Biomedical subjects

Stefan Heim

Publications and source records attributed to Stefan Heim.

8 recordsLinked to original sources

PubMed2006

BA 44 in Broca's area supports syntactic gender decisions in language production.

The involvement of Broca's area in syntactic gender processing has been shown for metalinguistic decisions in language comprehension and for natural speech production. These studies, however, are not directly comparable owing to the different methods used. The present functional magnetic resonance imaging study investigated gender processing during language production with metalinguistic decisions instead of natural production. Participants saw pictures of real objects and made gender decisions (GEN) about the picture names. Activation was compared with nonlinguistic decisions about geometrical objects (BASE). Broca's area was activated in the contrast GEN > BASE. Using cytoarchitectonic probability maps, the activation was localized at Brodmann's area 44. The data suggest that Brodmann's area 44 in Broca's area is a shared neural correlate for gender processing in production and comprehension.

Adult↗

PubMed2006

Testing anatomically specified hypotheses in functional imaging using cytoarchitectonic maps.

The statistical inference on functional imaging data is severely complicated by the embedded multiple testing problem. Defining a region of interest (ROI) where the activation is hypothesized a priori helps to circumvent this problem, since in this case the inference is restricted to fewer simultaneous tests, rendering it more sensitive. Cytoarchitectonic maps obtained from postmortem brains provide objective, a priori ROIs that can be used to test anatomically specified hypotheses about the localization of functional activations. We here analyzed three methods for the definition of ROIs based on probabilistic cytoarchitectonic maps. (1) ROIs defined by the volume assigned to a cytoarchitectonic area in the summary map of all areas (maximum probability map, MPM), (2) ROIs based on thresholding the individual probabilistic maps and (3) spherical ROIs build around the cytoarchitectonic center of gravity. The quality with which the thus defined ROIs represented the respective cytoarchitectonic areas as well as their sensitivity for detecting functional activations was subsequently statistically evaluated. Our data showed that the MPM method yields ROIs, which reflect most adequately the underlying anatomical hypotheses. These maps also show a high degree of sensitivity in the statistical analysis. We thus propose the use of MPMs for the definition of ROIs. In combination with thresholding based on the Gaussian random field theory, these ROIs can then be applied to test anatomically specified hypotheses in functional neuroimaging studies.

Artifacts↗

PubMed2006

Head motion during overt language production in functional magnetic resonance imaging.

Head motion parameters (translation, rotation) during an event-related functional magnetic resonance imaging experiment of overt picture naming were investigated for two fixation conditions. We compared normal fixation with cushions and belts with the additional use of a bite-bar. Neither mean nor maximum values differed between the two conditions for any of the parameters. By applying the head motion parameters to the cytoarchitectonically defined volume of the left Brodmann area 44, we demonstrated volume overlap of 95% (normal fixation) to 100% (bite-bar) that did not differ significantly between fixation conditions. The data encourage further use of overt language production in functional magnetic resonance imaging with careful head fixation but no bite-bar.

Adult↗

PubMed2006

The brain differentiates human and non-human grammars: functional localization and structural connectivity.

The human language faculty has been claimed to be grounded in the ability to process hierarchically structured sequences. This human ability goes beyond the capacity to process sequences with simple transitional probabilities of adjacent elements observable in non-human primates. Here we show that the processing of these two sequence types is supported by different areas in the human brain. Processing of local transitions is subserved by the left frontal operculum, a region that is phylogenetically older than Broca's area, which specifically holds responsible the computation of hierarchical dependencies. Tractography data revealing differential structural connectivity signatures for these two brain areas provide additional evidence for a segregation of two areas in the left inferior frontal cortex.

Adult↗

PubMed2006

Prosodic pitch accents in language comprehension and production: ERP data and acoustic analyses.

We used event-related potentials (ERPs) and acoustic analyses to investigate the processing of prosodic pitch accents as a function of their position in a sentence. Accents in sentence-medial positions were characterized by a higher fundamental frequency (F0) and an increased duration. They elicited two different negative ERP components around 400 ms, depending on the predictability of the accent. When the accent was predictable, the negativity was fronto-laterally distributed and identified as the previously known Expectancy Negativity. Unpredictable accents elicited a more broadly distributed N400 with a central maximum, reflecting difficulties in semantic processing. For sentence-initial pitch accents, words had a higher F0 but of the same duration as sentence-initial words without pitch accents. These pitch accents elicited a P200 but no negativity in a 400 ms time window. The P200 was modulated by the onset latency of the F0 peak rather than its magnitude. We discuss the possibility of a delayed processing of sentence-initial accents when the actual occurrence of an F0 peak can be identified by comparing the F0 of the sentence-initial word to a reduced F0 of a word occurring later in the sentence.

Acoustic Stimulation↗

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

A dual-route account for access to grammatical gender: evidence from functional MRI.

Research investigating the neural correlates of grammatical gender processing has provided contradictory evidence with respect to activation in the left inferior frontal gyrus (IFG). A possible account for these discrepancies is a dual-route model proposing explicit vs implicit access to the gender information. In this event-related fMRI experiment, we investigated this issue by taking into account different processing strategies reported by the subjects. The participants performed two tasks, a gender judgement of German nouns and a non-lexical baseline task (spacing of consonant letter strings). Depending on the reported strategy (silent production of the definite determiner or direct access to the gender information), different patterns of activation in the left IFG were observed. Direct access to gender information yielded activation in the inferior tip of BA 44, whereas the verbalisation strategy elicited activation in the superior portion of BA 44, BA 45/47, and the fronto-median wall. These results speak in favour of a dual-route account for modelling the access to grammatical gender information during language comprehension.

Adolescent↗

PubMed2005

The structure and dynamics of normal language processing: insights from neuroimaging.

This paper reviews current psycholinguistic and neuroimaging evidence on language processing with particular focus on the relationship between production and comprehension. In the first part, different methods of psycholinguistic research are introduced and examples for psycholinguistic models (production: Levelt et al. 1999; comprehension: Friederici 2002) are sketched. In the second part, the neural correlates of semantic, phonological, and syntactic processing are reviewed. For semantics and phonology there seem to be different fronto-temporal networks which are shared in production and comprehension. The results for the processing of syntactic information are not entirely conclusive. Yet the data reveal that phonological strategies may be used in syntactic tasks. This finding opens the discussion of alternative, phonology-based strategies for language processing. Such strategies are accounted for by dual-route models featuring one direct and one indirect route which often involves phonological processing. This insight leads to some tentative conclusions about remediation strategies in dyslexics with selective (e.g., phonological) deficits.

Brain Mapping↗