The Cognitive Role of the Globus Pallidus interna; Insights from Disease States.

The motor symptoms of both Parkinson's disease and focal dystonia arise from dysfunction of the basal ganglia, and are improved by pallidotomy or deep brain stimulation of the Globus Pallidus interna (GPi). However, Parkinson's disease is associated with a greater degree of basal ganglia-dependent learning impairment than dystonia. We attempt to understand this observation in terms of a comparison of the electrophysiology of the output of the basal ganglia between the two conditions. We use the natural experiment offered by Deep Brain Stimulation to compare GPi local field potential responses in subjects with Parkinson's disease compared to subjects with dystonia performing a forced-choice decision-making task with sensory feedback. In dystonic subjects, we found that auditory feedback was associated with the presence of high gamma oscillations nestled on a negative deflection, morphologically similar to sharp wave ripple complexes described in human rhinal cortex. These were not present in Parkinson's disease subjects. The temporal properties of the high gamma burst were modified by incorrect trial performance compared to correct trial performance. Both groups exhibited a robust low frequency response to 'incorrect' trial performance in dominant GPi but not non-dominant GPi at theta frequency. Our results suggest that cellular processes associated with striatum-dependent memory function may be selectively impaired in Parkinson's disease even if dopaminergic drugs are administered, but that error detection mechanisms are preserved

Intradural Spinal Cord Stimulation: Performance Modeling of a New Modality

Introduction: Intradural spinal cord stimulation (SCS) may offer significant therapeutic benefits for those with intractable axial and extremity pain, visceral pain, spasticity, autonomic dysfunction and related disorders. A novel intradural electrical stimulation device, limited by the boundaries of the thecal sac, CSF and spinal cord was developed to test this hypothesis. In order to optimize device function, we have explored finite element modeling (FEM).Methods: COMSOL®Multiphysics Electrical Currents was used to solve for fields and currents over a geometric model of a spinal cord segment. Cathodic and anodic currents are applied to the center and tips of the T-cross component of the electrode array to shape the stimulation field and constrain charge-balanced cathodic pulses to the target area.Results: Currents from the electrode sites can move the effective stimulation zone horizontally across the cord by a linear step method, which can be diversified considerably to gain greater depth of penetration relative to standard epidural SCS. It is also possible to prevent spread of the target area with no off-target action potential.Conclusion: Finite element modeling of a T-shaped intradural spinal cord stimulator predicts significant gains in field depth and current shaping that are beyond the reach of epidural stimulators. Future studies with in vivo models will investigate how this approach should first be tested in humans

Angle-resolved measurements of the photoelectron spin polarization in the photoionization of HI molecules

Böwering N, Müller M, Salzmann M, Heinzmann U. Angle-resolved measurements of the photoelectron spin polarization in the photoionization of HI molecules. Journal of Physics B: Atomic, Molecular and Optical Physics. 1991;24(22):4793-4801.Using circularly polarized synchrotron radiation, the 5p pi ionization of HI molecules is studied by means of angle-resolved photoelectron spin polarization spectroscopy. The energy dependences of the dynamical photoionization parameters are obtained and compared with an ab initio calculation of Raseev et al. (1987) and the corresponding data for the xenon atom. Angular distributions of the polarization component A( Theta ) yield complete parameter sets. A strong influence of electronic autoionization is observed and analysed in terms of partial contributions using the additional information contained in the polarization results

Spin-resolved photoelectron spectroscopy of HBr in the resonance region of electron autoionization

Salzmann M, Böwering N, Klausing H-W, Kuntze R, Heinzmann U. Spin-resolved photoelectron spectroscopy of HBr in the resonance region of electron autoionization. Journal of Physics B: Atomic, Molecular and Optical Physics. 1994;27(10):1981-1992