Estradiol Modulates Functional Brain Organization during the Menstrual Cycle: An Analysis of Interhemispheric Inhibition

According to the hypothesis of progesterone-mediated interhemispheric decoupling (Hausmann and Güntürkün, 2000), functional cerebral asymmetries (FCAs), which are stable in men and change during the menstrual cycle in women, are generated by interhemispheric inhibition of the dominant on the nondominant hemisphere. The change of lateralization during the menstrual cycle in women might indicate that sex hormones play an important role in modulating FCAs. We used functional magnetic resonance imaging to examine the role of estradiol in determining cyclic changes of interhemispheric inhibition. Women performed a word-matching task, while they were scanned twice during the cycle, once during the menstrual and once during the follicular phase. By use of a connectivity analysis we found that the inhibitory influence of left-hemispheric language areas on homotopic areas of the right hemisphere is strongest during the menses, resulting in a pronounced lateralization. During the follicular phase, due to rising estradiol levels, inhibition and thus functional cerebral asymmetries are reduced. These results reveal a powerful neuromodulatory action of estradiol on the dynamics of functional brain organization in the female brain. They may further contribute to the ongoing discussion of sex differences in brain function in that they help explain the dynamic part of functional brain organization in which the female differs from the male brain

The subcortical role of language processing: high level linguistic features such as ambiguity-resolution and the human brain; an fMRI study

In the present study, we were interested in the neurofunctional representations of ambiguity processing by using functional magnetic resonance imaging (fMRI). Twelve right-handed, healthy adults aged between 21 and 29 years (6 male, 6 female) underwent an ambiguity resolution task with 4 different conditions (dominant vs. non-dominant; dominant vs. distractor; non-dominant vs. distractor; distractor vs. distractor). After subtraction of the corresponding control task (distractor vs. distractor) we found significant activation especially in the thalamus and some parts of the basal ganglia (caudate nucleus, putamen). Our findings implicate a participation of the thalamus and other basal ganglia circuits in high level linguistic functions and match with theoretical considerations on this highly controversial topic. Subcortical neural circuits probably become activated when the language processing system cannot rely entirely on automatic mechanisms but has to recruit controlled processes as well. Furthermore, we found broad activation in the inferior parietal lobule, the prefrontal gyrus, pre-SMA and SMA and the cingulate cortex. This might reflect a strategic semantic search mechanism which probably can be illustrated with connectionist models of language processing. According to this, we hypothesize a neuroregulatory role for the thalamus and basal ganglia in regulating and monitoring the release of preformulated language segments for motor programming and semantic verification. According to our findings there is strong evidence, that especially the thalamus, the caudate nucleus, the cingulate cortex, the inferior parietal lobule and the prefrontal cortex are responsible for an accurate ambiguity resolution in the human brain

Feasibility of k-t BLAST for BOLD fMRI with a spin-echo based acquisition at 3 T and 7 T

OBJECTIVES: This study tested the feasibility of applying k-t BLAST to blood oxygen level dependent functional MRI of the brain at 3 Tesla (T) and at 7 T. Shorter echo train lengths, achieved through the application of k-t BLAST, are expected to counteract increased sensitivity to inhomogeneities in B0 at higher magnetic field strengths, especially in echo planar images, and reduce the relatively long acquisition times and high RF power deposition in spin-echo based methods. MATERIALS AND METHODS: k-t BLAST was combined with displaced UFLARE at 3 T and 7 T. Temporal and spatial fidelity of k-t BLAST were investigated using a test object, in which localized variations in signal intensity mimic activation-induced signal changes. fMRI was performed using typical box-car design finger tapping. In a separate analysis full k-space data were decimated to simulate k-t BLAST acquisitions and compare results with the fully sampled data, thereby avoiding physiological and noise differences between acquisitions. RESULTS: Activation can be detected at under-sampling factors as high as 16, whereas appropriately reconstructed data, under-sampled at factors below 8 entail insignificant loss of sensitivity and considerable reductions in acquisition times and RF power deposition. CONCLUSIONS: k-t BLAST is compatible with fMRI acquisitions and opens up possibilities including distortion-free T2*-weighted blood oxygen level dependent fMRI with displaced UFLARE at high magnetic field strengths

Extensive sampling and high-throughput sequencing reveal Posidoniomyces atricolor gen. et sp. nov. (Aigialaceae, Pleosporales) as the dominant root mycobiont of the dominant Mediterranean seagrass Posidonia oceanica

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Functional reorganisation in patients with right hemisphere stroke after training of alertness: a longitudinal PET and fMRI study in eight cases

In patients with alertness deficits due to right hemispheric vascular brain damage, training induced changes in the individual functional networks involved in intrinsic alertness were assessed in a longitudinal positron emission tomography (PET)/fMRI activation study. Patients were trained by administering the alertness routine of the AIXTENT computerized attention training or, in the control condition, by using a computerized training of verbal and topological memory. Before and after the training, both a PET/fMRI and a neuropsychological assessment were carried out. In this paper, we are presenting four patients after alertness training: three, whose alertness performance improved significantly after training, and one, who did not improve. In the patients showing behavioural improvement, the PET/fMRI activation after training revealed partial restitution of the right hemisphere (RH) functional network known to subserve intrinsic alertness in normal subjects, especially in the right dorsolateral or medial frontal cortex. For the patient without behavioural improvement, the PET activation after training showed an,increase of activation only in the left hemisphere. Out of the four patients in the memory training control group only one showed significant improvement of alertness. Another patient had an increase of right frontal activation after the training but this did not correspond to behavioural improvement. In a control group of six normal participants, repetition of the alertness activation paradigm in fMRI revealed a decrease of right frontal and parietal activation from the first to a second measurement after 3 weeks, in contrast to the observed training induced effects in the patients. (C) 2003 Elsevier Ltd. All rights reserved

eine fMRI-Fallstudie bei zwei Patienten nach schwerer Unfalltraumatisierung

Neuroimaging research on the neurobiology of chronic PTSD (posttraumatic stress disorder) has revealed structural and functional alterations primarily affecting areas of the medial temporal lobe (hippocampus, amygdala, and parahippocampal gyrus) and the frontal cortex known to be associated with the disorder. Using functional magnetic resonance imaging (fMRI), the present study studied the functional neuroanatomy of traumatic and non-traumatic emotional memory in two surgical patients who had sustained severe accident trauma. While patient 1 had developed acute PTSD following the traumatic event, patient 2 (control) did not. When confronted with traumatic (relative to negatively valenced non-traumatic) memory, the PTSD patient exhibited evidence for increased neural activity in the right and the left superior temporal lobe, the amygdala, the left angular gyrus, and the medial frontal gyrus, while the non-PTSD patient exposed to identical conditions showed increased activations in frontal and parietal regions. Both patients exhibited identical activation patterns when recalling non-traumatic memories relative to neutral memories. It is concluded that the pronounced activation patterns in the PTSD patient may be considered specific for acute PTSD, involved with the emotional arousal and the vivid visual recollections typical for the acute phase of the disorder.Neuere bildgebende Studien zur Neurobiologie der chronifizierten PTSD lassen vermuten, dass das Störungsbild sowohl mit funktionellen als auch strukturellen Veränderungen in umschriebenen Hirnregionen des medialen Temporallappens (Hippokampus, Amygdala, Parahippokampaler Gyrus) und des frontalen Cortex einhergeht. Die vorliegende fMRT(funktionelle Magnetresonanztomografie)-Studie untersuchte die funktionelle Neuroanatomie traumatischer und nicht-traumatischer Erinnerungen bei zwei chirurgischen Patienten nach schwerer Unfalltraumatisierung. Nur Patient 1 entwickelte eine akute PTSD, während Patient 2 ohne klinisch relevante PTSD-Symptomatik blieb. Konfrontiert mit der Unfallerinnerung (im Vergleich zu negativen, aber nicht traumatischen Erinnerungen) zeigte der PTSD-Patient vermehrte neuronale Aktivitäten im Bereich des rechten und linken superioren Temporallappens, im Bereich der Amygdalae, des linken Gyrus angularis, und des Gyrus frontalis medialis. Der Patient ohne PTSD-Symptome zeigte bei gleichen Untersuchungsbedingungen vermehrte neuronale Aktivitäten in frontalen und parietalen Regionen. Beide Patienten zeigten identische Aktivierungsmuster für den Vergleich negativer, nicht-traumatischer zu neutralen Erinnerungen. Die Untersuchungsergebnisse lassen vermuten, dass die besonderen Aktivierungsmuster bei dem Patienten mit akuter PTSD spezifisch für das Stadium einer akuten PTSD sind, die typischerweise durch sehr lebendige und emotional belastende Wiedererinnerungen der traumatischen Situation charakterisiert ist