René Vohn

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.

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.

Management of attentional resources in within‐modal and cross‐modal divided attention tasks: An fMRI study

In the present study, we were interested in distinguishing the cortical representations of within‐modal and cross‐modal divided attention tasks by using functional magnetic resonance imaging. Sixteen healthy male subjects aged between 21 and 30 years underwent two within‐modal (auditory/auditory, visual/visual) and one cross‐modal (auditory/visual) divided attention task, as well as related selective attention control conditions. After subtraction of the corresponding control task the three divided attention tasks, irrespective of sensory modality, revealed significant activation in a predominantly right hemisphere network involving the prefrontal cortex, the inferior parietal cortex, and the claustrum. Under the cross‐modal condition, however, the frontal and parietal activation was more extended and more bilateral and there also was stronger right hemisphere activation of the anterior cingulate cortex and the thalamus. In comparison to the within‐modal conditions additional bilateral frontal and left inferior parietal activation was found for the cross‐modal condition. The supplementary fronto‐parietal, anterior cingulate cortex, and thalamus activation in the auditory/visual condition could be argued to reflect an additional demand for coordination of two ongoing cross‐modal cognitive processes. Hum Brain Mapp, 2007.

A special role for numbers in working memory? An fMRI study

Although numbers carry averbal semantics (i.e., magnitude), they are often utilized in verbal Working Memory (vWM) tasks. However, vWM is thought to rely on a purely phonological code. Here, we tested the influence of (a) averbal semantics and (b) different tasks on performance in a vWM context by examining stimulus and task-specific variation of activity in the horizontal parts of the intraparietal sulcus (hIPS). The hIPS has previously been shown to subserve magnitude processing modulated by (a) specific stimuli and (b) specific tasks. Two variants of an n-back paradigm (comparison and identity match tasks) utilizing letters and numbers as stimulus material at different levels of vWM load were administered in 16 participants. Behavioral and functional imaging data reveal stimulus-specific modulation of activity in the hIPS suggesting a semantic influence of numbers. In the identity match task, numbers induced additional hIPS activation compared to letters while letters never induced additional hIPS activation when compared to numbers. Letters as compared to numbers only induced additional hIPS activation in the comparison task. These results question the assumption of a purely phonological code in vWM because hIPS activation subserving magnitude processing is modulated by stimulus semantics and task demands.

Long-term depression of pain-related cerebral activation in healthy man: An fMRI study

Electrical low‐frequency stimulation (LFS) of cutaneous afferents reliably induces long‐term depression (LTD) of nociception and pain in man. In this study LFS effects on cerebral activation were investigated by functional magnetic resonance imaging (fMRI).

The neurofunctional mechanisms of traumatic and non-traumatic memory in patients with acute PTSD following accident trauma

Neurofunctional alterations in acute posttraumatic stress disorder (PTSD) and changes thereof during the course of the disease are not well investigated. We used functional magnetic resonance imaging to assess the functional neuroanatomy of emotional memory in surgical patients with acute PTSD. Traumatic (relative to non-traumatic) memories increased neural activity in the amygdala, hippocampus, lateral temporal, retrosplenial, and anterior cingulate cortices. These regions are all implicated in memory and emotion. A comparison of findings with data on chronic PTSD suggests that brain circuits affected by the acute disorder are extended and unstable while chronic disease is characterized by circumscribed and stable neurofunctional abnormalities.

Evaluation of Spatial Processing in Virtual Reality Using Functional Magnetic Resonance Imaging (fMRI)

While the ecological validity of virtual reality (VR) applications is usually assessed by behavioral data or interrogation, an alternative approach on a neuronal level is offered by brain imaging methods. Because it is yet unclear if 3D space in virtual environments is processed analogically to the real world, we conducted a study investigating virtual spatial processing in the brain using functional magnetic resonance imaging (fMRI). Results show differences in VR spatial brain processing as compared to known brain activations in reality. Identifying differences and commonalities of brain processing in VR reveals limitations and holds important implications for VR therapy and training tools. When VR therapy aims at the rehabilitation of brain function and activity, differences in brain processing have to be taken into account for designing effective VR training tools. Furthermore, for an evaluation of possible restoration effects caused by VR training, it is necessary to integrate information about the brain activation networks elicited by the training. The present study provides an example for demonstrating the benefit of fMRI as an evaluation tool for the mental processes involved in virtual environments.

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.

Cerebral activations resulting from virtual dental treatment

Pain, and anxiety of pain, for some people are serious problems in dental treatment. It is a common practical experience that even entering a dental surgery office, or the sound of a dental drill, may evoke vegetative correlates of toothache without any underlying disease. This everyday phenomenon suggests the hypothesis of a corresponding activation of pain-related brain areas by virtual dental treatment. Twenty healthy subjects viewed two different video clips presenting a dental treatment from the first-person perspective (simulation movie) and a moving hand holding an electrical toothbrush (control movie). Using functional magnetic resonance imaging, the cerebral hemodynamic responses that occurred during simulation and control movies were compared. Virtual dental treatment was associated with increased activity in pain-related brain areas such as the cingulate cortex, the insula, and primary and secondary somatosensory cortexes (SI, SII). The brain activation pattern indicates not only affective-motivational but also sensory-discriminative pain components during virtual dental treatment in all volunteers. Volunteers with a higher level of dental anxiety showed stronger activation of SI and SII. This may be a result of their higher anticipation of pain.