Now showing 1 - 4 of 4
- PublicationExploration of the Generation and Suppression of Pathological Oscillatory Neural Activity in a Model of Deep Brain Stimulation in Parkinsons diseaseThis study explores possible mechanisms for the generation of pathological neural oscillatory activity associated with Parkinson’s disease in theoretical models. The suppression of the model oscillations with high frequency stimulation, analogous to the use of deep brain stimulation (DBS) in the treatment of Parkinson's disease, is also examined. The relationship between oscillation amplitude and the amplitude of the applied stimulation is explored theoretically and then compared with experimental data recorded in patients.
- PublicationMultiple Frequencies in the Basal Ganglia in Parkinsons DiseaseIn recent years, the authors have developed what appears to be a very successful phenomenological model for analyzing the role of deep brain stimulation (DBS) in alleviating the symptoms of Parkinson's disease. In this paper, we extend the scope of the model by using it to predict the generation of new frequencies from networks tuned to a specific frequency, or indeed not self-oscillatory at all. We have discussed two principal cases: firstly where the constituent systems are coupled in an excitatory-excitatory fashion, which we designate by ``+/+''; and secondly where the constituent systems are coupled in an excitatory-inhibitory fashion, which we designate ``+/-''. The model predicts that from a basic system tuned to tremor frequency we can generate an unlimited range of frequencies. We illustrate in particular, starting from systems which are initially non-oscillatory, that when the coupling coefficient exceeds a certain value, the system begins to oscillate at an amplitude which increases with the coupling strength. Another very interesting feature, which has been shown by colleagues of ours to arise through the coupling of complicated networks based on the physiology of the basal ganglia, can be illustrated by the root locus method which shows that increasing and decreasing frequencies of oscillation, existing simultaneously, have the property that their geometric mean remains substantially constant as the coupling strength is varied. We feel that with the present approach, we have provided another tool for understanding the existence and interaction of pathological oscillations which underlie, not only Parkinson's disease, but other conditions such as Tourette's syndrome, depression and epilepsy.
- PublicationAnalysis of Oscillatory Neural Activity in Series Network Models of Parkinson’s Disease During Deep Brain StimulationParkinson’s disease is a progressive, neurodegenerative disorder, characterized by hallmark motor symptoms. It is associated with pathological, oscillatory neural activity in the basal ganglia. Deep brain stimulation (DBS) is often successfully used to treat medically refractive Parkinson’s disease. However, the selection of stimulation parameters is based on qualitative assessment of the patient, which can result in a lengthy tuning period and a suboptimal choice of parameters. This study explores fourth order, control theory-based models of oscillatory activity in the basal ganglia. Describing function analysis is applied to examine possible mechanisms for the generation of oscillations in interacting nuclei and to investigate the suppression of oscillations with high-frequency stimulation. The theoretical results for the suppression of the oscillatory activity obtained using both the fourth-order model, and a previously described second-order model, are optimized to t clinically recorded local field potential data obtained from Parkinsonian patients with implanted DBS. Close agreement between the power of oscillations recorded for a range of stimulation amplitudes is observed (R2 =0 .690.99). The results suggest that the behavior of the system and the suppression of pathological neural oscillations with DBS is well described by the macroscopic models presented. The results also demonstrate that in this instance, a second-order model is sufficient to model the clinical data, without the need for added complexity. Describing the system behaviour with computationally efficient models could aid in the identification of optimal stimulation parameters for patients in a clinical environment.
257Scopus© Citations 17
- PublicationEffect of oral glucose supplementation on surface EMG during fatiguing dynamic exerciseThe aim of this study was to examine the effect of oral glucose supplementation on the surface electromyographic (sEMG) signal recorded during a dynamic, fatiguing exercise protocol. Five healthy subjects participated in the study. Blood glucose concentration and sEMG signals from five upper leg muscles were recorded during a cycling exercise performed at 70% VO2peak until task failure, on two separate occasions. Glucose was consumed at 15 minute intervals throughout one trial. The median frequency of the sEMG was observed to increase progressively throughout the exercise, with a greater increase in the with glucose condition. This is in direct contrast to the typical decrease in median frequency known to occur during a fatiguing isometric contraction. The result may indicate an increase in Na+ - K+- AT Pase activity during fatiguing dynamic exercise resulting in an increase in muscle fiber membrane excitability due to membrane hyperpolarization.
282Scopus© Citations 2