Monitoring brain activation changes in the early postoperative period after radical prostatectomy using fMRI.

Urinary incontinence is a major concern following radical prostatectomy. The etiology is multifactorial involving intrinsic sphincter deficiency and/or detrusor hyperactivity and/or decreased bladder compliance. Recent studies employing functional imaging methodology nicely demonstrated the reference regions of the micturition circuit. Based on these landmarks this work complements this field of research by studying patients with bladder dysfunction. Our aim was to evaluate, whether iatrogenic impairment of the pelvic floor muscles after retropubic radical prostatectomy (RRP) causes detectable changes in fMRI in the early postoperative period. fMRI was performed at 3T in 22 patients before and after RRP with urge to void due to a filled bladder. In a non-voiding model they were instructed to contract or to relax the pelvic floor muscles repetitively. As previously reported in healthy men, contraction and relaxation of pelvic floor muscles induced strong activations in the brainstem and more rostral areas in our group of patients before and after RRP. In general, all of them had stronger activations during contraction than during relaxation in all regions before and after the operation. Even though there was no difference in the activation level when relaxing the pelvic floor before and after the operation, we found stronger activation during contraction when comparing the preoperative with the postoperative level in some of the regions. The results suggest that the same cortical and subcortical networks can be demonstrated for micturition control in patients with prostate cancer as in healthy subjects. However, impaired pelvic floor muscle function after RRP seems to induce different activation intensities.

Gender differences in voluntary micturition control: an fMRI study.

In the last decade functional imaging has gained substantial importance for identifying cortical and subcortical brain regions being involved in the micturition circuit. However, possible gender differences are still a matter of debate. In the present study we used functional magnetic resonance imaging (fMRI) to determine micturition related brain regions in healthy men and compared them with those in women to elucidate gender-related differences. fMRI was performed at 3 T in 12 healthy men with urge to void due to a filled bladder. In a non-voiding model they were instructed to contract or to relax the pelvic floor muscles repetitively. As previously reported in women, contraction and relaxation of pelvic floor muscles induced strong activations in the brainstem and more rostral areas in our group of healthy men. In general, men had stronger activations during contraction than women in nearly all identified areas. In contrast, results for the relaxation condition were similar. Some of the differences between contraction and relaxation, formerly detected in females, could be found in our group of males as well. The results suggest that in women and men the same cortical and subcortical networks exist for micturition control. Especially, the well located activations in the putative pontine micturition centre and the periaqueductal grey could be identified in both sexes. However, pelvic floor muscle control seems to induce different activation intensities in men and women.

The posterior cingulate cortex and planum temporale/parietal operculum are activated by coherent visual motion.

The posterior cingulate cortex (PCC) is involved in higher order sensory and sensory-motor integration while the planum temporale/parietal operculum (PT/PO) junction takes part in auditory motion and vestibular processing. Both regions are activated during different types of visual stimulation. Here, we describe the response characteristics of the PCC and PT/PO to basic types of visual motion stimuli of different complexity (complex and simple coherent as well as incoherent motion). Functional magnetic resonance imaging (fMRI) was performed in 10 healthy subjects at 3 Tesla, whereby different moving dot stimuli (vertical, horizontal, rotational, radial, and random) were contrasted against a static dot pattern. All motion stimuli activated a distributed cortical network, including previously described motion-sensitive striate and extrastriate visual areas. Bilateral activations in the dorsal region of the PCC (dPCC) were evoked using coherent motion stimuli, irrespective of motion direction (vertical, horizontal, rotational, radial) with increasing activity and with higher complexity of the stimulus. In contrast, the PT/PO responded equally well to all of the different coherent motion types. Incoherent (random) motion yielded significantly less activation both in the dPCC and in the PT/PO area. These results suggest that the dPCC and the PT/PO take part in the processing of basic types of visual motion. However, in dPCC a possible effect of attentional modulation resulting in the higher activity evoked by the complex stimuli should also be considered. Further studies are warranted to incorporate these regions into the current model of the cortical motion processing network.

Cortical correlates of TMS-induced phantom hand movements revealed with concurrent TMS-fMRI.

We studied an amputee patient who experiences a conscious sense of movement (SoM) in her phantom hand, without significant activity in remaining muscles, when transcranial magnetic stimulation (TMS) is applied at appropriate intensity over the corresponding sector of contralateral motor cortex. We used the novel methodological combination of TMS during fMRI to reveal the neural correlates of her phantom SoM. A critical contrast concerned trials at intermediate TMS intensities: low enough not to produce overt activity in remaining muscles; but high enough to produce a phantom SoM on approximately half such trials. Comparing trials with versus without a phantom SoM reported phenomenally, for the same intermediate TMS intensities, factored out any non-specific TMS effects on brain activity to reveal neural correlates of the phantom SoM itself. Areas activated included primary motor cortex, dorsal premotor cortex, anterior intraparietal sulcus, and caudal supplementary motor area, regions that are also involved in some hand movement illusions and motor imagery in normals. This adds support to proposals that a conscious sense of movement for the hand can be conveyed by activity within corresponding motor-related cortical structures.

Voluntary pelvic floor muscle control--an fMRI study.

Storage and periodic expulsion of urine by the bladder are controlled by central pathways and organized as simple on-off switching circuits. Several reports concerning aspects of micturition control have identified distinct regions in the brainstem, like the pontine micturition center (PMC) and the periaqueductal gray (PAG), as well as the cerebellum, basal ganglia, limbic system, and cortical areas that are organized in a widespread network. The present study focused on the involvement of these specific brain regions in pelvic floor muscle control. Functional magnetic resonance imaging (fMRI) was performed at 3T in 11 healthy women with urge to void due to a filled bladder, who were instructed to either imitate voiding by releasing or to imitate interruption of voiding by contracting pelvic floor muscles. None of the subjects was able to start voiding during the experiments, presumably due to subconscious restraint resulting from the inconvenient situation. Relaxation and contraction of pelvic floor muscles induced strong and similar activation patterns including frontal cortex, sensory-motor cortex, cerebellum, and basal ganglia. Furthermore, well-localized activations in the PMC and the PAG were identified. To our knowledge, this is the first study using fMRI to demonstrate micturition-related activity in these brainstem structures. The presented approach proved to characterize the widespread central network in pelvic floor muscle control. Thus, in patients with voiding dysfunction, fMRI will be useful to elucidate the individual disturbance level.

Thresholding in correlation analyses of magnetic resonance functional neuroimaging.

The definition of objective and effective thresholds in MRI of human brain function is a crucial step in the analysis of paradigm-related activations. This paper introduces a user-independent and robust procedure that calculates statistical parametric maps based on correlation coefficients. Thresholds are introduced as p values and defined with respect to the physiologic noise distribution of the individual maps. Experimental examples from the human visual and motor system rely on dynamic acquisitions of gradient-echo echo-planar images (2.0 T, TR = 2,000 ms, 96 x 128 matrix) with blood oxygenation level-dependent contrast. The results demonstrate the disadvantages of thresholding with fixed correlation coefficients. In contrast, taking the individual noise into account allows for a derivation of p values and a reliable identification of highly significant activation centers. An adequate delineation of the spatial extent of activation may be achieved by adding directly neighboring pixels provided their correlation coefficients comply with a second lower p value threshold.

Functional MRI of cortical activations induced by transcranial magnetic stimulation (TMS).

The effects of repetitive transcranial magnetic stimulation (rTMS) on human brain activity and associated hemodynamics were investigated by blood-oxygenation-level-dependent (BOLD) MRI using echo-planar imaging at 2.0 T. Apart from bilateral activation of the auditory cortex by the audible rTMS discharges (23 bursts, 1 s duration, 10 Hz, 10-20 s interstimulus intervals), BOLD responses were restricted to cortical representations of actual finger movements performed either voluntarily or evoked by suprathreshold rTMS of the motor cortex. Neither subthreshold rTMS of the motor cortex nor suprathreshold rTMS of the lateral premotor cortex induced a detectable BOLD response. These findings suggest that neuronal depolarization as induced by rTMS modulates the spiking output of a brain area but does not automatically alter cerebral blood flow and oxygenation. The observation of BOLD MRI activations probably reflects the afferent intracortical processing of real movements.

Simultaneous EEG and functional MRI of epileptic activity: a case report.

OBJECTIVES: Attempts to localize the source of epileptic activity by linking electroencephalographic (EEG) abnormalities to blood oxygenation level-dependent (BOLD) magnetic resonance imaging (MRI) signal alterations are hampered mainly by EEG distortions during MRI, subject motion, and unknown hemodynamic response characteristics. METHODS: Using T2*-weighted echo-planar imaging at 2.0 T (2 s temporal resolution, 2 x 2 x 4 mm(3) spatial resolution), this work demonstrates strategies to alleviate some of these problems while studying a patient who had ideopathic generalized epilepsy with poly-spike and slow-wave complexes. RESULTS: Continuous EEG recordings during dynamic MRI (500 ms scanning, 1500 ms delay) and post-examination derivation of an EEG reference function for MRI analysis revealed positive BOLD MRI responses with temporal characteristics similar to those obtained for functional challenges. CONCLUSIONS: The ability to map focal epileptic activity and/or associated cognitive processing provides new potential for both epilepsy research and clinical patient management.

Regional modulation of BOLD MRI responses to human sensorimotor activation by transcranial direct current stimulation.

Blood oxygenation level dependent (BOLD) MRI was used to monitor modulations of human sensorimotor activity by prior transcranial direct current stimulation (tDCS). Activation maps for a right hand sequential finger opposition task were obtained for six subjects before as well as 0-5 min and 15-20 min after a 5-min period of 1 mA cathodal and, in a separate session, anodal tDCS of the left-hemispheric motor cortex. Cathodal tDCS resulted in a global decrease of the mean number of activated pixels by 38% (P < 0.01) 0-5 min after stimulation, which reduced to 28% (P < 0.05) 15-20 min after stimulation. A region-of-interest analysis revealed a 57% decrease of activated pixels (P < 0.001) in the supplementary motor area, but no change in the hand area of the primary motor cortex. Anodal tDCS yielded a nonsignificant 5% increase of activated pixels with no regional differences. These findings support the view that reduced neuroaxonal excitability after cathodal tDCS causes reduced brain activity. However, rather than affecting the primary sensorimotor input of an active task, the process appears to dampen those responses that rely on cortico-cortical connections and related processing. Magn Reson Med 45:196-201, 2001.

Artifacts caused by transcranial magnetic stimulation coils and EEG electrodes in T(2)*-weighted echo-planar imaging.

We investigated the effects of transcranial magnetic stimulation (TMS) coils and electroencephalographic (EEG) electrodes on T(2)*-weighted echo-planar images (EPI) at 2.0 T (gradient-echo EPI, mean TE = 53 ms, 2x2x4 mm(3)). In comparison with anatomic gradient-echo images (3D FLASH, TE = 4 ms, 1x1x1 mm(3)), T(2)*-weighted EPI acquisitions of a water-filled spherical phantom revealed severe signal losses and geometric distortions in the vicinity of TMS coils. Even remote effects were observed for image orientations perpendicular to the coil plane. EEG electrodes and the fixation gel caused milder localized distortions. In humans, complications were avoided by the large distance between the TMS coil and the cortical surface and when using an EPI orientation parallel to the plane of the coil. It is concluded that T(2)*-weighted EPI studies of human brain function may be performed without distortions caused by TMS coils and EEG electrodes.

Dipole-source analysis in a realistic head model in patients with focal epilepsy.

PURPOSE: By the use of three different head models in EEG dipole analysis, we tried to model the origin of interictal and ictal epileptic activity as precisely as possible. Further, as a control, a second evaluation was made by an independent group to control for interindividual reliability of the dipole source analysis. With the realistic head model (CURRY) considering cortex, skull, and skin segmentation, the spike source was located. METHODS: In five patients with mesial temporal epileptogenesis, confirmed by successful epilepsy surgery, the spike source was close to the hippocampus, with a mean distance of the dipole source from the hippocampus of 13.6 mm (range, 9-17.2 mm). In one case the ictal EEG also could be analyzed and resulted in a dipole-source localization comparable to the interictal source. RESULTS: In both head models using either pure cortex segmentation only or a concentric three-shell model, the dipole source was systematically dislocated in a more superior position. Data analysis by a second group with independently chosen EEG samples and identical individual head model resulted in deviations of <5.3 mm. Data analysis using independently selected spikes and independently segmented head models resulted in deviations < or =16.7 mm. CONCLUSIONS: In four cases of extratemporal epileptogenesis, the origin of interictal epileptiform discharges was localized to the suspected primary epileptogenic zone.

Spatial-frequency-related efficacy of visual stabilisation of posture.

The present study investigates the efficacy of visual stabilisation of posture for different spatial frequencies of a visual stimulus. Circular sine wave gratings were used to analyse the correlation between perception of motion in depth and stabilisation of fore-aft sway by the mechanism of detecting changes in target size. Body sway was recorded by a force-measuring platform (series A) and, in addition, by simultaneous tracking of infrared markers fixed to the subject's body (series B). Mean velocity and amplitude (RMS) of body sway were calculated in both sagittal (a-p) and lateral (l-r) planes. Sagittal sway was of least magnitude when viewing contrast gratings with lowest thresholds, whereas higher thresholds resulted in increasing sway parameters. As intended by the design of the stimuli, sagittal sway was correlated closer with the stabilising effect exerted by the different stimuli than was lateral sway. Sway velocity was reduced more efficiently, however, with a lower correlation with the psychophysical transfer function, than was RMS sway. Since sway velocity measured by the platform is suggested to depend to a greater extent on dynamic muscle forces generated at each individual body site the results indicate that visual information can be used to reduce and thereby optimise dynamic muscle action (sway velocity) even though static body sway is either not or less reduced. A comparable economisation of sway velocity but not of RMS sway was also seen at the end of posture investigations, indicative of positive training effects.

Selective activation of human cortical area V5A by a rotating visual stimulus in fMRI; implication of attentional mechanisms.

The human homologue of area V5A of rotation-selective cells in the monkey medial superior temporal area (MST) was identified using functional magnetic resonance imaging (fMRI). It was located within the border region of occipito-temporo-parietal cortex, in four of 10 subjects on both sides, and on the right or left side in three subjects each. The stimulus was a black-and-white sine-modulated windmill presented either stationary or in rotation phases of 1 s duration. Areas V1-V3 did not show up with this paradigm. Focusing attention by mentally counting the number of rotation phases ensured high signal intensity in V5A, whereas moving attention away by counting electric stimuli to the wrist diminished it despite persistent fixation of gaze to the centre of the windmill.

Soluble adhesion molecules (sVCAM-1 and sICAM-1) in cerebrospinal fluid and serum correlate with MRI activity in multiple sclerosis.

We performed a prospective study to correlate quantiative brain magnetic resonance imaging activity (gadolinium-diethylenetriaminepentaacetic acid enhancement) to cerebrospinal fluid and serum levels of soluble adhesion molecules in 46 patients with newly diagnosed multiple sclerosis (MS) and 30 control subjects with other diseases of the central nervous system. In all patients, magnetic resonance imaging of the brain and lumbar puncture were performed on the same day. In 32 (70%) of 46 MS patients, 8 (80%) of 10 patients with acute viral encephalitis, but none of the control subjects with noninflammatory diseases, gadolinium-enhancing lesions were detected. There was a significant correlation between the cerebrospinal fluid/serum ratios for soluble intercellular adhesion molecule-1 and soluble vascular cell adhesion molecule-1 as well as serum levels for both molecules and the area of gadolinium-enhancing lesions. No obvious correlation was observed between magnetic resonance imaging findings and cerebrospinal fluid cell count, protein concentration, or intrathecal immunoglobulin production. In patients with a single periventricular gadolinium-enhancing lesion (n = 16), we observed a strong negative correlation between the distance from the lateral ventricles and the cerebrospinal fluid/serum ratios for soluble intercellular adhesion molecule-1/albumin and soluble vascular cell adhesion molecule-1/albumin. These results suggest that intrathecal production of the two soluble adhesion molecules, as well as serum levels for soluble vascular cell adhesion molecule-1, in patients with MS reflect magnetic resonance imaging activity of typical periventricular lesions.

Changes in human motor cortex excitability induced by dopaminergic and anti-dopaminergic drugs.

Transcranial magnetic stimulation was used to probe the acute effect of a single oral dose of various dopaminergic (levodopa, selegiline, bromocriptine) and antidopaminergic drugs (sulpiride, haloperidol) on motor cortex excitability in healthy volunteers. Motor threshold, intracortical inhibition and intracortical facilitation were tested in the abductor digiti minimi muscle. The latter two parameters were studied in a conditioning-test paired stimulus paradigm. The principal findings were an increase in intracortical inhibition by bromocriptine, and, conversely, a decrease in intracortical inhibition and an increase in intracortical facilitation by haloperidol. Effects peaked at delays consistent with the pharmacokinetics of the two drugs and were fully reversible. In conclusion, dopamine receptor agonists and antagonists can be considered inverse modulators of motor cortex excitability: the former enhance inhibition while the latter reduce it. The relation of the present findings to current models of motor excitability abnormalities in movement disorders will be discussed.