Biomedical subjects

Stefan Zysset

Publications and source records attributed to Stefan Zysset.

At least 19 recordsLinked to original sources

PubMed2007

The role of the posterior superior temporal sulcus in the processing of unmarked transitivity.

Is it living or not? The ability to differentiate between animate and inanimate entities is of considerable value in everyday life, since it allows for the dissociation of individuals that may willfully cause an action from objects that cannot. The present fMRI study aimed to shed light on the neural correlates of animacy at a relational-interpretive level, i.e. on the role of animacy in the establishment of relations between entities that are more or less likely to cause an event and differ in their potential to act volitionally. To this end, we investigated the processing of visually presented transitive German sentences (nominative-accusative structures) in which the factors animacy and argument order were manipulated. The relations between the arguments differed in that the animate subject either acted on an inanimate object (a very natural construction in terms of transitivity) or on an animate object (resulting in a sentence deviating from an unmarked transitive structure). Participants performed an acceptability judgment task. Violations of unmarked transitivity yielded a significant activation increase within the posterior left superior temporal sulcus (pSTS), thus suggesting a specific role of this cortical region in the relational use of animacy information. This result indicates that the influence of animacy as a relational feature differs from the impact of this parameter on the word level and is in line with other neuroimaging studies showing an engagement of the pSTS when a matching between syntax and semantics is required. A comparison between object- and subject-initial conditions further revealed a robust effect of argument order in the pars opercularis of the left inferior frontal gyrus (a subregion of Broca's area), thereby replicating previous findings demonstrating a sensitivity of this region to fine-grained language-specific linearization rules.

Adult↗

PubMed2006

Variability of the BOLD response over time: an examination of within-session differences.

Model-based analysis methods for fMRI data assume a priori knowledge of the time course of the hemodynamic response (HR) in reaction to experimental stimuli or events. This knowledge is incorporated into the hemodynamic response function (HRF), which is a common model of the HR. Although it is already known that the HR varies across individuals and brain regions, few studies have investigated how variations within one session affect the results of statistical analysis using the general linear model (GLM). In this study, we formally tested for a possible variation of the BOLD response during prolonged functional measurement (120 min). To provoke performance of simple visual, motor, and cognitive tasks, we opted for a combination of a variant of the Stroop task and rotating L's. In selected regions of interest, time courses were extracted and compared with regard to mean and maximum amplitudes throughout the time of functional measurement. Additionally, parameter estimates derived from the GLM were tested for differences over time. Although differences between conditions were found to be significant, results did not show significant variance due to a within-factor time. Similarly, a temporal change in the relation between conditions, in terms of an interaction between the within-factor time and the within-factor condition, was not detectable by a repeated measures ANOVA. Similar results were obtained for analysis of mean and maximum amplitudes as well as for the analyses of parameter estimates.

Adult↗

PubMed2006

Linguistic prominence and Broca's area: the influence of animacy as a linearization principle.

Previous neuroimaging findings suggest a sensitivity of the pars opercularis of the left inferior frontal gyrus (i.e. a core subregion of Broca's area) to a number of linguistic dependencies governing the linear sequencing of information in a sentence (e.g. subjects should precede objects; the participant role hierarchy should be respected). The present study used event-related fMRI to examine the hitherto untested hypothesis that the violation of a linearization principle that is purely semantic in nature (animate arguments should precede inanimate arguments) would also lead to increased pars opercularis activation. To this end, we manipulated the features animacy and argument order in German sentences and found a significant increase of activation in the pars opercularis for a violation of the animacy principle even when the other factors mentioned above were controlled for. This result therefore calls for a "supra-syntactic" account of pars opercularis function in the real-time understanding of sentences.

Adult↗

PubMed2006

The parcellation of cortical areas using replicator dynamics in fMRI.

In this paper, we show that replicator dynamics can be used as an exploratory analysis tool to detect subregions of cortical areas on the basis of the similarity between fMRI time series. As similarity measure, we propose to use canonical correlation, a multivariate extension to the typically employed Pearson's correlation coefficient. We applied the replicator process to data obtained from two different experimental paradigms in the search for subregions within the left lateral frontal cortex (LFC). In both cases, the replicator process resulted in a parcellation that corresponds to a recently suggested subdivision of the LFC in anterior-posterior direction. Most notably, these results were very consistent when compared across different measurements of a single subject and across a group of subjects.

Brain Mapping↗

PubMed2006

The neural implementation of multi-attribute decision making: a parametric fMRI study with human subjects.

Decision making is not a unitary entity but involves rather a series of interdependent processes. Decisions entail a choice between two or more alternatives. Within the complex series of decisional processes, at least two levels can be differentiated: a first level of information integration (process level) and a second level of information interpretation (control level), leading to a subsequent motor response or cognitive process. The aim of this study was to investigate the neural network of these decisional processes. In a single trial fMRI study, we implemented a simple decision-making task, where subjects had to decide between two alternatives represented on five attributes. The similarity between the two alternatives was varied systematically in order to achieve a parametric variation of decisional effort. For easy trials, the two alternatives differed significantly in several attributes, whereas for difficult trials, the two alternatives differed only in small details. The results show a distributed neural network related to decisional effort. By means of time course analysis different subprocesses within this network could be differentiated: regions subserving the integration of the presented information (premotor areas and superior parietal lobe) and regions subserving the interpretation of this information (frontolateral and frontomedial cortex, anterior insula, and caudate) as well as a region in the inferior frontal junction updating task rules.

Adult↗

PubMed2006

Native and non-native reading of sentences: an fMRI experiment.

The processing of syntactic and semantic information in written sentences by native (L1) and non-native (L2) speakers was investigated in an fMRI experiment. This was done by means of a violation paradigm, in which participants read sentences containing either a syntactic, a semantic, or no violation. The results of this study were compared to those of a previous fMRI study, in which auditory sentence processing in L1 and L2 was investigated. The results indicate greater activation for L2 speakers as compared to L1 speakers when reading sentences in several language- and motor-related brain regions. The processing of syntactically incorrect sentences elicited no reliably greater activation in language areas in L2 speakers. In L1 speakers, on the other hand, syntactic processing, as compared to semantic processing, was associated with increased activation in left mid to posterior superior temporal gyrus. In response to the processing of semantically incorrect sentences, both L2 and L1 speakers demonstrated increased involvement of left inferior frontal gyrus. The results of this study were compared to a previously conducted fMRI study, which made use of identical sentence stimuli in the auditory modality. Results from the two studies are in general agreement with one another, although some differences in the response of brain areas very proximal to primary perceptual processing areas (i.e. primary auditory and visual cortex) were observed in conjunction with presentation in the different modalities. The combined results provide evidence that L1 and L2 speakers rely on the same cortical network to process language, although with a higher level of activation in some regions for L2 processing.

Adolescent↗

PubMed2005

Towards quantification of blood-flow changes during cognitive task activation using perfusion-based fMRI.

Multi-slice perfusion-based functional magnetic resonance imaging (p-fMRI) is demonstrated with a color-word Stroop task as an established cognitive paradigm. Continuous arterial spin labeling (CASL) of the blood in the left common carotid artery was applied for all repetitions of the functional run in a quasi-continuous fashion, i.e., it was interrupted only during image acquisition. For comparison, blood oxygen level dependent (BOLD) contrast was detected using conventional gradient-recalled echo (GE) echo planar imaging (EPI). Positive activations in BOLD imaging appeared in p-fMRI as negative signal changes corresponding to an enhanced transport of inverted water spins into the region of interest, i.e., increased cerebral blood flow (CBF). Regional differences between the localization of activations and the sensitivity of p-fMRI and BOLD-fMRI were observed as, for example, in the inferior frontal sulcus and in the intraparietal sulcus. Quantification of CBF changes during cognitive task activation was performed on a multi-subject basis and yielded CBF increases of the order of 20-30%.

Adult↗

PubMed2005

Who did what to whom? The neural basis of argument hierarchies during language comprehension.

The present fMRI study aimed at identifying neural correlates of the syntax-semantics interface in language comprehension. This was achieved by examining what we refer to as "argument hierarchy construction", i.e., determining which participant in a sentence is the "Actor" and which is the "Undergoer" of the event expressed by the verb. In order to identify the neural bases of argument hierarchy processing, we manipulated three factors known to influence the complexity of argument hierarchy construction in German, namely argument order, verb class and morphological ambiguity. Increased argument hierarchization demands engendered enhanced activation in a network of inferior frontal, posterior superior temporal, premotor and parietal areas. Moreover, components of this network were differentially modulated by the individual factors. In particular, the left posterior superior temporal sulcus showed an enhanced sensitivity for morphological information and the syntactic realization of the verb-based argument hierarchy, while the activation of the left inferior frontal gyrus (pars opercularis) corresponded to linearization demands and was independent of morphological information. We therefore argue that, for German, posterior superior temporal and inferior frontal regions engage in the extraction of actorhood from morphosyntactic structure and in the sequential realization of hierarchical interpretive dependencies, respectively.

Adult↗

PubMed2005

Regional impairment of cerebrovascular reactivity and BOLD signal in adults after stroke.

BACKGROUND AND PURPOSE: Comparative studies across populations using functional magnetic resonance imaging (fMRI) rely on a similar relationship between blood oxygen level-dependent (BOLD) signal and neural activity. However, in elderly and patients with cerebrovascular disease, impaired cerebrovascular dynamics and neurovascular coupling may explain differences in BOLD contrast across populations and brain regions. The purpose of the study was to determine whether poststroke patients have regional heterogeneities of cerebrovascular reactivity (CVR) and their potential influence on voxel-wise motor-related BOLD signal. METHODS: Using fMRI, 8 fully recovered patients from stroke in the frontal lobe without cortical lesion in the regions of interest located in the primary sensorimotor cortex (SMC), supplementary motor area (SMA), and cerebellum (CRB) were compared with 8 healthy subjects. Motor-related BOLD signal changes (%SC) were evaluated during simple unimanual and bimanual tasks, and CVR was evaluated during hyperventilation (HV). Analyses were performed using Lipsia software in SMC, SMA, and CRB. RESULTS: In controls, amplitudes of BOLD signal were symmetrical in all regions of interest during all motor tasks and HV. In patients, %SC was decreased in SMC and SMA of the lesioned hemisphere despite their apparent anatomical integrity for all tasks. Impaired CVR was a predictor of impaired motor-related BOLD response in the SMC during contralateral movements (beta=-1.87; R=-0.75; P=0.03). CONCLUSIONS: These preliminary findings suggest that CVR heterogeneities may account for task-related BOLD signal changes in patients after stroke.

Adult↗

PubMed2005

Distinct fMRI responses to laughter, speech, and sounds along the human peri-sylvian cortex.

In this event-related fMRI study, 12 right-handed volunteers heard human laughter, sentential speech, and nonvocal sounds in which global temporal and harmonic information were varied whilst they were performing a simple auditory target detection. This study aimed to delineate distinct peri-auditory regions which preferentially respond to laughter, speech, and nonvocal sounds. Results show that all three types of stimuli evoked blood-oxygen-level-dependent responses along the left and right peri-sylvian cortex. However, we observed differences in regional strength and lateralization in that (i) hearing human laughter preferentially involves auditory and somatosensory fields primarily in the right hemisphere, (ii) hearing spoken sentences activates left anterior and posterior lateral temporal regions, (iii) hearing nonvocal sounds recruits bilateral areas in the medial portion of Heschl's gyrus and at the medial wall of the posterior Sylvian Fissure (planum parietale and parietal operculum). Generally, the data imply a differential regional sensitivity of peri-sylvian areas to different auditory stimuli with the left hemisphere responding more strongly to speech and with the right hemisphere being more amenable to nonspeech stimuli. Interestingly, passive perception of human laughter activates brain regions which control motor (larynx) functions. This observation may speak to the issue of a dense intertwining of expressive and receptive mechanisms in the auditory domain. Furthermore, the present study provides evidence for a functional role of inferior parietal areas in auditory processing. Finally, a post hoc conjunction analysis meant to reveal the neural substrates of human vocal timbre demonstrates a particular preference of left and right lateral parts of the superior temporal lobes for stimuli which are made up of human voices relative to nonvocal sounds.

Acoustic Stimulation↗

PubMed2005

The emergence of the unmarked: a new perspective on the language-specific function of Broca's area.

A number of neuroimaging studies have implicated an involvement of Broca's area, particularly of the pars opercularis of the left inferior frontal gyrus (IFG), in the processing of complex (permuted) sentences. However, functional interpretations of this region's role range from very general (e.g., in terms of working memory) to highly specific (e.g., as supporting particular types of syntactic operations). A dissociation of these competing accounts is often impossible because in most cases, the language internal complexity of permuted sentence structures is accompanied invariably by increasing costs of a more general cognitive nature (e.g., working memory, task difficulty, and acceptability). We used functional magnetic resonance imaging to explore the precise nature of the pars opercularis activation in the processing of permuted sentences by examining the permutation of pronouns in German. Although clearly involving a permutation operation, sentences with an initial object pronoun behave like simple, subject-initial sentences (e.g., in terms of acceptability) because of a rule stating that pronouns should generally precede non-pro-nominal arguments. The results of the experiment show that in contrast to non-pro-nominal permutations, sentences with a permuted pronoun do not engender enhanced pars opercularis activation. Our findings therefore speak against both language-related working memory and transformation-based accounts of this region's role in sentence comprehension. Rather, we argue that the pars opercularis of the left IFG supports the language-specific linearization of hierarchical linguistic dependencies.

Adult↗

PubMed2005

The effect of esmolol on cerebral blood flow, cerebral vasoreactivity, and cognitive performance: a functional magnetic resonance imaging study.

BACKGROUND: Esmolol is often applied perioperatively to maintain stable hemodynamic conditions in neurosurgical patients. Little is known, however, about its effects on cerebral circulation. The authors employed functional magnetic resonance imaging based on blood oxygenation level-dependent contrast to explore the effect of esmolol on the human brain. The purpose of the study was to investigate the effect of esmolol on cerebral blood flow, cerebral vasoreactivity, and cognitive performance. METHODS: Ten healthy volunteers were investigated in two separate experimental sessions using functional magnetic resonance imaging. During the first experimental session, a hyperventilation task and a cognitive task, subjects had to perform both tasks twice, once after administration of an esmolol bolus of 1 mg/kg followed by a continuous infusion of 150 microg.kg.min and once without beta-blockade, in a random order. During the second experimental session subjects were scanned at resting state after administration of esmolol. Furthermore, the effect of the esmolol dose on hemodynamic changes caused by beta-adrenergic stimulation with orciprenaline was investigated. RESULTS: Esmolol decreased heart rate and blood pressure during the various experimental conditions and blunted the increase in heart rate and blood pressure caused by orciprenaline. Infusion of esmolol affects neither the blood oxygenation level-dependent contrast during the functional challenges nor the reaction times during the cognitive task. However, the esmolol bolus caused a brief blood oxygenation level-dependent contrast increase. CONCLUSION: The results indicate that effective beta-blockade with esmolol does not affect cerebral blood flow, cerebrovascular reactivity, or cognitive performance.

Adrenergic beta-Agonists↗

PubMed2004

Action-induced blindness with lateralized stimuli and responses.

Previous dual-task studies showed that the selection and/or execution of a response interfere with concurrent visual encoding (action-induced blindness). Four experiments examined how the lateralization of stimuli and responses might affect action-induced blindness. Participants responded to tones (S1) by pressing keys with the left or right hand (R1), and simultaneously identified stimuli (S2) presented to the left or right visual field. Results revealed a complex pattern of cross-talk effects between response preparation and visual encoding. Firstly, preparing a response generally impaired concurrent visual encoding. Secondly, action-induced blindness was equally present for ipsilaterally and contralaterally presented stimuli. Thirdly, response preparation facilitated processing of visual stimuli at ipsilateral locations, probably a case of action-centered attention. Finally, the facilitatory effect of R1-S2 correspondence on visual encoding was complemented by a S2-R1 correspondence effect on response execution. Thus, acting while seeing can have both beneficial and detrimental effects on identification performance at the same time.

Adolescent↗

PubMed2004

Where action impairs visual encoding: an event-related fMRI study.

Behavioral experiments revealed an impairment in a perceptual task when a motor task has to be planned in parallel. In two event-related fMRI experiments healthy participants performed a GO-NOGO motor task and a visual identification task. Thus, we were able to investigate the influence of a motor task on visual identification. The paradigm allowed to compare visually identical trials with and without a concurrently performed motor response. In Experiment 1, the visual task focused on shape identification, whereas in Experiment 2, the visual task focused on color identification. We found an action-dependent BOLD response modulation in extrastriate visual areas (V3, V3A in Experiment 1 and additionally V4 in Experiment 2). Thus, results demonstrate that the planning of an action has modulatory effects in brain areas concerned with early processes in visual encoding.

Adult↗

PubMed2004

Gender differences in the activation of inferior frontal cortex during emotional speech perception.

We investigated the brain regions that mediate the processing of emotional speech in men and women by presenting positive and negative words that were spoken with happy or angry prosody. Hence, emotional prosody and word valence were either congruous or incongruous. We assumed that an fRMI contrast between congruous and incongruous presentations would reveal the structures that mediate the interaction of emotional prosody and word valence. The left inferior frontal gyrus (IFG) was more strongly activated in incongruous as compared to congruous trials. This difference in IFG activity was significantly larger in women than in men. Moreover, the congruence effect was significant in women whereas it only appeared as a tendency in men. As the left IFG has been repeatedly implicated in semantic processing, these findings are taken as evidence that semantic processing in women is more susceptible to influences from emotional prosody than is semantic processing in men. Moreover, the present data suggest that the left IFG mediates increased semantic processing demands imposed by an incongruence between emotional prosody and word valence.

Adult↗

PubMed2004

Shortening intertrial intervals in event-related cognitive studies with near-infrared spectroscopy.

Functional near-infrared spectroscopy (fNIRS) enables imaging of brain activation by measuring changes in the concentration of oxy- and deoxy-hemoglobin (Hb). Shortening the length of the intertrial interval (ITI) seems to be a precondition for further cognitive event-related fNIRS experiments because it leads to higher statistical power. Therefore, this study investigated whether the ITI may be reduced from 12, 6, 4 s to at least 2 s. Brain activation was examined with a NIRO-300 spectrometer at the lateral prefrontal cortex in 17 healthy subjects during a randomized event-related color-word matching Stroop task. In the left lateral prefrontal cortex, the concentration of deoxy-Hb decreased significantly stronger during incongruent than neutral trials for an ITI of 12, 6, and 2 s due to coping with interference. For 4 s of ITI, no hemodynamic interference effect was detected, which was paralleled by low behavioral interference. Further, we examined whether the length of the ITI influenced the mean hemodynamic response. Shortening the ITI reduced the amplitude of oxy-Hb in contrast to deoxy-Hb, which remained almost unaltered. Summarizing results, randomized event-related cognitive fNIRS studies enable short ITIs particularly if changes in deoxy-Hb are considered.

Adult↗

PubMed2004

Prefrontal activation due to Stroop interference increases during development--an event-related fNIRS study.

Although it is well known that executive processes supported by the frontal lobe develop during childhood and adolescence, only one functional imaging study has used the Stroop task to investigate the relationship between frontal lobe function and cognition from a developmental point of view. Hence, we measured brain activation in the lateral prefrontal cortex of children with functional near-infrared imaging during an event-related, color-word matching Stroop task and compared results with a previous study, conducted with the same paradigm in adults. In children, the Stroop task elicited significant brain activation in the left lateral prefrontal cortex comparable to adults. However, the hemodynamic response occurred later in children than adults. Individual brain activation due to Stroop interference varied much more in children than adults, which was paralleled by a higher behavioral variance in children. Data suggest that children differed in their individual cognitive development independent of their chronological age more than adults. Brain activation due to Stroop interference increased with age in the dorsolateral prefrontal cortex in correlation with an improvement of behavioral performance. In conclusion, our results indicate that neuromaturational processes regarding resolution of Stroop interference may depend on increased ability to recruit frontal neural resources.

Adolescent↗

PubMed2003

Functional specialization within the anterior medial prefrontal cortex: a functional magnetic resonance imaging study with human subjects.

This study investigated the functional neuroanatomy of the anterior medial prefrontal cortex (aMPFC). Previous studies have shown that the aMPFC is involved in evaluative judgment and self-referential processes. Specifically, different sections of the aMPFC are differentially influenced by attention demanding processes. Whereas the dorsal section is supposed to be involved in self-referential processes, the ventral section is assumed to be attenuated during attention demanding processes. The present study investigates the involvement of the dorsal and ventral aMPFC in evaluative judgment by using functional magnetic resonance imaging with spin-echo echo-planar-imaging. Processes involved in evaluative judgment are attention-demanding, self-referential and activate regions in the dorsal and ventral section of the aMPFC. Attention demanding tasks do not necessarily lead to an attenuation of the ventral section of the aMPFC, a region mainly involved in emotional and affective processing.

Adult↗