Biomedical subjects

W Grodd

Publications and source records attributed to W Grodd.

At least 37 records · Page 2Linked to original sources

PubMed2001

Differential activation in parahippocampal and prefrontal cortex during word and face encoding tasks.

Episodic encoding is the first step in the formation of a memory trace. The relation between type of stimulus material and regional brain activation is not fully understood. We measured brain activation using fMRI in 12 healthy subjects during two experiments, word and face encoding. A widespread network of common activations in both tasks was present in the bilateral frontal (BA44/45), occipital (BA17/18/19) and fusiform gyri (BA37) as well as the right hippocampal formation (BA30). A region-of-interest-analysis for the hippocampal formation and dorsolateral prefrontal cortex (DLPFC) was performed additionally. During face encoding the right dorsal and during word encoding the bilateral ventral hippocampal region was activated. In the prefrontal cortex a lateralization to the left side was present only for word encoding. During encoding, activation in the inferior frontal and hippocampal cortex is modulated by the type of stimulus material.

Adult↗

PubMed2001

Early left periventricular brain lesions induce right hemispheric organization of speech.

Right-hemispheric organization of speech has been observed following early left-sided brain lesions involving the language cortex. The authors studied speech organization in hemiparetic patients with pre- and perinatally acquired lesions in the left periventricular white matter using fMRI, and found that right-hemisphere activation correlated with left facial motor tract involvement. This suggests that the impairment of speech motor output from the left hemisphere plays an important role in this alteration of language representation.

Adolescent↗

PubMed2001

Sensorimotor mapping of the human cerebellum: fMRI evidence of somatotopic organization.

Functional magnetic resonance imaging (fMRI) was employed to determine areas of activation in the cerebellar cortex in 46 human subjects during a series of motor tasks. To reduce the variance due to differences in individual anatomy, a specific transformational procedure for the cerebellum was introduced. The activation areas for movements of lips, tongue, hands, and feet were determined and found to be sharply confined to lobules and sublobules and their sagittal zones in the rostral and caudal spino-cerebellar cortex. There was a clear symmetry mirroring at the midline. The activation mapped as two distinct homunculoid representations. One, a more extended representation, was located upside down in the superior cerebellum, and a second one, doubled and smaller, in the inferior cerebellum. The two representations were remarkably similar to those proposed by Snider and Eldred [1951] five decades ago. In the upper representation, an intralimb somatotopy for the right elbow, wrist, and fingers was revealed. The maps seem to confirm earlier electrophysiological findings of sagittal zones in animals. They differ, however, from micromapping reports on fractured somatotopic maps in the cerebellar cortex of mammals. We assume that the representations that we observed are not solely the result of spatial integration of hemodynamic events underlying the fMRI method and may reflect integration of afferent peripheral and central information in the cerebellar cortex.

Adolescent↗

PubMed2001

Reliable detection of macromolecules in single-volume 1H NMR spectra of the human brain.

In short echo time proton MR spectra of the brain, resonances from macromolecules are visible. The macromolecular resonances in the 0.5-2.0 ppm region can be affected by lipid contamination arising from fat-containing regions outside the selected volume of interest (VOI). This study demonstrates that considerable lipid contamination may remain in stimulated echo acquisition mode (STEAM) spectra even if the spoiling of unwanted coherences is sufficient and the VOI is placed 2 cm or more away from fat-containing regions. The observed contamination was attributed to residual remote out-of-volume excitation, although only very small out-of-slice ripples of less than 0.2% of the in-slice excitation were found in the calculated excitation profile of the RF pulses. Spatial presaturation of fat-containing regions led to a sufficient suppression of the contamination and enabled the detection of highly reproducible macromolecular resonances. Thus, in single-volume spectroscopy as well as in spectroscopic imaging (SI or CSI), the combination of volume selection and outer volume presaturation, each in three dimensions, is highly recommended to ensure accurate detection and reliable evaluation of even small pathological alterations in macromolecules, e.g., proteins or lipids, or other resonances in the 0.5-2.0 ppm region.

Artifacts↗

PubMed2001

Differential contributions of motor cortex, basal ganglia, and cerebellum to speech motor control: effects of syllable repetition rate evaluated by fMRI.

In order to delineate the neuroanatomical correlates of speech motor control, functional magnetic resonance imaging was performed during silent repetitions of the syllable "ta" at three different rates (2.5, 4.0, and 5.5 Hz). Spatial extent and magnitude of hemodynamic responses at the level of the motor cortex showed a positive correlation to production frequencies. As concerns the basal ganglia, the lower rates (2.5 and 4.0 Hz) gave rise to higher magnitudes of activation within the left putamen as compared to the 5.5 Hz condition. In contrast, cerebellar responses were rather restricted to fast performance (4.0 and 5.5 Hz) and exhibited a shift in caudal direction during 5.5 as compared to 4.0 Hz. These findings corroborate the suggestion of a differential impact of various cortical and subcortical areas on speech motor control.

Adult↗

PubMed2001

Cerebral activation during anal and rectal stimulation.

While the rectum is innervated by visceral afferents, the anal canal is innervated by the somatosensory pudendal nerve. The representation of these two central domains of intestinal sensations in the human brain is largely unknown. Nonpainful pneumatic stimulation of the anal canal and the distal rectum using event-related functional magnetic resonance imaging (fMRI) was performed in eight healthy subjects. Subjective scaling of sensations revealed no differences in unpleasantness and pain during both stimuli. Both types of stimuli revealed fMRI activation in secondary somatosensory, insula, cingular gyrus, left inferior parietal, and right orbitofrontal cortex. Anal stimulation resulted in additional activation of primary sensory and motor cortex, supplementary motor area, and left cerebellum. We concluded that viscerorectal and somatosensory anal stimulation predominantly differ in their primary sensory activation and additional activation in motor areas. This motor response following aversive somatosensory stimuli may be caused by a reflexive avoidance reaction which is not observed after the more diffuse experienced visceral stimulation.

Adult↗

PubMed2001

Activation of right fronto-temporal cortex characterizes the 'living' category in semantic processing.

It is a vital ability for humans to distinguish between living and non-living objects. Whether the semantic features of these two classes of objects are represented in distinct brain areas, is unknown. In our study, words belonging to the categories 'living' and 'non-living' were presented visually to twelve right-handed volunteers, while brain activation was measured with event-related fMRI. Subjects had to judge whether the item belonged to one of these categories. Common areas of activation (P<0.05, corrected) during processing of both categories include the inferior occipital gyri bilaterally (BA 17/18), left inferior frontal gyrus (BA 44/45) and left inferior parietal lobe (BA 40). During processing of 'living' minus 'non-living' items, signal changes (P<0.05, corrected) were present in the the right inferior frontal (BA 47), middle temporal (BA 21) and fusiform gyrus (BA 19). Our results are in line with findings from patients with a deficit in semantic processing of living things, who specifically suffer from right hemispheric lesions.

Adult↗

PubMed2001

The influence of current direction on phosphene thresholds evoked by transcranial magnetic stimulation.

OBJECTIVES: To quantify phosphene thresholds evoked by transcranial magnetic stimulation (TMS) in the occipital cortex as a function of induced current direction. METHODS: Phosphene thresholds were determined in 6 subjects. We compared two stimulator types (Medtronic-Dantec and Magstim) with monophasic pulses using the standard figure-of-eight coils and systematically varied hemisphere (left and right) and induced current direction (latero-medial and medio-lateral). Each measurement was made 3 times, with a new stimulation site chosen for each repetition. Only those stimulation sites were investigated where phosphenes were restricted to one visual hemifield. Coil positions were stereotactically registered. Functional magnetic resonance imaging (fMRI) of retinotopic areas was performed in 5 subjects to individually characterize the borders of visual areas; TMS stimulation sites were coregistered with respect to visual areas. RESULTS: Despite large interindividual variance we found a consistent pattern of phosphene thresholds. They were significantly lower if the direction of the induced current was oriented from lateral to medial in the occipital lobe rather than vice versa. No difference with respect to the hemisphere was found. Threshold values normalized to the square root of the stored energy in the stimulators were lower with the Medtronic-Dantec device than with the Magstim device. fMRI revealed that stimulation sites generating unilateral phosphenes were situated at V2 and V3. Variability of phosphene thresholds was low within a cortical patch of 2x2cm(2). Stimulation over V1 yields phosphenes in both visual fields. CONCLUSIONS: The excitability of visual cortical areas depends on the direction of the induced current with a preference for latero-medial currents. Although the coil positions used in this study were centered over visual areas V2 and V3, we cannot rule out the possibility that subcortical structures or V1 could actually be the main generator for phosphenes.

Adult↗

PubMed2001

Proton MR spectroscopy reveals lactate in infantile neuroaxonal dystrophy (INAD).

Changes of cerebral metabolites detected by proton MR spectroscopy in two cases of infantile neuroaxonal dystrophy are described. A 6 11/12-year-old boy and a girl (aged 4 1/12 years at the first and 5 2/12 years at the second examination) with infantile neuroaxonal dystrophy were investigated by magnetic resonance imaging and spectroscopy of the basal ganglia. The signal intensity of the cerebellar cortex was increased on T2-weighted, proton density, and fluid attenuated inversion recovery images. The long echo time (135 ms) spectra revealed the presence of lactate in the basal ganglia of both cases in all investigations. The N-acetylaspartate/creatine ratio was reduced in Case 1 and in the second investigation of Case 2. The choline/creatine ratio was always increased. As the diagnosis of infantile neuroaxonal dystrophy is made by a synopsis of various clinical, neuropathological, neurophysiological, and neuroradiological data, the presence of lactate in the basal ganglia spectra may help to narrow down the diagnosis and can support the decision to perform more invasive diagnostic procedures (such as biopsies of skin, conjunctiva or even of the brain).

Aspartic Acid↗

PubMed2001

Functional MRI in a 6-year-old boy with unilateral cortical malformation: concordant representation of both hands in the unaffected hemisphere.

Functional magnetic resonance imaging (fMRI) was performed in a 6-year-old boy with a complex malformation of the right hemisphere who suffered from pharmaco-refractory epilepsy. Clinical examination revealed left-sided hemiparesis and marked mirror movements of the opposite hand both during paretic and non-paretic hand movements. Functional MRI of repetitive unimanual grasping demonstrated that the two hands share a common cortical representation located in the central motor region of the unaffected left hemisphere. The affected right hemisphere did not show any activation during either task. This case study demonstrates the feasibility and usefulness of motor fMRI in young children before they undergo epilepsy surgery.

Brain Mapping↗

PubMed2001

Phantom movements and pain. An fMRI study in upper limb amputees.

Using functional MRI, we investigated 14 upper limb amputees and seven healthy controls during the execution of hand and lip movements and imagined movements of the phantom limb or left hand. Only patients with phantom limb pain showed a shift of the lip representation into the deafferented primary motor and somatosensory hand areas during lip movements. Displacement of the lip representation in the primary motor and somatosensory cortex was positively correlated to the amount of phantom limb pain. Thalamic activation was only present during executed movements in the healthy controls. The cerebellum showed no evidence of reorganizational changes. In amputees, movement of the intact hand showed a level of activation similar to movement of the right dominant hand in the healthy controls. During imagination of moving the phantom hand, all patients showed significantly higher activation in the contralateral primary motor and somatosensory cortices compared with imagination of hand movements in the controls. In the patients with phantom limb pain but not the pain-free amputees, imagined movement of the phantom hand activated the neighbouring face area. These data suggest selective coactivation of the cortical hand and mouth areas in patients with phantom limb pain. This reorganizational change may be the neural correlate of phantom limb pain.

Adult↗

PubMed2001

Proton MR spectroscopy with metabolite-nulling reveals elevated macromolecules in acute multiple sclerosis.

Proton magnetic resonance spectroscopy has shown elevated signals in the spectral region of lipids in acute multiple sclerosis lesions. The metabolite-nulling technique allows the separation of macromolecules from other metabolites, such as lactate, N-acetyl-aspartate, creatine, choline and myo-inositol. Using this technique in studies on multiple sclerosis patients, we were able to differentiate macromolecules biochemically in acute and chronic multiple sclerosis lesions. Ten patients with acute, contrast-enhancing multiple sclerosis lesions, 10 patients with chronic lesions and 10 healthy control subjects were investigated with a 1.5 T whole body system, using a stimulated echo acquisition mode (STEAM) sequence with metabolite-nulling and outer volume saturation. Metabolites and macromolecules were quantitated absolutely. The 0.9 and 1.3 parts per million (p.p.m.) resonances of the macromolecules were significantly elevated in acute lesions compared with chronic lesions and healthy controls (P < 0.001 for 0.9 p.p.m., P < 0.05 for 1.3 p.p.m.). The macromolecular resonances at 2.1 and 3.0 p.p.m. in acute and chronic lesions were normal. N-acetyl-aspartate was significantly reduced in acute and chronic lesions compared with controls (P < 0.05 and P < 0.01, respectively). Choline was significantly elevated in acute lesions compared with controls (P < 0.05). Up to now, elevated resonances at 0.9 and 1.3 p.p.m. in acute lesions have been interpreted as lipids. In metabolite-nulled spectra, the macromolecular resonances did not fit those of lipids and might have been due to proteins or polypeptides containing the amino acids alanine, threonine, valine, leucine and isoleucine. These account for approximately 40% of the amino acids of myelin proteolipid protein and for approximately 20% of myelin basic protein. The increased macromolecular resonances at 0.9 and 1.3 p.p.m. may be interpreted as biochemical markers of myelin fragments and may be used as reliable markers of acute multiple sclerosis lesions as they provide clear discrimination among acute and chronic lesions and controls.

Acute Disease↗

PubMed2000

Response-related fMRI analysis during encoding and retrieval revealed differences in cerebral activation by retrieval success.

The aim of the study was to identify cerebral activation associated with sufficient or insufficient encoding, and with correct or false recognition. Fourteen volunteers performed two paradigms: explicit learning of words; and later retrieval of previously presented words. Items were classified according to the subjects' recognition performance. Echo-planar MRI of blood-oxygen-level-dependent signal changes was performed during encoding and retrieval. Response-related fMRI-analysis was used to compare activation associated with the subjects' retrieval success. During encoding, there was a trend towards increased activation of the left medial cingulate gyrus and of the right fusiform gyrus for later hits (correctly identified, learned target words) in comparison with misses (non-identified targets). During recognition, signal intensities associated with false alarms (falsely identified distractors) were significantly higher in left and right extrastriate cortex than those associated with hits, misses and correct rejections of distractors. Activation in the anterior cingulate gyrus during retrieval was related to reaction time and might be associated with the preparation or performance of motor response. Increased activation during false alarms might reflect a source-monitoring deficit or an increased subjective familiarity with distractors that have been most intensively processed in extrastriate visual cortex.

Adult↗

PubMed2000

The representation of articulation in the primary sensorimotor cortex.

Bilabial, alveolar and velar sounds are produced at different locations around the oral cavity. fMRI was used to localize cortical representation of articulation in seven healthy subjects during repetitive lip and vertical tongue movements as well as repetitive articulation of /pa/ (bilabial), /ta/ (alveolar), /ka/ (velar consonants) and a combination of all three in /pataka/. Centers of gravity (COG) analysis of fMRI activation in the primary motor (M1) and sensory cortex (S1) revealed /pa/- adjacent to lip representation and /ta/- articulation to tongue representation. The articulation of /pataka/ showed an activation pattern with a combination of the two M1/S1-components and additional activation in the supplementary motor area.

Adult↗

PubMed2000

Opposite hemispheric lateralization effects during speaking and singing at motor cortex, insula and cerebellum.

Aside from spoken language, singing represents a second mode of acoustic (auditory-vocal) communication in humans. As a new aspect of brain lateralization, functional magnetic resonance imaging (fMRI) revealed two complementary cerebral networks subserving singing and speaking. Reproduction of a non-lyrical tune elicited activation predominantly in the right motor cortex, the right anterior insula, and the left cerebellum whereas the opposite response pattern emerged during a speech task. In contrast to the hemodynamic responses within motor cortex and cerebellum, activation of the intrasylvian cortex turned out to be bound to overt task performance. These findings corroborate the assumption that the left insula supports the coordination of speech articulation. Similarly, the right insula might mediate temporo-spatial control of vocal tract musculature during overt singing. Both speech and melody production require the integration of sound structure or tonal patterns, respectively, with a speaker's emotions and attitudes. Considering the widespread interconnections with premotor cortex and limbic structures, the insula is especially suited for this task.

Adult↗

PubMed2000

Detection of a relation between respiration and CSF pulsation with an echoplanar technique.

The flow of cerebrospinal fluid (CSF) through the aqueduct was studied with an echoplanar imaging technique. Images (1024) of a slice perpendicular to the aqueduct were acquired with a repetition time of 107 msec and a flip angle of 90 degrees. This imaging technique is very sensitive for flow into the selected slice, although a quantitative assessment of flow velocities is not possible. Simultaneously with the image data acquisition, data from a pulse oximeter and a respiration belt were recorded. For each data point, a delay time to the preceding cardiac pulse was determined from the recorded pulse wave. The signal intensities could then be assigned to the cardiac cycle. Each cardiac interval was assigned to one of eight respiratory phases, and an average signal curve during the cardiac interval was calculated for each respiration phase. The evaluation showed to signal maxima within the cardiac interval, which could be identified as a downward flow at 10% and an upward flow at 80% of the cardiac pulse interval by measurements with additional saturation pulses. In examinations of 22 healthy volunteers, an influence of respiration on the flow through the aqueduct was found. In spite of interindividual variability, comparable effects could be observed in all volunteers. In the late expiration phase the caudally directed flow was at its maximum, whereas the cranially directed flow was maximal in the post-inspiration phase.

Adult↗

PubMed2000

The concreteness effect: evidence for dual coding and context availability.

The term concreteness effect refers to the observation that concrete nouns are processed faster and more accurately than abstract nouns in a variety of cognitive tasks. Two models have been proposed to explain the neuronal basis of the concreteness effect. The dual-coding theory attributes the advantage to the access of a right hemisphere image based system in addition to a verbal system by concrete words. The context availability theory argues that concrete words activate a broader contextual verbal support, which results in faster processing, but do not access a distinct image based system. We used event-related fMRI to detect the brain regions that subserve to the concreteness effect. We found greater activation in the lower right and left parietal lobes, in the left inferior frontal lobe and in the precuneus during encoding of concrete compared to abstract nouns. This makes a single exclusive theory unlikely and rather suggests a combination of both models. Superior encoding of concrete words in the present study may result from (1) greater verbal context resources reflected by the activation of left parietal and frontal associative areas, and (2) the additional activation of a non-verbal, perhaps spatial imagery-based system, in the right parietal lobe.

Adult↗

PubMed2000

Articulatory/phonetic sequencing at the level of the anterior perisylvian cortex: a functional magnetic resonance imaging (fMRI) study.

Damage to the anterior peri-intrasylvian cortex of the dominant hemisphere may give rise to a fairly consistent syndrome of articulatory deficits in the absence of relevant paresis of orofacial or laryngeal muscles (apraxia of speech, aphemia, or phonetic disintegration). The available clinical data are ambiguous with respect to the relevant lesion site, indicating either dysfunction of the premotor aspect of the lower precentral gyrus or the anterior insula in the depth of the Sylvian fissure. In order to further specify the functional anatomic substratum of this syndrome, functional magnetic resonance imaging (fMRI) was performed during reiteration of syllables differing in their demands on articulatory/phonetic sequencing (CV versus CCCV versus CVCVCV). Horizontal tongue movements and a polysyllabic lexical item served as control conditions. Repetition of the CV and CCCV monosyllables elicited a rather bilateral symmetric hemodynamic response at the level of the anterior and posterior bank of the central sulcus (primary sensorimotor cortex), whereas a more limited area of neural activity arose within this domain during production of lexical and nonlexical polysyllables, significantly or exclusively lateralized toward the left hemisphere. There is neurophysiological evidence that primary sensorimotor cortex mediates the "fractionation" of movements. Assuming that the polysyllables considered are organized as coarticulated higher-order units, the observed restricted and lateralized cortical activation pattern, most presumably, reflects a mode of "nonindividualized" motor control posing fewer demands on "movement fractionation." These findings may explain the clinical observation of disproportionately worse repetition of trisyllabic items as compared to monosyllables in apraxia of speech. The various test materials failed to elicit significant activation of the anterior insula. If at all, only horizontal tongue movements yielded a hemodynamic reaction extending beyond the sensorimotor cortex to premotor areas. Since limbic projections target the inferior dorsolateral frontal lobe, the enlarged region of activation during horizontal tongue movements might reflect increased attentional requirements of this task.

Adult↗