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To date, spatial encoding for MRI is based on linear X, Y and Z field gradients generated by dedicated X, Y and Z wire patterns. We recently introduced the dynamic multi-coil technique (DYNAMITE) for the generation of magnetic field shapes for biomedical MR applications from a set of individually driven localized coils. The benefits for B0 magnetic field homogenization have been shown, as well as proof of principle of radial and algebraic MRI. In this study the potential of DYNAMITE MRI is explored further and the first multi-slice MRI implementation in which all gradient fields are purely DYNAMITE based is presented. The obtained image fidelity is shown to be virtually identical to that of a conventional MRI system with dedicated X, Y and Z gradient coils. Comparable image quality is a milestone towards the establishment of fully functional DYNAMITE MRI (and shim) systems.

Purpose Intermolecular multiple quantum coherences (iMQCs) are a source of MR contrast with applications including temperature imaging, anisotropy mapping, and brown fat imaging. Because all applications are limited by signal-to-noise ratio (SNR), we developed a pulse sequence that detects intermolecular zero quantum coherences with improved SNR. Methods A previously developed pulse sequence that detects iMQCs, HOMOGENIZED with off resonance transfer (HOT), was modified with a multi-spin echo spatial encoding scheme (MSE-HOT). MSE-HOT uses a series of refocusing pulses to generate a stack of images that are averaged in postprocessing for higher SNR. MSE-HOT performance was quantified by measuring its temperature accuracy and precision during hyperthermia of ex vivo red bone marrow samples. Results MSE-HOT yielded a three-fold improvement in temperature precision relative to previous pulse sequences. Sources of improved precision were 1) echo averaging and 2) suppression of J-coupling in the methylene protons of fat. MSE-HOT measured temperature change with an accuracy of 0.6°C. Conclusion MSE-HOT improved the temperature accuracy and precision of HOT to a level that is sufficient for hyperthermia of bone marrow. Magn Reson Med, 2015. © 2015 Wiley Periodicals, Inc.

The current volume arose from a one-day pre-meeting workshop entitled “How Grammar Encodes Space in Tibeto-Burman” at the 48th International Conference on Sino-Tibetan Languages and Linguistics, which was held at the University of California, Santa Barbara in August of 2015.

Summary An emerging view suggests that spatial position is an integral component of working memory (WM), such that non-spatial features are bound to locations regardless of whether space is relevant [1, 2]. For instance, past work has shown that stimulus position is spontaneously remembered when non-spatial features are stored. Item recognition is enhanced when memoranda appear at the same location where they were encoded [3–5], and accessing non-spatial information elicits shifts of spatial attention to the original position of the stimulus [6, 7]. However, these findings do not establish that a persistent, active representation of stimulus position is maintained in WM because similar effects have also been documented following storage in long-term memory [8, 9]. Here we show that the spatial position of the memorandum is actively coded by persistent neural activity during a non-spatial WM task. We used a spatial encoding model in conjunction with electroencephalogram (EEG) measurements of oscillatory alpha-band (8–12 Hz) activity to track active representations of spatial position. The position of the stimulus varied trial to trial but was wholly irrelevant to the tasks. We nevertheless observed active neural representations of the original stimulus position that persisted throughout the retention interval. Further experiments established that these spatial representations are dependent on the volitional storage of non-spatial features rather than being a lingering effect of sensory energy or initial encoding demands. These findings provide strong evidence that online spatial representations are spontaneously maintained in WM—regardless of task relevance—during the storage of non-spatial features.

International audience; In longitudinal medical studies, multicomponent images of the tissues, acquired at a given stage of a disease, are used to provide information on the fate of the tissues. We propose a quantification of the predictive value of multicomponent images using information theory. To this end, we revisit the predictive information introduced for monodimensional time series and extend it to multicomponent images. The interest of this theoretical approach is illustrated on multicomponent magnetic resonance images acquired on stroke patients at acute and late stages, for which we propose an original and realistic model of noise together with a spatial encoding for the images. We address therefrom very practical questions such as the impact of noise on the predictability, the optimal choice of an observation scale and the predictability gain brought by the addition of imaging components.

The spin-lattice relaxation time (T1) plays a crucial role in the study of spin dynamics, signal optimization and data quantification. However, the measurement of chemical shift-specific T1 constants is hampered by the magnetic field inhomogeneity due to poorly shimmed external magnetic fields or intrinsic magnetic susceptibility heterogeneity in samples. In this study, we present a new protocol to determine chemical shift-specific T1 constants in inhomogeneous fields. Based on intermolecular double-quantum coherences, the new method can resolve overlapped peaks in inhomogeneous fields. The measurement results are in consistent with the measurements in homogeneous fields using the conventional method. Since spatial encoding technique is involved, the experimental time for the new method is very close to that for the conventional method. With the aid of T1 knowledge, some concealed information can be exploited by T1 weighting experiments.

We introduce a new approach for resolving the NMR spectra of mixtures that relies on the mutual diffusion of dissolved species when a concentration gradient is established within the NMR tube. This is achieved by cooling down a biphasic mixture of triethylamine and deuterated water below itsmixing temperature, where a single phase is expected. Until equilibriumis reached, a gradient of concentration, from‘pure’ triethylamine to ‘pure’ water, establishes within the tube. The amount of time required to reach this equilibrium is controlled by the mutual diffusion coefficient of both species. Moreover, a gradient of concentration exists for each additional compound dissolved in this system, related to the partition coefficient for that compound in the original biphasic state. Using slice selective experiments, it was possible to measure these concentration gradients and use them to separate signals from all the present species. We show the results acquired for a mixture composed of n-octanol, methanol, acetonitrile and benzene and compare themwith those obtained by pulse field gradient NMR.

This is an account of the forms and semantic dimensions of spatial relations in Manange (Tibeto-Burman, Tamangic; Nepal), with comparison to sister language Nar-Phu. Topological relations (“IN/ON/AT/NEAR”) in these languages are encoded by locative enclitics and also by a set of noun-like objects termed as “locational roots.” In Manange, the general locative enclitic is more frequently encountered for a wide range of topological relations, while in Nar-Phu, the opposite pattern is observed, i.e. more frequent use of locational roots. While the linguistic frame of reference system encoded in these forms is primarily relative (i.e. oriented on the speaker’s own viewing perspective), a more extrinsic/absolute system emerges with certain verbs of motion in these languages, with verbs like “come,” “go,” and certain verbs of placement or posture orienting to arbitrary fixed bearings such as slope. This account also provides some examples of cultural or metaphorical extensions of spatial forms as they are encountered in connected speech.

Non-Cartesian parallel imaging has played an important role in reducing data acquisition time in MRI. The use of non-Cartesian trajectories can enable more efficient coverage of k-space, which can be leveraged to reduce scan times. These trajectories can be undersampled to achieve even faster scan times, but the resulting images may contain aliasing artifacts. Just as Cartesian parallel imaging can be used to reconstruct images from undersampled Cartesian data, non-Cartesian parallel imaging methods can mitigate aliasing artifacts by using additional spatial encoding information in the form of the nonhomogeneous sensitivities of multi-coil phased arrays. This review will begin with an overview of non-Cartesian k-space trajectories and their sampling properties, followed by an in-depth discussion of several selected non-Cartesian parallel imaging algorithms. Three representative non-Cartesian parallel imaging methods will be described, including Conjugate Gradient SENSE (CG SENSE), non-Cartesian generalized autocalibrating partially parallel acquisition (GRAPPA), and Iterative Self-Consistent Parallel Imaging Reconstruction (SPIRiT). After a discussion of these three techniques, several potential promising clinical applications of non-Cartesian parallel imaging will be covered.

Existing open magnetic resonance imaging (MRI) systems use biplanar gradient coils for the spatial encoding of signals. We propose using novel oval gradient coils for an open vertical-field MRI. We designed oval gradients for a 0.3 T open MRI system and showed that such a system could outperform a traditional biplanar gradient system while maintaining adequate gradient homogeneity and subject accessibility. Such oval gradient coils would exhibit high efficiency, low inductance and resistance, and high switching capability. Although the designed oval Y and Z coils showed more heat dissipation and less cooling capability than biplanar coils with the same gap, they showed an efficient heat-dissipation path to the surrounding air, which would alleviate the heat problem. The performance of the designed oval-coil system was demonstrated experimentally by imaging a human hand.

International audience; We show that the acquisition of 3D diffusion-ordered NMR spectroscopy (DOSY) experiments can be accelerated significantly with the use of spatial encoding (SPEN). The SPEN DOSY approach is discussed, analysed with numerical simulation, and illustrated on a mixture of small molecules.

The hippocampus is well known as a central site for memory processing—critical for storing and later retrieving the experiences events of daily life so they can be used to shape future behavior. Much of what we know about the physiology underlying hippocampal function comes from spatial navigation studies in rodents, which have allowed great strides in understanding how the hippocampus represents experience at the cellular level. However, it remains a challenge to reconcile our knowledge of spatial encoding in the hippocampus with its demonstrated role in memory-dependent tasks in both humans and other animals. Moreover, our understanding of how networks of neurons coordinate their activity within and across hippocampal subregions to enable the encoding, consolidation, and retrieval of memories is incomplete. In this chapter, we explore how information may be represented at the cellular level and processed via coordinated patterns of activity throughout the subregions of the hippocampal network.

A cylindrical head gradient insert for human imaging with non-linear spatial encoding magnetic fields (SEMs) has been designed, optimized and successfully integrated with a modified 3T clinical MR system. This PatLoc (parallel acquisition technique using localized gradients) SEM coil uses SEMs that resemble second-order magnetic shim fields, but with much higher amplitude as well as the possibility for rapid switching. This work describes the optimization of a coil design and measurement methods to characterize its SEMs, induced self-eddy currents and concomitant fields. Magnetic field maps of the SEMs are measured and it is demonstrated that the induced self-eddy current magnetic fields are small and can be compensated. A method to measure concomitant fields is presented and those fields are compared to simulated data. Finally, in vivo human images acquired using the PatLoc system are presented and discussed.

Purpose A proof-of-concept study was performed to assess the technical feasibility of using magnetic materials to generate spatial encoding fields. Theory and Methods Spatially varying magnetic fields were generated by the placement of markers with different volume susceptibilities within the imaging volume. No linear gradients were used for spatial encoding during the signal acquisition. A signal-encoding model is described for reconstructing the images encoded with these field perturbations. Simulation and proof-of-concept experimental results are presented. Experiments were performed using field perturbations from a cylindrical marker as an example of the new encoding fields. Based on this experimental setup, annular rings were reconstructed from signals encoded with the new fields. Results Simulation results were presented for different acquisition parameters. Proof-of-concept was supported by the correspondence of regions in an image reconstructed from experimental data compared to those in a conventional gradient-echo image. Experimental results showed that inclusions of dimensions 1.5 mm in size could be resolved with the experimental setup. Conclusion This study shows the technical feasibility of using magnetic markers to produce encoding fields. Magnetic materials will allow generating spatial encoding fields, which can be tailored to an imaging application with less complexity and at lower cost compared to the use of gradient inserts. Magn Reson Med 72:399–408, 2014. © 2013 Wiley Periodicals, Inc.

Two new pulse sequences via Hadamard frequency encoding and spatial encoding are proposed to achieve high-resolution intermolecular double-quantum coherence correlation spectroscopy (iDQC-COSY) in inhomogeneous fields within a few scans. Hadamard encoding and spatial encoding are utilized to reduce acquisition time, while iDQC is used to remove the influence of inhomogeneous fields. Two Hadamard encoded schemes, namely, solute Hadamard encoding and solvent Hadamard encoding, are different in the two sequences. Detail analyses of the advantages and disadvantages of the two sequences are carried out. Acquisition times are both shortened by orders of magnitude. Experiments are performed to show their efficiencies.

On aging, spatial memory declines to some degree in both, rodents and humans. It is unknown, however, whether aging brings about a decline of encoding and retrieval of spatial information in parallel. The present study examined spatial encoding and retrieval in male CD-1 mice at 4, 9, and 12 months of age in a complex dry-land maze. The total time to reach the goal zone was age-dependent favoring mice at 4 months of age. We showed previously that moving time represents encoding of spatial information and resting time represents recall of previously learned spatial information. The average moving time decreased from 69.8 ± 5.3 s (mean ± SEM), 69.7 ± 8.0 s, and 78.9 ± 4.9 s to 17.0 ± 2.3 s (p

Spatial discontinuations occuring in cities introduce ambiguity in people´s mental spatial encoding and wayfinding bahavior. How do we encode and classify such misalignments? Twenty participants were asked to classify a total of 51 icons showing an upward-moving line being misaligned to the right and left as well as starting straight. The results show that subjects were very sensitive to slight discontinuations occurring to the vertical lines and that there was not exact symmetry between the left and right axis, meaning that the pieces slightly misaligned to the left were encoded differently than those misaligned to the right.

This chapter provides a quick introduction to the basics of MRI, adequate for understanding of the terminology and concepts used in Phase-Contrast MR Angiography (PC-MRA). Chapter begins with a description of signal generation, followed by an explanation for the need of spatial encoding necessary for derivation of the Fourier imaging approximation. A brief introduction to the magnetization dynamics using Bloch equation, with extension to small tip angle approximation is also provided. The chapter concludes with an introduction to the basic principle of flow measurement using PC-MRA, and the need for additional flow encoding gradients.

The integration of signals originating at different times and/or locations defines the stimulus features extracted and represented by a sensory system. As such, understanding this issue is central to understanding sensory coding. Here, we focus on spatial integration by ganglion cells, the output

We investigated whether chimpanzees, bonobos, and orangutans encoded the location of a reward hidden underneath one of three identical cups in relation to (1) the other cups in the array-i.e., the relative position of the baited cup within the array; or (2) the landmarks surrounding the cups-e.g., the edge of the table. Apes witnessed the hiding of a food reward under one of three cups forming a straight line on a platform. After 30 s, they were allowed to search for the reward. In three different experiments, we varied the distance of the cups to the edge of the platform and the distance between the cups. Results showed that both manipulated variables affected apes' retrieval accuracy. Subjects' retrieval accuracy was higher for the outer cups compared with the Middle cup, especially if the outer cups were located next to the platform's edge. Additionally, the larger the distance between the cups, the better performance became.

Two 1-D phase-encode sequences for T 2 mapping, namely CPMG-prepared SPRITE and spin-echo SPI, are presented and compared in terms of image quality, accuracy of T 2 measurements and the measurement time. The sequences implement two different approaches to acquiring T 2 -weighted images: in the CPMG-prepared SPRITE, the T 2 -weighting of magnetization precedes the spatial encoding, while in the spin-echo SPI, the T 2 -weighting follows the spatial encoding. The sequences are intended primarily for T 2 mapping of fluids in porous solids, where using frequency encode techniques may be problematic either due to local gradient distortions or too short T 2 . Their possible applications include monitoring fluid-flow processes in rocks, cement paste hydration, curing of rubber, filtering paramagnetic impurities and other processes accomplished by changing site-specific T 2 .

Spatially-encoded single-scan NMR offers an enormous improvement in speed for multidimensional NMR measurements. A typical two-dimensional experiment can be completed in less than a second. This review offers a simple and largely pictorial description of the basic concepts underpinning this ingenious technique, and outlines the relationship to conventional NMR methodology. Simple vector model descriptions are presented with the goal of understanding the basic spin physics of this complex experiment. Detailed and more mathematical treatments can be found in the original publications of Frydman and coworkers, listed among the cited references. © 2011 Wiley Periodicals, Inc. Concepts Magn Reson Part A 38A: 1–6, 2011.

We analyze the storage and retrieval of a weak light pulse, having two orthogonally (circularly) polarized components, onto an atomic ensemble of four-level atoms of the tripod type driven by a far detuned coupling field. The atoms are subject to a longitudinal magnetic field which produces a spatially varying Zeeman splitting of the lower levels along the medium and allows for a spatial encoding of the different angular frequencies of the input pulse during the storage phase. A single reversion of the external magnetic field results in a rephasing of the dipoles and leads to the release of the stored signals. The shape of the recovered pulse is a time-reversal copy of the input pulse. The application of an additional reversion of the magnetic field during the storage phase allows the release of a copy of the input pulse without time reversal. We also show that the system may operate like an all-optical multiplexer when considering two impinging optical fields which have orthogonal components. The proposal has potential applications in quantum information processing.

MRI at high magnetic field strengths promises to deliver clearer images of the body’s structure and function. However, high-field MRI currently faces several substantial engineering challenges before it can be considered robust and safe enough for routine clinical use. Challenges include increased radiofrequency (RF) energy deposition that can create unsafe patient heating, large main field inhomogeneities that prevent functional neuroimaging in the lower brain and inhomogeneous RFs transmit fields that cause spatially varying image contrast. Patient-tailored multidimensional RF excitation pulses have been proposed as a means to address many of these challenges. While these pulses show significant promise, their effectiveness has been severely limited by their long durations. Parallel excitation using multiple RF transmit coils driven simultaneously is a new technology that has been proposed to reduce multidimensional pulse durations. Parallel excitation provides an instantaneous spatial encoding mechanis...

Single-scan MRI underlies a wide variety of clinical and research activities, including functional and diffusion studies. Most common among these “ultrafast” MRI approaches is echo-planar imaging. Notwithstanding its proven success, echo-planar imaging still faces a number of limitations, particularly as a result of susceptibility heterogeneities and of chemical shift effects that can become acute at high fields. The present study explores a new approach for acquiring multidimensional MR images in a single scan, which possesses a higher built-in immunity to this kind of heterogeneity while retaining echo-planar imaging's temporal and spatial performances. This new protocol combines a novel approach to multidimensional spectroscopy, based on the spatial encoding of the spin interactions, with image reconstruction algorithms based on super-resolution principles. Single-scan two-dimensional MRI examples of the performance improvements provided by the resulting imaging protocol are illustrated using phantom-based and in vivo experiments. Magn Reson Med, 2010. © 2010 Wiley-Liss, Inc.

Previous research showed that drawing facilitates memory (Bruck, Melnyk, & Ceci, 2000; Butler, Gross, & Hayne, 1995; Gross & Hayne, 1999). The current study investigated whether drawing strategies could predict spatial memory. Children show a developmental change from drawing object-place binding (object-based coding) to object-region binding (space-based coding) when constructing spatial boundaries around matching Wertheimer stimuli (Common Region Test [CRT], Lange-Kuttner, 2006). In the present sample, girls showed the predicted age difference —from object-place to object-region binding—in the CRT. However, a U-shaped development for object-region binding was revealed in boys, with already most of the 6-year-old boys showing this type of spatial binding. Object-place binding was mainly used by boys from low socio-economic (SES) background. Boys’ spatial memory was more improved when they showed object-region binding than girls’ spatial memory. However, girls had closed the gap between object and place memory already at age 8, while this was the case in boys only at age 10. Multiple regression analyses revealed that socio-economic status (SES) was a more powerful predictor for spatial memory than age in boys, but not in girls. There were no gender differences in spatial encoding and memory in the group of 10-year-olds. It is suggested that gender-specific preferences for object-place and object-region binding were absent at age 10 because unit-based and region based spatial coding may merge like the paral-lel discrete and continuous number systems which become integrated with age (Feigenson, Dehaene, & Spelke, 2004).Keywords: object and place memory, spatial binding, gender differences, drawing, Spatial Memory Development Index (SMDI)

The ability to accelerate the spatial encoding process during a chemical shift imaging (CSI) scan of hyperpolarized compounds is demonstrated through parallel imaging. A hardware setup designed to simultaneously acquire 13C data from multiple receivers is presented here. A system consisting of four preamplifiers, four gain stages, a transmit coil, and a four receive channel rat coil was built for single channel excitation and simultaneous multi-channel detection of 13C signals. The hardware setup was integrated with commercial scanner electronics, allowing the system to function similar to a conventional proton multi-channel setup, except at a different frequency. The ability to perform parallel imaging is demonstrated in vivo. CSI data from the accelerated scans are reconstructed using a self-calibrated multi-spectral parallel imaging algorithm, by using lower resolution coil sensitivity maps obtained from the central region of k-space. The advantages and disadvantages of parallel imaging in the context of imaging hyperpolarized compounds are discussed. Copyright © 2009 John Wiley & Sons, Ltd.

Pulsed Field Gradients (PFGs) have become ubiquitous tools not only for Magnetic Resonance Imaging (MRI), but also for NMR experiments designed to study translational diffusion, for spatial encoding in ultra-fast spectroscopy, for the selection of desirable coherence transfer pathways, for the suppression of solvent signals, and for the elimination of zero-quantum coherences. Some of these experiments can only be carried out if three orthogonal gradients are available, while others can also be implemented using a single gradient, albeit at some expense of performance. This paper discusses some of the advantages of triple- with respect to single-gradient probes. By way of examples we discuss (i) the measurement of small diffusion coefficients making use of the long spin-lattice relaxation times of nuclei with low gyromagnetic ratios gamma such as nitrogen-15, and (ii) the elimination of zero-quantum coherences in Exchange or Nuclear Overhauser Spectroscopy (EXSY or NOESY) experiments, as well as in methods relying on long-lived (singlet) states to study very slow exchange or diffusion processes.

The main aim of this work is to present an overview of the nuclear quadrupole resonance (NQR) spectroscopy capabilities for solid state imaging and detection of illegal substances, such as explosives and drugs. We briefly discuss the evolution of different NQR imaging techniques, in particular those involving spatial encoding which permit conservation of spectroscopic information. It has been shown that plastic explosives and other forbidden substances cannot be easily detected by means of conventional inspection techniques, such as those based on conventional X-ray technology. For this kind of applications, the experimental results show that the information inferred from NQR spectroscopy provides excellent means to perform volumetric and surface detection of dangerous explosive and drug compounds.

Working memory (WM) is a system for the online storage of information. An emerging view is that neuronal oscillations coordinate the cellular assemblies that code the content of WM. In line with this view, previous work has demonstrated that oscillatory activity in the alpha band (8–12 Hz) plays a role in WM maintenance, but the exact contributions of this activity have remained unclear. Here, we used an inverted spatial encoding model in combination with electroencephalography (EEG) to test whether the topographic distribution of alpha-band activity tracks spatial representations held in WM. Participants in three experiments performed spatial WM tasks that required them to remember the precise angular location of a sample stimulus for 1,000-1,750 ms. Across all three experiments, we found that the topographic distribution of alpha-band activity tracked the specific location that was held in WM. Evoked (i.e., activity phase-locked to stimulus onset) and total (i.e., activity regardless of phase) power across a range of low-frequency bands transiently tracked the location of the sample stimulus following stimulus onset. However, only total power in the alpha band tracked the content of spatial WM throughout the memory delay period, which enabled reconstruction of location-selective channel tuning functions (CTFs). These findings demonstrate that alpha-band activity is directly related to the coding of spatial representations held in WM and provide a promising method for tracking the content of this online memory system.

Roman coins play an important role to understand the Roman empire because they convey rich information about key historical events of the time. Moreover, as large amounts of coins are daily traded over the Internet, it becomes necessary to develop automatic coin recognition systems to prevent illegal trades. In this paper, we describe a new large annotated database of over 2800 Roman coin images and propose an effective automated system for recognition of coins that leverages this new coin image set. As the use of succinct spatial-appearance relationships is critical for accurate coin recognition, we suggest two competing methods, adapted for the coin domain, to accomplish this task.

When magnetic resonance tomography is used in clinical practice a large number of different imaging techniques (sequences) are applied for the imaging. Despite this large number of sequences, which is often difficult to keep track of, all types of sequence work largely according to the same or very similar principles. In this continuing education course these principles are elaborated and the elements that make up a sequence are explained. These elements working together make it possible to assign the signals received from the receiver coil to their point of origin within the body. This first part of the further training is devoted largely to basic observations on spatial encoding of the signals, but also to the difference between 2D and 3D sequences. In addition, the techniques generally used in clinical practice for multislice imaging with 2D images are discussed in some detail.

La spectroscopie multidimensionnelle joue des roles essentiels dans la resonance magnetique moderne. Elle apporte une amelioration de la resolution, sans laquelle de nombreuses applications en chimie organique et inorganique resteraient impossibles ; elle est utilisee comme outil de base dans la determination et l'elucidation de structures biologiques complexes et fait partie integrante du protocole de formation de l'image en IRM. La presente revue decrit une recente approche que nous avons developpee, permettant l'acquisition de donnees RMN 2D completes en une seule acquisition continue. A condition que le signal soit suffisamment fort, le temps d'acquisition des experiences de RMN multidimensionnelle peut etre raccourci de plusieurs ordres de grandeur. Cette nouvelle methodologie est compatible avec les sequences d'impulsions multidimensionnelles (COSY, TOCSY, HSQC, IRM) et peut etre mise en oeuvre avec un equipement informatique conventionnel. Le codage spatial des interactions RMN, qui constitue le nouveau principe de ce protocole RMN utra-rapide, est discute et des exemples de ses performances sont donnes, avec une variete d'acquisitions par IRM et RMN 2D homo- et heteronucleaire. Pour citer cet article: L. Frydman, C. R. Chimie 9 (2006).

The conjoint retention hypothesis (CRH) claims that students recall more text information when they study geographic maps in addition to text than when they study text alone, because the maps are encoded spatially (Kulhavy, Lee, & Caterino, 1985). This claim was recently challenged by Griffin and Robinson (2000), who found no advantage for maps over feature lists in facilitating text recall. In two experiments, we crossed maps and lists with icons and names (c.f., Griffin & Robinson), and employed materials and methodology very similar to those used in previous CRH studies by Kulhavy and colleagues (Kulhavy, Stock, Verdi, Rittschof, and Savenye, 1993; Stock, Kulhavy, Peterson, Hancock, & Verdi, 1995). In addition, we included a concurrent task to measure spatial encoding, as did Griffin and Robinson. No advantages were found for maps over lists in facilitating text recall, nor were maps processed in a more spatial manner than litsts. Instead, it appears that the key stimulus feature for facilitating text recall is mimetic icons (i.e., icons that represent features) rather than the spatial characteristics of geographic maps, a finding that supports dual-coding theory (Paivio, 1986), but not the CRH.

Long-term potentiation (LTP) in the CA1 area of the hippocampus depends critically on the statistical characteristics of its stimulus. The ability of optical imaging to record spatial distribution has made it possible to examine systematically the effect of higher-order statistical characteristics, such as the correlation between successive pairs of inter-stimulus intervals (ISIs) on the induction of LTP. Therefore, the function of frequency (first-order) and temporal pattern (second-order) was examined using this imaging technique. To investigate the dependence of LTP on frequency, periodic stimuli with the same number of pulses were applied at different frequencies (1–10 Hz, n = 200) to Schaffer commissural-collateral fibers. While stimulus frequencies from 2–10 Hz induced LTP of varying magnitudes and low-frequency stimuli (1 Hz) induced long-term depression (LTD), spatial distribution remained consistent. These results suggest that induction frequency has a greater effect on the magnitude of LTP than on its spatial distribution. By employing nonperiodic stimuli at the same mean frequency (2 Hz), the effect of varying the temporal structure of a stimulus was also investigated. As the correlation of successive ISIs was increased from negative to positive, not only did the magnitude of LTP increase, there was also a statistically significant change in the spatial distribution of LTP. Interestingly, when a strong negatively correlated stimulus was applied, both LTP and LTD were simultaneously observed in the CA1 area. It was also found that the magnitude of LTP 200–300 μm distal to the cellular layer was larger than that of the LTP induced proximal (

Many hippocampal neurons (place cells) appear to represent a particular location within an environment (their place field). This property would appear to be central to hippocampal involvement in navigation based on spatial memory. Although a navigationally useful representation might also include information about distal goals, having a place field and being able to represent a distal goal would appear to be mutually exclusive place cell properties. Our simulations demonstrate, however, that information about goal direction can be simply derived from the changes in place field density that occur when place fields shift location in a goal-directed manner. Previous reports that place fields respond dynamically to shifts in goal location may, therefore, represent the operation of such a system.

In order to decrease the total duration of 2D J-resolved 2D spectroscopic imaging, a fast spatial encoding by spiral trajectories was developed and added to a 2D J-resolved pulse sequence. Data were acquired on a rat brain in vivo at 7 T. Total acquisition time was about 42 min for a voxel size of 27 μl. A signal-to-noise ratio of 16.3 was measured on the NAA peak, enabling the reconstruction of metabolite maps for the main peaks. To cite this article: B. Hiba, A. Ziegler, C. R. Chimie 7 (2004).

The present experiment examined how spatial judgments influenced target detection in a visual search task. Digital and analogue display formats were studied together with odd/even vs. above/below judgments. The results indicated an overall advantage for digital display formats, however, the advantage was mediated by the type of judgments that were made. Format differences were minimal when individuals were required to make judgments that involved spatial encoding. Ergonomic implications are addressed.

We tested detection of changes to eye position, eye color (brightness), mouth position, and mouth color in frontal views of faces. Two faces were presented sequentially for 555 ms each, with a blank screen of 120 ms separating the two. Faces were presented either both upright or both inverted. Measures of detection ( d') were calculated for several different degrees of change for each of the four dimensions of change. We first compared results to an earlier experiment that used an oddity design, in which subjects indicated which of three simultaneously viewed and otherwise identical faces had been altered on one of these four dimensions. Subjects in both of these experiments were partially cued, in that they knew the four possible types of changes that could occur on a given trial. The change-detection results correlated well with the oddity data. They confirmed that face inversion had little effect upon detection of changes in eye color, a moderate effect upon detection of eye-position or mouth-color changes, and caused a drastic reduction in the detection of mouth-position changes. An experiment in which uncued and fully cued subjects were compared showed that cueing significantly improved detection of feature color changes, but there was little difference between upright and inverted faces. Full cueing eliminated all effects of inversion. Compared to partial cueing, changes in mouth color were poorly detected by uncued subjects. Last, a change in the frequency of the base (unaltered) face in an experiment from 75% to 40% showed that increased short-term familiarity decreased the detection of eye changes and increased the detection of mouth changes, regardless of face orientation and the type of change made (color or position). We conclude that uncued subjects encode the spatial relations of features more than the colors of features, that mouth color in particular is not considered a relevant dimension for encoding, and that familiarization redistributes attention from more to less salient facial regions. Inversion effects are not simply an exaggeration of the salience effects revealed by withdrawing cueing, but represent an interaction of spatial encoding with salience, in that the greatest inversion effects occur for spatial shifts in less salient facial regions, and can be eliminated through the use of focused attention.