Temporal dynamics of the default mode network characterise meditation induced alterations in consciousness

Current research suggests that human consciousness is associated with complex, synchronous interactions between multiple cortical networks. In particular, the default mode network (DMN) of the resting brain is thought to be altered by changes in consciousness, including the meditative state. However, it remains unclear how meditation alters the fast and ever-changing dynamics of brain activity within this network. Here we addressed this question using simultaneous electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) to compare the spatial extents and temporal dynamics of the DMN during rest and meditation. Using fMRI, we identified key reductions in the posterior cingulate hub of the DMN, along with increases in right frontal and left temporal areas, in experienced meditators during rest and during meditation, in comparison to healthy controls (HCs). We employed the simultaneously recorded EEG data to identify the topographical microstate corresponding to activation of the DMN. Analysis of the temporal dynamics of this microstate revealed that the average duration and frequency of occurrence of DMN microstate was higher in meditators compared to HCs. Both these temporal parameters increased during meditation, reflecting the state effect of meditation. In particular, we found that the alteration in the duration of the DMN microstate when meditators entered the meditative state correlated negatively with their years of meditation experience. This reflected a trait effect of meditation, highlighting its role in producing durable changes in temporal dynamics of the DMN. Taken together, these findings shed new light on short and long-term consequences of meditation practice on this key brain network

Resting state networks analysis using simultaneous EEG-fMRI for epilepsy patient

peer reviewedThe resting state EEG-fMRI has opened a new avenue in not only neuro cognitive studies but it has also found practical utility in clinical applications. We studied the Resting State Networks on Epilepsy Patient to understand the neuronal substrates involved in epilepsy. Five epilepsy patients were undertaken for simultaneous EEG-fMRI study. EEG microstates was computed and was considered as explanatory variables in the GLM design for the analysis of fMRI data in an event related design. z-stats and independent component was examined for simultaneous EEG-fMRI. We hypothesized that it's possible to analyze the affected brain areas for epileptiform discharges in epileptic patients at resting state. Microstates convolved functional image and its independent components using hybrid technique including both the neuronal and hemodynamic information was demonstrated on patients structural image. From this result we conclude that using EEG microstate and Independent Component Analysis (ICA) of resting fMRI we may examine the brain areas involved in resting state brain discharge. Also it will be useful for the analysis of EEG-fMRI data in which electrical epileptic discharge are not apparent on scalp EEG at the time of data acquisition. © 2013 Springer

Radiation Safety for Anesthesiologists and Other Personnel on Simultaneous PET/MRI: Possible Radiation Exposure from Patients While Performing Prolonged Duration Scans

This observational study was conducted owing to the challenges of the positron emission tomography/magnetic resonance imaging (PET/MRI) that requires longer duration scanning of radiopharmaceutical injected patient and added MRI environment. The aim of this study was to assess radiation dose at different distances from the patient and the radiation burden to anesthesiologist and other personnel in performing PET/MRI under general anesthesia or sedation. First, the pre- and postscan whole body radiation exposure (WBE) from the patient were obtained for 45 minutes (n = 109) after injection of the radiopharmaceutical. The WBE was obtained at specific distances from brain (10, 30, and 100 cm) and abdomen (10 and 30cm) of patients undergoing F18 fluorodeoxyglucose PET/MRI brain or whole body studies. Second, WBE of the anesthesiologist and other staff working was separately measured using pocket dosimeters during the whole procedure. In brain scans, the mean absorbed dose rates (ADR) of prescan (45 minutes) and postscan (45 minutes) were 44.4 and 31.1 μSv at 10 cm, 14.9 and 9.7μSv at 30 cm, and 3.5 and 2.8 μSv at 100 cm, respectively, from surface of head. Similarly, it was 54.8 and 30.3 μSv at 10 cm, 23 and 13.6μSv at 30 cm, respectively, from surface of abdomen. In WB scans, the mean ADR was higher than the brain scans. Anesthesiologist exposure overall was found to be 4.84 µSv/patient/scan (112 patients). The anesthesiologist receives a safe mean effective dose in PET/MRI scanning. With good training and adequate planning, it is possible to decrease the radiation exposure to all the concerned personnel including anesthesiologists

Cerebral tubercular thrombophlebitis presenting as venous infarct: Magnetic resonance imaging and pathologic correlation

Central nervous system involvement by tuberculosis to produce basal meningitis, hydrocephalus, arteritis and infarcts is well-known, the brunt of the pathology being borne by the arterial vasculature to produce neurological sequelae. However, tuberculous thrombophlebitis causing venous infarction is exceedingly rare. We present imaging and pathological features of two autopsy proven cases of tuberculous thrombophlebitis with venous infarcts involving superficial venous system in one and deep venous system in the other. This is the first study presenting radiopathologic correlation of this rare complication. Tuberculous thrombophlebitis should be suspected if basal exudates and multiple white matter T2 hyperintensities are seen on neuroimaging and the imaging protocol should include both magnetic resonance arteriogram and venogram

Temporal dynamics of the default mode network characterise meditation induced alterations in consciousness

Current research suggests that human consciousness is associated with complex, synchronous interactions between multiple cortical networks. In particular, the default mode network (DMN) of the resting brain is thought to be altered by changes in consciousness, including the meditative state. However, it remains unclear how meditation alters the fast and ever-changing dynamics of brain activity within this network. Here, we addressed this question using simultaneous electroencephalography (EEG) and functional imaging (fMRI) to compare the spatial extents and temporal dynamics of the DMN during rest and meditation. Using fMRI, we identified key reductions in the posterior cingulate hub of the DMN, along with increases in right frontal and left temporal areas, in experienced meditators during rest and during meditation, in comparison to healthy controls. We employed the simultaneously recorded EEG data to identify the topographical microstate corresponding to the DMN. Analysis of the temporal dynamics of this microstate revealed that the average duration and frequency of occurrence of DMN microstate was higher in meditators compared to healthy controls. Both these temporal parameters increased during meditation, reflecting the state effect of meditation. In particular, we found that the alteration in the duration of the DMN microstate when meditators entered the meditative state correlated negatively with their years of meditation experience. This reflected a trait effect of meditation, highlighting its role in producing durable changes in temporal dynamics of the DMN. Taken together, these findings shed new light on short and long-term consequences of meditation practice on this key brain network