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.

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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.

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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.

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). In 17 healthy volunteers, nociceptive fibers of right hand dorsum were electrically stimulated via a concentric electrode. Test stimulation sessions consisted of three alternating stimulation periods and rest periods. They were performed before (Pre) and after (Post) conditioning LFS (1200 stimuli, 1Hz) or 20 min break (Control). Volunteers rated sensory and affective pain perception. Before LFS, test stimulation produced activation in bilateral primary and secondary somatosensory cortex (S1,S2), insula, anterior cingulate cortex (ACC), superior temporal cortex (STG), prefrontal cortex and right inferior parietal lobule (IPL). After LFS, exclusively right IPL was activated. Contrast between Pre and Post LFS indicated significant activity decrease in bilateral S1,S2, and ACC and right insula, IPL, and STG. Pre Control and Pre LFS were not different. Activity in Control experiments remained unchanged. Sensory and affective pain rating solely decreased after LFS. Subsequent regression analysis showed significant correlation between pain relief and increased activity after LFS in ACC, anterior insula, striatum, frontal and temporal cortex. The study revealed LTD of pain-related cerebral activation, involving sensory, affective, cognitive, and attentional processes. Positive correlation between pain relief and increased brain activation after LFS may indicate involvement of endogenous pain control mechanisms in LTD. These experiments may help to judge the potency of LTD for future chronic pain treatment.

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.