Functional imaging of sympathetic activation during mental stress.

Activation of the sympathetic nervous system (SNS) is essential in adapting to environmental stressors and in maintaining homeostasis. This reaction can also turn into maladaptation, associated with a wide spectrum of stress-related diseases. Up to now, the cortical mechanisms of sympathetic activation in acute mental stress have not been sufficiently characterized. We therefore investigated cerebral activation applying functional magnetic resonance imaging (fMRI) during performance of a mental stress task with graded levels of difficulty, i.e. four versions of a Stroop task (Colour Word Interference Test, CWT) in healthy subjects. To analyze stress-associated sympathetic activation, skin conductance and heart rate were continuously recorded. The results show that sympathetic activation through mental stress is associated with distinct cerebral regions being immediately involved in task performance (visual, motor, and premotor areas). Other activated regions (right insula, dorsolateral superior frontal gyrus, cerebellar regions) are unrelated to task performance. These latter regions have previously been considered to be involved in mediating different stress responses. The results might furthermore serve as a basis for future investigations of the connection between these cortical regions in the generation of stress-related diseases.

Neural correlates of hemispheric dominance and ipsilaterality within the vestibular system.

Earlier functional imaging studies on the processing of vestibular information mainly focused on cortical activations due to stimulation of the horizontal semicircular canals in right-handers. Two factors were found to determine its processing in the temporo-parietal cortex: a dominance of the non-dominant hemisphere and an ipsilaterality of the neural pathways. In an investigation of the role of these factors in the vestibular otoliths, we used vestibular evoked myogenic potentials (VEMPs) in a fMRI study of monaural saccular-otolith stimulation. Our aim was to (1) analyze the hemispheric dominance for saccular-otolith information in healthy left-handers, (2) determine if there is a predominance of the ipsilateral saccular-otolith projection, and (3) evaluate the impact of both factors on the temporo-parieto-insular activation pattern. A block design with three stimulation and rest conditions was applied: (1) 102 dB-VEMP stimulation; (2) 65 dB-control-acoustic stimulation, (3) 102 dB-white-noise-control stimulation. After subtraction of acoustic side effects, bilateral activations were found in the posterior insula, the superior/middle/transverse temporal gyri, and the inferior parietal lobule. The distribution of the saccular-otolith activations was influenced by the two factors but with topographic disparity: whereas the inferior parts of the temporo-parietal cortex were mainly influenced by the ipsilaterality of the pathways, the upper parts reflected the dominance of the non-dominant hemisphere. This is in contrast to the processing of acoustic stimulation, which showed a predominance of the contralateral pathways. Our study proves the importance of the hemispheric preponderance also in left-handers, which is of relevance in the superior parts of the insula gyrus V, the inferior parietal lobule, and the superior temporal gyri.

Cortical representation of saccular vestibular stimulation: VEMPs in fMRI.

Short tone bursts trigger a vestibular evoked myogenic potential (VEMP), an inhibitory potential which reflects a component of the vestibulocollic reflex (VCR). These potentials arise as a result of activation of the sacculus and are expressed through the vestibulo-collic reflex (VCR). Up to now, the ascending projections of the sacculus are unknown in humans, only the representation of the semicircular canals or the entire vestibular nerve has been demonstrated. The aim of this study was to determine whether a sacculus stimulus that evoked VEMPs could activate vestibular cortical areas in fMRI. To determine this, we studied the differential effects of unilateral VEMP stimulation in 21 healthy right-handers in a clinical 1.5 T scanner while wearing piezo electric headphones. A unilateral VEMP stimulus and two auditory control stimuli were given in randomized order over the stimulated ear. A random effects statistical analysis was done with SPM2 (p<0.05, corrected). After exclusion of the auditory effects, the major findings were as follows: (i) significant activations were located in the multisensory cortical vestibular network within both hemispheres, including the posterior insular cortex, the middle and superior temporal gyri, and the inferior parietal cortex. (ii) The activation pattern was elicited bilaterally with a predominance of the right hemisphere in right-handers. (iii) Saccular vestibular projection was predominantly ipsilateral, whereas (iv) pure acoustic stimuli were processed with a predominance of the respective contralateral and mainly in the left hemisphere. This is the first demonstration by means of fMRI of the cortical representation of the saccular input at cortical level. The activation pattern is similar to that known from the stimulation of the entire vestibular nerve or the horizontal semicircular canal. Our data give evidence of a task-dependent separation of the processing within the vestibular otolith and the auditory systems in the two hemispheres.

Combined spike-related functional MRI and multiple source analysis in the non-invasive spike localization of benign rolandic epilepsy.

OBJECTIVE: To localize the irritative zone in children by combined spike-related fMRI and EEG multiple source analysis (MSA) in children with benign rolandic epilepsy. METHODS: Interictal spikes were averaged and localized using MSA, and source locations were displayed in the anatomical 3D-MRI in 11 patients (5-12 yrs, median 10). Interictal spikes were additionally recorded during the fMRI acquisition (EEG-fMRI), and the fMRI sequences were correlated off-line with the EEG spikes. RESULTS: MSA revealed an initial central dipole in all patients, including the face or hand area. A second dipolar source was mostly consistent with propagated activity. BOLD activations from EEG-fMRI, consistent with the locations of the initial dipoles, were found in four patients. We found additional large areas of BOLD activations in 3 of these subjects extending into the sylvian fissure and the insula. These were identified as propagated activity by MSA using the short time differences in the source waveforms. CONCLUSIONS: MSA provided reliable localization of the spike onset zone in all children with benign rolandic epilepsy. Using the combination of EEG-fMRI and MSA we were able to discriminate the spike onset zone from propagated epileptiform source activity, using the spatial resolution of the EEG-fMRI technique and the temporal resolution of the MSA. However, the sensitivity of the EEG-fMRI technique was low and further improvements of the technique are warranted. SIGNIFICANCE: This study shows that a combination of EEG-fMRI and MSA may be a powerful tool to describe the irritative zone of patients with idiopathic focal epilepsies. Clinical studies in patients with non-idiopathic focal epilepsies may clarify whether both techniques can be used as complementary clinical tools to localize the onset of interictal epileptic activity in focal epilepsies.

Alexithymia and impoverished dream content: evidence from rapid eye movement sleep awakenings.

OBJECTIVE: Despite the repeated suggestion in the literature of an association between impoverished dream processes and alexithymia, little systematic research has been conducted. METHODS: Eight nonclinical adults scoring in the alexithymia range and eight nonclinical adults scoring in the nonalexithymia range on a measure of alexithymia were awakened for dream reports during their second, third, and fourth rapid eye movement periods on the second of two consecutive polygraphically monitored nights in a sleep laboratory. RESULTS: The alexithymic and nonalexithymic groups did not differ in the number of dreams reported or the number of words used in the description of their dreams. The two groups also did not differ in their self-reports of the emotional valence associated with their dream experiences. In contrast, the dream reports of the alexithymic group were rated as less fantastic than the dream reports of the nonalexithymic group. CONCLUSIONS: These findings provide additional evidence that alexithymia involves restricted imaginative processes.

Improved resolution of magnetic resonance microscopy in examination of skin tumors.

Magnetic resonance imaging has become increasingly important for visualization and tissue differentiation of internal organs. Because of limited resolution, investigation of skin has been of little diagnostic value so far. We combined a homogeneous magnetic field of 9.4 T, as used in magnetic resonance spectroscopy, with gradient fields of 11.7 G/cm and an imaging unit to obtain a voxel resolution of 40 x 40 x 300 microm(3). With this magnetic resonance microscopy unit, we studied normal skin, 12 nevocellular nevi, 20 basal cell carcinomas, 8 melanomas, and 8 seborrheic keratoses after excision in vitro. The specimens were visualized in spin-echo images. The proton relaxation times T1 and T2 were determined for the different skin layers and tumor tissues. Interpretation of the spin-echo images was based on comparison with the correlating histology. Epidermis, dermis, subcutaneous tissue, and hair follicle complexes could be distinguished. Stratum corneum and hairs emitted no signal. All tumors presented as distinct, signal-rich, homogeneous structures within the dark, signal-poor dermis. Their shape corresponded to their outline in the histologic sections. Buds of superficial basal cell carcinomas could be resolved. The proton relaxation times T1 and T2 were significantly different among all skin layers and tumors. Our results demonstrate that with sufficient resolution, differentiation of skin tumors is possible using magnetic resonance imaging.

MR relaxometry: estimating overhydration in renal failure.

An MR method is described for estimating overhydration in patients suffering from renal failure. In 29 healthy volunteers, the fat content of a selected slice of the lower limb was correlated to the overall T1-relaxation time (r = -0.97, p < 0.000001). When compared with the normal T1 of the voluntary group, delta T1 was calculated having regard to the individual fat content in 74 MR studies of 22 overhydrated patients. MR results were correlated with the difference between clinically estimated dry and the actual body weight (r = 0.6, p < 0.000001). In an intraindividual follow-up (11 studies) MRI was shown to provide good correlation to the actual body weight (r = 0.9, p < 0.0005) and fluid balance (r = 0.87, p < 0.001).

Changes of soft-tissue water examined with magnetic resonance and electrical impedance tomography: an in vivo experiment.

The purpose of this study was the examination of short-term changes in soft-tissue water under in vivo conditions. In 12 healthy volunteers the water distribution of a selected slice of the lower limb was examined after change of position and rapid infusion of 0.9% saline solution. Two methods were used for data acquisition: magnetic resonance imaging (MRI) (Repetition Time (TR) = 1600 msec, Inversion Time (TI) = 300 msec, Echo Time (TE) = 22 msec) and electrical impedance tomography (EIT). In orthostatic equilibrium all 12 volunteers demonstrated changes of MR signal intensity and resistivity in the range of 12% and 7%, respectively. After infusion, mean changes of signal intensity and resistivity were 7% and 4%, respectively. The overall correlation of MRI and EIT was -0.96 (p < 0.001). Results indicate that inversion recovery sequences are a sensitive method of detecting in vivo changes of water distribution in selected areas of the body.