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Biomedical subjects

K Zilles

Publications and source records attributed to K Zilles.

At least 91 records · Page 5Linked to original sources
PubMed2000

Brodmann's areas 17 and 18 brought into stereotaxic space-where and how variable?

Studies on structural-functional associations in the visual system require precise information on the location and variability of Brodmann's areas 17 and 18. Usually, these studies are based on the Talairach atlas, which does not rely on cytoarchitectonic observations, but on comparisons of macroscopic features in the Talairach brain and Brodmann's drawing. In addition, in this atlas are found only the approximate positions of cytoarchitectonic areas and not the exact borders. We have cytoarchitectonically mapped both areas in 10 human brains and marked their borders in corresponding computerized images. Borders were defined on the basis of quantitative cytoarchitecture and multivariate statistics. In addition to borders of areas 17 and 18, subparcellations within both areas were found. The cytoarchitectonically defined areas were 3-D reconstructed and transferred into the stereotaxic space of the standard reference brain. Surface rendering of the brains revealed high individual variability in size and shape of the areas and in the relationship to the free surface and sulci. Ranges and centers of gravity of both areas were calculated in Talairach coordinates. The positions of areas 17 and 18 in the stereotaxic space differed between the hemispheres. Both areas reached significantly more caudal and medial positions on the left than on the right. Probability maps were created in which the degree of overlap in each stereotaxic position was quantified. These maps of areas 17 and 18 are the first of their kind and contain precise stereotaxic information on both interhemispheric and interindividual differences.

Adult↗
PubMed2000

Areas 3a, 3b, and 1 of human primary somatosensory cortex. Part 2. Spatial normalization to standard anatomical space.

Interindividual topographical variability of cytoarchitectonically defined somatosensory areas 3a, 3b, and 1 was analyzed in the standard anatomical format of a computerized brain atlas. T1-weighted magnetic resonance images were obtained from 10 postmortem brains. The brains were serially sectioned at 20 mcm, sections were stained for cell bodies, and areas 3a, 3b, and 1 were defined with an observer-independent cytoarchitectonic technique. After correction of the sections for deformations due to histological processing, the 3-D reconstructed histological volumes of the individual brains and the volume representations of the cytoarchitectonic areas were adapted to the reference brain of a computerized atlas. Corresponding areas were superimposed in the 3-D space of the reference brain. These population maps describe, for each voxel, how many brains have a representation of one particular cytoarchitectonic area. Each area's extent is very variable across different brains, but representations of areas 3a, 3b, and 1 in >/=50% of the brains were found in the fundus of the central sulcus, its caudal bank, and on the crown of the postcentral gyrus, respectively. Volumes of interest (VOIs) were defined for each area in which >/=50% of the brains have a representation of that area. Despite close spatial relationship of areas 3a, 3b, and 1 in the postcentral gyrus, the three VOIs overlap by <1% of their volumes. Functional imaging data can now be brought into the same standard anatomical format, and changes in regional cerebral blood flow can be calculated in VOIs of areas 3a, 3b, and 1, which are derived from genuine cytoarchitectonic data.

Adult↗
PubMed2000

Correlation between human personality and neural activity in cerebral cortex.

Personality traits are a variance of behavioral patterns among individuals and may reflect a variance of brain activity, but their neurobiological explanation is still a matter of debate. Cloninger proposed three dimensions of personality traits, each of which has strong correlation with activity in a specific central monoaminergic system. Although this theory has been supported by physiological and genetic studies, it is still unclear how these personality parameters are correlated with the activity of the cortical networks which control human behavior. Here we measured the regional cerebral blood flow (rCBF) at rest in 30 normal volunteers who completed the personality inventory of Cloninger. Voxel-by-voxel analysis was employed to identify cortical regions where the rCBF showed significant correlation with any of the three personality parameters. Statistically significant correlation was observed in several paralimbic and neocortical regions and was consistent with the assumed monoaminergic influence on neural activity and the distribution of its projections, in each personality dimension. The results suggest that activity in a variety of cortical regions is associated with human personality traits and lend support to Cloninger's theory concerning central monoaminergic influence on human personality traits.

Adult↗
PubMed2000

The effect of sequence repeat time on auditory cortex stimulation during phonetic discrimination.

Acoustic noise generated by the MR scanner gradient system during fMRI studies of auditory function is a very significant potential confound. Despite these deleterious effects, fMRI of the auditory cortex has been successful and numerous practitioners have circumvented the problem of acoustic masking noise. In the context of auditory cortex fMRI, the sequence repeat time (TR) has the effect of altering the length of time during which the scanner is quiet. Indeed, the move to whole-brain fMRI makes the problem of acoustic noise more acute and points to the need to examine the role of TR and its influence on the BOLD signal. The aim of this study was to examine the effect of varying the TR time on activation of auditory cortex during presentation and performance of a phonetic discrimination task. The results presented here demonstrate that the influence of sequence repeat time is considerable. For a short repeat time it is likely that the noise from the scanner is a significant mask and hinders accurate task performance. At the other extreme, a repeat time of 9 s is also suboptimal, probably due to attentional effects and lack of concentration and not least because of the longer overall measurement times. The results of this study point to a complicated interplay between psychophysical factors as well as physical parameters; attention, acoustic noise, total duration of the experiment, consideration of the volume of acquisition, and overall difficulty of the task have to be assessed and balanced. For the paradigm used here, the results suggest an optimal TR of around 6 s for a 16-slice acquisition.

Artifacts↗
PubMed2000

The effect of switching between sequential and repetitive movements on cortical activation.

We used whole-head functional magnetic resonance imaging (fMRI) to investigate the effect of switching between different sequential and repetitive movements in the context of conditional and fixed tasks. Four different movement tasks were applied: (1) unpredictable switching between two movement sequences comprising six submovements each according to visual cues (SEQ-VC); (2) unpredictable switching between repetitive movement of one finger according to visual cues (REP-VC); (3) performance of the same sequential movements used for SEQ-VC but in a fixed mode triggered by a visual stimulus (SEQ-FIX); (4) performance of the repetitive movements used for REP-FIX but in a fixed mode by a visual stimulus (REP-FIX). The statistical group analysis of the hemodynamic responses revealed the following results: (1) the SEQ-VC compared to the SEQ-FIX condition (switching between movement sequences) engendered stronger activations in the left rostral supplementary motor area (pre-SMA), bilaterally in the posterior parietal lobule, the left ventral premotor area, and the visual cortices; (2) the REP-VC compared to the REP-FIX condition (switching between repetitive movements) only revealed stronger activation in extra-striate areas. We hypothesize that during switching of movement sequences higher motor control aspects are involved including movement selection, updating of motor plans, as well as recalling and restoring motor plans. The repetitive movements are too simple in order to evoke additional activations in the medial and lateral premotor areas, as well as in parietal areas.

Adult↗
PubMed2000

The effect of verbal feedback on motor learning--a PET study. Positron emission tomography.

The purpose of this study was to investigate brain mechanisms underlying feedback effects on motor learning. We measured human brain activity using positron emission tomography (PET) during length-of-line drawing tasks in the presence or absence of verbal feedback, i.e., information on the precision of motor performance. The average error in responses was significantly lower and the percentage of correct responses was significantly higher in the case of tasks with feedback than those in the absence of feedback. The contralateral sensorimotor, premotor, supplementary motor, the right prefrontal, bilateral parietal and temporal, and anterior cingulate cortices, and the left basal ganglia were activated during all the line-drawing tasks. The right lateral prefrontal and occipital cortices and the left basal ganglia exhibited marked increase in activity after learning. The right inferior parietal and the anterior cingulate cortices were activated in the presence of feedback which provided information on how the subjects should correct their performances. The results indicate that these brain areas may play an important role in representing knowledge of results during motor learning and that appropriate feedback may facilitate motor learning.

Adult↗
PubMed2000

Functional neuroanatomy of the primate isocortical motor system.

The concept of the primate motor cortex based on the cytoarchitectonic subdivision into areas 4 and 6 according to Brodmann or the functional subdivision into primary motor, supplementary motor, and lateral premotor cortex has changed in recent years. Instead, this cortical region is now regarded as a complex mosaic of different areas. This review article gives an overview of the structure and function of the isocortical part of the motor cortex in the macaque and human brain. In the macaque monkey, the primary motor cortex (Brodmann's area 4 or area F1) with its giant pyramidal or Betz cells lies immediately anterior to the central sulcus. The non-primary motor cortex (Brodmann's area 6) lies further rostrally and can be subdivided into three groups of areas: the supplementary motor areas "SMA proper" (area F3) and "pre-SMA" (area F6) on the mesial cortical surface, the dorsolateral premotor cortex (areas F2 and F7) on the dorsolateral convexity, and the ventrolateral premotor cortex (areas F4 and F5) on the ventrolateral convexity. The primary motor cortex is mainly involved in controlling kinematic and dynamic parameters of voluntary movements, whereas non-primary motor areas are more related to preparing voluntary movements in response to a variety of internal or external cues. Since a structural map of the human isocortical motor system as detailed as in the macaque is not yet available, homologies between the two species have not been firmly established. There is increasing evidence, however, that a similar organizational principle (i.e., primary motor cortex, supplementary motor areas, dorso- and ventrolateral premotor cortex) also exists in humans. Imaging studies have revealed that functional gradients can be discerned within the human non-primary motor cortex. More rostral cortical regions are active when a motor task is nonroutine, whereas more routine motor actions engage more caudal areas.

Animals↗
PubMed2000

Comparison of overall brain volume and midsagittal corpus callosum surface area as obtained from NMR scans and direct anatomical measures: a within-subject study on autopsy brains.

Formalin fixed brains obtained from autopsy were studied by magnetic resonance imaging, using FLASH and MPR sequences. The overall volume and the midsagittal surface area of the corpus callosum (cc) of these brains were also directly measured by water displacement for overall volume determination and morphometry for cc surface area measures, allowing comparisons of these measures in a within-subject design. Thin NMR sections (1 mm thickness for FLASH and 1.25 mm for MPR) yielded overall brain volume estimates that did not differ significantly from direct volume estimations but thicker (5 mm) sections led to a significant overestimation of brain volume for NMR measures relative to direct displacement measures. There was no overall effect of type of NMR measure: FLASH and MPR scans did not yield significantly different values for overall brain volume or callosal surface area. Direct and NMR measures of the corpus callosum surface at midsagittal level did not yield significantly different estimates.

Aged↗
PubMed2000

'Where' depends on 'what': a differential functional anatomy for position discrimination in one- versus two-dimensions.

Line bisection is widely used as a clinical test of spatial cognition in patients with left visuospatial neglect after right hemisphere lesion. Surprisingly, many neglect patients who show severe impairment on marking the center of horizontal lines can accurately mark the center of squares. That these patients with left neglect are also typically poor at judging whether lines are correctly prebisected implies that the deficit can be perceptual rather than motoric. These findings suggest a differential neural basis for one- and two-dimensional visual position discrimination that we investigated with functional neuroimaging (fMRI). Normal subjects judged whether, in premarked lines or squares, the mark was placed centrally. Line center judgements differentially activated right parietal cortex, while square center judgements differentially activated the lingual gyrus bilaterally. These distinct neural bases for one- and two-dimensional visuospatial judgements help explain the observed clinical dissociations by showing that as a stimulus becomes a better, more 'object-like' gestalt, the ventral visuoperceptive route assumes more responsibility for assessing position within the object.

Adult↗
PubMed2000

Interhemispheric asymmetry of the human motor cortex related to handedness and gender.

Most people are right-handed, preferring the right hand for skilled as well as unskilled activities, but a notable proportion are mixed-handed, preferring to use the right hand for some actions and the left hand for others. Assuming a structural/functional correlation in the motor system we tested whether asymmetries in hand performance in consistent right and left handers as well as in mixed handers are associated with anatomical asymmetries in the motor cortex. In vivo MR morphometry was used for analyzing interhemispheric asymmetry in the depth of the central sulcus in the region of cortical hand representation of 103 healthy subjects. Subjects were tested both for hand preference and hand performance. As expected, left-right differences in hand performance differed significantly between consistent right, consistent left and mixed handers and were independent on gender. Male consistent right handers showed a significant deeper central sulcus on the left hemisphere than on the right. Anatomical asymmetries decreased significantly from male consistent right over mixed to consistent left handers. Sixty two per cent of consistent left handers revealed a deeper central sulcus on the right than on the left hemisphere, but for the group as a whole this rightward asymmetry was not significant. No interhemispheric asymmetry was found in females. Thus, anatomical asymmetry was associated with handedness only in males, but not in females, suggesting sex differences in the cortical organization of hand movements.

Adolescent↗
PubMed2000

Laminar characteristics of functional connectivity in rat barrel cortex revealed by stimulation with caged-glutamate.

In rodent somatosensory (barrel) cortex input is processed by whisker-related columns before the integrated output is fed into behaviorally-relevant circuits. The layer-specific activation patterns of the rat barrel cortex were examined with a set-up for scanning functional connectivity in brain slices. Flash-induced release of caged-glutamate at a large number of stimulation sites was used in combination with simultaneous field potential recordings from layers II to VI with five electrodes. The field potentials revealed striking differences between the cortical layers. Glutamate-release in layer IV and lower layer III was most effective in evoking excitation in all other cortical layers, whereas field potentials recorded from layer IV itself were caused by stimulation of a very restricted columnar zone only. Field potentials in layers II and III were strongly driven by stimulation in layer IV and less consistently and much weaker by layer V. Layer V was the only lamina capable of responding to stimulation of all other cortical layers, thus displaying the largest input maps. Layer VI possessed functional connectivity intrinsically and with layer V. These data lead us to suggest that thalamic input may be boosted by its main target layer IV to start a sequence of excitation in layer IV, passing to the supragranular layers and finally reaching the infragranular layers. This sequence is likely to be backed-up by other simultaneous steps of transmission including a layer IV-to-V interaction. We proposed that the increasing size of the receptive fields when sampling granular, supragranular and infragranular layers in vivo, might have its functional basis in the laminar interactions described here in an in vitro preparation.

Animals↗
PubMed2000

Exploration of a novel environment leads to the expression of inducible transcription factors in barrel-related columns.

Tactile information acquired through the vibrissae is of high behavioral relevance for rodents. Numerous physiological studies have shown adaptive plasticity of cortical receptive field properties due to stimulation and/or manipulation of the whiskers. However, the cellular mechanisms leading to these plastic processes remain largely unknown. Although genomic responses are anticipated to take place in this sequel, virtually no data so far exist for freely behaving animals concerning this issue. Thus, adult rats were placed overnight in an enriched environment and most of them were also subjected to clipping of different sets of whiskers. This type of stimulation led to a specific and statistically significant increase in the expression of the protein products of the inducible transcription factors c-Fos, JunB, inducible cyclic-AMP early repressor and Krox-24 (also frequently named Zif268 or Egr-1), but not c-Jun. The response was found in columns of the barrel cortex corresponding to the stimulated vibrissae; it displayed a layer-specific pattern. However, no induction of transcription factors was observed in the subcortical relay stations of the whisker-to-barrel pathway, i.e. the trigeminal nuclei and the ventrobasal complex. These results strongly suggest that a coordinated transcriptional response is initiated in the barrel cortex as a consequence of processing of novel environmental stimuli.

Animals↗
PubMed2000

A stereological approach to human cortical architecture: identification and delineation of cortical areas.

Stereology offers a variety of procedures to analyze quantitatively the regional and laminar organization in cytoarchitectonically defined areas of the human cerebral cortex. Conventional anatomical atlases are of little help in localizing specific cortical areas, since most of them are based on a single brain and use highly observer-dependent criteria for the delineation of cortical areas. In consequence, numerous cortical maps exist which greatly differ with respect to number, position, size and extent of cortical areas. We describe a novel algorithm-based procedure for the delineation of cortical areas, which exploits the automated estimation of volume densities of cortical cell bodies. Spatial sampling of the laminar pattern is performed with density profiles, followed by multivariate analysis of the profiles' shape, which locates the cytoarchitectonic borders between neighboring cortical areas at sites where the laminar pattern changes significantly. The borders are then mapped to a human brain atlas system comprising tools for three dimensional reconstruction, visualization and morphometric analysis. A sample of brains with labeled cortical areas is warped into the reference brain of the atlas system in order to generate a population map of the cortical areas, which describes the intersubject variability in spatial conformation of cortical areas. These population maps provide a novel tool for the interpretation of images obtained with functional imaging techniques.

Brain Mapping↗
PubMed2000

Unilateral upregulation of cyclooxygenase-2 following cerebral, cortical photothrombosis in the rat: suppression by MK-801 and co-distribution with enzymes involved in the oxidative stress cascade.

Cyclooxygenase-2 (COX-2) is an essential enzyme for prostaglandin synthesis from arachidonic acid, during which considerable amounts of superoxide are produced. During pathological conditions, superoxide and nitric oxide (NO) rapidly form peroxynitrite, a potent cytotoxin, causing symptoms referred to as oxidative stress response. Superoxide is controlled by enzymes such as manganese- or copper-zinc-dependent superoxide dismutase (Mn-SOD, CuZn-SOD), glutathione peroxidase (GPx) and antioxidants derived from heme oxygenase (HO) activity such as biliverdin and bilirubin. NO derives from 3 NO-synthases (NOS I-III) from which the calcium-dependent NOS-I and III are activated rapidly due to hyperexcitation. We studied the induction of COX-2 by immunohistochemistry at days 1, 2 and 5 following cortical photothrombosis in normal and MK-801 treated rats. The results showed a weak constitutive, neuronal expression of COX-2 in cortex and amygdala. Layers II+III contained considerably more COX-2 than infragranular layers. One and 2 days following injury COX-2 was highly upregulated in the supragranular layers of the whole injured hemisphere compared with sham-operated animals and compared to the contralateral unlesioned hemisphere, whereas at day 5 COX-2 levels had returned to baseline. MK-801 treatment caused a reduction in COX-2 upregulation at day one and by day 2 no significant differences between injured and contralateral hemisphere were measurable. COX-2 positive neurons were found in close association with NOS-I containing neurons and their fibers but were not colocalized. In addition, codistribution of COX-2 was found with HO-1, CuZn-SOD and GPx containing cells, whereas COX-2 was colocalized with HO-2 and/or MnSOD in cortical neurons.

Amygdala↗
PubMed2000

Recognition of emotional prosody and verbal components of spoken language: an fMRI study.

This study examined the neural areas involved in the recognition of both emotional prosody and phonemic components of words expressed in spoken language using echo-planar, functional magnetic resonance imaging (fMRI). Ten right-handed males were asked to discriminate words based on either expressed emotional tone (angry, happy, sad, or neutral) or phonemic characteristics, specifically, initial consonant sound (bower, dower, power, or tower). Significant bilateral activity was observed in the detection of both emotional and verbal aspects of language when compared to baseline activity. We found that the detection of emotion compared with verbal detection resulted in significant activity in the right inferior frontal lobe. Conversely, the detection of verbal stimuli compared with the detection of emotion activated left inferior frontal lobe regions most significantly. Specific analysis of the anterior auditory cortex revealed increased right hemisphere activity during the detection of emotion compared to activity during verbal detection. These findings illustrate bilateral involvement in the detection of emotion in language while concomitantly showing significantly lateralized activity in both emotional and verbal detection, in both the temporal and frontal lobes.

Adult↗
PubMed2000

Light and confocal laser-scanning microscopical evidences for complementary patterns of glial fibrillary acidic protein and Wisteria floribunda agglutinin labeled structures in human and rat brain.

We investigated the pattern of glial fibrillary acidic protein (GFAP) and Wisteria floribunda agglutinin (WFA) labeled structures in the superior colliculus and in the somatosensory cortex of humans and rats of different age groups using immunohistochemical methods, light and confocal laser-scanning microscopy. We never found a double labeling of WFA and GFAP positive structures neither in the superior colliculus nor in the cortex of both man and rat. The complementary pattern of WFA and GFAP labeling was present both at the macroscopic and microscopic level. We found a clear prevalence of either WFA or GFAP expression in the arborization of the astrocytes as well as in the pattern of lamination.

Age Factors↗
PubMed2000

Neurofilament protein distribution in the macaque monkey dorsolateral premotor cortex.

Regional and laminar distribution patterns of neurofilament proteins in the dorsolateral premotor cortex (PMd) were studied with monoclonal antibody SMI-32 in five adult macaque monkeys and compared with the cytoarchitectonical features of the PMd. Our goal was to reveal whether the increasing functional diversity of the PMd which electrophysiological studies have unravelled over the last years is reflected on a structural level by differences in the neurochemical phenotype. Differences in size, shape and packing density of immunopositive layer III and V pyramidal cells define areas much more clearly than do differences in cytoarchitecture. The PMd can be subdivided into a rostral and a caudal part at a level slightly anterior to the genu of the arcuate sulcus. The extent of these two areas matches the two cytoarchitectonically defined areas F7 and F2, respectively. Within area F2, differences in layer V immunoreactive neurons define a dorsal (F2d) and a ventral (F2v) region. The border between areas F2d and F2v lies at the superior precentral dimple and cannot be detected cytoarchitectonically in Nissl-stained sections. Neurofilament proteins are involved in the stabilization of the cytoskeleton of the axon and have been correlated with axonal size and conduction velocity of nerve fibres. This regional variability in the neurochemical phenotype of layer V within the caudal PMd may reflect a differential organization of the descending output from this part of the premotor cortex. It might also be related to differences in the motor control of voluntary arm and leg movements.

Animals↗