Biomedical subjects

Cornelius Weiller

Publications and source records attributed to Cornelius Weiller.

54 records · Page 3Linked to original sources

PubMed2003

The human action recognition system and its relationship to Broca's area: an fMRI study.

Primate studies have identified populations of neurons that are capable of action recognition. These "mirror neurons" show spiking activity both when the monkey executes or observes a grasping movement. These neurons are located in the ventral premotor cortex, possibly the homologue of "Broca's area" in human. This led to the speculation that action recognition and language production share a common system [Trends Neurosci. 21 (1998), 188]. To test this hypothesis, we combined an action recognition with a language production (VERB) and a grasping movement task (MOVE) by using functional magnetic resonance imaging. Action recognition-related activation was observed in the left inferior frontal gyrus and on the border between the inferior frontal gyrus and precentral gyrus (defined as IFG/PG), the ventral occipitotemporal junction, the superior and inferior parietal cortex, and in the intraparietal sulcus in the left hemisphere. An overlap of activations due to the language production, movement execution, and action recognition was found in the parietal cortex, the left inferior frontal gyrus, and the IFG-PG border (IFG/PG). The activation peaks of action recognition and verb generation were always different in single subjects, but no consistent spatial relationship was detected, in accord with the hypothesis that action recognition and language production share a common functional architecture.

Algorithms↗

PubMed2003

Repeated premotor rTMS leads to cumulative plastic changes of motor cortex excitability in humans.

We explored the aftereffects of two premotor 1 Hz rTMS sessions on motor cortex excitability in healthy humans. In experiment 1, 11 healthy right-handed volunteers received 20-min submotor threshold 1 Hz rTMS trains over the left premotor cortex on 2 consecutive days. Left motor cortex excitability was determined at baseline, immediately after, 30, 60, 120 min, and 24 h after each rTMS session. We measured motor thresholds, amplitudes of motor-evoked potentials, silent periods, and paired-pulse excitability at interstimulus intervals (ISI) of 3-7, 10, and 15 ms. In experiment 2, 5 volunteers received two identical rTMS trains on Days 1 and 7. Measurements were carried out on Day 1 (first rTMS train), Day 2, and Day 7 (second rTMS train). In experiment 1 there was a selective increase of paired pulse facilitation at an ISI of 7 ms after rTMS lasting for less than 30 min on Day 1. This effect was also present after rTMS on Day 2. However, it persisted for at least 2 h. In experiment 2 the same extra facilitation was induced by rTMS on Days 1 and 7 but not on Day 2. It lasted for less than 30 min on both Day 1 and Day 7. We conclude that 1 Hz premotor rTMS leads to cumulative plastic changes of intrinsic motor cortex excitability when repeated within 24 h but not after 1 week, implying the formation of memory after the first rTMS train lasting more than a day but less than a week.

Adult↗

PubMed2003

The influence of extra- and intracranial artery disease on the BOLD signal in FMRI.

Functional MRI is based on the vascular response due to neuronal activation. The underlying mechanism of fMRI is the blood oxygenation level-dependent (BOLD) effect-a complex interplay between changes in the cerebral metabolisation rate of oxygen (CMRO2), neurovascular coupling, and the resulting hemodynamic response. An intact neurovascular coupling is essential for the detection of the BOLD signal and it seems likely that a disturbed cerebrovascular reserve capacity (CVRC) alters the BOLD response. We tested the hypothesis that extra- or intracranial artery disease influences the BOLD signal. Twenty-one patients with extra- or intracranial stenosis were studied with BOLD sensitive T2*-weighted MRI. All patients presented with transient or prolonged reversible ischemic symptoms ipsilateral to the artery disease but were asymptomatic at the time point of the MRI study. fMRI was performed employing a simple motor task (fist closure right and left). Additionally, the CVRC was assessed applying carbogen gas during serial T2*-weighted MRI for the calculation of CO(2) reactivity maps of the relative signal change. Signal differences between both hemispheres were compared in individual subjects and with healthy subjects. Patients with disturbed CVRC in the CO(2) reactivity maps showed either a significantly reduced (n = 5) or a negative (n = 1) BOLD signal in the affected compared to the unaffected primary sensorimotor cortex during fist closure. Patients with intact CVRC showed no significant BOLD signal differences between affected and unaffected hemisphere. Extra- or intracranial artery disease influences CVRC and consequently the BOLD signal. This observation is important for the clinical application of fMRI paradigms.

Adult↗

PubMed2003

Broca's area and the language instinct.

Language acquisition in humans relies on abilities like abstraction and use of syntactic rules, which are absent in other animals. The neural correlate of acquiring new linguistic competence was investigated with two functional magnetic resonance imaging (fMRI) studies. German native speakers learned a sample of 'real' grammatical rules of different languages (Italian or Japanese), which, although parametrically different, follow the universal principles of grammar (UG). Activity during this task was compared with that during a task that involved learning 'unreal' rules of language. 'Unreal' rules were obtained manipulating the original two languages; they used the same lexicon as Italian or Japanese, but were linguistically illegal, as they violated the principles of UG. Increase of activation over time in Broca's area was specific for 'real' language acquisition only, independent of the kind of language. Thus, in Broca's area, biological constraints and language experience interact to enable linguistic competence for a new language.

Adult↗

PubMed2003

Functional properties and interaction of the anterior and posterior intraparietal areas in humans.

In the monkey the lateral bank of the anterior part of the intraparietal sulcus (area AIP), contains neurons that are involved in visually guided, object-related hand movements. It has also been shown that neurons in the caudal part of the intraparietal sulcus (area CIP) preferentially respond to 3D surface orientation. According to these results, it has been hypothesized that neurons in area CIP primarily encode the 3D features of an object and forwards this information to area AIP. AIP then utilizes this information for appropriate hand actions towards the object. Based on analogies to these primate studies, recent neuroimaging studies have suggested human homologues of areas AIP and CIP, however, the functional interaction between these areas remains unclear. Our event related fMRI study was designed to address specifically the question, how CIP and AIP interact in the process of adjustment of hand orientation towards objects. Volunteers were asked to perform three tasks: discrimination of surface orientation, imaging of visually guided hand movements and execution of visually guided hand movements. Our data show that the human AIP was activated both during discrimination of surface orientation and during the subsequent spatial adjustment of the thumb and index finger position towards the surface orientation. In contrast, human CIP was activated by the surface orientation but not by spatial adjustment of finger position. These data clearly indicate that the function of human CIP is more involved in coding 3D features of the objects, whereas human AIP is more involved in visually guided hand movements, similar to its role in the monkey.

Adult↗

PubMed2003

Noninvasive monitoring of cerebral oxygenation during vasomotor reactivity tests by a new near-infrared spectroscopy device.

BACKGROUND: Spatially resolved spectroscopy is a recently developed technique for noninvasive monitoring of cerebral tissue oxygenation using the photon diffusion theory. METHODS: We studied this technique with a new, commercial near-infrared spectroscopy (NIRS) device during vasomotor reactivity tests in 28 healthy volunteers (mean age 31.0 years; SD 10.6 years) and compared it with values assessed by the modified Beer-Lambert law and indices from simultaneous transcranial Doppler sonography of both middle cerebral arteries. We measured O(2) reactivity as percentage change of cerebral blood flow velocity (CBFV), as absolute change in the concentrations (measured in micromol/l) of oxygenated (HbO(2)), deoxygenated (Hb) and total hemoglobin (HbT), and as change in the tissue oxygenation index (TOI) during inhalation of 100% oxygen. CO(2) reactivity was calculated as percentage change of CBFV (NCR), as absolute change in the concentrations of HbO(2), Hb, and HbT (micromol/l), and as change in TOI (%) per 1% increase in end-tidal CO(2). RESULTS: One hundred percent oxygen inhalation lead to a decrease in CBFV (mean +/- SD: left -8.0 +/- 7.0%, p = 0.000; right -9.6 +/- 7.6%, p = 0.000), an increase in HbO(2) (0.99 +/- 1.07 micromol/l), Hbdiff (2.23 +/- 1.72 micromol/l), and TOI (3.1 +/- 1.5%), and a decrease in Hb (-1.22 +/- 0.74 micromol/l), significant from baseline values (p = 0.0000). CO(2) reactivity was: NCR left 25.4 +/- 14.7%; NCR right 25.9 +/- 13.4%; HbO(2) 1.99 +/- 0.97 micromol/l; Hb -1.24 +/- 0.81 micromol/l; HbT 0.81 +/- 1.0 micromol/l, and TOI 3.7 +/- 2.2%. O(2) reactivity in TCD did not correlate with NIRS reactivities (Pearson p > 0.05), but NCR did correlate with changes in HbO(2), Hb, and TOI (Pearson p < 0.01). TOI was closely related to indices derived from the Beer-Lambert law (Pearson p < 0.03), but not with mean arterial blood pressure or skin blood flow during vasomotor reactivity tests. CONCLUSION: Spatially resolved spectroscopy provides an encouraging, noninvasive new tool to study cerebral tissue oxygenation during vasomotor reactivity tests consistent with physiological changes.

Adult↗

PubMed2003

Sensitivity and interrater agreement of CT and diffusion-weighted MR imaging in hyperacute stroke.

BACKGROUND AND PURPOSE: Previous acute stroke studies found diffusion-weighted (DW) imaging superior to CT for detection of early ischemic signs (EIS). However, these findings were confounded by a large time interval in favor of DW imaging. We compared DW images and CT scans obtained with a short time delay in patients with acute stroke to define the sensitivity and interrater agreement of both imaging techniques. METHODS: CT scans and DW images were obtained within 6 hours of symptom onset in 46 patients with acute stroke. Three neuroradiologists and three neurologists reviewed the images for EIS in five regions of the middle cerebral artery (MCA) territory and estimated the extent of EIS (< or > one-third of the MCA territory). RESULTS: The mean delay between imaging with both modalities was 24.5 minutes (range, 10-41 minutes). Forty-five of 46 patients had an ischemic stroke. EIS were seen on 33 of 45 CT scans (73% sensitivity; 95% confidence interval [CI]: 58-85%) and on 42 of 45 DW images (93% sensitivity; 94% CI: 82-99%). Interrater agreement was moderate (kappa = 0.57) for CT and excellent (kappa = 0.85) for DW imaging. CT studies had a moderate interrater agreement for estimation of EIS greater than one-third of the MCA territory (kappa = 0.40), whereas DW imaging showed good results (kappa = 0.68). Sensitivity for detection of greater than one-third of the MCA territory was equally poor (57%, 95% CI: 29-82%) for both CT and DW imaging. CONCLUSION: DW imaging helped identify EIS with higher sensitivity than that of CT. The interrater variability of the one-third rule was high for CT, and thus the clinical applicability of CT is limited. Our results support the application of stroke MR imaging for the treatment of patients with acute stroke.

Acute Disease↗

PubMed2003

Horner syndrome related to ipsilateral carotid wall hematoma after stent placement for the treatment of carotid stenoses.

BACKGROUND AND PURPOSE: We prospectively studied the incidence and natural history of Horner syndrome following stent-supported percutaneous angioplasty of the carotid artery (SPAC). We assessed the hypothesis that postinterventional Horner syndrome is related to ipsilateral carotid wall hematoma. METHODS: We performed duplex sonography of the carotid arteries and clinical examination in 28 consecutive patients before and 4 hours +/- 2, 24 hours +/- 2, and 7 days +/- 1 after SPAC. RESULTS: Within 24 hours +/- 2 after SPAC, 11 of the 28 patients developed ipsilateral Horner syndrome. Ten of these 11 patients had a postinterventional sonographic appearance of a carotid wall hematoma, whereas only two of the 17 patients without Horner syndrome had this finding (P <.001). In all patients, both Horner syndrome and carotid wall hematoma had resolved 7 days +/- 1 after SPAC. CONCLUSION: Horner syndrome appears to be a common yet transient event after SPAC. Although postinterventional Horner syndrome is significantly related to ipsilateral carotid wall hematoma, causality of the procedure-related formation of a carotid wall hematoma and oculosympathetic disturbance remains unproven.

Adult↗

PubMed2002

The role of medial temporal lobe structures in implicit learning: an event-related FMRI study.

The medial temporal lobe (MTL) has been associated with declarative learning of flexible relational rules and the basal ganglia with implicit learning of stimulus-response mappings. It remains an open question of whether MTL or basal ganglia are involved when learning flexible relational contingencies without awareness. We studied learning of an explicit stimulus-response association with fMRI. Embedded in this explicit task was a hidden structure that was learnt implicitly. Implicit learning of the sequential regularities of the "hidden rule" activated the ventral perirhinal cortex, within the MTL, whereas learning the fixed stimulus-response associations activated the basal ganglia, indicating that the function of the MTL and the basal ganglia depends on the learned material and not necessarily on the participants' awareness.

Adult↗

PubMed2002

Short-term effect of cigarette smoking on CO(2)-induced vasomotor reactivity in man: a study with near-infrared spectroscopy and tanscranial Doppler sonography.

Cigarette smoking is a major risk factor for stroke, and quitting reduces the stroke risk within a few years. The aim of our study was to clarify whether CO(2)-induced vasomotor reactivity (VMR) is impaired in smokers after smoking a cigarette as a possible factor of an increased stroke risk. We compared VMR of 23 healthy smokers assessed at baseline, immediately, and 30 min after smoking a cigarette (1.2 mg nicotine) with values from nonsmoking, age-matched controls (n=24), obtained at identical time intervals. Cerebral blood flow velocities (CBFV) of both middle cerebral arteries (transcranial Doppler sonography), changes in concentration of cerebral oxygenated, deoxygenated, and total hemoglobin (HbO(2), Hb, and HbT, near-infrared spectroscopy), mean arterial blood pressure (MAP), and skin blood flow were recorded during normo- and hypercapnia. VMR was calculated as percentage change in CBFV and as micromolar change in concentration of HbO(2), Hb, and HbT per 1% increase in endtidal CO(2). CBFV in smokers was increased at baseline (left, p<0.05; right, p=0.05), immediately (p<0.01), and 30 min after smoking (p<0.05) as compared with nonsmokers. MAP rose immediately after smoking (p<0.01) and declined after 30 min. VMR in smokers at baseline did not differ from controls, decreased immediately after smoking (p<0.05), and normalized after 30 min (p>0.05). Increased baseline CBFV in smokers after smoking might be due to arteriolar dilation, increased MAP, and possibly constriction of basal cerebral arteries. Impaired VMR for about 30 min after smoking reflects endothelial dysfunction. This might contribute to the enhanced stroke risk in smokers.

Adult↗

PubMed2002

Visuomotor control within a distributed parieto-frontal network.

The aim of this functional magnetic resonance imaging study was to investigate differences in visuomotor control with increasing task complexity. Twelve right-handed volunteers were asked to perform their signature under different degrees of visual control: internally generated movement with closed eyes, signing with open eyes, tracking the line of the projected signature forwards, and tracking the line of the projected signature backwards. There was a gradual onset and disappearance of activation within a distributed network. Parietal, lateral and medial frontal brain areas were activated during all conditions, confirming the involvement of a parieto-frontal system. The weight of activation shifted with increasing task complexity. Internally generated movements activated predominantly the inferior parietal lobule and the ventral premotor cortex, as well as the rostral cingulate area, pre-supplementary motor area (pre-SMA) and SMA proper. Opening the eyes reduced SMA and cingulate activation and activated increasingly the occipito-parietal areas with higher task complexity. Visually guided movements produced an activation predominantly in the superior parietal lobule and dorsal premotor cortex. This study bridges human activation studies with the results of neurophysiological studies with monkeys. It confirms a gradual transition of visuomotor control with increasing task complexity within a distributed parieto-frontal network.

Adult↗

PubMed2002

Disconnection of speech-relevant brain areas in persistent developmental stuttering.

BACKGROUND: The neuronal basis of persistent developmental stuttering is unknown. The disorder could be related to a reduced left hemisphere dominance, which functional neuroimaging data suggest might lead to right hemispheric motor and premotor overactivation. Alternatively, the core deficit underlying stuttering might be located in the speech-dominant left hemisphere. Furthermore, magnetoencephalography study results show profound timing disturbances between areas involved in language preparation and execution in the left hemisphere, suggesting that persistent developmental stuttering might be related to impaired neuronal communication, possibly caused by a disruption of white matter fibre tracts. We aimed to establish whether disconnection between speech-related cortical areas was the structural basis of persistent developmental stuttering. METHODS: We analysed the speech of 15 people with persistent developmental stuttering and 15 closely matched controls for the percentage of syllables stuttered. We used diffusion tensor imaging to assess participants' brain tissue structure, and used and two-sample t test to compare diffusion characteristics between groups. FINDINGS: Diffusion characteristics of the group with persistent developmental stuttering and controls differed significantly immediately below the laryngeal and tongue representation in the left sensorimotor cortex (mean difference in fractional anisotropy 0.04 [95% CI 0.03-0.05]). INTERPRETATION: Our findings show that persistent developmental stuttering results from disturbed timing of activation in speech-relevant brain areas, and suggest that right hemisphere overactivation merely reflects a compensatory mechanism, analogous to right hemisphere activation in aphasia.

Adult↗

PubMed2002

Dissociable neural responses related to pain intensity, stimulus intensity, and stimulus awareness within the anterior cingulate cortex: a parametric single-trial laser functional magnetic resonance imaging study.

Neuroimaging studies have demonstrated activations in the anterior cingulate cortex (ACC) related to the affective component of pain, but not to stimulus intensity. However, it is possible that the low spatial resolution of positron emission tomography, as used in the majority of these studies, obscured areas coding stimulus intensity. We revisited this issue, using a parametric single-trial functional magnetic resonance imaging design, and investigated pain, stimulus intensity, and stimulus awareness (i.e., pain unrelated) responses within the ACC in nine healthy volunteers. Four different stimulus intensities ranging from warm to painful (300-600 mJ) were applied with a thulium yttrium-aluminum granite infrared laser in a randomized order and rated by the subjects on a five point scale (P0-P4). Pain-related regions in the ventral posterior ACC showed a response that did not distinguish between innocuous trials (P0 and P1) but showed a positive linear relationship with the blood oxygenation level-dependent contrast signal for painful trials (P2-P4). Regions in the dorsal anterior ACC along the cingulate sulcus differentiated between P0 (not perceived) and P1 but exhibited no additional signal increase with P2; these regions are related to stimulus awareness and probably to cognitive processing. Most importantly, we identified a region in the dorsal posterior ACC showing a response that discriminated between nonpainful trials (P0 and P1); therefore, this region was simply related to basic sensory processing and not to pain intensity. Stimulus-related activations were all located adjacent to the cingulate motor area, highlighting the strategic link of stimulus processing and response generation in the posterior ACC.

Adult↗

PubMed2002

Negative dip in BOLD fMRI is caused by blood flow--oxygen consumption uncoupling in humans.

The sensitivity of MRI for local changes in the deoxyhemoglobin concentration is the basis of the blood oxygen level dependent (BOLD) effect. Time-resolved fMRI studies during visual activation show an early signal intensity (SI) decrease indicating a short lasting uncoupling of oxygen consumption and cerebral blood flow (CBF) before a SI increase due to the overcompensating hemodynamic response occurs. Normal neuronal activity may be preserved despite absent vascular responsiveness. Here we show that a negative BOLD effect occurs during motor activation in an asymptomatic patient with severely disturbed cerebral autoregulation due to extracranial artery disease. This is thought to be due to oxygen consumption in the absence of a hemodynamic response. This rare case of a persisting uncoupling of oxygen metabolism and CBF serves as a model that supports changes of the cerebral blood oxygen saturation as the major contributor of the BOLD effect.

Aged↗

PubMed2002

Reduction of excitability ("inhibition") in the ipsilateral primary motor cortex is mirrored by fMRI signal decreases.

Functional magnetic resonance imaging (fMRI) was used to investigate how focal cortical inhibition affects the blood oxygen level-dependent (BOLD) signal. Phasic low force pinch grip reduces excitability of the ipsilateral primary motor cortex. This task was used to study BOLD signal changes during inhibition. Six right-handed normal volunteers participated in the study. They were asked to perform a right-handed pinch grip repetitively at 1 Hz and 5% of their individual maximal voluntary contraction (MVC). Data were acquired with a 1.5 Tesla Magnetom and continuous multislice T2*-weighted images. The contralateral primary motor cortex (M1) revealed an activation in the knob-shaped hand representation of the central sulcus area. More importantly, a decreased (often referred to as "negative") BOLD signal in the ipsilateral M1 was observed. We suggest phasic low force pinch grip as a reproducible, easy model of focal inhibition. Decreased cortical excitability presents as decreased BOLD signal using fMRI.

Adult↗

PubMed2002

Recovery of motor and language abilities after stroke: the contribution of functional imaging.

In recent years, functional imaging techniques, like functional magnetic resonance imaging (fMRI), positron emission tomography (PET), and transcranial magnetic stimulation (TMS), have shown that the improvement of motor and language function after ischemic stroke is accompanied by extensive reorganizational changes in the human cortex. To better understand these changes and to judge to what extent they could be responsible for clinical improvement, some basic principles of the organization of the motor and language system are discussed.Non-invasive functional imaging can have only a limited contribution in determining which of the possible underlying neural mechanisms, as they are known from animal experiments, play a role in functional recovery. However, they make it possible to define the functional consequences of anatomical lesions in individual patients and to correlate these functional consequences in the motor and language system with the clinical deficit. They can be used to assess the influence on the cortical reorganization of established and newer physiotherapies, logopedics and medical intervention, and they could be a useful tool in determining prognosis.

Animals↗

PubMed2002

Severe ADC decreases do not predict irreversible tissue damage in humans.

BACKGROUND AND PURPOSE: A mismatch between diffusion- and perfusion-weighted MRI is thought to define tissue at risk of infarction. This concept is based on the assumption that diffusion slowing of and decreases in the apparent diffusion coefficient (ADC) serve as indicator of tissue proceeding to infarction. We tested this hypothesis. METHODS: MRI (diffusion weighted, perfusion weighted, MRA, T2 weighted) was performed in 15 patients with acute stroke within 2.9+/-0.8 hours (mean+/-SD) of onset and on days 1 and 7. After intraindividual realignment of the ADC maps, the development of ADC range volumes and ADC values was determined. RESULTS: An increase (354%, group A1) in the total ADC-based lesion volume below a threshold of < 80% occurred in 4 patients on day 1, persisting on day 7 with a pronounced increase of ADC range volumes with low ADC values. An increase in total ADC-based lesion volume (201%, group A2) followed by a secondary drop to day 7 was found in 7 patients. A significant reduction in total ADC-based lesion volume (14%, group B) was found in 4 patients. ADC-based lesion volume increase was associated with persistent vessel occlusion in group A, whereas recanalization in group B resulted in ADC volume decrease. ADC normalization was observed independently from the degree of the initial ADC decrease on days 1 and 7 in group B. CONCLUSIONS: In line with results from animal experiments, ADC decreases do not reliably indicate tissue infarction Even severely decreased ADC values may normalize in human stroke, and it seems likely that ADC normalization depends on the duration and severity of ischemia rather than the absolute value.

Aged↗

PubMedDate not supplied

The relevance of the nature of learned associations for the differentiation of human memory systems.

In a previous functional magnetic resonance imaging (fMRI) study we demonstrated an involvement of the medial temporal lobe (MTL) during an implicit learning task. We concluded that the MTL was engaged because of the complex contingencies that were implicitly learned. In addition, the basal ganglia demonstrated effects of a paralleled proceduralization of fixed stimulus-response associations. In the present study we directly tested the hypothesis that the MTL activation depends upon implementing the complex regularity in task material, whereas activation of basal ganglia does not. Therefore, we rearranged task material such that it did not contain any complex regularity. The statistical comparison of behavioral and fMRI data between the materials allowed for isolating effects that were directly related to the implicit learning process regarding the complex regularity. The results showed a reliable difference of fMRI signal limited to the MTL, indicating a specific functional role of the MTL in implicit learning of complex contingencies. Furthermore, no difference of BOLD (Blood-Oxygenation Level Dependent) signal in the basal ganglia and cerebellum were detected, supporting the assumption of a functional involvement of the structures in proceduralization of simple stimulus-response associations but not in implicitly learning complex relations. We therefore conclude that the nature of the learned associations is relevant for determining the neuronal focus of learning, rather than the accompanying awareness.

Adult↗