Anodal vs cathodal stimulation of motor cortex: a modeling study.

OBJECTIVE: To explore the effects of electrical stimulation performed by an anode, a cathode or a bipole positioned over the motor cortex for chronic pain management. METHODS: A realistic 3D volume conductor model of the human precentral gyrus (motor cortex) was used to calculate the stimulus-induced electrical field. The subsequent response of neural elements in the precentral gyrus and in the anterior wall and lip of the central sulcus was simulated using compartmental neuron models including the axon, soma and dendritic trunk. RESULTS: While neural elements perpendicular to the electrode surface are preferentially excited by anodal stimulation, cathodal stimulation excites those with a direction component parallel to its surface. When stimulating bipolarly, the excitation of neural elements parallel to the bipole axis is additionally facilitated. The polarity of the contact over the precentral gyrus determines the predominant response. Inclusion of the soma-dendritic model generally reduces the excitation threshold as compared to simple axon model. CONCLUSIONS: Electrode polarity and electrode position over the precentral gyrus and central sulcus have a large and distinct influence on the response of cortical neural elements to stimuli. SIGNIFICANCE: Modeling studies like this can help to identify the effects of electrical stimulation on cortical neural tissue, elucidate mechanisms of action and ultimately to optimize the therapy.     

A model of the viscoelastic behavior of flowable resin composites prior to setting

Objective

The aim of this study is to develop fractional derivative models for the assessment of viscoelastic properties related to handling characteristics of dental resin composites belonging to two classes: flowable (Revolution Formula 2 and Filtek Ultimate) and posterior “bulk-fill” flowable base (Smart Dentin Replace).

Methods

Rheological measurements on all materials tested in this study were performed using dynamic oscillatory rheometer at temperature of 23 °C. A parallel plates module with a diameter of 20 mm was used to measure the properties of the resin composites tested. We developed two models to describe the obtained data: the generalized Newton model and the generalized Zener model (the so-called three parameter model). Both models contain fractional derivatives of Riemann–Liouville type. By determining the parameters of the model we were able to fit experimental data with high accuracy.

Results

Our results show that flowable “bulk-fill” resin-composite material (SDR) has distinct properties as compared to other two flowable resin composite materials (Revolution Formula 2 and Filtek Ultimate). Thus, previously found SDR properties as “bulk-fill” flowable base results in the fact that it is described by generalized Zener model (i.e., it has properties of solid like viscoelastic material).

Significance

Our model may be used to predict behavior of tested composites in different flow conditions. The SDR has initially small almost constant complex viscosity showing that it has good self-leveling property.     

Serial position learning effects in patients with aneurysms of the anterior communicating artery

Ruptured and repaired Anterior Communicating Artery (ACoA) aneurysm can result in devastating impairments involving memory, executive function, confabulation, and personality changes. This study tested serial position learning effects (SPEs) in patients following repaired and ruptured ACoA aneurysm, using results on the Rey Auditory Verbal Learning Test (RAVLT). Thirty patients with ruptured aneurysms of the ACoA and 31 matched controls were included in the study. The primacy-recency effects were maintained during five learning trials in ACoA group, albeit at an overall lower level than in the controls. There was no difference in primacy-recency relation across five learning trials in ACoA group. On the delayed recall trial the patient group demonstrated neither a primacy, nor a recency phenomenon, reflecting a lack of recall of any parts of the word list. This kind of primacy-recency profile across learning trials in ACoA group has no similarity with SPE results in frontal lesion groups, or with SPE distributions in other amnesic disorders, despite the fact that memory and executive deficits were evident in our ACoA group.     

In vitro-Kulturen von Arctostaphylos-Arten, 1. Mitt. Entwicklung einer in vitro-Kulturmethode für Arctostaphylos uva- ursi und A. nevadensis

In Vitro Cultures of Arctostaphylos, I: Elucidation of an In Vitro Culture Method for Arctostaphylos uva-ursi and A. nevadensis Arctostaphylos uva-ursi (Ericaceae) and the American species Arctostaphylos nevadensis were cultivated in vitro for the first time. Excised shoot tips of about 0,5 mm length could be regenerated to well rooted plants within 15 weeks on a basic medium after Murashige and Skoog¹³⁾ and a rooting medium after Randolph and Cox¹⁴⁾.     

Plastic surgery in the treatment of primary cutaneous melanoma

Surgery is still the most effective treatment modality of skin melanoma. The margins of excision are determined by the thickness of primary tumor. From January 1999 to December 2001, 99 patients (57 male and 42 female, of the average age 55), were surgically treated at the Clinic for Plastic Surgery and Burns of the Military Medical Academy. The most usual localization of the primary tumor was the back (23.23%), followed by the forearm, and the lower leg. Regarding the clinical type of the melanoma, nodular melanoma dominated (62.62%). Microscopic staging of the melanoma (classification according to Clark and Breslow), showed that the majority of patients already suffered from the advanced primary disease, which called for radical excision and the choice of reconstructive methods in the closure of post-excision defects. The reconstructive plastic surgical methods enabled the closure of post-excision tissue defects, regardless of their size, structure, and localization. During the closure of post-excision defects, direct wound closure or split skin draft was performed in 76.76% of patients. Flaps were applied in 19.19% of patients with the primary melanoma of the head, face, foot, and hand. The sufficiency of the available reconstructive procedures makes plastic surgery irreplaceable in the surgical treatment of the primary melanoma of the skin.