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  • Use of the Radionics Image Fusiontrade mark and Stereoplantrade mark programs for target localization in functional neurosurgery.

    3 July 2018

    We describe the use of Radionics Image Fusiontrade mark and Stereoplantrade mark in defining the target for thalamotomy and pallidotomy in functional surgery for parkinsonism and tremor. Using this to fuse and spatially correct magnetic resonance imaging (MRI) to computed tomography (CT) images our calculated targets were a mean of 0.6 +/- 1.5 mm from the end target determined physiologically by stimulation. This is significantly better than the values of 2.6 +/- 1.6 mm for thalamic targets and 7.1 +/- 3.7 mm for pallidal targets using CT alone. As a consequence, determination of the target and the lesion making are routinely performed in one pass of the electrode allowing for faster, more accurate and, we believe, safer functional procedures.

  • Extracting burst and tonic components from surface electromyograms in dystonia using adaptive wavelet shrinkage.

    3 July 2018

    The compound surface electromyograms (EMGs) recorded from patients with dystonia commonly contains superimposed bursting and tonic activity representing various motor symptoms. It is desirable to differentially extract them from the compound EMGs so that different symptoms can be more specifically investigated and different mechanisms revealed. A non-linear denoising approach based on wavelet transformation was investigated by applying soft thresholding to the wavelet coefficients. Thresholds were determined according to three different principles and two models. Different techniques for wavelet shrinkage were investigated for separating burst and tonic activity in the compound EMGs. The combination of Stein's unbiased risk estimate principle with a non-white noise model proved optimal for separating burst and tonic activity. These turned out to be exponentially related; and the temporal relationships between antagonist muscle contractions could now be seen clearly. We conclude that adaptive soft-thresholding wavelet shrinkage provides effective separation of burst and tonic activity in the compound EMG in dystonia. This separation should improve our understanding of the pathophysiology of dystonia.

  • Optimising coherence estimation to assess the functional correlation of tremor-related activity between the subthalamic nucleus and the forearm muscles.

    3 July 2018

    Application of coherence estimation needs not only to correctly estimate coherence values but also to efficiently test the statistical significance of the estimates. In the present report, we have explained the approach of optimising a coherence estimator by restricting its normalised bias error and random error. In addition to the commonly used independence threshold, two more tests based on the probability of detection and the exact confidence interval have been proposed for detecting the significance of the coherence estimates. All three methods have been used to evaluate the significant functional correlation between oscillatory field potentials (FPs) in the subthalamic nucleus (STN) and the surface electromyogram (EMG) of the forearm muscles during tremor in Parkinson's disease.

  • Time-frequency analysis of transient neuromuscular events: dynamic changes in activity of the subthalamic nucleus and forearm muscles related to the intermittent resting tremor.

    3 July 2018

    In order to investigate the dynamic change in transient neuromuscular events and the functional correlation between the neural and muscular activity, local field potentials (LFPs) of the subthalamic nucleus (STN) and surface electromyograms (sEMGs) over several episodes of transient resting tremor from a patient with Parkinson's disease were quantitatively characterised in time-frequency domain using short-time Fourier transform and continuous wavelet transform. Events of onset and cessation of the tremor-related activity in the STN and muscles were correlated to reveal the temporal relationship between the two signals. A significant suppression in the power of the STN LFPs in the beta band (10-30 Hz) preceded the onset of resting tremor, which was presented as the increases in the power at the tremor frequency (3.0-4.5 Hz) in both STN LFPs and surface EMGs. Over the episodes of the intermittent resting tremor, the power of the STN LFPs in the beta band and the power of sEMGs in the tremor frequency band change in an alternating pattern with a significant exponential correlation (P(STN) = 16.8+62.3 x exp(-P(EMG)/6270.7); R2 = 0.72; p < 0.05). Significant linear correlation in the power values at the tremor frequency appears between STN LFPs and sEMGs (P(STN) = 65.1 + 2.1 x 10(-4)P(EMG); R2 = 0.41; p < 0.05). In comparison with short-time Fourier transform, similar results could be achieved using continuous wavelet transform of an appropriate wavelet with a higher temporal resolution but larger distortion in the high frequency.

  • The physiologically modulated electrode potentials at the depth electrode-brain interface in humans.

    3 July 2018

    To study the modulated electrical potential specifically related to the electrode-brain interface (EBI) in deep brain stimulation (DBS) under physiological condition, we quantitatively identified the physiologically modulated electrode potentials by decomposing the local field potentials (LFPs) recorded from 11 patients (18 electrodes in four different brain regions) who underwent DBS, and correlated them with simultaneously recorded physiological signals of blood pressure (BP) and respiration. Results showed that electrode potentials were modulated by BP and respiration and could be detected as a specific component of the compound LFP signals with a mean (+/-S.D.) amplitude of 6.9+/-1.7 microV. The detection rate and amplitude of the modulated electrode potentials were independent from brain regions and neurological disorders. The current approach can be used to study the changes in properties of the EBI under physiological condition and to investigate the effects of the EBI on the 'crossing' current of either the neural signals to be recorded or the electrical pulses for neurostimulation.

  • Pedunculopontine nucleus electric stimulation alleviates akinesia independently of dopaminergic mechanisms.

    3 July 2018

    The symptom of Parkinson's disease that is most disabling and difficult to treat is akinesia. We have previously shown that low-frequency stimulation of the pedunculopontine nucleus can alleviate such akinesia in a macaque rendered Parkinsonian using 1-methyl 4-phenyl 1,2,3,6-tetrahydropyridine. Here, we have extended that study to show that adding stimulation of the pedunculopontine nucleus to levodopa treatment in this Parkinsonian monkey increased its motor activity significantly more than levodopa alone. This additivity suggests that pedunculopontine nucleus stimulation may improve movement by acting at a site downstream from where levodopa therapy affects the basal ganglia.