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Katrin Amunts

Publications and source records attributed to Katrin Amunts.

At least 37 records · Page 2Linked to original sources
PubMed2005

The role of the left Brodmann's areas 44 and 45 in reading words and pseudowords.

In this functional magnetic resonance imaging (fMRI) study, we investigated the influence of two task (lexical decision, LDT; phonological decision, PDT) on activation in Broca's region (left Brodmann's areas [BA] 44 and 45) during the processing of visually presented words and pseudowords. Reaction times were longer for pseudowords than words in LDT but did not differ in PDT. By combining the fMRI data with cytoarchitectonic anatomical probability maps, we demonstrated that the left BA 44 and BA 45 were stronger activated for pseudowords than for words. Separate analyses for LDT and PDT revealed that the left BA 44 was activated in both tasks, whereas left BA 45 was only involved in LDT. The results are interpreted within a dual-route model of reading with the left BA 44 supporting grapheme-to-phoneme conversion and the left BA 45 being related to explicit lexical search.

Adult↗
PubMed2005

Dependence of amygdala activation on echo time: results from olfactory fMRI experiments.

Echo time dependence of the BOLD sensitivity is an important topic in fMRI whenever brain regions are considered where the EPI data quality suffers from susceptibility gradients. Here, an fMRI study is presented showing that a reduced echo time EPI sequence significantly enhances the statistical inference in subcortical (limbic) brain regions, with special focus on the amygdala. As a consequence, to facilitate whole-brain fMRI with optimal echo times, a sequence with slice-dependent echo time is demonstrated with a focus on structures suffering from susceptibility changes. The applicability of this method is shown in a second fMRI study aimed at both, cortical, and limbic brain regions. The results are in good agreement with theoretical descriptions of the BOLD sensitivity under the influence of susceptibility gradients.

Adult↗
PubMed2005

White matter fiber tracts of the human brain: three-dimensional mapping at microscopic resolution, topography and intersubject variability.

The position and extent of individual fiber tracts within the white matter of human brains can be identified in vivo using diffusion tensor imaging (DTI) and fiber tracking methods. Previous to this study, however, the lack of three-dimensional (3-D) probability maps precluded comparing the anatomical precision of MRI studies with microscopically defined fiber tracts in human postmortem brains. The present study provides 3-D registered maps of the topography, course and intersubject variability of major fiber tracts, which were identified at microscopic resolution. The analyzed tracts include the corticospinal tract, optic and acoustic radiations, fornix, cingulum, corpus callosum, superior longitudinal, superior and inferior occipito-frontal and uncinate fascicles; sources and targets of fiber tracts include the lateral and medial geniculate nuclei and mamillary bodies. Tracts and nuclei were identified in serial myelin-stained histological sections of ten postmortem brains. The sections were 3-D reconstructed and registered to a standardized stereotaxic space of an in vivo MR reference brain by means of linear and non-linear, elastic transformations. The individual fiber tracts and nuclei were superimposed in the reference space, and probability maps were generated as a quantitative measure of intersubject variability for each voxel of the stereotaxic space. This study presents the first stereotaxic atlas of the course, location and extent of fiber tracts and related nuclei based on microscopically defined localization and topographic data taken at multiple levels on each of the three orthogonal planes. The maps are useful for evaluating and identifying fiber bundles in DTI, for localizing subcortical lesions visible in anatomical MR images and for studying neuronal connectivity.

Adult↗
PubMed2005

The human parietal operculum. I. Cytoarchitectonic mapping of subdivisions.

The human secondary somatosensory cortex (SII) is located on the parietal operculum, as shown by intraoperative stimulation and functional imaging studies. The position and extent of the anatomical correlates of this functionally defined region, however, are still unknown. We have therefore histologically mapped the putative anatomical correlates of the SII cortex in cell-body-stained histological sections of 10 human postmortem brains using quantitative cytoarchitectonic analysis. The gray level index (GLI), which is an indicator of the volume fraction of nerve cell bodies, was measured in the parietal operculum. GLI profiles as measures of the laminar pattern of the cortex were extracted perpendicular to cortical layers. Cytoarchitectonic borders were detected observer-independently by multivariate statistical analysis of the laminar profiles. Four cytoarchitectonic areas (termed OP 1-4) were identified. This cytoarchitectonic heterogeneity of the parietal operculum corresponds to results of functional imaging studies on the human SII cortex and data from non-human primates where multiple subregions within SII have been demonstrated by electrophysiological and connectivity studies.

Brain Mapping↗
PubMed2005

The human parietal operculum. II. Stereotaxic maps and correlation with functional imaging results.

In this study we describe the localization of the cytoarchitectonic subdivisions of the human parietal operculum in stereotaxic space and relate these anatomically defined cortical areas to the location of the functionally defined secondary somatosensory cortex (SII cortex) using a meta-analysis of functional imaging results. The human parietal operculum consists of four distinct cytoarchitectonic areas (OP 1-4) as shown in the preceding publication. The 10 cytoarchitectonically examined brains were 3-D-reconstructed and spatially normalized to the T1-weighted single-subject template of the Montreal Neurological Institute (MNI). A probabilistic map was calculated for each area in this standard stereotaxic space. A cytoarchitectonic summary map of the four cortical areas on the human parietal operculum which combines these probabilistic maps was subsequently computed for the comparison with a meta-analysis of functional locations of SII. The meta-analysis used the results from 57 fMRI and PET studies and allowed the comparison of the functionally defined SII region to the cytoarchitectonic map of the parietal operculum. The functional localization of SII showed a good match to the cytoarchitectonically defined region. Therefore the cytoarchitectonic maps of OP 1-4 of the human parietal operculum can be interpreted as an anatomical correlate of the (functionally defined) human SII region. Our results also suggest that the SII foci reported in functional imaging studies may actually reflect activations in either of its architectonic subregions.

Brain Mapping↗
PubMed2005

A new SPM toolbox for combining probabilistic cytoarchitectonic maps and functional imaging data.

Correlating the activation foci identified in functional imaging studies of the human brain with structural (e.g., cytoarchitectonic) information on the activated areas is a major methodological challenge for neuroscience research. We here present a new approach to make use of three-dimensional probabilistic cytoarchitectonic maps, as obtained from the analysis of human post-mortem brains, for correlating microscopical, anatomical and functional imaging data of the cerebral cortex. We introduce a new, MATLAB based toolbox for the SPM2 software package which enables the integration of probabilistic cytoarchitectonic maps and results of functional imaging studies. The toolbox includes the functionality for the construction of summary maps combining probability of several cortical areas by finding the most probable assignment of each voxel to one of these areas. Its main feature is to provide several measures defining the degree of correspondence between architectonic areas and functional foci. The software, together with the presently available probability maps, is available as open source software to the neuroimaging community. This new toolbox provides an easy-to-use tool for the integrated analysis of functional and anatomical data in a common reference space.

Brain↗
PubMed2005

High-resolution MRI reflects myeloarchitecture and cytoarchitecture of human cerebral cortex.

Maps of cytoarchitectonically defined cortical areas have proven to be a valuable tool for anatomic localization of activated brain regions revealed by functional imaging studies. However, architectonic data require observations in a sample of postmortem brains. They can only be used reliably for comparison with functional data as probabilistic maps after spatial normalization to a common reference space. The complete architectonic analysis of an individual living brain has not been achievable to date, because the relationship remains unclear between laminar gray value changes of cerebral cortex in magnetic resonance (MR) images and those of cyto- and myeloarchitectonic histologic sections. We examined intensity profiles through the cortex in five imaging modalities: in vivo T1 and postmortem T2 MRI, one cell body stain, and two myelin stains. After visualizing the dissimilarities in the shapes of these profiles using a canonical analysis, differences between the profiles from the different image modalities were compared quantitatively. Subsequently, the profiles extracted from the in vivo T1-weighted images were estimated from profiles extracted from cyto- and myeloarchitectonic sections using linear combinations. We could verify statistically the mixed nature of the cortical T1 signal obtained in vivo: The MR intensity profiles were significantly more similar to myeloarchitectonic than to cytoarchitectonic profiles, but a weighted sum of both fitted the T1 profiles best.

Brain Mapping↗
PubMed2005

Analysis of neuroreceptor PET-data based on cytoarchitectonic maximum probability maps: a feasibility study.

Three-dimensional maximum probability maps (MPMs) of cytoarchitectonically defined cortical regions based on postmortem histological studies have recently been made available in the stereotaxic reference space of the Montreal Neurological Institute (MNI) single subject template. This permits the use of cytoarchitectonic maps for the analysis of functional in vivo datasets, including neuroreceptor positron emission tomography (PET) studies. In this feasibility study, we used 5-hydroxytryptamine 2A (5-HT2A) receptor PET to test the applicability of maximum cytoarchitectonic probability maps for quantitative analysis. As the outcome parameter, we extracted local distribution volume ratios (DVRs) from 19 cytoarchitectonically defined volumes of interest (VOIs) per hemisphere from five healthy subjects. The experimental design included a forward ('PET to atlas' normalization) and a backward ('atlas to PET' normalization) procedure to double-check the stability of transformation and overlay. Resulting DVRs were compared with receptor densities (RDs) obtained from postmortem [3H]ketanserin autoradiography of multiple areas. Correlations between the bi-directional normalization procedures (r = 0.89; 38 VOIs) as well as between in vivo and vitro data (nine VOIs; r = 0.64 and r = 0.47 for forward and backward procedure, respectively) suggest that the implementation of cytoarchitectonic maximum probability maps is a promising method for an accurate and observer-independent analysis of neuroreceptor PET data.

Adult↗
PubMed2005

Human V5/MT+: comparison of functional and cytoarchitectonic data.

To date, the delineation of the human visual "motion area" still relies on functional paradigms originally devised to identify monkey area MT. Using fMRI, we have identified putative human area V5/MT+ in normals by modelling the BOLD responses to alternating radially moving and stationary dot patterns. Functional activations were compared with cytoarchitectonic probability maps of its putative correlate area hOc5, which was calculated based upon data from histological sections of ten human post-mortem brains. Bilateral visual cortex activations were seen in the single subject dynamic versus stationary contrasts and in the group random-effects analysis. Comparison of group data with area hOc5 revealed that 19.0%/39.5% of the right/left functional activation was assigned to the right/left hOc5. Conversely, 83.2%/53.5% of the right/left hOc5 was functionally activated. Comparison of functional probability maps (fPM) with area hOc5 showed that 28.6%/18.1% of the fPM was assigned to hOc5. In turn, 84.9%/41.5% of the area hOc5 was covered by the respective fPM. Thus, random-effects data and fPMs yielded similar results. The present study shows for the first time the correspondence between the functionally defined human V5/MT+ and the post-mortem cytoarchitectonic area hOc5.

Adolescent↗
PubMed2005

Broca's region: from action to language.

Broca's region, classically considered a motor speech-production area, is involved in action understanding and imitation. It also seems to help in sequencing of actions. Broca's region might have evolved for interindividual communication, both by gestures and speech.

Animals↗
PubMed2004

Analysis of neural mechanisms underlying verbal fluency in cytoarchitectonically defined stereotaxic space--the roles of Brodmann areas 44 and 45.

We investigated neural activations underlying a verbal fluency task and cytoarchitectonic probabilistic maps of Broca's speech region (Brodmann's areas 44 and 45). To do so, we reanalyzed data from a previous functional magnetic resonance imaging (fMRI) [Brain 125 (2002) 1024] and from a cytoarchitectonic study [J. Comp. Neurol. 412 (1999) 319] and developed a method to combine both data sets. In the fMRI experiment, verbal fluency was investigated in 11 healthy volunteers, who covertly produced words from predefined categories. A factorial design was used with factors verbal class (semantic vs. overlearned fluency) and switching between categories (no vs. yes). fMRI data analysis employed SPM99 (Statistical Parametric Mapping). Cytoarchitectonic maps of areas 44 and 45 were derived from histologic sections of 10 postmortem brains. Both the in vivo fMRI and postmortem MR data were warped to a common reference brain using a new elastic warping tool. Cytoarchitectonic probability maps with stereotaxic information about intersubject variability were calculated for both areas and superimposed on the functional data, which showed the involvement of left hemisphere areas with verbal fluency relative to the baseline. Semantic relative to overlearned fluency showed greater involvement of left area 45 than of 44. Thus, although both areas participate in verbal fluency, they do so differentially. Left area 45 is more involved in semantic aspects of language processing, while area 44 is probably involved in high-level aspects of programming speech production per se. The combination of functional data analysis with a new elastic warping tool and cytoarchitectonic maps opens new perspectives for analyzing the cortical networks involved in language.

Adult↗
PubMed2004

Outstanding language competence and cytoarchitecture in Broca's speech region.

Studies on brains of individuals with an exceptional mental capacity are of widespread interest. Here, we analyze the cytoarchitecture of areas 44 and 45 (anatomical correlates of Broca's speech region) of a person with a documented extraordinary competence in language performance (Emil Krebs, E.K.), and compared it with 11 control brains. Morphometry and multivariate statistical analysis revealed significant cytoarchitectonic differences between E.K. and the controls in left and right areas 44, in right 45, and in interhemispheric asymmetries. We conclude, that the exceptional language competence of E.K. may be related to distinct cytoarchitectonic features in Broca's region.

Adult↗
PubMed2003

Broca's region: cytoarchitectonic asymmetry and developmental changes.

Functional imaging and clinical studies in children and adults have provided evidence of developmental changes in the hemispheric specialization for language. Whereas cytoarchitectonic asymmetry has been demonstrated in Broca's region of adults, the anatomical correlates of developmental changes in language dominance are largely unknown. In the present postmortem study of 34 human brains (ages ranging from 3.5 months to 85 years), the cytoarchitecture of areas 44 and 45 as the putative anatomical correlates of Broca's region, their developmental changes, and interhemispheric asymmetry were analyzed. Asymmetry as estimated by Euclidean distances between feature vectors of cytoarchitectonic profiles of left and right areas 44 and 45 was already found in 1-year-old infants. Asymmetry tended to increase with age, which was significant in area 45, but not in area 44. An adult-like, left-larger-than-right asymmetry in the volume fraction of cell bodies [gray level index (GLI)] was reached at approximately 5 years in area 45 and 11 years in area 44. These time points indicate a delayed development of the cytoarchitectonic asymmetry in Broca's region in comparison with that of the primary motor cortex. It may be hypothesized that the delayed maturation is the microstructural basis of the development of language abilities and the influence of language practice on cytoarchitecture during childhood. Interhemispheric asymmetry in the cytoarchitecture of areas 44 and 45 continues to change throughout life. We conclude that the cytoarchitectonic asymmetry of areas 44 and 45 is a result of microstructural plasticity that endures throughout almost the whole lifespan.

Adult↗
PubMed2003

Regional cerebral blood flow correlations of somatosensory areas 3a, 3b, 1, and 2 in humans during rest: a PET and cytoarchitectural study.

The concept of functional connectivity relies on the assumption that cortical areas that are directly anatomically connected will show correlations in regional blood flow (rCBF) or regional metabolism. We studied correlations of rCBF of cytoarchitectural areas 3a, 3b, 1, and 2 in the brains of 37 subjects scanned with PET during a rest condition. The cytoarchitectural areas, delineated from 10 postmortem brains with statistical methods, were transformed into the same standard anatomical format as the resting PET images. In areas 3a, 3b, and 1, somatotopically corresponding regions were intercorrelated. Area 2 was correlated with the dorsal pre-motor area. These results were in accordance with the somatosensory connectivity in macaque monkeys. In contrast, we also found correlations between areas 3b and 1 with area 4a, and SMA, and among the left and right hand sector of areas 3a, 3b, and 1. Furthermore, there were no correlations between areas 3b, 1, and 2 with SII or other areas in the parietal operculum, nor of other areas known to be directly connected with areas 3a, 3b, 1, and 2 in macaques. This indicates that rCBF correlations between cortical areas during the rest state only partly reflect their connectivity and that this approach lacks sensitivity and is prone to reveal spurious or indirect connectivity.

Adult↗
PubMed2003

Within-task switching in the verbal domain.

Task-switching, a term that covers a wide range of different cognitive processes, is a topic of considerable current interest. We draw particular attention to verbal within-task switching in neurological patients and healthy volunteers. The paradigm employs two types of fluency tasks: (i) semantic category verbal fluency in which subjects covertly produce words from a predefined superordinate semantic category and (ii) automatic speech tasks in which subjects produce words from overlearned sequences. In the single-category conditions, words are produced from one category at a time; in the switching conditions, words are produced alternately from three categories. For example, the semantic categories could be fruits, cars, and furniture and the automatic categories could be days of the week, letters of the alphabet, and months of the year. In a previous fMRI study of healthy volunteers, the main group effect of switching (semantic category and automatic speech) relative to single-category fluency (semantic category and automatic speech) showed significant activations (p < 0.05 corrected) only in bilateral superior posterior parietal cortex, Brain 125, 1024-1038). There was no significant prefrontal activation as a main effect of switching. In this paper we present further results from that experiment which show a surprising lack of consistent frontal lobe switch activations in single-subject analyses. These findings are discussed in relation to other neuroimaging studies of task-switching and the role of convergent neuropsychological data from patients with neurodegenerative disease.

Brain↗
PubMed2003

Activation of Broca's area during the production of spoken and signed language: a combined cytoarchitectonic mapping and PET analysis.

Broca's area in the inferior frontal gyrus consists of two cytoarchitectonically defined regions-Brodmann areas (BA) 44 and 45. Combining probabilistic maps of these two areas with functional neuroimaging data obtained using PET, it is shown that BA45, not BA44, is activated by both speech and signing during the production of language narratives in bilingual subjects fluent from early childhood in both American Sign Language (ASL) and English when the generation of complex movements and sounds is taken into account. It is BA44, not BA45, that is activated by the generation of complex articulatory movements of oral/laryngeal or limb musculature. The same patterns of activation are found for oral language production in a group of English speaking monolingual subjects. These findings implicate BA45 as the part of Broca's area that is fundamental to the modality-independent aspects of language generation.

Adult↗
PubMed2003

Quantitative T1 mapping of hepatic encephalopathy using magnetic resonance imaging.

Changes are shown in the spin-lattice (T1) relaxation time caused by the putative deposition of manganese in various brain regions of hepatic encephalopathy (HE) patients using a novel and fast magnetic resonance imaging (MRI) method for quantitative relaxation time mapping. A new method, T1 mapping with partial inversion recovery (TAPIR), was used to obtain a series of T1-weighted images to produce T1 maps. Imaging of 15 control subjects and 11 patients was performed on a 1.5T MRI scanner. The measurement time per patient with this technique, including adjustments, was approximately 5 minutes. Regions of interest in the globus pallidus, the caudate nucleus, the posterior and anterior limbs of the internal capsule, the putamen, the frontal and occipital white matter, the white matter of the corona radiata, the occipital visual and frontal cortices, and the thalamus were interactively defined in the left hemisphere and analyzed with respect to their T1 values. T1 changes in the brains of HE patients can be determined quantitatively with TAPIR in short, clinically relevant measurement times. Significant correlations between the change in T1 and HE severity have been shown in the globus pallidus, the caudate nucleus, and the posterior limb of the internal capsule. No significant correlation of T1 with grade of HE was found in the putamen, frontal white matter, white matter of the corona radiata, white matter in the occipital lobe, the anterior limb of the internal capsule, visual cortex, thalamus, or frontal cortex. In conclusion, these measurements show that T1 mapping is feasible in short, clinically relevant acquisition times.

Adult↗