Gerard Mennessier

Evolution of Brain Impedance in Dystonic Patients Treated by GPi Electrical Stimulation

Deep Brain Stimulation is an effective treatment of generalized dystonia. Optimal stimulation parameters vary between patients. This article investigates the influence of electrical brain impedance and delivered current on the brain response to stimulation. Twenty‐four patients were bilaterally stimulated in the globus pallidus internus through two implanted four‐contact electrodes. The variation of brain impedance and current measurements was correlated with stimulation parameters, time course, and clinical outcome. When a contact was activated, a statistically significant and reversible decrease of brain impedance was found. Impedance and current values and their variations with time significantly differed between patients. The absolute impedance did not significantly correlate with the final outcome. We conclude that the reversible decrease of impedance reflects an adaptive long‐term mechanism, which could be due to a plasticity phenomenon, but has no prognostic value. Impedance and current measurements give new complementary information for parameter adjustment and trouble shooting and should therefore be included in all patients’ follow‐up.

Stereotactic model of the electrical distribution within the internal globus pallidus during deep brain stimulation

Deep brain stimulation (DBS) of the internal globus pallidus (GPi) is an established surgical technique for the treatment of movement disorders. The objective of this study was to propose a computational stereotactic model of the electrical distribution around the electrode within the targeted GPi in order to optimize parameter adjustment in clinical practice. The outline of the GPi can be defined precisely by using stereotactic magnetic resonance imaging (MRI) and from this it is possible to model its three-dimensional structure. The electrode and the distribution of the patient-specific parameters can then be co-registered with the GPi volume. By using this methodology, it is possible to visualize and measure the relationship between the electrical distribution of patient-specific parameters and the morphology of the GPi. The model could be applied in clinical practice to help determine the threshold for achieving a therapeutic effect and consequently may aid in optimizing parameter settings for individual patients.

Prognostic value of globus pallidus internus volume in primary dystonia treated by deep brain stimulation

OBJECT Given that improvement is variable from one patient to another, the authors analyzed the impact of globus pallidus internus (GPi) volume on the result of deep brain stimulation (DBS) by comparing highly and less improved patients with primary dystonodyskinetic syndromes. METHODS A stereotactic model was developed to visualize and quantify the relationship between the isofield lines generated by the DBS lead and GPi target. The model was used in 30 right-handed selected patients with primary dystonodyskinetic syndromes who had been treated using bilateral stimulation of the sensorimotor GPi. Ten healthy control individuals were also included in the study. First, the authors compared the GPi volumes between patients and healthy controls. Second, the stimulated GPi volumes, that is, the intersection between the volume of each isofield value and the GPi volumes, were compared between less improved and highly improved patients. RESULTS Improvement in the Burke-Fahn-Marsden Dystonia Rating Scales motor score was rated > 90% in 20 patients (97 +/- 4.6%) and < 60% in 10 patients (56.9 +/- 6%). The mean volume of the right (461.8 +/- 81.8 mm(3)) and left (406.6 +/- 113.2 mm(3)) GPi in patients showing less response to DBS was significantly smaller than the GPi volume of patients who responded well (right 539.9 +/- 86.6 mm(3), left 510.6 +/- 88.7 mm(3)) and healthy controls (right 557.8 +/- 109.1 mm(3), left 525.1 +/- 40.8 mm(3)). CONCLUSIONS On the left side, the mean stimulated volumes (isofield line range 0.2-1 V/mm) were significantly larger in highly improved than in less improved patients. In this model, the threshold for functional effect was calculated at 0.2 V/mm.

Gluonium nature of the σ/f0(600) from its coupling to KK¯

Abstract We extract the K + K − couplings of the isoscalar scalar mesons σ / f 0 ( 600 ) and f 0 ( 980 ) from π π → π π / K K ¯ scatterings. We find respectively about 0.6(2) and 2.0(3) for the ratios of the K + K − over π + π − couplings of the σ and f 0 ( 980 ) , which we compare with some other determinations. The (relative) strong coupling of the σ → K ¯ K , together with its tiny “direct” γγ and its large hadronic widths, are in favour of a large gluonium/glueball component of the σ-meson, as predicted by QCD spectral sum rules (QSSR) ⊕ some low-energy theorems (LET). These properties then suggest that the σ can be (up to some mixing) a scalar meson associated to the U ( 1 ) V conformal anomaly like the η ′ -meson to the U ( 1 ) A anomaly.

Gluonium nature of the sigma/f(0)(600) from its coupling to K anti-K

Abstract We extract the K + K − couplings of the isoscalar scalar mesons σ / f 0 ( 600 ) and f 0 ( 980 ) from π π → π π / K K ¯ scatterings. We find respectively about 0.6(2) and 2.0(3) for the ratios of the K + K − over π + π − couplings of the σ and f 0 ( 980 ) , which we compare with some other determinations. The (relative) strong coupling of the σ → K ¯ K , together with its tiny “direct” γγ and its large hadronic widths, are in favour of a large gluonium/glueball component of the σ-meson, as predicted by QCD spectral sum rules (QSSR) ⊕ some low-energy theorems (LET). These properties then suggest that the σ can be (up to some mixing) a scalar meson associated to the U ( 1 ) V conformal anomaly like the η ′ -meson to the U ( 1 ) A anomaly.

A target-specific electrode and lead design for internal globus pallidus deep brain stimulation.

In nearly all deep brain stimulation (DBS) applications, the same quadripolar electrode design is used for different anatomical targets even if shape and volume differences exist between nuclei. Taking into account the electrode location within the internal globus pallidus (GPi) and the size of the GPi, 2 electrodes were designed in order to improve the therapeutic benefit, to minimize side effects from DBS and to obtain a more homogeneous electric field distribution. The electrodes were evaluated numerically by using a stereotactic model measuring the correlation between the electric field and the GPi. The model was applied to 26 dystonodyskinetic patients who underwent surgery for a bilateral lead implantation into the posteroventral part of the GPi. The designed electrodes produced a more homogeneous distribution of the electric field than the quadripolar electrode.

Co-registration of Stereotactic MRI and Isofieldlines During Deep Brain Stimulation

OBJECT The parameter adjustment process during deep brain stimulation (DBS) for dystonia remains time consuming and based on clinical observation alone. The aim was to correlate the electric field with the GPi anatomy to be able to study the stimulated volume. METHODS We developed a computer-assisted method (model) for visualizing electric field in reference to the stereotactic space. Electric field values were correlated with the GPi anatomy (stereotactic Magnetic Resonance Imaging) in one reference patient. RESULTS Using this methodology it becomes possible to correlate the electric field distributions for patient specific parameters with the anatomical information. The application to one patient showed that the 0.1V/mm isofieldline fits best with the lateral GPi borders at the level of the stimulated contacts. CONCLUSIONS The electric field is a crucial parameter as it is assumed to be responsible for triggering action potentials. Electric field visualisation allows the calculation of the stimulated volume for a given isoline. Its application to our whole patient population might help in determining a threshold for obtaining a therapeutic effect, to date unknown, and consequently in optimizing the parameter setting in each patient.

Topological Control of Life and Death in Non-Proliferative Epithelia

Programmed cell death is one of the most fascinating demonstrations of the plasticity of biological systems. It is classically described to act upstream of and govern major developmental patterning processes (e.g. inter-digitations in vertebrates, ommatidia in Drosophila). We show here the first evidence that massive apoptosis can also be controlled and coordinated by a pre-established pattern of a specific ‘master cell’ population. This new concept is supported by the development and validation of an original model of cell patterning. Ciona intestinalis eggs are surrounded by a three-layered follicular organization composed of 60 elongated floating extensions made of as many outer and inner cells, and indirectly spread through an extracellular matrix over 1200 test cells. Experimental and selective ablation of outer and inner cells results in the abrogation of apoptosis in respective remaining neighbouring test cells. In addition incubation of outer/inner follicular cell-depleted eggs with a soluble extract of apoptotic outer/inner cells partially restores apoptosis to apoptotic-defective test cells. The 60 inner follicular cells were thus identified as ‘apoptotic master’ cells which collectively are induction sites for programmed cell death of the underlying test cells. The position of apoptotic master cells is controlled by topological constraints exhibiting a tetrahedral symmetry, and each cell spreads over and can control the destiny of 20 smaller test cells, which leads to optimized apoptosis signalling.

Low-mass scalar production in γγ scattering

We estimate the I = 0 scalar meson σ / f 0 ( 600 ) γ γ widths, from ππ and γγ scattering data below 700 MeV using an improved analytic K-matrix model.