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K Zilles

Publications and source records attributed to K Zilles.

At least 19 recordsLinked to original sources
PubMed2007

Impaired maze performance in aged rats is accompanied by increased density of NMDA, 5-HT1A, and alpha-adrenoceptor binding in hippocampus.

Using quantitative receptor autoradiography, we assessed binding site densities and distribution patterns of glutamate, GABA(A), acetylcholine (ACh), and monoamine receptors in the hippocampus of 32-month-old Fischer 344/Brown Norway rats. Prior to autoradiography, the rats were divided into two groups according to their retention performance in a water maze reference memory task, which was assessed 1 week after 8 days of daily maze training. The animals of the inferior group showed less long-term retention of the hidden-platform task but did not differ from superior rats in their navigation performance during place training and cued trials. The decreased retention performance in the group of inferior learners was primarily accompanied by increased alpha(1)-adrenoceptors in all hippocampal subregions under inspection (CA1-CA4 and dentate gyrus), while elevated alpha(2)-adrenoceptor binding was observed in the CA1 region and DG. Furthermore, inferior learners had higher NMDA binding in the CA2 and CA4 and increased 5-HT(1A) binding sites in the CA2, CA3, and CA4 region. No significant differences between inferior and superior learners were evident with regard to AMPA, kainate, GABA(A), muscarinergic M(1), dopamine D(1), and 5-HT(2) binding densities in any hippocampal region analyzed. These results show that increased NMDA, 5-HT(1A), and alpha-adrenoceptor binding in the hippocampus is associated with a decline in spatial memory. The increased receptor binding observed in the group of old rats with inferior maze performance might be the result of neural adaptation triggered by age-related changes in synaptic connectivity and/or synaptic activity.

Adrenergic Agents↗
PubMed2006

A new method for fast quantitative mapping of absolute water content in vivo.

The presence of brain edema, in its various forms, is an accompanying feature of many diseased states. Although the localized occurrence of brain edema may be demonstrated with MRI, the quantitative determination of absolute water content, an aspect that could play an important role in the objective evaluation of the dynamics of brain edema and the monitoring of the efficiency of treatment, is much more demanding. We present a method for the localized and quantitative measurement of absolute water content based on the combination of two fast multi-slice and multi-time point sequences QUTE and TAPIR for mapping the T(2)* and T(1) relaxation times, respectively. Incorporation of corrections for local B(1) field miscalibrations, temperature differences between the subject and a reference probe placed in the FOV, receiver profile inhomogeneities and T(1) saturation effects are included and allow the determination of water content with anatomical resolution and a precision >98%. The method was validated in phantom studies and was applied to the localized in vivo measurement of water content in a group of normal individuals and a patient with brain tumor. The results demonstrate that in vivo measurement of regional absolute water content is possible in clinically relevant measurement times with a statistical and systematic measurement error of <2%.

Adult↗
PubMed2005

A comparison of three SPRITE techniques for the quantitative 3D imaging of the 23Na spin density on a 4T whole-body machine.

Sodium density maps acquired with three SPRITE-based methods have been compared in terms of the resulting quantitative information as well as image quality and acquisition times. Consideration of factors relevant for the clinical implementation of SPRITE shows that the Conical-SPRITE variant is preferred because of a 20-fold reduction in acquisition time, slightly improved image quality, and no loss of quantitative information. The acquisition of a 3D data set (32x32x16; FOV=256x256x160 mm) for the quantitative determination of sodium density is demonstrated. In vivo Conical-SPRITE 23Na images of the brain of a healthy volunteer were acquired in 30 min with a resolution of 7.5x7.5x7.5 mm and a signal-to-noise ratio of 23 in cerebrospinal fluid and 17 in brain tissue.

Brain↗
PubMed2005

Dual-contrast echo planar imaging with keyhole: application to dynamic contrast-enhanced perfusion studies.

A new EPI-based method is presented which features optimized sampling of k-space enabling the integrated acquisition of two gradient echo images. The first of these images is predominantly T1 weighted and the second is T*2 weighted. The new method combines echo sharing of sparsely acquired high spatial frequency components with the keyhole technique and half-Fourier image reconstruction. The feasibility of acquiring high spatial and temporal resolution in vivo images for perfusion mapping is demonstrated. In contrast to most current perfusion methods, which acquire the T1- and T*2-weighted images in separate acquisitions, the need for image co-registration here is obviated since both sets of images are EPI-based and are acquired within the same measurement.

Brain↗
PubMed2005

Linking retinotopic fMRI mapping and anatomical probability maps of human occipital areas V1 and V2.

Using functional MRI, we characterized field sign maps of the occipital cortex and created three-dimensional maps of these areas. By averaging the individual maps into group maps, probability maps of functionally defined V1 or V2 were determined and compared to anatomical probability maps of Brodmann areas BA17 and BA18 derived from cytoarchitectonic analysis (Amunts, K., Malikovic, A., Mohlberg, H., Schormann, T., Zilles, K., 2000. Brodmann's areas 17 and 18 brought into stereotaxic space-where and how variable? NeuroImage 11, 66-84). Comparison of areas BA17/V1 and BA18/V2 revealed good agreement of the anatomical and functional probability maps. Taking into account that our functional stimulation (due to constraints of the visual angle of stimulation achievable in the MR scanner) only identified parts of V1 and V2, for statistical evaluation of the spatial correlation of V1 and BA17, or V2 and BA18, respectively, the a priori measure kappa was calculated testing the hypothesis that a region can only be part of functionally defined V1 or V2 if it is also in anatomically defined BA17 or BA18, respectively. kappa = 1 means the hypothesis is fully true, kappa = 0 means functionally and anatomically defined visual areas are independent. When applying this measure to the probability maps, kappa was equal to 0.84 for both V1/BA17 and V2/BA18. The data thus show a good correspondence of functionally and anatomically derived segregations of early visual processing areas and serve as a basis for employing anatomical probability maps of V1 and V2 in group analyses to characterize functional activations of early visual processing areas.

Adult↗
PubMed2005

Imaging of copper, zinc, and other elements in thin section of human brain samples (hippocampus) by laser ablation inductively coupled plasma mass spectrometry.

Laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) was used to produce images of element distribution in 20-microm thin sections of human brain tissue. The sample surface was scanned (raster area approximately 80 mm(2)) with a focused laser beam (wavelength 213 nm, diameter of laser crater 50 microm, and laser power density 3 x 10(9) W cm(-2)) in a cooled laser ablation chamber developed for these measurements. The laser ablation system was coupled to a double-focusing sector field ICPMS. Ion intensities of 31P+, 32S+, 56Fe+, 63Cu+, 64Zn+, 232Th+, and 238U+ were measured within the area of interest of the human brain tissue (hippocampus) by LA-ICPMS. The quantitative determination of copper, zinc, uranium, and thorium distribution in thin slices of the human hippocampus was performed using matrix-matched laboratory standards. In addition, a new arrangement in solution-based calibration using a micronebulizer, which was inserted directly into the laser ablation chamber, was applied for validation of synthetic laboratory standard. The mass spectrometric analysis yielded an inhomogeneous distribution (layered structure) for P, S, Cu, and Zn in thin brain sections of the hippocampus. In contrast, Th and U are more homogeneously distributed at a low-concentration level with detection limits in the low-nanogram per gram range. The unique analytical capability and the limits of LA-ICPMS will be demonstrated for the imaging of element distribution in thin cross sections of brain tissue from the hippocampus. LA-ICPMS provides new information on the spatial element distribution of the layered structure in thin sections of brain tissues from the hippocampus.

Brain Chemistry↗
PubMed2005

Cytoarchitectonic mapping of the human amygdala, hippocampal region and entorhinal cortex: intersubject variability and probability maps.

Probabilistic maps of neocortical areas and subcortical fiber tracts, warped to a common reference brain, have been published using microscopic architectonic parcellations in ten human postmortem brains. The maps have been successfully applied as topographical references for the anatomical localization of activations observed in functional imaging studies. Here, for the first time, we present stereotaxic, probabilistic maps of the hippocampus, the amygdala and the entorhinal cortex and some of their subdivisions. Cytoarchitectonic mapping was performed in serial, cell-body stained histological sections. The positions and the extent of cytoarchitectonically defined structures were traced in digitized histological sections, 3-D reconstructed and warped to the reference space of the MNI single subject brain using both linear and non-linear elastic tools of alignment. The probability maps and volumes of all structures were calculated. The precise localization of the borders of the mapped regions cannot be predicted consistently by macroanatomical landmarks. Many borders, e.g. between the subiculum and entorhinal cortex, subiculum and Cornu ammonis, and amygdala and hippocampus, do not match sulcal landmarks such as the bottom of a sulcus. Only microscopic observation enables the precise localization of the borders of these brain regions. The superposition of the cytoarchitectonic maps in the common spatial reference system shows a considerably lower degree of intersubject variability in size and position of the allocortical structures and nuclei than the previously delineated neocortical areas. For the first time, the present observations provide cytoarchitectonically verified maps of the human amygdala, hippocampus and entorhinal cortex, which take into account the stereotaxic position of the brain structures as well as intersubject variability. We believe that these maps are efficient tools for the precise microstructural localization of fMRI, PET and anatomical MR data, both in healthy and pathologically altered brains.

Aged↗
PubMed2005

Quantitative architectural analysis: a new approach to cortical mapping.

Recent progress in anatomical and functional MRI has revived the demand for a reliable, topographic map of the human cerebral cortex. Till date, interpretations of specific activations found in functional imaging studies and their topographical analysis in a spatial reference system are, often, still based on classical architectonic maps. The most commonly used reference atlas is that of Brodmann and his successors, despite its severe inherent drawbacks. One obvious weakness in traditional, architectural mapping is the subjective nature of localising borders between cortical areas, by means of a purely visual, microscopical examination of histological specimens. To overcome this limitation, more objective, quantitative mapping procedures have been established in the past years. The quantification of the neocortical, laminar pattern by defining intensity line profiles across the cortical layers, has a long tradition. During the last years, this method has been extended to enable a reliable, reproducible mapping of the cortex based on image analysis and multivariate statistics. Methodological approaches to such algorithm-based, cortical mapping were published for various architectural modalities. In our contribution, principles of algorithm-based mapping are described for cyto- and receptorarchitecture. In a cytoarchitectural parcellation of the human auditory cortex, using a sliding window procedure, the classical areal pattern of the human superior temporal gyrus was modified by a replacing of Brodmann's areas 41, 42, 22 and parts of area 21, with a novel, more detailed map. An extension and optimisation of the sliding window procedure to the specific requirements of receptorarchitectonic mapping, is also described using the macaque central sulcus and adjacent superior parietal lobule as a second, biologically independent example. Algorithm-based mapping procedures, however, are not limited to these two architectural modalities, but can be applied to all images in which a laminar cortical pattern can be detected and quantified, e.g. myeloarchitectonic and in vivo high resolution MR imaging. Defining cortical borders, based on changes in cortical lamination in high resolution, in vivo structural MR images will result in a rapid increase of our knowledge on the structural parcellation of the human cerebral cortex.

Algorithms↗
PubMed2005

Multimodal architectonic mapping of human superior temporal gyrus.

Although it is generally accepted that human superior temporal gyrus is activated by a huge variety of auditory and linguistic tasks, little is known about the exact positions and extents of cortical areas that are located on the lateral convexity of the gyrus (e.g., Brodmann's area 22). Such information, however, is relevant for a rigorous testing of structural-functional relationships in both normal volunteers and patients suffering from disorders of auditory and language perception. The present combined cytoarchitectonic and receptorarchitectonic study identifies a distinct area (Te3) in the lateral bulge of the superior temporal gyrus by using an algorithm-based approach for the detection of cortical borders. Our mapping data show that, in contrast to Brodmann's area (BA) 22, only small portions of Te3 reach the dorsal and ventral banks of the gyrus. Therefore, we labelled the newly defined area as "Te3" and not as "BA 22". The cytoarchitectonically defined borders of Te3 coincide with abrupt changes in the receptorarchitecture of several classical neurotransmitters, suggesting that Te3 represents a functionally relevant area of the human superior temporal gyrus. Since position and extent of area Te3 varied considerably between subjects, probability maps were created that show for each voxel of the standard references space, the frequency with which Te3 was present in it. These maps, in combination with previously published maps of the primary auditory cortex, can directly be compared with functional imaging data, and may open new perspectives for the analysis of structural-functional correlations in the human auditory and language systems.

Algorithms↗
PubMed2005

Consequences of large interindividual variability for human brain atlases: converging macroscopical imaging and microscopical neuroanatomy.

In human brain imaging studies, it is common practice to use the Talairach stereotaxic reference system for signifying the convergence of brain function and structure. In nearly all neuroimaging reports, the studied cortical areas are specified further with a Brodmann Area (BA) number. This specification is based upon macroscopic extrapolation from Brodmann's projection maps into the Talairach atlas rather than upon a real microscopic cytoarchitectonic study. In this review we argue that such a specification of Brodmann area(s) via the Talairach atlas is not appropriate. Cytoarchitectonic studies reviewed in this paper show large interindividual differences in 3-D location of primary sensory cortical areas (visual cortex) as well as heteromodal associational areas (prefrontal cortical areas), even after correction for differences in brain size and shape. Thus, the simple use of Brodmann cortical areas derived from the Talairach atlas can lead to erroneous results in the specification of pertinent BA. This in turn can further lead to wrong hypotheses on brain system(s) involved in normal functions or in specific brain disorders. In addition, we will briefly discuss the different 'Brodmann' nomenclatures which are in use for the cerebral cortex.

Adult↗
PubMed2005

Difficulty of perceptual spatiotemporal integration modulates the neural activity of left inferior parietal cortex.

The integration of spatial and temporal information is a prerequisite for skilled movements. Likewise, spatial and temporal information must be integrated to predict the potential collision (or otherwise) of two moving objects. In a previous blocked functional magnetic resonance imaging (fMRI) study [Neuroimage 20 (2003) S82] we showed that collision judgments (relative to size judgments) provoked a significant increase in neural activity in the left inferior parietal cortex (supramarginal gyrus). This result suggests that this region is involved in the integration of perceptual spatiotemporal information in addition to its known involvement in programming skilled actions. To further investigate the impact of the integration of temporal and spatial information on the left parietal cortex we conducted an event-related fMRI study in which we varied the difficulty of the collision (and the size) judgment tasks parametrically. Reaction times and error rates were used as behavioral measures of increasing task demands. There was a significant linear increase in reaction times and error rates during the collision and the size tasks over the four levels of task difficulty. A linear increase of the blood oxygen level-dependent signal in the left inferior parietal cortex was found only for the collision, not for the size, conditions. Neural activation in the left inferior parietal cortex thus paralleled the increasing demands on spatiotemporal integration. This result confirms that the left supramarginal gyrus integrates spatial and temporal information irrespective of motor demands.

Adult↗
PubMed2005

No postnatal doubling of number of neurons in human Broca's areas (Brodmann areas 44 and 45)? A stereological study.

In this study we explored whether a postnatal doubling of the total number of neurons occurs in the human Brodmann areas 44 and 45 (Broca's area). We describe the most recent error prediction formulae and their application for the modern stereological estimators for volume and number of neurons. We estimated the number of neurons in 3D optical disector probes systematically random sampled throughout the entire Brodmann areas (BA) 44 and 45 in developing and young adult cases. In the relatively small number of male and female cases studied no substantial postnatal increase in total number of neurons occurred in areas 44 and 45; the volume of these areas reached adult values around 7 years. In addition, we did find indications that a shift from a right-over-left to a left-over-right asymmetry may occur in the volume of BA 45 during postnatal development. No major asymmetry in total number of neurons in BA 44 and 45 was detected.

Adult↗
PubMed2004

On the benefits of not trying: brain activity and connectivity reflecting the interactions of explicit and implicit sequence learning.

Under certain circumstances, implicit, automatic learning may be attenuated by explicit memory processes. We explored the brain basis of this phenomenon in a functional magnetic resonance imaging (fMRI) study of motor sequence learning. Using a factorial design that crossed subjective intention to learn (explicit versus implicit) with sequence difficulty (a standard versus a more complex alternating sequence), we show that explicit attempts to learn the difficult sequence produce a failure of implicit learning and, in a follow-up behavioural experiment, that this failure represents a suppression of learning itself rather than of the expression of learning. This suppression is associated with sustained right frontal activation and attenuation of learning-related changes in the medial temporal lobe and the thalamus. Furthermore, this condition is characterized by a reversal of the fronto-thalamic connectivity observed with unimpaired implicit learning. The findings demonstrate a neural basis for a well-known behavioural effect: the deleterious impact of an explicit search upon implicit learning.

Adult↗
PubMed2004

Somatotopy and attentional modulation of the human parietal and opercular regions.

The somatotopical organization of the postcentral gyrus is well known, but less is known about the somatotopical organization of area 2, the somatosensory association areas in the postparietal cortex, and the parietal operculum. The extent to which these areas are modulated by attention is also poorly understood. For these reasons, we measured the BOLD signal when rectangular parallelepipeds of varying shape were presented to the immobile right hand or right foot of 10 subjects either discriminating these or just being stimulated. Activation areas in each subject were mapped against cytoarchitectural probability maps of area 2, IP1, and IP2 along the intraparietal sulcus and the parietal opercular areas OP1-OP4. In area 2, the somatotopical representation of the hand and foot were distinctly separate, whereas there was considerable overlap in IP1 and no clear evidence of separate representations in OP1, OP4, and IP2. The overlap of hand and foot representations increased in the following order: area 3a, 3b, 1, 2, IP1, OP4, IP2, and OP1. There were significant foot representations but no hand representations in right (ipsilateral) areas 3a, 3b, and 1. Shape discrimination using the foot as opposed to stimulation enhanced the signal in OP4 bilaterally, whereas discrimination with the hand enhanced the signal bilaterally in area 2, IP1, and IP2. These results indicate that somatosensory areas in humans are arranged from strong somatotopy into no somatotopy in the following order: 3a, 3b, 1, 2, IP1, OP4, IP2, and OP1. Higher order areas such as IP1, IP2, and OP4 showed task-related attentional enhancement.

Adult↗
PubMed2004

A functional magnetic resonance imaging study of local/global processing with stimulus presentation in the peripheral visual hemifields.

When stimuli are presented in the left or right visual fields, hemispheric specialization for global and local processing in occipital areas is attenuated. Using functional magnetic resonance imaging, we investigated how this attenuation is compensated for when information must cross the corpus callosum to reach the areas specialized for global and local processing. We presented hierarchically nested letters (e.g. a large E made of smaller E's) to the right or the left visual hemifield while subjects fixated centrally. In half the trials, subjects indicated whether the global aspect and in the other half whether the local aspect of the stimulus matched a pre-specified target letter. Visual hemifield presentations showed the expected contralateral activations of occipital cortex. The main effects of locally or globally directed attention did not show any differential occipital activations, but the right anterior cingulate cortex was activated differentially during local processing. Region-of-interest-based analyses showed increased neural activity in left posterior occipital cortex during local processing when stimuli were presented in the left hemifield. During global processing with stimulus presentation to the right hemifield, the right posterior occipital cortex was activated. Activation of right anterior cingulate cortex during local processing is likely to reflect the suppression of global processing precedence in order to select correctly the local stimulus level. The activations in left (local) and right (global) occipital areas are likely to reflect the top-down augmentation of stimulus information that has been degraded by callosal crossing in order to access the hemisphere specialized for local or global processing.

Adult↗
PubMed2004

Neural correlates of first-person perspective as one constituent of human self-consciousness.

Taking the first-person perspective (1PP) centered upon one's own body as opposed to the third-person perspective (3PP), which enables us to take the viewpoint of someone else, is constitutive for human self-consciousness. At the underlying representational or cognitive level, these operations are processed in an egocentric reference frame, where locations are represented centered around another person's (3PP) or one's own perspective (1PP). To study 3PP and 1PP, both operating in egocentric frames, a virtual scene with an avatar and red balls in a room was presented from different camera viewpoints to normal volunteers (n = 11) in a functional magnetic resonance imaging experiment. The task for the subjects was to count the objects as seen either from the avatar's perspective (3PP) or one's own perspective (1PP). The scene was presented either from a ground view (GV ) or an aerial view (AV ) to investigate the effect of view on perspective taking. The factors perspective (3PP vs. 1PP) and view (GV vs. AV ) were arranged in a two-factorial way. Reaction times were increased and percent correctness scores were decreased in 3PP as opposed to 1PP. To detect the neural mechanisms associated with perspective taking, functional magnetic resonance imaging was employed. Data were analyzed using SPM'99 in each subject and non-parametric statistics on the group level. Activations common to 3PP and 1PP (relative to baseline) were observed in a network of occipital, parietal, and prefrontal areas. Deactivations common to 3PP and 1PP (relative to baseline) were observed predominantly in mesial (i.e., parasagittal) cortical and lateral superior temporal areas bilaterally. Differential increases of neural activity were found in mesial superior parietal and right premotor cortex during 3PP (relative to 1PP), whereas differential increases during 1PP (relative to 3PP) were found in mesial prefrontal cortex, posterior cingulate cortex, and superior temporal cortex bilaterally. The data suggest that in addition to joint neural mechanisms, for example, due to visuospatial processing and decision making, 3PP and 1PP rely on differential neural processes. Mesial cortical areas are involved in decisional processes when the spatial task is solved from one's own viewpoint, whereas egocentric operations from another person's perspective differentially draw upon cortical areas known to be involved in spatial cognition.

Adult↗