Rob Luypaert

Neurocognitive effects of HF-rTMS over the dorsolateral prefrontal cortex on the attentional processing of emotional information in healthy women an event-related fMRI study

Current evidence concerning the neurocircuitry underlying the interplay between attention and emotion is mainly correlational. We used high-frequency repetitive Transcranial Magnetic Stimulation (HF-rTMS) to experimentally manipulate activity within the right or left dorsolateral prefrontal cortex (DLPFC) of healthy women and examined changes in attentional processing of emotional information using an emotional modification of the exogenous cueing task during event-related fMRI. Right prefrontal HF-rTMS resulted in impaired disengagement from angry faces, associated with decreased activation within the right DLPFC, dorsal anterior cingulate cortex (dACC) and left superior parietal gyrus, combined with increased activity within the right amygdala. Left prefrontal HF-rTMS resulted in diminished attentional engagement by angry faces and was associated with increased activity within the right DLPFC, dACC, right superior parietal gyrus and left orbitofrontal cortex. The present observations are in line with reports of a functionally interactive network of cortical-limbic pathways that play a central role in emotion regulation.

Individual differences in local gray and white matter volumes reflect differences in temperament and character: A voxel-based morphometry study in healthy young females

The psychobiological personality model of Cloninger distinguishes four heritable temperament traits (harm avoidance (HA), novelty seeking (NS), reward dependence (RD) and persistence (P)) and three character traits (self-directedness (SD), cooperativeness (CO) and self-transcendence (ST)) which develop during lifetime. Prior research already showed that individual differences in temperament are reflected in structural variances in specific brain areas. In this study, we used voxel-based morphometry (VBM) to correlate the different temperament and character traits with local gray and white matter volumes (GMV and WMV) in young healthy female volunteers. We found correlations between the temperament traits and GMV and WMV in the frontal, temporal and limbic regions involved in controlling and generating the corresponding behavior as proposed in Cloningers theory: anxious for HA, impulsive for NS, reward-directed for RD and goal-directed for P. The character traits correlated with GMV and WMV in the frontal, temporal and limbic regions involved in the corresponding cognitive tasks: self-reflection for SD, mentalizing and empathizing with others for CO and religious belief for ST. This study shows that individual variations in brain morphology can be related to the temperament and character dimensions, and lends support to the hypothesis of a neurobiological basis of personality traits.

Inter-individual differences in the habitual use of cognitive reappraisal and expressive suppression are associated with variations in prefrontal cognitive control for emotional information: An event related fMRI study

Two different emotion regulation strategies, cognitive reappraisal and expressive suppression, are strongly associated with increased neural activity in the prefrontal cognitive control network. In this event-related fMRI study, we investigated whether individual differences in habitual reappraisal and suppression tendencies are related to differences in prefrontal cognitive control processes for emotional information. In order to measure cognitive control over inhibiting a dominant response to happy or sad stimuli (in favor of the opposite valence), thirty-one healthy female participants performed the Cued Emotional Conflict Task (CECT). The Emotion Regulation Questionnaire was used to measure individual differences in everyday use of emotion regulation. Results demonstrate that high reappraisers are behaviorally faster and exert more fronto-cingulate activity when inhibiting a response to sad faces (compared to happy faces, FDR corrected). On the other hand, suppression scores are not correlated with performance to CECT trials. Interestingly, suppression scores are associated with higher amygdala activation during the inhibition of a response to sad faces (compared to happy faces). These data suggest that habitual reappraisal is associated with underlying functional cognitive control processes to inhibit a dominant response to negative material. In contrast, the effort to control negative material has negative consequences in individuals who have a tendency to suppress emotions.

Deconvolution of dynamic contrast-enhanced MRI data by linear inversion: Choice of the regularization parameter

Truncated singular value decomposition (TSVD) is an effective method for the deconvolution of dynamic contrast‐enhanced MRI. Two robust methods for the selection of the truncation threshold on a pixel‐by‐pixel basis—generalized cross validation (GCV) and the L‐curve criterion (LCC)—were optimized and compared to paradigms in the literature. The methods lead to improvements in the estimate of the residue function and of its maximum and converge properly with SNR. The oscillations typically observed in the solution vanish entirely and perfusion is more accurately estimated at small mean transit times. This results in improved image contrast and increased sensitivity to perfusion abnormalities, at the cost of 1–2 min in calculation time and isolated instabilities in the image. It is argued that the latter problem may be resolved by optimization. Simulated results for GCV and LCC are equivalent in terms of performance, but GCV is faster. Magn Reson Med 52:209–213, 2004.

How brooding minds inhibit negative material: An event-related fMRI study

Depressive brooding - a passive ruminative focus on ones problems, negative mood and their consequences - is a thinking style that places individuals at a greater risk to develop future psychopathology. In this study, we investigated whether inter-individual differences in depressive brooding are related to neural differences underlying the inhibition of a dominant response towards negative information in favor of the concurrent (positive) response. To exclude the possibility that information processes would be confounded by sustained negative mood or enhanced stress responses, a sample of thirty never-depressed healthy individuals was selected. The Cued Emotional Control Task (CECT) was used to index the ability to enhance cognitive control when encountering a negative stimulus associated with an incompatible stimulus-response mapping. Individual brooding scores were not related to behavioral performances on the CECT. On the other hand, whole brain analyses demonstrated that trait depressive brooding scores were positively associated with activation in the posterior parts of the dorsal anterior cingulate cortex (pdACC) while successfully inhibiting a response to negative relative to positive information. These findings demonstrate that brooding minds need to recruit more pdACC activation when inhibiting a dominant response towards negative information (in favor of a response towards positive), although they are performing similarly as low brooders at the behavioral level. Future research should investigate whether and how these brooding related neural adjustments in healthy volunteers are related to future psychopathology.

Combined T1-based perfusion MRI and MR angiography in kidney: First experience in normals and pathology

OBJECTIVESnTo investigate the feasibility of implementing quantitative T1-perfusion in the routine MRA-protocol and to obtain a first experience in normals and pathology.nnnMATERIALS AND METHODSnFor perfusion imaging, IR-prepared FLASH (one 4 mm slice at mid-renal level, TR 4.4 ms, TE 2.2 ms, TI 180 ms, FA 50 degrees , matrix 128 x 256, bandwidth per pixel 300, 400 dynamics, temporal resolution 0.3 s, total measurement time 2 min) was applied during the injection of 10 ml of standard 0.5 mmol/ml Gadolinium-DTPA solution at 2 ml/s, followed by 3DCE-MRA with bolus tracking (TR 5.4, TE 1.4, FA 40 degrees , matrix 192 x 512, NSA 1, slice thickness 1.5 mm), using a second dose of 0.1 mmol Gadolinium-DTPA per kg body weight with a maximum of 20 ml. The T1-weighted signals (perfusion data) were converted to tissue tracer concentrations and deconvolved with an inflow corrected AIF; blood flow, distribution volume, mean transit time and blood flow heterogeneity were derived.nnnRESULTSnMRA quality was uncompromised by the first bolus administered for perfusion purposes. In the normals, average cortical RBF, RVD and MTT were 1.2 ml/min/ml (S.D. 0.3 ml/min/ml), 0.4 ml/ml (S.D. 0.1 ml/ml) and 21s (S.D. 4s). These RBF values are lower than those found in the literature, probably due to residual AIF inflow effects. The sensitivity of the technique was sufficient to demonstrate altered perfusion in the examples of pathology.nnnCONCLUSIONnCombined quantitative T1-perfusion and MRA have a potential for noninvasive renovascular screening and may provide an anatomical and physiological evaluation of renal status.

MR phase imaging to quantify bone volume fraction: Computer simulations and in vivo measurements

Magnetic resonance phase images can be used to assess trabecular bone by measuring the standard deviation of the phases in a region of interest. The standard deviation of regional phase measurements reflects the degree of magnetic field inhomogeneity caused by susceptibility differences between bone and marrow. A 3D computer model of trabecular bone was developed and then used to explore the influence of bone volume fraction and imaging parameters such as pixel size and slice width on the standard deviation of regional phase measurements. The results from these tests show that with appropriate selection of these parameters, phase spread strongly reflects variations in trabecular bone density (a correlation of R(2) = 0.98 with bone volume fraction between 0 and 10%). The technique was then applied in vivo on the radius of 25 patients who already had a bone density scan with peripheral quantitative tomography and a correlation between phase standard deviation and trabecular bone density was found (R(2) = 0.46).

Quantitative Ultrasound of the Calcaneus: An In Vivo Comparison with Dual-Energy X-ray Absorptiometry and Magnetic Resonance Imaging

The current study was performed in a clinical setting and aimed to evaluate the relationship between quantitative ultrasound (QUS) of the calcaneus with bone mineral density (BMD) assessed with dual-energy X-ray absorptiometry (DXA) and with variables derived from magnetic resonance imaging (MRI). Thirty-two postmenopausal women (mean age 61 years) were studied at the level of the nondominant calcaneus. QUS was performed using a DTU-one device including parametric imaging and yielded speed of sound (SOS) and broadband ultrasound attenuation (BUA) data. DXA was performed at a matched region of interest (ROI) in the calcaneus, using a Hologic QDR 4500 device. MRI, also performed at a matched ROI, yielded, using a Siemens Magnetom Vision device, the inverse of the transverse relaxation time (1/T(2)(*)) and the phase standard deviation (PSD). The strongest relationship between QUS and the other variables involved BUA and BMD (r &equals: 0.677, p < 0.001); 1/T(2)(*) showed a trend to correlation with SOS (r = 0.359, p = 0. 044) and with BMD (r = 0.364, p = 0.040), while the relationship between 1/T(2)(*) and BUA, PSD and BUA, PSD and SOS, PSD and BMD remained far from significance. Regression analysis of QUS, DXA, and MRI variables against age showed a trend to significant decline only for 1/T(2)(*) (r = -0.409, p = 0.020). In conclusion, this study shows that BUA of the calcaneus has the best correlation with BMD, and that, at least in a clinical setting, the ability of QUS to give information about bone structure is limited.

Age dependence of T1 perfusion MRI-based hemodynamic parameters in human kidneys.

To determine the association between renal cortical perfusion parameters from T1‐DCE magnetic resonance imaging (MRI) and age in human kidney.