higher initial moisture content results in a substrate that performs better during peroxide delignification, and consequently enzymatic hydrolysis. Furthermore, a post steam‐explosion refining step increased hemicellulose‐derived sugar recovery and was most effectively delignified (to as low as 6.5%). The refined substrate could be enzymatically hydrolyzed to very high levels (98%) and relatively fast rates (1.23 g/L/h). © 2004 Wiley Periodicals, Inc.
Managing distributed shared arrays in a bulk‐synchronous parallel programming environment
Authors: Kessler Christoph W.
Published: January 2004

NestStep is a parallel programming language for the BSP (bulk‐hronous parallel) programming model. In this article we describe the concept of distributed shared arrays in NestStep and its implementation on top of MPI. In particular, we present a novel method for runtime scheduling of irregular, direct remote accesses to sections of distributed shared arrays. Our method, which is fully parallelized, uses conventional two‐sided message passing and thus avoids the overhead of a standard implementation of direct remote memory access based on one‐sided communication. The main prerequisite is that the given program is structured in a BSP‐compliant way. Copyright © 2004 John Wiley & Sons, Ltd.
Data partitioning‐based parallel irregular reductions
Authors: Gutiérrez Eladio , Plata Oscar , Zapata Emilio L.
Published: January 2004

Different parallelization methods for irregular reductions on shared memory multiprocessors have been proposed in the literature in recent years. We have classified all these methods and analyzed them in terms of a set of properties: data locality, memory overhead, exploited parallelism, and workload balancing. In this paper we propose several techniques to increase the amount of exploited parallelism and to introduce load balancing into an important class of these methods. Regarding parallelism, the proposed solution is based on the partial expansion of the reduction array. Load balancing is discussed in terms of two techniques. The first technique is a generic one, as it deals with any kind of load imbalance present in the problem domain. The second technique handles a special case of load imbalance which occurs whenever a large number of write operations are concentrated on small regions of the reduction arrays. Efficient implementations of the proposed optimizing solutions for a particular method are presented, experimentally tested on static and dynamic kernel codes, and compared with other parallel reduction methods. Copyright © 2004 John Wiley & Sons, Ltd.
Group‐SPMD programming with orthogonal processor groups
Authors: Rauber Thomas , Reilein Robert , Rünger Gudula
Published: January 2004

Many programs for message‐passing machines can benefit from an implementation in a group‐SPMD programming model due to the potential to reduce communication overhead and to increase scalability. In this paper, we consider group‐SPMD programs exploiting different orthogonal processor partitions in one program. For each program this is a fixed set of predefined processor partitions given by the parallel hyperplanes of a two‐ or multi‐dimensional virtual processor organization. We introduce a library built on top of MPI to support the programming with those orthogonal processor groups. The parallel programming model is appropriate for applications with a multi‐dimensional task grid and task dependencies mainly aligned in the dimensions of the task grid. The library can be used to specify the appropriate processor partitions, which are then created by the library, and to define the mapping of tasks to the processor hyperplanes. Examples from numerical analysis illustrate the programming style and show that the runtime on distributed memory machines can be considerably reduced by using the library. Copyright © 2004 John Wiley & Sons, Ltd.
The effect of cache models on iterative compilation for combined tiling and unrolling
Authors: Knijnenburg P. M. W. , Kisuki T. , Gallivan K. , O'Boyle M. F. P.
Published: January 2004

Iterative compilation, where we search for the best program transformation based on profile feedback information, has been highly successful in determining good program optimizations, typically outperforming all static approaches. However, this benefit has come at a price, namely, a large number of executions of the target program which in many cases is unacceptable. This paper is concerned with reducing the number of program executions needed by iterative compilation by incorporating static models. We examine how static models may be incorporated into a purely iterative approach by developing several characterized heuristics. We empirically explore the tradeoff between reducing the number of executions required and the ultimate performance achieved for differing parameters or slack factors. We focus on tiling and unrolling as transformations and cache models as a test case for the feasibility of this approach. We show that a highly accurate model, used as a filter to profiling and appropriately parameterized, can reduce the number of executions by 50%. We also show that using a simple model to rank transformations and profiling, only those with the highest ranking can reduce the number of executions even further up to 70%, in cases where there is only a limited number of profiles available. We conclude that a production compiler might perform best using the last approach, gaining the benefit of iterative compilation at a much reduced cost. Copyright © 2004 John Wiley & Sons, Ltd.
A fast and accurate method for determining a lower bound on execution time
Authors: Fursin G. , O'Boyle M. F. P. , Temam O. , Watts G.
Published: January 2004

In performance critical applications, memory latency is frequently the dominant overhead. In many cases, automatic compiler‐based optimizations to improve memory performance are limited and programmers frequently resort to manual optimization techniques. However, this process is tedious and time‐consuming. Furthermore, as the potential benefit from optimization is unknown there is no way to judge the amount of effort worth expending, nor when the process can stop, i.e. when optimal memory performance has been achieved or sufficiently approached. Architecture simulators can provide such information but designing an accurate model of an existing architecture is difficult and simulation times are excessively long. In this article, we propose and implement a technique that is both fast and reasonably accurate for estimating a lower bound on execution time for scientific applications. This technique has been tested on a wide range of programs from the SPEC benchmark suite and two commercial applications, where it has been used to guide a manual optimization process and iterative compilation. We compare our technique with that of a simulator with an ideal memory behaviour and demonstrate that our technique provides comparable information on memory performance and yet is over two orders of magnitude faster. We further show that our technique is considerably more accurate than hardware counters. Copyright © 2004 John Wiley & Sons, Ltd.
Seismic microzonation of the greater Bangkok area using microtremor observations
Authors: Tuladhar Rabin , Yamazaki Fumio , Warnitchai Pennung , Saita Jun
Published: January 2004

Bangkok, the capital city of Thailand, is located at a remote distance from seismic sources. However, it has a substantial risk from these distant earthquakes due to the ability of the underlying soft clay to amplify ground motions. It is therefore imperative to conduct a detailed seismic hazard assessment of the area. Seismic microzonation of big cities, like Bangkok, provides a basis for site‐specific hazard analysis, which can assist in systematic earthquake mitigation programs. In this study, a seismic microzonation map for the greater Bangkok area is constructed using microtremor observations. Microtremor observations were carried out at more than 150 sites in the greater Bangkok area. The predominant periods of the ground were determined from the horizontal‐to‐vertical (H/V) spectral ratio technique. A microzonation map was then developed for the greater Bangkok area based on the observations. Moreover, the transfer functions were calculated for the soil profile at eight sites, using the computer program SHAKE91, to validate the results from the microtremor analysis. The areas near the Gulf of Thailand, underlaid by a thick soft clay layer, were found to have long natural periods ranging from 0.8s to 1.2s. However, the areas outside the lower central plain have shorter predominant periods of less than 0.4s. The study shows that there is a great possibility of long‐period ground vibration in Bangkok, especially in the areas near the Gulf of Thailand. This may have severe effects on long‐period structures, such as high‐rise buildings and long‐span bridges. Copyright © 2003 John Wiley & Sons, Ltd.
The effect of an interface boundary layer on the resonance properties of a buried structure
Authors: Karinski Y. S. , Shershnev V. V. , Yankelevsky D. Z.
Published: January 2004

This paper presents a model for the analysis of the diffraction of plane waves at a cavity in an infinite homogeneous linear elastic medium supported by a segmented lining. An elastic boundary layer is introduced between the cavity lining and the infinite medium. The boundary layer is simulated by ‘elastic boundary conditions’ in which the stress is proportional to the relative displacement of the lining and of the surrounding medium boundary.

A closed‐form analytical solution of the problem was obtained using the Fourier–Bessel series, the convergence of which was proven. It was shown that the number of series terms required to obtain a desired level of accuracy can be determined in advance.

Using amplitude–frequency response analysis it was shown that the boundary layer produces additional ‘pseudo‐resonance’ frequencies that depend on the layer properties. These frequencies are almost identical to the eigenvalues obtained from the simple analysis of a segmented elastically supported lining. Copyright © 2003 John Wiley & Sons, Ltd.
Non‐linear seismic response of the rail‐counterweight system in elevators in buildings
Authors: Singh Mahendra P. , Rildova  , Suarez Luis E.
Published: January 2004

Elevators in buildings serve a very important function and are among the critical components of an essential facility. They have several mechanical and electrical components that are known to be susceptible to damage during earthquake occurrences. The counterweights, being the heaviest, are among their most vulnerable components. The ASME code has made several provisions to improve the performance of the counterweights in seismic events. To evaluate their performance under code‐mandated provisions, it is necessary that a comprehensive and realistic analytical model is used. This paper uses a detailed model of a counterweight of a traction elevator to study its in‐plane and out‐of‐plane dynamic behavior. The model incorporates the multiple support inputs and flexibilities of the counterweight guidance system along with their non‐linearities caused by the clearance limitations. The study examines the effect of changing clearances, variability of input motions, and the use of tie brackets on the system response, and evaluates the impact of some of the code provisions on the dynamic behavior of the system. Copyright © 2003 John Wiley & Sons, Ltd.
A discontinuous Galerkin method for seismic soil–structure interaction analysis in the time domain
Authors: Park Si‐Hwan , Antin Nicolas
Published: January 2004

A technique for modeling transient wave propagation in unbounded media is extended and applied to seismic soil–structure interaction analysis in the time domain. The technique, based on the discontinuous Galerkin method, requires lower computational cost and less storage than the boundary element method, and the time‐stepping scheme resulting from Newmark's method in conjunction with the technique is unconditionally stable, allowing for efficient and robust time‐domain computations. To extend the technique to cases characterized by seismic excitation, the free‐field motion is used to compute effective forces, which are introduced on the boundary of the computational domain containing the structure and the soil in the vicinity of the structure. A numerical example on a dam–foundation system subjected to seismic excitation demonstrates the performance of the method. Copyright © 2003 John Wiley & Sons, Ltd.
Utilities privatization and the environmental processes employed by the Department of Defense—One firm's experience
Authors: Hammontree Jimmie
Published: February 2004

C.H. Guernsey & Company (GUERNSEY) has played a key role in the Department of Defense Utility Privatization Initiative. This paper will provide a brief overview of the privatization initiative, environmental issues, and GUERNSEY's role in privatization. The presentation will outline the National Environmental Policy Act (NEPA) process and the Environmental Baseline Survey (EBS) process as they relate specifically to the privatization of utilities.

GUERNSEY has identified several key elements necessary for successful completion of the environmental documentation that supports the privatization of utilities. Successful privatization projects depend heavily on communicating with the client, educating the client about how the environmental needs relate to the privatization process, and coordinating/interacting with the client from the beginning phases of scope generation to the delivery of the final documents. Environmental stewardship is also a must. © 2004 Wiley Periodicals, Inc.
Changes in effective connectivity models in the presence of task‐correlated motion: An fMRI study
Authors: Gavrilescu Maria , Stuart Geoffrey W. , Waites Anthony , Jackson Graeme , Svalbe Imants D. , Egan Gary F.
Published: January 2004

We investigated the effects of motion‐correction strategy and time course selection method when structural equation modeling is applied to fMRI data in the presence of task‐correlated motion. Three motion‐correction methods were employed for a group of 12 subjects performing an orthographic lexical retrieval task: (1) a rigid body realignment as implemented in SPM99, (2) a rigid body realignment combined with the inclusion of motion parameters in the statistical model, and (3) the FLIRT motion correction followed by an ICA analysis aiming to identify and remove the motion‐related components and the ghosting artifacts. For each motion correction, the time courses of the activated regions were selected in three ways: (1) using the voxels with the highest Z scores, (2) using the average across all the statistically significant voxels in the region of interest, and (3) using a within‐region, across‐subjects, singular value decomposition. The resulting models of effective connectivity were markedly different, although the activation pattern was not substantially altered by the motion‐correction method. Higher values for the path coefficients were obtained for the models fitted to the covariance matrices based on the average time courses than for the covariance matrices based on a single voxel time course. Our results suggest caution with the interpretation of task‐induced changes in effective connectivity since, for higher‐order cognitive brain functions, multiple models can be fitted to a given data set and these models cannot be rejected on an anatomical or cognitive basis. Hum. Brain Mapping 21:49–63, 2004. © 2003 Wiley‐Liss, Inc.
Effects of skull thickness, anisotropy, and inhomogeneity on forward EEG/ERP computations using a spherical three‐dimensional resistor mesh model
Authors: Chauveau Nicolas , Franceries Xavier , Doyon Bernard , Rigaud Bernard , Morucci Jean Pierre , Celsis Pierre
Published: January 2004

Bone thickness, anisotropy, and inhomogeneity have been reported to induce important variations in electroencephalogram (EEG) scalp potentials. To study this effect, we used an original three‐dimensional (3‐D) resistor mesh model described in spherical coordinates, consisting of 67,464 elements and 22,105 nodes arranged in 36 different concentric layers. After validation of the model by comparison with the analytic solution, potential variations induced by geometric and electrical skull modifications were investigated at the surface in the dipole plane and along the dipole axis, for several eccentricities and bone thicknesses. The resistor mesh permits one to obtain various configurations, as local modifications are introduced very easily. This has allowed several head models to be designed to study the effects of skull properties (thickness, anisotropy, and heterogeneity) on scalp surface potentials. Results show a decrease of potentials in bone, depending on bone thickness, and a very small decrease through the scalp layer. Nevertheless, similar scalp potentials can be obtained using either a thick scalp layer and a thin skull layer, and vice versa. It is thus important to take into account skull and scalp thicknesses, because the drop of potential in bone depends on both. The use of three different layers for skull instead of one leads to small differences in potential values and patterns. In contrast, the introduction of a hole in the skull highly increases the maximum potential value (by a factor of 11.5 in our case), because of the absence of potential drop in the corresponding volume. The inverse solution without any a priori knowledge indicates that the model with the hole gives the largest errors in both position and dipolar moment. Our results indicate that the resistor mesh model can be used as a robust and user‐friendly simulation tool in EEG or event‐related potentials. It makes it possible to build up real head models directly from anatomic magnetic resonance imaging without tessellation, and is able to take into account head heterogeneities very simply by changing volume elements conductivity. Hum. Brain Mapping 21:84–95, 2004. © 2003 Wiley‐Liss, Inc.
Functional brain mapping during free viewing of natural scenes
Authors: Bartels Andreas , Zeki Semir
Published: January 2004

Previous imaging studies have used mostly perceptually abstracted, idealized, or static stimuli to show segregation of function in the cerebral cortex. We wanted to learn whether functional segregation is maintained during more natural, complex, and dynamic conditions when many features have to be processed simultaneously, and identify regions whose activity correlates with the perception of specific features. To achieve this, we used functional magnetic resonance imaging (fMRI) to measure brain activity when human observers viewed freely dynamic natural scenes (a James Bond movie). The intensity with which they perceived different features (color, faces, language, and human bodies) was assessed psychometrically in separate sessions. In all subjects different features were perceived with a high degree of independence over time. We found that the perception of each feature correlated with activity in separate, specialized areas whose activity also varied independently. We conclude that even in natural conditions, when many features have to be processed simultaneously, functional specialization is preserved. Our method thus opens a new way of brain mapping, which allows the localization of a multitude of brain areas based on a single experiment using uncontrolled, natural stimuli. Furthermore, our results show that the intensity of activity in a specialized area is linearly correlated with the intensity of its perceptual experience. This leads us to suggest that each specialized area is directly responsible for the creation of a feature‐specific conscious percept (a microconsciousness). Hum. Brain Mapp. 21:75–83, 2004. © 2003 Wiley‐Liss, Inc.
Mapping the time course of nonconscious and conscious perception of fear: An integration of central and peripheral measures
Authors: Williams Leanne M. , Liddell Belinda J. , Rathjen Jennifer , Brown Kerri J. , Gray Jeffrey , Phillips Mary , Young Andy , Gordon Evian
Published: January 2004

Neuroimaging studies using backward masking suggest that conscious and nonconscious responses to complex signals of fear (facial expressions) occur via parallel cortical and subcortical circuits. Little is known, however, about the temporal differentiation of these responses. Psychophysics procedures were first used to determine objective thresholds for both nonconscious detection (face vs. blank screen) and discrimination (fear vs. neutral face) in a backward masking paradigm. Event‐related potentials (ERPs) were then recorded (n = 20) using these thresholds. Ten blocks of masked fear and neutral faces were presented under each threshold condition. Simultaneously recorded skin conductance responses (SCRs) provided an independent index of stimulus perception. It was found that Fear stimuli evoked faster SCR rise times than did neutral stimuli across all conditions, indicating that emotional content influenced responses, regardless of awareness. In the first 400 msec of processing, ERPs dissociated the time course of conscious (enhanced N4 component) from nonconscious (enhanced N2 component) perception of fear, relative to neutral. Nonconscious detection of fear also elicited relatively faster P1 responses within 100 msec post‐stimulus. The N2 may provide a temporal correlate of the initial sensory processing of salient facial configurations, which is enhanced when top‐down cortical feedback is precluded. By contrast, the N4 may index the conscious integration of emotion stimuli in working memory, subserved by greater cortical engagement. Hum. Brain Mapping 21:64–74, 2004. © 2003 Wiley‐Liss, Inc.
Rollvection versus linearvection: Comparison of brain activations in PET
Authors: Deutschländer Angela , Bense Sandra , Stephan Thomas , Schwaiger Markus , Dieterich Marianne , Brandt Thomas
Published: January 2004

We conducted a PET study to directly compare the differential effects of visual motion stimulation that induced either rollvection about the line of sight or forward linearvection along this axis in the same subjects. The main question was, whether the areas that respond to vection are identical or separate and distinct for rollvection and linearvection. Eleven healthy volunteers were exposed to large‐field (100° × 60°) visual motion stimulation consisting of (1) dots accelerating from a focus of expansion to the edge of the screen (forward linearvection) and (2) dots rotating counterclockwise in the frontal plane (clockwise rollvection). These two stimuli, which induced apparent self‐motion in all subjects, were compared to each other and to a stationary visual pattern. Linearvection and rollvection led to bilateral activations of visual areas including medial parieto‐occipital (PO), occipito‐temporal (MT/V5), and ventral occipital (fusiform gyri) cortical areas, as well as superior parietal sites. Activations in the polar visual cortex around the calcarine sulcus (BA 17, BA 18) were larger and more significant during linearvection. Temporo‐parietal sites displayed higher activity levels during rollvection. Differential activation of PO or MT/V5 was not found. Both stimuli led to simultaneous deactivations of retroinsular regions (more pronounced during linearvection); this is compatible with an inhibitory interaction between the visual and the vestibular systems for motion perception. Hum. Brain Mapp. 21:143–153, 2004. © 2004 Wiley‐Liss, Inc.
Different areas of human non‐primary auditory cortex are activated by sounds with spatial and nonspatial properties
Authors: Hart Heledd C. , Palmer Alan R. , Hall Deborah A.
Published: January 2004

In humans, neuroimaging studies have identified the planum temporale to be particularly responsive to both spatial and nonspatial attributes of sound. However, a functional segregation of the planum temporale along these acoustic dimensions has not been firmly established. We evaluated this scheme in a factorial design using modulated sounds that generated a percept of motion (spatial) or frequency modulation (nonspatial). In addition, these sounds were presented in the context of a motion detection and a frequency‐modulation detection task to investigate the cortical effects of directing attention to different perceptual attributes of the sound. Motion produced stronger activation in the medial part of the planum temporale and frequency‐modulation produced stronger activation in the lateral part of the planum temporale, as well as an additional non‐primary area lateral to Heschl's gyrus. These separate subregions are consistent with the notion of divergent processing streams for spatial and nonspatial auditory information. Activation in the superior parietal cortex, putatively involved in the spatial pathway, was dependent on the task of motion detection and not simply on the presence of acoustic cues for motion. This finding suggests that the listening task is an important determinant of how the processing stream is engaged. Hum. Brain Mapping 21:178–190, 2004. © 2004 Wiley‐Liss, Inc.
Behavioral conflict, anterior cingulate cortex, and experiment duration: Implications of diverging data
Authors: Erickson Kirk I. , Milham Michael P. , Colcombe Stanley J. , Kramer Arthur F. , Banich Marie T. , Webb Andrew , Cohen Neal J.
Published: January 2004

We investigated the relationship between behavioral measures of conflict and the degree of activity in the anterior cingulate cortex (ACC). We reanalyzed an existing data set that employed the Stroop task using functional magnetic resonance imaging [Milham et al., Brain Cogn 2002;49:277–296]. Although we found no changes in the behavioral measures of conflict from the first to the second half of task performance, we found a reliable reduction in the activity of the anterior cingulate cortex. This result suggests the lack of a strong relationship between behavioral measurements of conflict and anterior cingulate activity. A concomitant increase in dorsolateral prefrontal cortex activity was also found, which may reflect a tradeoff in the neural substrates involved in supporting conflict resolution, detection, or monitoring processes. A second analysis of the data revealed that the duration of an experiment can dramatically affect interpretations of the results, including the roles in which particular regions are thought to play in cognition. These results are discussed in relation to current conceptions of ACC's role in attentional control. In addition, we discuss the implication of our results with current conceptions of conflict and of its instantiation in the brain. Hum. Brain Mapping 21:96–105, 2004. © 2003 Wiley‐Liss, Inc.
The effect of stimulus intensity on brain responses evoked by transcranial magnetic stimulation
Authors: Komssi Soile , Kähkönen Seppo , Ilmoniemi Risto J.
Published: January 2004

To better understand the neuronal effects of transcranial magnetic stimulation (TMS), we studied how the TMS‐evoked brain responses depend on stimulation intensity. We measured electroencephalographic (EEG) responses to motor‐cortex TMS, estimated the intensity dependence of the overall brain response, and compared it to a theoretical model for the intensity dependence of the TMS‐evoked neuronal activity. Left and right motor cortices of seven volunteers were stimulated at intensities of 60, 80, 100, and 120% of the motor threshold (MT). A figure‐of‐eight coil (diameter of each loop 4 cm) was used for focal stimulation. EEG was recorded with 60 scalp electrodes. The intensity of 60% of MT was sufficient to produce a distinct global mean field amplitude (GMFA) waveform in all subjects. The GMFA, reflecting the overall brain response, was composed of four peaks, appearing at 15 ± 5 msec (Peak I), 44 ± 10 msec (II), 102 ± 18 msec (III), and 185 ± 13 msec (IV). The peak amplitudes depended nonlinearly on intensity. This nonlinearity was most pronounced for Peaks I and II, whose amplitudes appeared to sample the initial part of the sigmoid‐shaped curve modeling the strength of TMS‐evoked neuronal activity. Although the response amplitude increased with stimulus intensity, scalp distributions of the potential were relatively similar for the four intensities. The results imply that TMS is able to evoke measurable brain activity at low stimulus intensities, probably significantly below 60% of MT. The shape of the response‐stimulus intensity curve may be an indicator of the activation state of the brain. Hum. Brain Mapp. 21:154–164, 2004. © 2004 Wiley‐Liss, Inc.
Simple and complex movement‐associated functional MRI changes in patients at presentation with clinically isolated syndromes suggestive of multiple sclerosis
Authors: Filippi Massimo , Rocca Maria A. , Mezzapesa Domenico M. , Ghezzi Angelo , Falini Andrea , Martinelli Vittorio , Scotti Giuseppe , Comi Giancarlo
Published: January 2004

Using functional magnetic resonance imaging (fMRI), we investigated whether movement‐associated functional changes of the brain are present in patients who are, most likely, at the earliest stage of multiple sclerosis (MS). Functional MRI exams were obtained from 16 patients at presentation with clinically isolated syndromes (CIS) suggestive of MS and 15 sex‐ and age‐matched healthy volunteers during the performance of three simple and one more complex motor tasks with fully normal functioning extremities. fMRI analysis was performed using statistical parametric mapping (SPM99). Compared to healthy volunteers, CIS patients had increased activations of the contralateral primary sensorimotor cortex (SMC), secondary somatosensory cortex (SII), and inferior frontal gyrus (IFG), when performing a simple motor task with the dominant hand. The increased recruitment of the contralateral primary SMC was also found during the performance of the same motor task with the non‐dominant hand and with the dominant foot. In this latter case, an anterior shift of the center of activation of this region was detected. During the performance of a complex motor task with the dominant upper and lower limbs, CIS patients had an increased recruitment of a widespread network (including the frontal lobe, the insula, the thalamus), usually considered to function in motor, sensory, and multimodal integration processing. The comparison of brain activations during the performance of simple vs. complex motor tasks showed that the movement‐associated somatotopic organization of the cerebral and cerebellar cortices was retained in patients with CIS. Cortical reorganization occurs in patients at presentation with CIS highly suggestive of MS. Local synaptic reorganization, recruitment of parallel existing pathways, and reorganization of distant sites are all likely to contribute to the observed functional changes. Hum. Brain Mapping 21:106–115, 2004. © 2003 Wiley‐Liss, Inc.
Imaging a cognitive model of apraxia: The neural substrate of gesture‐specific cognitive processes
Authors: Peigneux Philippe , Van der Linden Martial , Garraux Gaetan , Laureys Steven , Degueldre Christian , Aerts Joel , Del Fiore Guy , Moonen Gustave , Luxen Andre , Salmon Eric
Published: January 2004

The present study aimed to ascertain the neuroanatomical basis of an influential neuropsychological model for upper limb apraxia [Rothi LJ, et al. The Neuropsychology of Action. 1997. Hove, UK: Psychology Press]. Regional cerebral blood flow was measured in healthy volunteers using H215O PET during performance of four tasks commonly used for testing upper limb apraxia, i.e., pantomime of familiar gestures on verbal command, imitation of familiar gestures, imitation of novel gestures, and an action‐semantic task that consisted in matching objects for functional use. We also re‐analysed data from a previous PET study in which we investigated the neural basis of the visual analysis of gestures. First, we found that two sets of discrete brain areas are predominantly engaged in the imitation of familiar and novel gestures, respectively. Segregated brain activation for novel gesture imitation concur with neuropsychological reports to support the hypothesis that knowledge about the organization of the human body mediates the transition from visual perception to motor execution when imitating novel gestures [Goldenberg Neuropsychologia 1995;33:63–72]. Second, conjunction analyses revealed distinctive neural bases for most of the gesture‐specific cognitive processes proposed in this cognitive model of upper limb apraxia. However, a functional analysis of brain imaging data suggested that one single memory store may be used for “to‐be‐perceived” and “to‐be‐produced” gestural representations, departing from Rothi et al.'s proposal. Based on the above considerations, we suggest and discuss a revised model for upper limb apraxia that might best account for both brain imaging findings and neuropsychological dissociations reported in the apraxia literature. Hum. Brain Mapp. 21:119–142, 2004. © 2004 Wiley‐Liss, Inc.
Reciprocal modulation and attenuation in the prefrontal cortex: An fMRI study on emotional–cognitive interaction
Authors: Northoff Georg , Heinzel Alexander , Bermpohl Felix , Niese Robert , Pfennig Andrea , Pascual‐Leone Alvaro , Schlaug Gottfried
Published: January 2004

Everyday and clinical experience demonstrate strong interactions between emotions and cognitions. Nevertheless the neural correlates underlying emotional–cognitive interaction remain unclear. Using event‐related fMRI, we investigated BOLD‐signal increases and decreases in medial and lateral prefrontal cortical regions during emotional and non‐emotional judgment of photographs taken from the International Affective Picture System (IAPS). Emotional and non‐emotional judgment conditions were compared to each other as well as with baseline allowing for distinction between relative signal changes (comparison between conditions) and true signal changes (referring to baseline). We have found that: (1) both emotional and non‐emotional judgment of IAPS pictures were characterized by signal increases in ventrally and dorsally located lateral prefrontal cortical areas and concurrent signal decreases in ventro‐ and dorsomedial prefrontal cortex; (2) direct comparison between emotional and non‐emotional judgment showed relative signal increases in ventro‐ and dorsomedial prefrontal cortex, and in contrast, relative signal increases were detected in ventrally and dorsally located lateral prefrontal cortical areas when comparing non‐emotional to emotional judgment; and (3) as shown in separate comparisons with baseline, these relative signal changes were due to smaller signal decreases in ventro‐ and dorsomedial prefrontal cortex and smaller signal increases in ventrally and dorsally located lateral prefrontal cortical areas during emotional judgment. Therefore, the emotional load of a cognitive task lead to both less deactivation of medial prefrontal regions and, at the same time, less activation of lateral prefrontal regions. Analogous patterns of reciprocal modulation and attenuation have previously been described for other cortical regions such as visual and auditory areas. Reciprocal modulation and attenuation in medial and lateral prefrontal cortex might constitute the neurophysiologic basis for emotional–cognitive interaction as observed in both healthy and psychiatric subjects. Hum. Brain Mapping 21:202–212, 2004. © 2004 Wiley‐Liss, Inc.