离子选择电极电位法研究S2O8^2—与I^—反应动力学

用离子选择电极电位法对S_2O_8~(2-)-Ⅰ~-体系反应动力学问题进行了探讨,研究了离子强度对反应速度的影响。结果表明:离子选择电极电位法可用于此体系的动力学研究,并且得到满意的结果;提出了该电极适用的浓度条件;得出生成CuI~+步骤为催化反应决定步骤的新结论;随着离子强度的增加dE/dt值增大,即反应速度加快。     

Altered corticomotor representation in patients with Parkinson's disease.

In 6 patients with Parkinson's disease (PD) and 6 age-matched controls, transcranial magnetic stimulation was applied at 56 regions over the motor cortex and premotor cortex of each hemisphere, with the first dorsal interosseous (FDI) muscle of both hands activated at 15% maximum voluntary contraction during stimulation. For each site, motor evoked potential (MEP) landmarks were recovered, including MEP amplitude, MEP onset latency, and silent period duration. Scaled MEP amplitudes were used to construct individual cortical maps of the FDI muscles. The maps revealed an anterior displacement of the muscle representation in PD patients. This anterior shift over motor cortical areas may reflect increased contributions of corticocortical connections between motor cortex and premotor cortical areas, possibly enhanced by the visual feedback aspect of the task. These alterations may reflect adaptations to the impairments in striatocortical circuits in PD.     

Auditory Perception and the Control of Spatially Coordinated Action of Deaf and Hearing Children

From birth onwards, auditory stimulation directs and intensifies visual orientation behaviour. In deaf children, by definition, auditory perception cannot take place and cannot, therefore, make a contribution to visual orientation to objects approaching from outside the initial field of view. In experiment 1, a difference in catching ability is demonstrated between deaf and hearing children (10-13 years of age) when the ball approached from the periphery or from outside the field of view. No differences in catching ability between the two groups occurred when the ball approached from within the field of view. A second experiment was conducted in order to determine if differences in catching ability between deaf and hearing children could be attributed to execution of slow orientating movements and/or slow reaction time as a result of the auditory loss. The deaf children showed slower reaction times. No differences were found in movement times between deaf and hearing children. Overall, the findings suggest that a lack of auditory stimulation during development can lead to deficiencies in the coordination of actions such as catching which are both spatially and temporally constrained.     

Cortical Reorganization Allows for Motor Recovery after Crossed Cerebrocerebellar Atrophy

The authors report the case of a 33-year-old woman who exhibited, at the age of 17, a left-sided hemiplegia, which was followed by good motor recovery, though with a permanent deficit in fine finger movements. She had a widespread loss of neural tissue in the right hemisphere (crossed cerebrocerebellar atrophy), including (1) marked atrophy and thinning of the precentral and postcentral gyri; (2) widespread deep white matter destruction, including the corticospinal tract; and (3) crossed cerebellar atrophy. Except over the supplementary motor area (SMA), transcranial magnetic stimulation did not elicit motor evoked potentials in the affected hand. Nevertheless, during opening and closing of the affected hand, functional magnetic resonance imaging showed an activation of the lesioned primary sensorimotor cortex (SMC), as well as of the intact SMA and the parietal areas, but not of the ipsilateral motor areas. The authors speculate that recovery was achieved by a motor command generated in the SMC and the parietal cortex, passing through corticospinal axons originating in the SMA.     

术中皮质体感诱发电位与电刺激术定位脑功能区

目的探讨脑功能区手术中利用脑皮质体感诱发电位(SEP)及直接皮质电刺激定位脑功能区的方法及意义。方法对10例脑功能区病变病人在唤醒麻醉下进行手术，利用皮质SEP及皮质直接电刺激定位感觉区、运动区及语占区，住保护脑功能区的前提下，手术切除病变。结果7例病人利用SEP及皮质电刺激确定出运动感觉区，其中4例利用SEP位相倒置确定出中央沟，3例病变位于左侧额颞叶的病人通过皮质直接电刺激确定出语言区?术后功能均较术前明显好转。结论术中SEP及直接皮质电刺激可准确、实时确定脑功能区，最大程度地保护功能，切除病变。     

Intensity-dependent regional cerebral blood flow during 1-Hz repetitive transcranial magnetic stimulation (rTMS) in healthy volunteers studied with H215O positron emission tomography: I. Effects of primary motor cortex rTMS.

BACKGROUND: Repetitive transcranial magnetic stimulation (rTMS) affects the excitability of the motor cortex and is thought to influence activity in other brain areas as well. We combined the administration of varying intensities of 1-Hz rTMS of the motor cortex with simultaneous positron emission tomography (PET) to delineate local and distant effects on brain activity. METHODS: Ten healthy subjects received 1-Hz rTMS to the optimal position over motor cortex (M1) for producing a twitch in the right hand at 80, 90, 100, 110, and 120% of the twitch threshold, while regional cerebral blood flow (rCBF) was measured using H(2)(15)O and PET. Repetitive transcranial magnetic stimulation (rTMS) was delivered in 75-pulse trains at each intensity every 10 min through a figure-eight coil. The regional relationship of stimulation intensity to normalized rCBF was assessed statistically. RESULTS: Intensity-dependent rCBF increases were produced under the M1 stimulation site in ipsilateral primary auditory cortex, contralateral cerebellum, and bilateral putamen, insula, and red nucleus. Intensity-dependent reductions in rCBF occurred in contralateral frontal and parietal cortices and bilateral anterior cingulate gyrus and occipital cortex. CONCLUSIONS: This study demonstrates that 1-Hz rTMS delivered to the primary motor cortex (M1) produces intensity-dependent increases in brain activity locally and has associated effects in distant sites with known connections to M1.     

Electrophysiologic target localization in posteroventral pallidotomy

Summary The current interest in stereotactic posteroventral pallidotomy (PVP) for treating Parkinson's disease and the variability of published results have raised questions regarding techniques for target localization. In our technique the probe is guided to the optimum target at the most ventral pallidum and ansa lenticularis by macroelectrode stimulation of the internal capsule and optic tract from within the globus pallidus, with the thresholds providing a relative measure of the electrode proximity to these structures. We have characterized these localizing macroelectrode stimulation parameters in 57 posteroventral pallidotomies with consistent anatomic lesion placement, excellent outcome, and no complications.Using a 1.8 × 2.0 mm radiofrequency electrode for macroelectrode stimulation (RFG-3C, Radionics Inc.), minimum voltages (thresholds) to activate motor (at a frequency of 2 Hz) or visual (at a frequency of 100 Hz) responses as well as impedance measurements were obtained at the final target (Tf) and at distances proximal to Tf along the electrode trajectory. The visual and motor threshold voltages at Tf via our standard approach angles (50 ° above base plane, 20 ° from the sagittal plane), had a range of 1.0 to 1.5 V, and 2.0 to 3.5 V respectively. We also found that as the probe approaches Tf there is a significant decrease in voltage thresholds for motor (P<.0001) and visual (P<.0001) responses in an individual patient indicating that the probe is converging on these structures. Increases in impedance between Tf, 2–3 mm, and 4–5 mm proximal to Tf were also statistically significant (P<.0001). Microelectrode recording of electrophysiological neuronal activity at various points along the trajectory towards the target showed distinct firing patters providing identification of the globus pallidus externus and internus, ansa lenticularis, and optic tract.Macroelectrode electrophysiological stimulation within the target volume, inducing threshold responses in the internal capsule and optic tract, provides for accurate localization of the most effective PVP target in the ansa lenticularis. In unresponsive patients, the utilization of microelectrode recording for the identification of the pallidal borders and the optic tract improves safety.     

Post-operative progress of dystonia patients following globus pallidus internus deep brain stimulation

In the current era of functional surgery for movement disorders, deep brain stimulation (DBS) of the globus pallidus internus (GPi) is emerging as the favoured intervention for patients with dystonia. Here we report our results in 20 patients with medically intractable dystonia treated with GPi stimulation. The series comprised 14 patients with generalized dystonia and six with spasmodic torticollis. Although comparisons were limited by differences in their respective neurological rating scales, chronic DBS clearly benefited both patient groups. Data conveying the rate of change in neurological function following intervention are also presented, demonstrating the gradual but progressive and sustained nature of improvement following stimulation of the GPi in dystonic patients.     

Peripheral nerve stimulation during MRI: Effects of high gradient amplitudes and switching rates

The application of high gradient amplitudes and switching rates for MRI and spectroscopy, resulting in short rise times for the gradient field and high changes of the magnetic flux density in the patient, is known to possibly evoke peripheral nerve stimulation (PNS) in patients. These effects have been studied on 20 volunteers under different experimental circumstances. The results of these measurements are partially in line with earlier findings reported in the literature. New information is found for the dependence of the PNS threshold level as a function of the rise time of the gradient waveform. The PNS threshold level, expressed in terms of dB/dt, is found to be proportional with t^?05, where t is the switch time for the gradients. Indications are found that |B|, the modulus of the gradient vector field, is more closely related to the PNS threshold level than B_z, the imaging component of the gradient field. From the experiments, it is furthermore concluded that only for the imaging protocols characterized by the application of long bipolar repetitive gradient pulse trains, such as echo-planar imaging, PNS is expected at the reported threshold levels. For the protocols based on spin echo, turbo spin echo, inversion recovery, fast field echo, etc., characterized by shorter gradient pulse trains, the threshold levels are expected to be much higher.