1,721,073 research outputs found
The direction of oscillation in spiral drawings can be used to differentiate distal and proximal arm tremor
No full textThe assessment of the extent of involvement of the distal and proximal joints in a complex arm tremor is important clinically, as tremor generated around the distal and proximal arm joints can be differentially alleviated by surgical intervention to the thalamic and subthalamic targets, respectively. We observed that the tremor present in spiral drawings shows a diagonal directional preference. We hypothesized that the directional preference of tremor within spiral drawings could be related to the involvement of different arm joints. In this study, we tested this hypothesis by: (1) studying simulated tremulous drawings performed by healthy subjects with the joints selectively restrained; (2) recording surface EMGs from the forearm extensor and deltoid muscles during drawing; and (3) mathematical modelling the kinematics of the arm in 2D drawings. Our data showed that a “main diagonal” axis of orientation of the tremor along the orientation of the forearm indicates a predominantly proximal tremor driven by the shoulder, and a “cross diagonal” axis of orientation of tremor (i.e. perpendicular to the forearm) indicates that the tremor is predominantly distal and driven by the elbow or wrist. We conclude that the spiral drawing task can be used as an objective and quantitative method for differentiating the involvement of the proximal and distal arm joints in complex arm tremors
Time-frequency analysis of transient neuromuscular events: dynamic changes in activity of the subthalamic nucleus and forearm muscles related to the intermittent resting tremor
No full textIn 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 ceasing 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 - 30Hz) preceded the onset of resting tremor which was presented as the increases in the power at the tremor frequency (3.0 - 4.5Hz) 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 (PSTN = 16.8 + 62.3*exp(-PEMG/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 (PSTN = 65.1 + 2.1*10-4PEMG; 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
Physiological and harmonic components in neuromuscular coherence in Parkinsonian tremor
No full textObjective: To differentiate physiological from harmonic components in coherence analysis of the tremor-related neural and muscular signals by comparing power, cross-power and coherence spectra. Methods: Influences of waveform, burst-width and additional noise on generating harmonic peaks in the power, cross-power and coherence spectra were studied using simulated signals. The local field potentials of the subthalamic nucleus (STN) and the EMGs of the contralateral forearm muscles in PD patients with rest tremor were analysed.Results: (1) Waveform had significant effect on generating harmonics; (2) noise significantly decreased the coherence values in a frequency-dependent fashion; and (3) cross-spectrum showed high resistance to harmonics. Among six examples of paired LFP-EMG signals, significant coherence appeared at the tremor frequency only, both the tremor and double tremor frequencies and the double-tremor frequency only. Conclusions: In coherence analysis of neural and muscular signals, distortion in waveform generates significant harmonic peaks in the coherence spectra and the coherence values of both physiological and harmonic components are modulated by extra noise or non-tremor related activity. Significance: The physiological or harmonic nature of a coherence peak at the double tremor frequency may be differentiated when the coherence spectra are compared with the power spectra and in particular the cross-spectra
Extracting burst and tonic components from surface electromyograms in dystonia using adaptive wavelet shrinkage
No full textThe compound surface 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
Different mechanisms may generate sustained hypertonic and rhythmic bursting muscle activity in idiopathic dystonia
No full textDespite that deep brain stimulation (DBS) of the globus pallidus internus (GPi) is emerging as the favored intervention for patients with medically intractable dystonia, the pathophysiological mechanisms of dystonia are largely unclear. In eight patients with primary dystonia who were treated with bilateral chronic pallidal stimulation, we correlated symptom-related electromyogram (EMG) activity of the most affected muscles with the local field potentials (LFPs) recorded from the globus pallidus electrodes. In 5 dystonic patients with mobile involuntary movements, rhythmic EMG bursts in the contralateral muscles were coherent with the oscillations in the pallidal LFPs at the burst frequency. In contrast, no significant coherence was seen between EMG and LFPs either for the sustained activity separated out from the compound EMGs in those 5 cases, or in the EMGs in 3 other cases without mobile involuntary movements and rhythmic EMG bursts. In comparison with the resting condition, in both active and passive movements, significant modulation in the GPi LFPs was seen in the range of 8–16 Hz. The finding of significant coherence between GPi oscillations and rhythmic EMG bursts but not sustained tonic EMG activity suggests that the synchronized pallidal activity may be directly related to the rhythmic involuntary movements. In contrast, the sustained hypertonic muscle activity may be represented by less synchronized activity in the pallidum. Thus, the pallidum may play different roles in generating different components of the dystonic symptom complex
Optimising coherence estimation to assess the functional correlation of tremor-related activity between the subthalamic nucleus and forearm muscles
No full textApplication 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
The effects of volitional breathing and carbon dioxide inhalation on human local field potentials
Full text linkBreathing is an automatic process that we hardly pay any attention to in our daily life. As a social species, we interact using body movement, speech and emotion and these actions require modification of the respiratory pattern. While we understood how the respiratory rhythm is generated, we do not have clear evidence on how higher cortical signals modulate the respiratory pattern. The deep cortical structures in the human brain are inaccessible under normal circumstances, and deep brain stimulation electrode recordings offer an opportunity to understand the neurophysiological interactions ofdeeper brain structures. In this thesis, I investigated deep brain stimulation recordings from implanted electrodes in chronic neuropathic pain subjects in the right and left anterior cingulate cortices, the ventral posterior lateral nucleus of the thalamus and periventricular gray region. The objectives of this research were to elucidate the feed-forward mechanisms of volitional breathing, cortical autonomic regulation, and to investigate whether any of the investigated nuclei haveany carbon dioxide-sensitive neurons which may encode respiratory sensation. The results show lateralisation of the cortical autonomic control whereby the left anterior cingulate exhibits increases in beta band activity (30 to 90 Hz) with cognition and vocalisation tasks. Meanwhile, right anterior cingulate activity increases with hyperoxia. Respiration using various carbon dioxide concentrations shows a constant rise in the alpha band (8 to 14 Hz) activity in the PVG which suggests a sensitive, nonspecific neuronal activity related to systemic carbon dioxide levels
Novel approaches to studying the role of the anterior cingulate cortex in cognition and Parkinson's disease
Full text linkThe motor symptoms of Parkinson's disease (PD) have been linked to the emergence of exaggerated oscillatory activity in the 13 - 35 Hz beta range in recordings of the basal ganglia (BG) thalamocortical circuit of PD patients and animal models. PD patients and animal models also express dopamine-dependent cognitive impairments, implying effects of dopamine loss on the function of the anterior cingulate cortex (ACC). This thesis examines the electrophysiological behavior of the BG thalamocortical circuit in PD and dopamine-normal states during cognitive and motor activity. In vivo recordings in the BG of PD and dystonic patients were used to study the influence of dopamine during a test of executive function. Normal executive function was also investigated in the dopamine-healthy ACC of chronic pain patients. Both the BG and ACC exhibited lateralized electrophysiological responses to feedback valence. The BG also exhibited dopamine-sensitive event-related behavior. In additional experiments, chronically implanted recording electrodes in awake, behaving hemiparkinsonian rats were used to examine the transmission of synchronized oscillatory activity from the BG, through the ventral medial (VM) thalamus, to the ACC. Modulation of subthalamic nucleus, VM thalamus, and ACC activity during a simple cognitive/movement task was also investigated in hemiparkinsonian rats. Findings in the rat model suggest that ACC-mediated executive function is dopamine-sensitive and is reflected in the regionâs electrophysiology. These results may provide further insight into the significance of excessive oscillatory activity in PD and its influence on cognitive systems.</p
Enhancing motor performance in the healthy and Parkinsonian brain: adaptation, oscillations, and electrical stimulation
Full text linkParkinson's disease (PD) is characterized by debilitating impairments in motor control arising from pathophysiological alterations in basal ganglia circuitry and function. In this research thesis two main approaches, namely electrical recording and stimulation, are combined in order to better understand motor performance in Parkinson's disease and ways it might be improved. Three main types of motor behaviors are studied: discrete ballistic movement, repetitive movement, and motor adaptation. First, deep brain stimulation (DBS) of the subthalamic nucleus (STN) was shown to improve the velocity of discrete, ballistic movements in PD. The neural correlates of ballistic movements were then studied by recording from the STN of PD patients, revealing onset of beta-range desynchronization prior to, and gamma-range frequency synchronization during, performance of fast arm reaches. To determine a causal role for these oscillatory frequencies in motor behavior, the motor cortex of healthy humans was stimulated at either beta or gamma frequency during a 'go/no-go' grip force task. Beta stimulation resulted in slower force generation on 'go' trials but enhanced inhibition during 'no-go' trials, whereas gamma stimulation resulted in faster force generation on 'go' trials. Second, STN DBS resulted in improved repetitive tapping performance in PD patients through a reduction in variability. Recordings from the STN demonstrated that repetitive movement was accompanied by a substantial and persistent suppression of beta oscillatory activity. Third, Parkinson's patients were tested on a motor adaptation task, revealing intact learning but impaired retention of a visuomotor rotation. Application of direct current stimulation of the motor cortex resulted in enhanced adaptation during both learning and retention in PD patients and healthy controls. These results causally implicate the basal ganglia and oscillatory activity in motor control, provide insight into the neuronal mechanisms of motor performance and adaptation, and demonstrate promising new avenues for enhancing motor control in Parkinson's disease
The sensory and motor representation of synchronized oscillations in the globus pallidus in patients with primary dystonia
No full textIn 15 patients with primary dystonia (six cervical and nine generalized dystonias) who were treated with bilateral chronic pallidal stimulation, we investigated the sensorimotor modulation of the oscillatory local field potentials (LFPs) recorded from the pallidal electrodes. We correlated these with the surface electromyograms in the affected muscles. The effects of involuntary, passive and voluntary movement and muscle-tendon vibration on frequency ranges of 0–3 Hz, theta (3–8 Hz), alpha (8–12 Hz), low (12–20 Hz) and high beta (20–30 Hz), and low (30–60 Hz) and high gamma (60–90 Hz) power were recorded and compared between cervical and generalized dystonia groups. Significant decreases in LFP synchronization at 8–20 Hz occurred during the sensory modulation produced by voluntary or passive movement or vibration. Voluntary movement also caused increased gamma band activity (30–90 Hz). Dystonic involuntary muscle spasms were specifically associated with increased theta, alpha and low beta (3–18 Hz). Furthermore, the increase in the frequency range of 3–20 Hz correlated with the strength of the muscle spasms and preceded them by ~320 ms. Differences in modulation of pallidal oscillation between cervical and generalized dystonias were also revealed. This study yields new insights into the pathophysiological mechanisms of primary dystonias and their treatment using pallidal deep brain stimulation
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