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S Knecht

Publications and source records attributed to S Knecht.

At least 37 records · Page 2Linked to original sources
PubMed2003

Neuroimaging evidence for cortical involvement in the preparation and in the act of swallowing.

This study employed whole head magnetoencephalography and synthetic aperture magnetometry to investigate the cortical topography of the preparation and the execution of volitional and reflexive water swallowing and of a simple tongue movement. Concerning movement execution, activation of the mid-lateral primary sensorimotor cortex was strongly lateralized to the left during volitional water swallowing, less strongly lateralized to the left during reflexive water swallowing, and not lateralized at all during tongue movement. In contrast, the preparation for both volitional water swallowing and tongue movement showed a bilateral activation of the primary sensorimotor cortex. No activation was seen prior to reflexive water swallowing. Activation of the left insula and frontal operculum was observed only during both the preparation and the execution of volitional water swallowing. These new findings suggest a left hemispheric dominance for the cortical control of swallowing in humans.

Adult↗
PubMed2002

When finding words becomes difficult: is there activation of the subdominant hemisphere?

Language-related activation has been observed in the right cerebral hemisphere by functional imaging in dysphasic patients who had partially recovered from a left hemispheric ischemic stroke with aphasia. It has been cautioned that, because dysphasic patients have difficulties in retrieving words, a right-hemisphere activation could be the result of an unspecific increase in global brain activation because of an increased effort. To test this hypothesis, we increased the difficulty of finding words in a word completion task in healthy subjects (n = 14) and measured hemispheric activation by functional transcranial Doppler sonography (fTCD). The sensitivity of fTCD for this approach was validated with an established motor paradigm by detecting a steady increase in bilateral cerebral perfusion in parallel to increasing the speed of finger tapping. Conversely, in the linguistic task, increasing the difficulty of word completion did not change task related perfusion of the dominant or subdominant hemisphere (repeated measurement ANOVA: P = 0.8). These results demonstrate that difficult to perform word searches do not lead to an additional involvement of the subdominant hemisphere. This suggests that after stroke, language-related activation of the subdominant hemisphere is not simply an effort-related effect.

Adult↗
PubMed2002

[Neuropsychological disorders in amyotrophic lateral sclerosis].

Amyotrophic lateral sclerosis (ALS) has traditionally been assumed to be a purely motor disturbance. It is now recognized that 2-5% of patients with ALS develop frontotemporal dementia. Additionally, neuropsychological analysis and functional imaging suggest that a proportion of patients with classical ALS also have neuropsychological impairment. On postmortem examination, ALS patients classified as not demented showed atrophy of the frontotemporal cortex. Conversely, in patients with frontotemporal dementia without known motor impairment, atrophy of spinal and bulbar neurons were found on postmortem examination. It is still not known whether patients with ALS and neuropsychological impairment form a distinct subgroup or if they are part of a continuous spectrum that runs from pure motor impairment to pure neuropsychological impairment.

Aphasia↗
PubMed2002

Degree of language lateralization determines susceptibility to unilateral brain lesions.

Language is considered a function of either the left or, in exceptional cases, the right side of the brain. Functional imaging studies show, however, that in the general population a graded continuum from left hemispheric to right hemispheric language lateralization exists. To determine the functional relevance of lateralization differences, we suppressed language regions using transcranial magnetic stimulation (TMS) in healthy human subjects who differed in lateralization of language-related brain activation. Language disruption correlated with both the degree and side of lateralization. Subjects with weak lateralization (more bilaterality) were less affected by either left- or right-side TMS than were subjects with strong lateralization to one hemisphere. Thus in some people, language processing seems to be distributed evenly between the hemispheres, allowing for ready compensation after a unilateral lesion.

Adult↗
PubMed2001

D-amphetamine does not improve outcome of somatosensory training.

BACKGROUND: D-amphetamine has been shown to affect early stages of stroke recovery, and may have a beneficial effect on functions when administered later after stroke. OBJECTIVE: To test D-amphetamine effects on skill acquisition after the acute or subacute stages of stroke, when lesion-related structural changes have consolidated. METHODS: Sixteen healthy subjects were treated with D-amphetamine during a 4-week training of tactile frequency discrimination in a placebo-controlled, double-blind design. RESULTS: All subjects improved significantly in tactile temporal acuity. However, improvement did not differ in subjects treated with or without D-amphetamine. CONCLUSION: No beneficial effect of D-amphetamine on somatosensory training improvements was found in healthy subjects.

Adult↗
PubMed2001

Language and spatial attention can lateralize to the same hemisphere in healthy humans.

BACKGROUND: Disorders of language classically occur after left brain lesions, and disorders of spatial attention after right brain lesions. It is unclear whether the hemispheric dissociation of functions is a fixed pattern of brain organization. OBJECTIVE: The authors determined whether lateralization of language and lateralization of spatial attention also dissociate in people with atypical (i.e., right hemispheric) language dominance. METHODS: The authors selected 10 subjects with typical, i.e., left hemispheric, and 10 with atypical, i.e., right hemispheric, language representation on a random basis from a sample of 326 healthy volunteers examined with functional transcranial Doppler sonography (fTCD) for language dominance. In these subjects, hemispheric lateralization of cerebral perfusion during a line bisection task was determined with fTCD. RESULTS: The authors found a dissociation between dominance for language and spatial attention in all but four subjects. In the latter subjects, there was a significant lateralization to the right hemisphere for both tasks. The four subjects showed normal intellectual, linguistic, and spatial performance, with normal EEG and MRI scans of the brain. CONCLUSION: Even in the absence of brain pathology, the same hemisphere can be dominant in control of both language and spatial attention.

Adult↗
PubMed2001

Functional reorganization of the human primary somatosensory cortex after acute pain demonstrated by magnetoencephalography.

The somatosensory system is capable of functional reorganization following peripheral denervation or training. Studies on human amputees with phantom limb pain provided evidence that these reorganizational changes are modulated through nociceptive input. In the present study we used magnetoencephalographic recordings of six healthy volunteers to assess whether acute pain by itself causes a reorganization of the primary somatosensory cortex. After the induction of an intense experimental pain at the thenar of the left hand by intradermal injection of capsaicin, the extent of the cortical hand representation and the distance between the hand representation and the localization of the lip decreased. A likely mechanism for this acute reorganization is that pain induced hyperresponsiveness of the left thenar to tactile input from neighboring body sites.

Acute Disease↗
PubMed2001

Behavioural relevance of atypical language lateralization in healthy subjects.

In most humans, language is lateralized to the left side of the brain. It has been speculated that this hemispheric specialization is a prerequisite for the full realization of linguistic potential. Using standardized questionnaires and performance measures, we attempted to determine if there are behavioural correlates of atypical, i.e. right-hemispheric and bilateral, language lateralization. The side and degree of language lateralization were determined by measuring the hemispheric perfusion differences by functional transcranial Doppler ultrasonography during a word generation task in healthy volunteers. Subjects with left (n = 264), bilateral (n = 31) or right (n = 31) hemisphere language representation did not differ significantly with respect to mastery of foreign languages, academic achievement, artistic talents, verbal fluency or (as assessed in a representative subgroup) in intelligence or speed of linguistic processing. These findings suggest that atypical hemispheric specialization for language, i.e. right-hemisphere or bilateral specialization, is not associated with major impairments of linguistic faculties in otherwise healthy subjects.

Adolescent↗
PubMed2000

Language lateralization in healthy right-handers.

Our knowledge about the variability of cerebral language lateralization is derived from studies of patients with brain lesions and thus possible secondary reorganization of cerebral functions. In healthy right-handed subjects 'atypical', i.e. right hemisphere language dominance, has generally been assumed to be exceedingly rare. To test this assumption we measured language lateralization in 188 healthy subjects with moderate and strong right-handedness (59% females) by a new non-invasive, quantitative technique previously validated by direct comparison with the intracarotid amobarbital procedure. During a word generation task the averaged hemispheric perfusion differences within the territories of the middle cerebral arteries were determined. (i) The natural distribution of language lateralization was found to occur along a bimodal continuum. (ii) Lateralization was equivalent in men and women. (iii) Right hemisphere dominance was found in 7.5% of subjects. These findings indicate that atypical language dominance in healthy right-handed subjects of either sex is considerably more common than previously suspected.

Adolescent↗
PubMed2000

Handedness and hemispheric language dominance in healthy humans.

In most people the left hemisphere of the brain is dominant for language. Because of the increased incidence of atypical right-hemispheric language in left-handed neurological patients, a systematic association between handedness and dominance has long been suspected. To clarify the relationship between handedness and language dominance in healthy subjects, we measured lateralization directly by functional transcranial Doppler sonography in 326 healthy individuals using a word-generation task. The incidence of right-hemisphere language dominance was found to increase linearly with the degree of left-handedness, from 4% in strong right-handers (handedness = 100) to 15% in ambidextrous individuals and 27% in strong left-handers (handedness = -100). The relationship could be approximated by the formula: f1.gif" BORDER="0">. These results clearly demonstrate that the relationship between handedness and language dominance is not an artefact of cerebral pathology but a natural phenomenon.

Adolescent↗
PubMed2000

Assessment of hemispheric language lateralization: a comparison between fMRI and fTCD.

The cerebral blood flow velocity (CBFV) in the basal arteries during a word-generation task was assessed by functional transcranial Doppler ultrasonography (fTCD) and by functional magnetic resonance imaging (fMRI). The study investigates how event-related CBFV modulations in the middle cerebral artery (MCA) relate to regional cerebral blood flow (rCBF) changes. Both fMRI and fTCD were used in 13 subjects (7 men, 6 women, aged 21 to 44 years). The maximum difference of relative CBFV changes between the left and right MCA during the word-generation task was used as the language laterality index (LIfTCD). For the fMRI examination during the nearly identical language task, the corresponding index was defined by LIfMRI = 100(N(L) - N(R))/(N(L) + N(R)), where N(L) and N(R) refer to the numbers of voxels activated in the left and right hemisphere, respectively. The evoked CBFV changes expressed by LIfTCD and the corresponding laterality index, LIfMRI, estimated by fMRI showed a close linear relation (regression analysis: r = 0.95, p < 0.0001). The results of this study demonstrate that language-related velocity changes in the MCAs relate to rCBF increases in a linear fashion. Since the laterality indices assessed by fMRI and fTCD are in such close agreement both techniques can therefore be used in a complementary way.

Adult↗
PubMed2000

Optimized activation of the primary sensorimotor cortex for clinical functional MR imaging.

BACKGROUND AND PURPOSE: One application of functional MR imaging is to identify the primary sensorimotor cortex (M1 and S1) around the central sulcus before brain surgery. However, it has been shown that undesirable coactivation of nonprimary motor areas, such as the supplementary motor area and the premotor area, can interfere with the identification of the primary motor cortex, especially in patients with distorted anatomic landmarks. We therefore sought to design a simple functional MR imaging paradigm for selective activation of the primary sensorimotor cortex. METHODS: Different paradigms using finger tapping for motor activation were examined and compared with respect to the distribution of activated voxels in primary and nonprimary cortical areas. Studies were conducted in 14 healthy volunteers using a blood oxygen level-dependent multislice echo-planar imaging sequence. RESULTS: The most selective activation of the primary sensorimotor cortex was obtained with a paradigm combining right-sided finger tapping as the activation condition with left-sided finger tapping as the control condition. Analysis of the signal time course of primary and nonprimary areas revealed that the highly selective primary motor activation was due to it being restricted to contralateral finger movements, as opposed to the nonprimary motor areas, which were activated by ipsilateral, contralateral, and bilateral finger movements alike. CONCLUSION: When performing functional MR imaging to determine the location of the primary sensorimotor cortex, one should compare unilateral voluntary movements as the activation condition with contralateral movements as the control condition to accentuate activation of the primary motor area and to suppress undesirable coactivation of nonprimary motor areas.

Adult↗
PubMed1999

Cortical asymmetries of the human somatosensory hand representation in right- and left-handers.

Hemispheric asymmetry is known for higher brain functions like language and attention. We tested whether such an asymmetry also exists in the representation of elementary sensory functions. Magnetic source imaging was used to compare the cortical somatosensory hand representation in seven right- and five left-handed individuals. In all right-handers the representation of the dominant hand was larger than the contralateral one in the corresponding hemispheres. In contrast, only two out of five left-handers revealed a larger representation of the dominant left hand compared to the right one. In agreement with previous findings on the lateralization of language and attention, there is a strong correlation between handedness and the extent of the cortical hand representation in right-, but not in left-handers. We conclude that a profound functional hemispheric asymmetry also exists in primary sensory cortices.

Adult↗
PubMed1999

Cortical tuning: a function of anticipated stimulus intensity.

We investigated the activation of the brain during anticipation of tactile stimuli by continuous cerebral blood flow velocity (CBFV) monitoring with bilateral transcranial Doppler sonography. A forced choice paradigm was performed where a first group of subjects (n=16) was expecting suprathreshold and a second group (n=19) was anticipating threshold tactile stimuli to the index finger after a cueing tone. During the anticipation of suprathreshold stimuli the CBFV always exhibited a significantly stronger increase in the right hemisphere than in the left, even when stimuli were anticipated at the right index finger. Conversely when stimuli at perception threshold were expected, the respective contralateral hemisphere showed a significantly stronger perfusion increase. These data show that preparatory activation of the brain during stimulus anticipation is dependant on the expected stimulus intensity.

Acoustic Stimulation↗
PubMed1999

[Neuronal plasticity exemplified by the somatosensory system].

The mammalian brain is capable of a substantial functional reorganization, manifesting on a cortical somatotopical and on a behavioral level. Possible mechanisms are reviewed based on the work by others and ourselves on somatosensory reorganization in humans. The somatosensory system is characterized by divergent projections from the periphery to the cerebral cortex. Changes in synaptic weights allow for reorganization of sensory processing: On one side, limb amputation will result in a representational "invasion" of the differentiated cortex from neighboring regions with concomitant perceptual changes. On the other side, sensorimotor training can increase the representational cortical zone of a limb. Plastic changes can be temporary or persistent. Modulating factors like pain and certain drugs seem to induce a permissive state in the cortex resulting in enhanced reorganization. Thus, specific physical training combined with pharmacoceutical modulation holds promise to improve functional recovery after brain lesions.

Afferent Pathways↗
PubMed1999

Clinical applications of functional MRI at 1.0 T: motor and language studies in healthy subjects and patients.

In this article we describe clinical applications of functional MRI (fMRI) at 1.0 T. All experiments were performed on a commercially available 1.0-T system (Magnetom Impact Expert, Siemens AG, Erlangen, Germany) using a blood oxygen level-dependent (BOLD)-sensitive multi-slice EPI technique (TE 66 ms, 4 mm slice thickness, 210 mm field of view, 64 x 64 acquisition matrix). Different paradigms for localization of the motor cortex and for language lateralization were tested in healthy subjects and patients. Methodological considerations concerning the development of the paradigms are also described. In all healthy subjects, motor activation elicited BOLD signal changes in the sensorimotor cortex, permitting identification of primary motor and sensory cortical areas. Furthermore, focal activation of different cortical areas by a language task was possible in 6 of 10 subjects. Nineteen motor studies were performed in 18 patients with supratentorial lesions, in most cases prior to neurosurgical procedures. In 14 studies, fMRI results demonstrated the localization of the motor hand areas relative to the lesion. The results proved valuable for preoperative planning and contributed to therapeutical decisions. We conclude that functional MRI for clinically relevant applications, such as localization of motor and language function, is feasible even at a field strength of 1.0 T without dedicated equipment.

Adult↗