A Kinematic And Electromyographic Study Of The Mechanisms Contributing To Cerebellar Intention Tremor And Dysmetria

The kinematic and electromyographic (EMG) characteristics of cerebellar tremor and dysmetria were investigated in six Cebus monkeys. Cerebellar dysfunction was produced by reversible cooling lesions of the dentate and interposed nuclei. The aims of the study were (1) to compare the characteristics of the cerebellar intention tremor that occurs after the end of a voluntary movement (static or terminal tremor) with the tremor that occurs after the limb has been perturbed, (2) to determine the role played by stretch-evoked activity in generating this tremor, (3) to investigate the nature of the tremor that occurs during a voluntary movement (kinetic tremor) and (4) to describe the characteristics of dysmetric movements.;It was found that the static intention tremor after an elbow movement had the same characteristics as the tremor that occurs after a perturbation of the same limb. The frequency of the tremor in both situations was affected in a similar way by different mechanical loads and neither was dependent on visual feedback of limb position. Stretch-evoked proprioceptive activity was essential to produce the classic 3-4Hz cerebellar intention tremor.;The kinetic tremor was associated with an early burst of EMG activity in the antagonist muscle. This burst was no longer accurately programmed and appeared to be produced from stretch of the antagonist muscle. This antagonist burst was followed by a second burst of activity in the agonist muscle. This burst had the properties of a motor-servo as it was independent of vision, of short latency (50-80 ms) from the time of the deflection in trajectory produced by the early antagonist and its size was directly proportional to the size of the deflection.;Dysmetric (hypermetric) movements made during cerebellar cooling were asymmetric; that is, they had accelerations of long duration and small magnitude and decelerations of short duration and large magnitude. Control movements of all amplitudes, on the other hand, are nearly symmetric. Thus dysmetric movements were not simply inappropriately triggered normal movements. Hypermetric movements were associated with prolonged and less phasic bursts of agonist activity and a delayed burst of antagonist activity.;It is concluded that cerebellar disorders result from inappropriate stretch-evoked activity and from disordered descending central commands

Uncooled bolometer response of a low noise La2/3Sr1/3MnO3 thin film

We report measurements of the optical responses of a La2/3Sr1/3MnO3 (LSMO) sample at a wavelength of 533 nm in the 300-400 K range. The 200 nm thick film was grown by pulsed laser deposition on (100) SrTiO3 substrate and showed remarkably low noise. At 335 K the temperature coefficient of the resistance of a 100 micrometers wide 300 micrometers long LSMO line was 0.017 K-1 and the normalized Hooge parameter was 9 e-30 m3, which is among the lowest reported values. We then measured an optical sensitivity at I = 5 mA of 10.4 V.W-1 and corresponding noise equivalent power (NEP) values of 8.1 e-10 W.Hz-1/2 and 3.3 e-10 W. Hz-1/2 at 30 Hz and above 1kHz, respectively. Simple considerations on bias current conditions and thermal conductance G are finally given for further sensitivity improvements using LSMO films. The performances were indeed demonstrated on bulk substrates with G of 10-3 W.K-1. One could expect a NEP reduction by three orders of magnitude if a membrane-type geometry was used, which makes this LSMO device competitive against commercially available uncooled bolometers.Comment: 15 pages. Accepted for publication in Appl. Phys. Let

DNA-binding mechanism and evolution of replication protein A

Replication Protein A (RPA) is a heterotrimeric single stranded DNA-binding protein with essential roles in DNA replication, recombination and repair. Little is known about the structure of RPA in Archaea, the third domain of life. By using an integrative structural, biochemical and biophysical approach, we extensively characterize RPA from Pyrococcus abyssi in the presence and absence of DNA. The obtained X-ray and cryo-EM structures reveal that the trimerization core and interactions promoting RPA clustering on ssDNA are shared between archaea and eukaryotes. However, we also identified a helical domain named AROD (Acidic Rpa1 OB-binding Domain), and showed that, in Archaea, RPA forms an unanticipated tetrameric supercomplex in the absence of DNA. The four RPA molecules clustered within the tetramer could efficiently coat and protect stretches of ssDNA created by the advancing replisome. Finally, our results provide insights into the evolution of this primordial replication factor in eukaryotes