Jürgen Hennig

Ventral and dorsal pathways for language

Built on an analogy between the visual and auditory systems, the following dual stream model for language processing was suggested recently: a dorsal stream is involved in mapping sound to articulation, and a ventral stream in mapping sound to meaning. The goal of the study presented here was to test the neuroanatomical basis of this model. Combining functional magnetic resonance imaging (fMRI) with a novel diffusion tensor imaging (DTI)-based tractography method we were able to identify the most probable anatomical pathways connecting brain regions activated during two prototypical language tasks. Sublexical repetition of speech is subserved by a dorsal pathway, connecting the superior temporal lobe and premotor cortices in the frontal lobe via the arcuate and superior longitudinal fascicle. In contrast, higher-level language comprehension is mediated by a ventral pathway connecting the middle temporal lobe and the ventrolateral prefrontal cortex via the extreme capsule. Thus, according to our findings, the function of the dorsal route, traditionally considered to be the major language pathway, is mainly restricted to sensory-motor mapping of sound to articulation, whereas linguistic processing of sound to meaning requires temporofrontal interaction transmitted via the ventral route.

Proton magnetic resonance spectroscopy studies on human brain Myo-inositol in hypo-osmolarity and hepatic encephalopathy

BACKGROUND/AIMS Recent in vivo studies using proton magnetic resonance (1H-MR) spectroscopy showed low levels of myo-inositol in the brain in hepatic encephalopathy; the pathogenetic relevance of this observation is unclear. METHODS Myo-inositol and glutamine levels in the brain were studied in vivo by 1H-MR spectroscopy in patients with hypo-osmolarity and hepatic encephalopathy. RESULTS A patient with severe plasma hypo-osmolarity (222 mOsm/L) had almost undetectable signals for myo-inositol and glutamine/glutamate in the brain. Both signals reappeared after normalization of plasma osmolarity, suggesting that both myo-inositol and glutamine were released as organic osmolytes from the brain. A decreased cerebral myo-inositol signal is also found in low-grade hepatic encephalopathy but is accompanied by an increased glutamine signal. Cirrhotics without hepatic encephalopathy have near-normal inositol signals, and patients with acquired immunodeficiency syndrome encephalopathy have increased inositol signals. CONCLUSIONS The 1H-MR spectroscopic myo-inositol signal in the human brain predominantly reflects an osmosensitive inositol pool. It is hypothesized that its depletion in latent hepatic encephalopathy points to a disturbance of cell volume homeostasis in the brain as an early pathogenetic event. This may partly be caused by a hyperammonemia-induced glutamine accumulation in the brain.

The Processing of First- and Second-Order Motion in Human Visual Cortex Assessed by Functional Magnetic Resonance Imaging (fMRI)

We have examined the activity levels produced in various areas of the human occipital cortex in response to various motion stimuli using functional magnetic resonance imaging (fMRI) methods. In addition to standard luminance-defined (first-order) motion, three types of second-order motion were used. The areas examined were the motion area V5 (MT) and the following areas that were delineated using retinotopic mapping procedures: V1, V2, V3, VP, V3A, and a new area that we refer to as V3B. Area V5 is strongly activated by second-order as well as by first-order motion. This activation is highly motion-specific. Areas V1 and V2 give good responses to all motion stimuli, but the activity seems to be related primarily to the local spatial and temporal structure in the image rather than to motion processing. Area V3 and its ventral counterpart VP also respond well to all our stimuli and show a slightly greater degree of motion specificity than do V1 and V2. Unlike V1 and V2, the response in V3 and VP is significantly greater for second-order motion than for first-order motion. This trend is evident, but less marked, in V3A and V3B and absent in V5. The results are consistent with the hypothesis that first-order motion sensitivity arises in V1, that second-order motion is first represented explicitly in V3 and VP, and that V5 (and perhaps also V3A and V3B) is involved in further processing of motion information, including the integration of motion signals of the two types.

Time-resolved 3D MR velocity mapping at 3T: Improved navigator-gated assessment of vascular anatomy and blood flow

To evaluate an improved image acquisition and data‐processing strategy for assessing aortic vascular geometry and 3D blood flow at 3T.

Multiecho imaging sequences with low refocusing flip angles

Abstract A simple algorithm is presented, which permits recognition of all echos occurring in periodic multipulse sequences. The calculated and observed signal amplitudes are considerably higher than expected from primary echo formation alone. T2 relaxation time measurements neglecting the formation of stimulated and indirect echoes lead to erroneous results. A method is demonstrated for a T2-sensitive multiecho experiment. A RARE experiment based on these principles delivers sufficient signal intensity even with small refocusing flip angles.

Frontolimbic brain abnormalities in patients with borderline personality disorder: a volumetric magnetic resonance imaging study.

BACKGROUND Dual frontolimbic brain pathology has been suggested as a possible correlate of impulsivity and aggressive behavior. One previous study reported volume loss of the hippocampus and the amygdala in patients with borderline personality disorder. We measured limbic and prefrontal brain volumes to test the hypothesis that frontolimbic brain pathology might be associated with borderline personality disorder. METHODS Eight unmedicated female patients with borderline personality disorder and eight matched healthy controls were studied. The volumes of the hippocampus, amygdala, and orbitofrontal, dorsolateral prefrontal, and anterior cingulate cortex were measured in the patients using magnetic resonance imaging volumetry and compared to those obtained in the controls. RESULTS We found a significant reduction of hippocampal and amygdala volumes in borderline personality disorder. There was a significant 24% reduction of the left orbitofrontal and a 26% reduction of the right anterior cingulate cortex in borderline personality disorder. Only left orbitofrontal volumes correlated significantly with amygdala volumes. CONCLUSIONS While volume loss of a single brain structure like the hippocampus is quite an unspecific finding in neuropsychiatry, the patterns of volume loss of the amygdala, hippocampus, and left orbitofrontal and right anterior cingulate cortex might differentiate borderline personality disorder from other neuropsychiatric conditions.

Quantitative 2D and 3D phase contrast MRI: Optimized analysis of blood flow and vessel wall parameters

Quantification of CINE phase contrast (PC)‐MRI data is a challenging task because of the limited spatiotemporal resolution and signal‐to‐noise ratio (SNR). The method presented in this work combines B‐spline interpolation and Greens theorem to provide optimized quantification of blood flow and vessel wall parameters. The B‐spline model provided optimal derivatives of the measured three‐directional blood velocities onto the vessel contour, as required for vectorial wall shear stress (WSS) computation. Eight planes distributed along the entire thoracic aorta were evaluated in a 19‐volunteer study using both high‐spatiotemporal‐resolution planar two‐dimensional (2D)‐CINE‐PC (∼1.4 × 1.4 mm2/24.4 ms) and lower‐resolution 3D‐CINE‐PC (∼2.8 × 1.6 × 3 mm3/48.6 ms) with three‐directional velocity encoding. Synthetic data, error propagation, and interindividual, intermodality, and interobserver variability were used to evaluate the reliability and reproducibility of the method. While the impact of MR measurement noise was only minor, the limited resolution of PC‐MRI introduced systematic WSS underestimations. In vivo data demonstrated close agreement for flow and WSS between 2D‐ and 3D‐CINE‐PC as well as observers, and confirmed the reliability of the method. WSS analysis along the aorta revealed the presence of a circumferential WSS component accounting for 10–20%. Initial results in a patient with atherosclerosis suggest the potential of the method for understanding the formation and progression of cardiovascular diseases. Magn Reson Med 60:1218–1231, 2008.

Magnetic resonance imaging of freely moving objects: prospective real-time motion correction using an external optical motion tracking system.

Subject motion and associated artefacts limit the applicability of MRI and the achievable quality of the images acquired. In this paper, a fully integrated method for prospective correction of arbitrary rigid body motion employing an external motion tracking device is demonstrated for the first time. The position of the imaging volume is updated prior to every excitation of the spin system. The performance of the available tracking hardware and its connection to the MR imager is analyzed in detail. With the introduction of a novel calibration procedure the accuracy of motion correction is improved compared to previous approaches. Together with the high geometry update rate even freely moving objects can be imaged without motion related artefacts. The high performance and image quality improvement in case of subject motion are demonstrated for various imaging techniques such as gradient and spin echo, as well as echo planar imaging.

Original articleFrontolimbic brain abnormalities in patients with borderline personality disorder: a volumetric magnetic resonance imaging study

BACKGROUND Dual frontolimbic brain pathology has been suggested as a possible correlate of impulsivity and aggressive behavior. One previous study reported volume loss of the hippocampus and the amygdala in patients with borderline personality disorder. We measured limbic and prefrontal brain volumes to test the hypothesis that frontolimbic brain pathology might be associated with borderline personality disorder. METHODS Eight unmedicated female patients with borderline personality disorder and eight matched healthy controls were studied. The volumes of the hippocampus, amygdala, and orbitofrontal, dorsolateral prefrontal, and anterior cingulate cortex were measured in the patients using magnetic resonance imaging volumetry and compared to those obtained in the controls. RESULTS We found a significant reduction of hippocampal and amygdala volumes in borderline personality disorder. There was a significant 24% reduction of the left orbitofrontal and a 26% reduction of the right anterior cingulate cortex in borderline personality disorder. Only left orbitofrontal volumes correlated significantly with amygdala volumes. CONCLUSIONS While volume loss of a single brain structure like the hippocampus is quite an unspecific finding in neuropsychiatry, the patterns of volume loss of the amygdala, hippocampus, and left orbitofrontal and right anterior cingulate cortex might differentiate borderline personality disorder from other neuropsychiatric conditions.

Magnetization preparation during the steady state: Fat-saturated 3D TrueFISP

A novel fat saturation scheme is proposed which combines spectral fat saturation with a steady‐state 3D true Fast Imaging with Steady Precesson (TrueFISP) sequence. Fat saturation consisted of a conventional frequency‐selective excitation pulse surrounded by spoiler gradients. This saturation block was periodically repeated within a continuously running TrueFISP sequence. Except for the fat signals, the steady‐state signal formation and the resulting image contrast of TrueFISP was not modified by the periodically inserted fat saturation block. This was achieved by a α/2 flip‐back pulse before the fat saturation block, which stores the established steady‐state transverse magnetization as pure longitudinal magnetization. After fat saturation this longitudinal magnetization was excited by a α/2 preparation pulse to continue the TrueFISP acquisition. The resulting images show contrast identical to conventional TrueFISP images, but without the usually very bright fat signals. The short repetition time allows acquisition of a 3D data set of the abdomen within a single breath‐hold. Magn Reson Med 45:1075–1080, 2001.