Effects of skull thickness, anisotropy, and inhomogeneity on forward EEG/ERP computations using a spherical three-dimensional resistor mesh model

Bone thickness, anisotropy, and inhomogeneity have been reported to induce important variations in electroencephalogram (EEG) scalp potentials. To study this effect, we used an original three-dimensional (3-D) resistor mesh model described in spherical coordinates, consisting of 67,464 elements and 22,105 nodes arranged in 36 different concentric layers. After validation of the model by comparison with the analytic solution, potential variations induced by geometric and electrical skull modifications were investigated at the surface in the dipole plane and along the dipole axis, for several eccentricities and bone thicknesses. The resistor mesh permits one to obtain various configurations, as local modifications are introduced very easily. This has allowed several head models to be designed to study the effects of skull properties (thickness, anisotropy, and heterogeneity) on scalp surface potentials. Results show a decrease of potentials in bone, depending on bone thickness, and a very small decrease through the scalp layer. Nevertheless, similar scalp potentials can be obtained using either a thick scalp layer and a thin skull layer, and vice versa. It is thus important to take into account skull and scalp thicknesses, because the drop of potential in bone depends on both. The use of three different layers for skull instead of one leads to small differences in potential values and patterns. In contrast, the introduction of a hole in the skull highly increases the maximum potential value (by a factor of 11.5 in our case), because of the absence of potential drop in the corresponding volume. The inverse solution without any a priori knowledge indicates that the model with the hole gives the largest errors in both position and dipolar moment. Our results indicate that the resistor mesh model can be used as a robust and user-friendly simulation tool in EEG or event-related potentials. It makes it possible to build up real head models directly from anatomic magnetic resonance imaging without tessellation, and is able to take into account head heterogeneities very simply by changing volume elements conductivity. Hum. Brain Mapping 21:84-95, 2004.     

Accidental MCI in healthy subjects: a prospective longitudinal study.

A study was realized on 130 healthy and autonomous volunteers (60-80 years old) who met specific medical and functional inclusion criteria. A comprehensive battery of neuropsychological tests was performed at baseline (M0), 6 and 12 months (M6, M12). At M0 the results indicated that 65% were cognitively normal on each of all the neuropsychological tests, whereas 35% presented a cognitive deficit on one or more tests. At M12, 52% of the subjects who had a cognitive deficit at M0 remained impaired, whereas 48% normalized their scores: they performed as well as the subjects classified normal at M0. The results also indicated that the subjects who remained impaired at M12, had at M0 low scores on three tests or more, whereas the ones who normalized their scores had one or two failed tests. This study focuses on the risk of false positive cases and shows that low scores can be accidental. The authors propose decision rules allowing to reduce the risk of false positive cases. The observation of accidental impairment invites to be cautious and makes this 1-year follow-up study particularly relevant, since a 1-year follow-up is generally needed to diagnose very mild dementia.     

Hypertension and dementia

Hypertension is one of the principal risk factors for cerebrovascular diseases. Several epidemiologic studies have also indicated a positive correlation between cognitive decline or dementia and blood pressure level. Indeed, the results of most longitudinal studies show that cognitive functioning is often inversely proportional to blood pressure values measured 15 or 20 years previously. Cerebral infarcts, lacunae, and white matter changes are implicated in the pathogenesis of vascular dementia, but may also favor the development of Alzheimer’s disease. Microcirculation disorders and endothelial dysfunctions are also advanced to explain the deterioration in cognitive functions in hypertensive subjects. Data from recent therapeutic trials open the way to the prevention of dementia (vascular or Alzheimer’s type) by antihypertensive treatments and must be confirmed by other studies.     

Chronic varicella zoster in a child infected with human immunodeficiency virus: case report and review of the literature.

Chronic zoster represents an infrequent presentation of varicella zoster virus infection. It is observed with increased frequency in patients infected with human immunodeficiency virus, especially when their lymphocyte counts are depressed. We report a child infected with human immunodeficiency virus who showed a long-standing cutaneous zoster lesion and was treated for a prolonged period of time with acyclovir. The occurrence of resistance to acyclovir by varicella zoster virus was suspected based on the clinical picture. The clinical and laboratory features of this case and a review of the literature are presented.     

Analysis of unsaturated fatty acids of endoneurium and perineurium from normal and degenerating rat sciatic nerve. Morphological correlations

The major portion of the endoneurial lipids is found in myelin. Since perineurial cells differ morphologically from endoneurial cell components, we attempted to determine whether these morphological differences also extended to a difference in fatty acid (FA) composition. Under normal circumstances, unsaturated FAs are more abundant than saturated ones (55-60% of total FAs) in endoneurium and perineurium. A characteristic biochemical difference between these two structures lies in the distribution of linoleic acid (C18:2(n-6)) which represents 20% of total FAs in perineurium and only 2% in endoneurium. Wallerian degeneration takes place after injection of pure glycerol into the endoneurium. This is followed by regeneration characterized by a proliferation of perineurial cells infiltrating the center of the nerve fascicule forming microcompartments. The changes in linoleic acid content reflect these morphological changes. A marked increase in linoleic acid is detected in the endoneurial fraction in parallel with the observed infiltration of perineurial cells into the nerve fascicule.     

Sequential somatostatin and gastrin releases in response to secretin in rat in vivo.

Secretin in known to inhibit gastric acid secretion. Exogenous secretin has also been shown to have a biphasic effect on acid secretion, being stimulatory then inhibitory. To explain this effect, we studied the timing of gastrin, somatostatin, and HCl releases in the gastric lumen in response to an i.v. bolus of secretin (360 pmol) or saline in conscious rats provided with a chronic double gastric fistula and having had or not antrectomy. After secretin but not saline, an immediate and transient increase in acid and gastrin secretions was first observed. After a 4 min lag, a dramatic increase in somatostatin secretion was then observed, together with a 90 percent inhibition of acid secretion and a return of gastrin release to basal level. Twenty min after secretin administration, a rebound increase in acid and gastrin outputs occurred, whereas somatostatin output returned to basal level. The secretin-induced somatostatin release was higher in rats with antrectomy than in those without antrectomy suggesting that the observed somatostatin output mostly originated from the fundus. This present study suggests that a bolus of secretin induced a gastrin release and thus could stimulate acid secretion. These pharmacological findings could provide an explanation for the so-called paradoxical secretin-induced stimulation of gastrin secretion in particular conditions.     

Effects of a low dose of naltrexone on glucose-induced allesthesia and hunger in humans

In order to study the effects of a low dose of the opioid antagonist naltrexone on ingestive behavior for sucrose in humans, preference for sucrose solutions and feelings of hunger were scored on visual analogical scale by 14 healthy subjects with or without naltrexone. Effects of intragastric glucose load or water, and naltrexone (25 mg) or placebo were tested. At this low dose, naltrexone alone had a slight effect on allesthesia, and it produced a strong potentiation of glucose-induced allesthesia.     

A Simple In Vitro Test to Evaluate Biocompatibility of Dialysis Membranes

As arachidonic acid metabolites are implicated in hypersensitivityreactions, we measured arachidonic acid metabolites of dialysedpatient's granulocytes, preincubated with different dialysismembranes. Results indicate that cuprophan and cellulose acetatemembranes partially inhibit in vitro production of 15-HETE and5-HETE, whereas polyacrylonitrile membrane does not. This suggeststhat polyacrylonitrile is a more biocompatible membrane.     

Management of renal transplant urolithiasis: a multicentre study by the French Urology Association Transplantation Committee

Purpose

Urolithiasis is rare among renal transplant recipients and its management has not been clearly defined.

Methods

This multicentre retrospective study was organised by the Comité de Transplantation de l’Association Française d’Urologie (French Urology Association transplantation committee). Statistical analysis was performed with SPSS 19 software.

Results

Ninety-five patients were included in this study. Renal transplant urolithiasis was an incidental finding in 55% of cases, mostly on a routine follow-up ultrasound examination. One half of symptomatic stones were due to urinary tract infection and the other half were due to an episode of acute renal failure. The initial management following diagnosis of urolithiasis was double J stenting (27%), nephrostomy tube placement (21%), or watchful waiting (52%). Definitive management consisted of: watchful waiting (48%), extracorporeal lithotripsy (13%), rigid or flexible ureteroscopy (26%), percutaneous nephrolithotomy (11%) and surgical pyelotomy (2%). All transplants remained functional following treatment of the stone. The main limitation is the retrospective design.

Conclusions

The incidence of lithiasis could be higher in kidney transplanted patients due to a possible anatomical or metabolical abnormalities. The therapeutic management of renal transplant urolithiasis appears to be comparable to that of native kidney urolithiasis.

     

Metabolic syndrome and low high-density lipoprotein cholesterol are associated with adverse pathological features in patients with prostate cancer treated by radical prostatectomy

Background

Previous studies have suggested a link between metabolic syndrome (MetS) and prostate cancer (PCa). In the present study, we aimed to assess the association between MetS and markers of PCa aggressiveness on radical prostatectomy (RP).