Interindividual variation of cerebral activation during encoding and retrieval of words

The aim of the present study was to compare the cerebral activation associated with encoding and retrieval in individual subjects with the average activation in the same group of subjects. Twelve volunteers performed two paradigms: 1) intentional encoding of words, and 2) recognition of learned words intermixed with new distracters. Echo-planar magnetic resonance imaging (MRI) of BOLD signal changes was used to compare cerebral activation between active and resting conditions. During encoding, activation of the left precentral gyrus related to the motor response was observed in some subjects. Averaged data showed increased activation of the left precentral gyrus, the supplementary motor area (SMA), the left inferior frontal gyrus and in the left temporo-occipital junction. During recognition, motor response-related activity was found in the precentral cortex and SMA in most subjects. Activation in other brain areas showed considerable interindividual variation. In the entire group, recognition showed activation of the left dorsolateral prefrontal cortex, the precentral gyrus, the SMA, and the temporo-occipital junction. The total amount and the distribution of task-related cerebral activation varies considerably between individuals and might correspond to individual preferences of cognitive strategies. The investigation of these interindividual variations will be an exciting scientific challenge in the near future.

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.

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.

Video camera and light system for application in magnetic resonance scanners

The direct observation and simultaneous recording of subject behavior, e.g. facial movements, during MR imaging is necessary for a variety of functional imaging studies involving phenomena such as emotions, humor, mood, etc. Such observation is also valuable for the monitoring of very ill or young patients. We describe a color video camera and light system which works within the functioning scanner. The camera acquires high resolution video sequences during conventional T(1)-weighted and functional T(2)*-weighted imaging. When fixed to the head coil artefacts during the MRI-acquisition were insignificant. The video allows observation of the face detailed enough to permit FACS scoring of facial expressions. We therefore propose that it can be applied for a wide variety of studies needing visual feedback of subject behavior.

Does glucagon stimulation predict oral glucose tolerance in patients after simultaneous pancreas-kidney transplantation?

BACKGROUND

Exogenous glucagon rapidly stimulates insulin secretion. This test has been used to estimate insulin secretory capacity, which may predict oral glucose tolerance in patients after pancreas transplantation.

METHODS

In 32 pancreas-kidney transplant recipients, in 10 nondiabetic kidney transplant recipients, and in 9 healthy control subjects, a glucagon stimulation test (1 mg i.v.) and a 75-g oral glucose tolerance test were performed with determination of glucose, insulin, and C-peptide profiles.

RESULTS

Of 16 pancreas transplant recipients with the lowest insulin responses after glucagon, 7 had an impaired oral glucose tolerance, in contrast to 1 of 16 with high insulin responses (P=0.037). A low insulin response after glucagon was associated with significantly lower 120-min glucose concentrations (P=0.043) and a lower integrated incremental insulin response after oral glucose (P=0.006).

CONCLUSIONS

In pancreas-kidney transplant recipients, a low insulin response after intravenous glucagon predicts a reduced insulin response after oral glucose and an impaired oral glucose tolerance. This simple test may be helpful in the follow-up of pancreas transplant recipients.

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.

fMRI evaluation of somatotopic representation in human primary motor cortex

We used fMRI to map foot, elbow, fist, thumb, index finger, and lip movements in 30 healthy subjects. For each movement type confidence intervals of representational sites in the primary motor cortex (M1) were evaluated. In order to improve the precision of their anatomical localization and to optimize the mapping of cortical activation sites, we used both the assessment of locations in the conventional 3D system and a 2D projection method. In addition to the computation of activation maxima of activation clusters within the precentral gyrus, centers of gravity were determined. Both methods showed a high overlap of their representational confidence intervals. The 2D-projection method revealed statistically significant distinct intralimb locations, e.g., elbow versus index finger movements and index finger versus thumb movements. Increased degree of complexity of finger movements resulted in a spread of the somatotopic location toward the arm representation. The 2D-projection method-based fMRI evaluation of limb movements showed high precision and was able to reveal differences in intralimb movement comparisons. fMRI activation revealed a clear somatotopic order of movement representation in M1 and also reflected different degrees of complexity of movement.

Functional MRI of cerebral activation during encoding and retrieval of words

The aims of the present study were to identify the cerebral structures associated with encoding and retrieval of verbal material. To circumvent the inherent disadvantages of the conventional block designs used in functional magnetic resonance imaging (MRI), an event-related design compared activation related to randomly intermixed old and new words during recognition. To support the validity of results, both nonparametric analyses in regions of interest (ROI) and statistical parametric mapping (SPM 96) were used. Twelve healthy volunteers, ages 22-35 years, performed three tasks: intentional encoding of words, recognition of old (previously learned) words, and discrimination between words and nonwords, a task to control for visual input and motor output during recognition. Echo-planar magnetic resonance imaging of blood-level, oxygen-dependent, task-related changes was used to compare cerebral activity under active and resting conditions as well as to detect event-related activity within blocks of trials. Comparable results were obtained following nonparametric statistical analysis of selected ROI and SPM. Encoding of words was associated with increased activity in the left inferior frontal gyrus, including Broca's area and in the left parietal association cortex. Event-related data analysis revealed activation of the right medial frontal gyrus, the right anterior cingulate gyrus, and parietal association cortices during recognition of previously presented words. In the lexical decision task, words in comparison with nonwords were associated with activation of the left parietal association cortex. The right medial frontal gyrus, the right anterior cingulate gyrus, and the right parietal association cortex are likely to be involved in episodic memory functions during recognition of previously presented verbal material. The comparison of event-related activation occurring within one trial block instead of among several trial blocks may significantly improve the performance of memory studies.

Activation of cortical and cerebellar motor areas during executed and imagined hand movements: an fMRI study

Brain activation during executed (EM) and imagined movements (IM) of the right and left hand was studied in 10 healthy right-handed subjects using functional magnetic resonance imagining (fMRI). Low electromyographic (EMG) activity of the musculi flexor digitorum superficialis and high vividness of the imagined movements were trained prior to image acquisition. Regional cerebral activation was measured by fMRI during EM and IM and compared to resting conditions. Anatomically selected regions of interest (ROIs) were marked interactively over the entire brain. In each ROI activated pixels above a t value of 2.45 (p<0.01) were counted and analyzed. In all subjects the supplementary motor area (SMA), the premotor cortex (PMC), and the primary motor cortex (M1) showed significant activation during both EM and IM; the somatosensory cortex (S1) was significantly activated only during EM. Ipsilateral cerebellar activation was decreased during IM compared to EM. In the cerebellum, IM and EM differed in their foci of maximal activation: Highest ipsilateral activation of the cerebellum was observed in the anterior lobe (Larsell lobule H IV) during EM, whereas a lower maximum was found about 2-cm dorsolateral (Larsell lobule H VII) during IM. The prefrontal and parietal regions revealed no significant changes during both conditions. The results of cortical activity support the hypothesis that motor imagery and motor performance possess similar neural substrates. The differential activation in the cerebellum during EM and IM is in accordance with the assumption that the posterior cerebellum is involved in the inhibition of movement execution during imagination.

Activation of human language processing brain regions after the presentation of random letter strings demonstrated with event-related functional magnetic resonance imaging

This study addresses the question, to what extent the processing of meaningless random letter strings involves classical language related brain regions. Using event-related functional magnetic resonance imaging (fMRI), which allows random stimulus presentation, we could demonstrate activation in the left inferior frontal gyrus, the left superior temporal gyrus, left parietal and occipital regions after the presentation of random letter strings compared to real words. The activation in these classical language related brain areas reflects an intense lexical evaluation process of the meaningless stimuli. Real words contrasted with random letter strings activated the left angular gyrus, bilateral precuneus and the left posterior cingulate gyrus, which may reflect the access of higher semantic associations.

Dynamical cluster analysis of cortical fMRI activation

Localized changes in cortical blood oxygenation during voluntary movements were examined with functional magnetic resonance imaging (fMRI) and evaluated with a new dynamical cluster analysis (DCA) method. fMRI was performed during finger movements with eight subjects on a 1.5-T scanner using single-slice echo planar imaging with a 107-ms repetition time. Clustering based on similarity of the detailed signal time courses requires besides the used distance measure no assumptions about spatial location and extension of activation sites or the shape of the expected activation time course. We discuss the basic requirements on a clustering algorithm for fMRI data. It is shown that with respect to easy adjustment of the quantization error and reproducibility of the results DCA outperforms the standard k-means algorithm. In contrast to currently used clustering methods for fMRI, like k-means or fuzzy k-means, DCA extracts the appropriate number and initial shapes of representative signal time courses from data properties during run time. With DCA we simultaneously calculate a two-dimensional projection of cluster centers (MDS) and data points for online visualization of the results. We describe the new DCA method and show for the well-studied motor task that it detects cortical activation loci and provides additional information by discriminating different shapes and phases of hemodynamic responses. Robustness of activity detection is demonstrated with respect to repeated DCA runs and effects of different data preprocessing are shown. As an example of how DCA enables further analysis we examined activation onset times. In areas SMA, M1, and S1 simultaneous and sequential activation (in the given order) was found.

Improvement of the acquisition of a large amount of MR images on a conventional whole body system

Modern whole body MR systems are equipped with echo-planar-imaging capability, which allows the measurement of a single slice in a fraction of a second or of thousands of images in few minutes. A considerable restriction to the acquisition of series containing large amounts of images in patient examinations is the time-consuming data handling time of the images at conventional systems, which includes the time to insert the images into the systems database. We propose the arrangement of several images on a new image with a large matrix size like a mosaic. The handling time depends mostly on the number of images without consideration of their matrix size. Therefore, image handling is strongly reduced by the use of such mosaic images.

Suture-mediated percutaneous closure of antegrade femoral arterial access sites in patients who have received full anticoagulation therapy

PURPOSE

To assess the feasibility and clinical usefulness of suture-mediated closure of femoral arterial access sites after antegrade puncture for peripheral arterial interventions.

MATERIALS AND METHODS

Eighty consecutive patients (49 men, 31 women; mean age +/- SD, 65.4 years +/- 12.3) who had undergone femoropopliteal angioplasty underwent suture-mediated percutaneous closure with 6-, 7-, or 8-F devices. Patients received heparin intravenously and aspirin orally and were immobilized for 1 hour after the intervention. All patients underwent a physical examination the day after the procedure. Color-coded duplex ultrasonography was performed in those patients (n = 27 [33%]) who were obese, were experiencing pain, and had suspicious clinical findings. After 3 months, an identical clinical examination was performed in every third patient.

RESULTS

Hemostasis was achieved in 77 (96%) patients; one of 80 patients required blood transfusions and surgery despite an initially successful closure. The closure devices could be deployed in 78 (98%) patients; two of 80 patients needed compression because of a steep angulation of the puncture track and suture entrapment. Adjunctive compression was necessary in two (3%) of the remaining 78 patients. Mean time to hemostasis in the 78 patients who had successful device deployment was 5.2 minutes (range, 3.0-21.0 minutes). Minor complications (i.e., three small hematomas, a pseudoaneurysm, and a small lymphatic fistula) occurred in five (6%) patients.

CONCLUSION

Suture-mediated percutaneous closure of antegrade puncture sites in the groin is feasible. Problems may arise in antegrade punctures owing to steep device angulation.

Reorganization in the primary motor cortex after spinal cord injury - A functional Magnetic Resonance (fMRI) study

Activation maps in the primary motor cortex (M1) were investigated in three patients with complete spinal cord injury (SCI) at level TH3, TH7 and TH9 and in one patient with an incomplete spinal cord injury at level L1 during right elbow (4 patients), right thumb (4 patients), bilateral lip (2 patients) and right foot (3 patients during imagined, 1 patient during executed) movements using functional Magnetic Resonance Imaging (fMRI). Compared to controls fMRI activation maps of patients with complete paraplegia showed a cranial displacement of the activation maxima in the contralateral primary motor cortex during elbow movement of 13.3mm, whereas the maxima of thumb and lip movements were not altered. The patient with an incomplete spinal cord injury revealed no displacement of elbow activation maxima. The reorganization is likely to occur on the cortical and not on the spinal level.