Katrin Morgen

Investigation of mindfulness meditation practitioners with voxel-based morphometry

Mindfulness meditators practice the non-judgmental observation of the ongoing stream of internal experiences as they arise. Using voxel-based morphometry, this study investigated MRI brain images of 20 mindfulness (Vipassana) meditators (mean practice 8.6 years; 2 h daily) and compared the regional gray matter concentration to that of non-meditators matched for sex, age, education and handedness. Meditators were predicted to show greater gray matter concentration in regions that are typically activated during meditation. Results confirmed greater gray matter concentration for meditators in the right anterior insula, which is involved in interoceptive awareness. This group difference presumably reflects the training of bodily awareness during mindfulness meditation. Furthermore, meditators had greater gray matter concentration in the left inferior temporal gyrus and right hippocampus. Both regions have previously been found to be involved in meditation. The mean value of gray matter concentration in the left inferior temporal gyrus was predictable by the amount of meditation training, corroborating the assumption of a causal impact of meditation training on gray matter concentration in this region. Results suggest that meditation practice is associated with structural differences in regions that are typically activated during meditation and in regions that are relevant for the task of meditation.

Evidence for a direct association between cortical atrophy and cognitive impairment in relapsing–remitting MS

Cognitive deficits affecting memory, attention and speed of information processing are common in multiple sclerosis (MS). The mechanisms of cognitive impairment remain unclear. Here, we examined the association between neuropsychological test performance and brain atrophy in a group of mildly disabled patients with relapsing-remitting MS. We applied voxel-based morphometry (SPM2) to investigate the distribution of brain atrophy in relation to cognitive performance. Patients had lower scores than control subjects on tests of memory and executive function, including the PASAT, Digit Span Backward and a test of short-term verbal memory (Memo). Among patients, but not healthy controls, performance on the PASAT, a comprehensive measure of cognitive function and reference task for the cognitive evaluation of MS-patients, correlated with global grey matter volume as well as with grey matter volume in regions associated with working memory and executive function, including bilateral prefrontal cortex, precentral gyrus and superior parietal cortex as well as right cerebellum. Compared to healthy subjects, patients showed a volume reduction in left temporal and prefrontal cortex, recently identified as areas predominantly affected by diffuse brain atrophy in MS. A comparison of low performers in the patient group with their matched control subjects showed more extensive and bilateral temporal and frontal volume reductions as well as bilateral parietal volume loss, compatible with the progression of atrophy found in more advanced MS-patients. These findings indicate that MS-related deficits in cognition are closely associated with cortical atrophy.

Relationship between regional hemodynamic activity and simultaneously recorded EEG-theta associated with mental arithmetic-induced workload

Theta increases with workload and is associated with numerous processes including working memory, problem solving, encoding, or self monitoring. These processes, in turn, involve numerous structures of the brain. However, the relationship between regional brain activity and the occurrence of theta remains unclear. In the present study, simultaneous EEG‐fMRI recordings were used to investigate the functional topography of theta. EEG‐theta was enhanced by mental arithmetic‐induced workload. For the EEG‐constrained fMRI analysis, theta‐reference time‐series were extracted from the EEG, reflecting the strength of theta occurrence during the time course of the experiment. Theta occurrence was mainly associated with activation of the insular cortex, hippocampus, superior temporal areas, cingulate cortex, superior parietal, and frontal areas. Though observation of temporal and insular activation is in accord with the theory that theta specifically reflects encoding processes, the involvement of several other brain regions implies that surface‐recorded theta represents comprehensive functional brain states rather than specific processes in the brain. The results provide further evidence for the concept that emergent theta band oscillations represent dynamic functional binding of widely distributed cortical assemblies, essential for cognitive processing. This binding process may form the source of surface‐recorded EEG theta. Hum Brain Mapp, 2006.

Utilizing the ventriloquism-effect to investigate audio-visual binding.

Audio-visual binding - as subset of crossmodal integration - describes the combination of information across both these senses to the subjective unified perception of a bound object. We investigated audio-visual binding by using the ventriloquism-effect (localization of a sound is biased towards and by a simultaneous visual stimulus) to act as an indicator for perceived binding. Simple visual and auditory stimuli were presented synchronously or asynchronously. fMRI was recorded during task performance (n = 19 subjects) in order to reveal activation in areas discussed to be involved in multisensory processing in the literature. Contrasting trials with reported ventriloquism-effect versus the no-binding condition revealed activation in the insula, superior temporal sulcus and parieto-occipital sulcus. Implementing the ventriloquism-effect allows us to relate these activations to consciousness-related processes, which probably are different from stimulus-driven multisensory integration in subcortical areas.

Ring-enhancement in multiple sclerosis: marker of disease severity

Correlations between conventional MRI measures of disease activity and clinical disability in multiple sclerosis (MS) have been disappointing. Because ring-enhancing lesions may reflect a more destructive pathology, we tested their potential association with disease severity. We evaluated active lesions with regard to their enhancement pattern on serial magnetic resonance images in a cohort of 28 patients with relapsing-remitting MS. The percentage of ring-enhancing lesions correlated with EDSS, T2 lesion load and duration of disease and predicted the occurrence of relapses during the baseline period of observation as well as after 3 years of follow-up in multiple logistic regression analysis. The findings suggest that the pathological process reflected by ring-enhancing lesions may contribute to more severe clinical disease.

Interferon-β1b leads to a short-term increase of soluble but long-term stabilisation of cell surface bound adhesion molecules in multiple sclerosis

Abstract.Adhesion molecules (AMs) are believed to regulate the transmigration of blood leukocytes across the blood-brain barrier (BBB), which is an essential step in the pathogenesis of multiple sclerosis (MS). Previous studies have investigated changes of the soluble forms of AM during interferon-β1b (IFN-β1b) treatment in MS patients. In this study, we analysed the influence of IFN-β1b treatment on the cell surface bound forms of the AMs cICAM-1 and cICAM-3 on blood mononuclear cells (MNC). Sixty-eight patients with relapsing-remitting MS were enrolled in this open study; thirty of them were treated with IFN-β1b. Blood samples were collected every three months over a period of 18 months. The expression levels of cell surface bound forms of AM on blood MNC were measured by two colour flow cytometry analysis. sVCAM-1, sICAM-1 and sICAM-3 were determined by ELISA. We found a short-term induction effect on the serum concentrations of sICAM-1 and sVCAM-1 after three months of IFN-β1b treatment. The expression levels of cell surface bound AMs on blood MNC remained stable during treatment. Untreated MS patients, however, showed a continuous decrease in the expression of cell surface bound AM expression over 18 months. Stabilisation of the expression of cell surface bound AMs on blood MNC may indicate the beneficial effects of IFN-β1b therapy in MS patients.

Contrast-enhanced MRI lesions during treatment with interferonβ-1b predict increase in T1 black hole volume in patients with relapsing-remitting multiple sclerosis

T1 black holes (BH) have been found to represent focal areas of substantial central nervous system tissue damage in multiple sclerosis (MS) patients. We examined the development of T1 BH over a three-year period of treatment with interferon (IFN)β-1b in a group of 20 patients with relapsing-remitting MS. The number of contrast-enhancing lesions (CEL) after one year of treatment predicted a change in the T1 BH volume in the following two years. In patients without CEL, the T1 BH volume remained stable, whereas it increased in patients with CEL. The occurrence of CEL in patients treated with IFNβ may indicate a heightened risk of accumulating T1 BH.

Synchronized measurement of simultaneous EEG–fMRI: A simulation study

OBJECTIVE The quality of averaged gradient artifact subtraction from EEG recorded during fMRI is highly dependent on the accuracy of gradient artifact sampling. Even small sampling shifts (e.g. a single datapoint at 5kHz) increase the variance of the sampled gradient artifacts because of very steep slopes in the signal time course. Hence, although principally gradient artifacts are invariant signals because of their technical origin, variance attributed to sampling errors attenuates the effect of artifact removal. Recently, it has been shown that synchronizing the EEG-amplifier clock to the MR-scanner control-device clock improves artifact reduction by subtraction. METHODS In order to investigate the synchronized measurement of combined EEG-fMRI, we used simulated EEG by measuring function generator signals in the MR-scanner. Only the usage of known signals allows an assessment of the improvement in accuracy of artifact recording by synchronized compared to non-synchronized measurement, since the signal is identical in both conditions. RESULTS After averaged gradient artifact subtraction synchronized recorded signals were apparently less distorted than non-synchronized recorded signals. Spectral analyses revealed that especially artifact frequencies above 50Hz had less power in restored synchronized compared to restored non-synchronized recorded signals. Computed total signal variances were not always less in restored synchronized compared to restored non-synchronized recorded signals. CONCLUSIONS Taken together, synchronizing simultaneous EEG-fMRI measurement is a useful enhancement for averaged gradient artifact subtraction although post-correction filtering is still necessary. SIGNIFICANCE Our results support the recent finding that synchronization improves the quality of averaged gradient artifact subtraction. However, quantitatively we could not verify a systematic benefit of recording electrical signals during fMRI synchronously rather than non-synchronously to the MR-scanner control-device clock.