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Biomedical subjects

Tipu Aziz

Publications and source records attributed to Tipu Aziz.

17 recordsLinked to original sources
PubMed2006

Involvement of human basal ganglia in offline feedback control of voluntary movement.

Practice makes perfect, but the neural substrates of trial-to-trial learning in motor tasks remain unclear. There is some evidence that the basal ganglia process feedback-related information to modify learning in essentially cognitive tasks , but the evidence that these key motor structures are involved in offline feedback-related improvement of performance in motor tasks is paradoxically limited. Lesion studies in adult zebra finches suggest that the avian basal ganglia are involved in the transmission or production of an error signal during song . However, patients with Huntington's disease, in which there is prominent basal ganglia dysfunction, are not impaired in error-dependent modulation of future trial performance . By directly recording from the subthalamic nucleus in patients with Parkinson's disease, we demonstrate that this nucleus processes error in trial performance at short latency. Local evoked activity is greatest in response to smallest errors and influences the programming of subsequent movements. Accordingly, motor parameters are least likely to change after the greatest evoked responses so that accurately performed trials tend to precede other accurate trials. This relationship is disrupted by electrical stimulation of the nucleus at high frequency. Thus, the human subthalamic nucleus is involved in feedback-based learning.

Aged↗
PubMed2005

Effect of GPi DBS on functional imaging of the brain in dystonia.

Five patients with idiopathic dystonic conditions, treated successfully with deep brain stimulation (DBS) of the globus pallidus internus (GPi), were studied using single-photon emission tomography (SPET) in order to evaluate brain perfusion in the presence and absence of DBS. Comparison was made between the "on" and "off" DBS scans on an individual basis and also as part of a group analysis. Whilst the individual data suggested great regional variation in cerebral perfusion between individuals, the results of the group analysis revealed several topographically similar areas of the brain where relative hyperperfusion in the absence of DBS was common to all patients. Based on these results we postulate on possible mechanisms for this phenomenon.

Adult↗
PubMed2004

Increased risk of lead fracture and migration in dystonia compared with other movement disorders following deep brain stimulation.

Deep brain stimulation (DBS) therapy is a continually expanding field in the functional neurosurgical treatment of movement disorders. However, the occurrence of adverse events related to implanted hardware cannot be overlooked. We report on a specific feature noted in our experience of DBS-related complications. From 1998 until present we have found an overall rate of 5.3% of DBS electrode lead dysfunction (out of 133 patients) in our series (slipped leads 2.3%, lead fracture 3.8%). Interestingly, all of these failures occurred in dystonia patients (18.4% of all dystonia patients and 9.2% of all electrodes). We postulate on mechanisms that may explain why these complications predominate in this group of patients.

Adolescent↗
PubMed2003

Patterning of globus pallidus local field potentials differs between Parkinson's disease and dystonia.

Here we test the hypothesis that there are distinct temporal patterns of synchronized neuronal activity in the pallidum that characterize untreated and treated parkinsonism and dystonia. To this end we recorded local field potentials (LFPs) from the caudal and rostral contact pairs of macroelectrodes implanted into the pallidum of patients for the treatment of Parkinson's disease (12 cases recorded on and off medication, 17 macroelectrodes) and dystonia (10 cases, 19 macroelectrodes). Percentage LFP power in the 11-30 Hz band was decreased and that in the 4-10 Hz band increased across both contact pairs in treated Parkinson's disease compared with untreated Parkinson's disease. Dystonic patients had even less 11-30 Hz power and greater 4-10 Hz power compared with untreated or treated Parkinson's disease patients. The change in the 4-10 Hz band in patients with dystonia was particularly manifest in the more rostral contact pair, presumed to be within or bridging the globus pallidus externus. We conclude that untreated and treated Parkinson's disease and dystonia are characterized by different spatiotemporal patterns of activity in the human pallidum.

Adult↗
PubMed2003

Globus pallidus internus deep brain stimulation for dystonic conditions: a prospective audit.

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 target in the treatment of patients with dystonia. The results of 25 consecutive patients with medically intractable dystonia (12 with generalised dystonia, 7 with spasmodic torticollis, and 6 with other types of dystonia) treated with GPi stimulation are reported. Although comparisons were limited by differences in their respective neurological rating scales, chronic DBS benefited all groups, resulting in clear and progressive improvements in their condition. This study clearly demonstrates that DBS of the GPi provides amelioration of intractable dystonia.

Adolescent↗
PubMed2003

Executive cognitive deficits in primary dystonia.

Primary dystonia is a disorder of movement for which no consistent pathophysiology has been identified; in the absence of evidence to the contrary, it is assumed to be cognitively benign. We have studied a clinically heterogeneous group of 14 patients with primary dystonia on a battery of neuropsychological tests. Despite well-preserved speed of information processing, language, spatial, memory and general intellectual skills relative to normal controls, we have identified a constellation of attentional-executive cognitive deficits on the Cambridge Neuropsychological Test Automated Battery (CANTAB). Specifically, patients demonstrated significant difficulties negotiating the extra-dimensional set-shifting phase of the IED task. The implications of these findings for the pathophysiology of primary dystonia are discussed. This is, to the best of our knowledge, the first report of a significant cognitive deficit in patients with primary dystonia.

Adult↗
PubMed2003

Estimating the costs of surgical innovations: the case for subthalamic nucleus stimulation in the treatment of advanced Parkinson's disease.

We estimated the current cost of deep brain stimulation surgery targeted on the subthalamic nucleus. The method used was a cost analysis using typical resource use patterns and unit costs from a leading surgical centre, detailed equipment costs from the manufacturer, and sensitivity analysis. Resource use was based on patients with advanced Parkinson's disease. The main outcome measure was the likely total health service costs per patient, including preoperative assessment, surgery, and postoperative management over a 5-year period. The preoperative assessment, surgery, and discounted follow-up costs associated with subthalamic nucleus surgery were estimated at approximately UK Pounds 32,526 per patient over 5 years. Almost 70% of these costs are attributable to the initial costs of the equipment and the likely follow-up and replacement costs of the equipment. These costs will be affected mainly by future equipment costs and their replacement period and are relatively insensitive to preoperative assessment staff costs, length of hospital stay after surgery, and imaging costs. This cost estimate should be of use to researchers, health care managers, policy makers, and surgeons working in this area. Providing an estimate of the cost of this new procedure will provide a baseline for tracking future changes in costs and will assist the production of cost-effectiveness estimates.

Data Collection↗
PubMed2003

Thalamic field potentials in chronic central pain treated by periventricular gray stimulation -- a series of eight cases.

Chronic deep brain stimulation (DBS) of the periventricular gray (PVG) has been used for the treatment of chronic central pain for decades. In recent years motor cortex stimulation (MCS) has largely supplanted DBS in the surgical management of intractable neuropathic pain of central origin. However, MCS provides satisfactory pain relief in about 50-75% of cases, a range comparable to that reported for DBS (none of the reports are in placebo-controlled studies and hence the further need for caution in evaluating and comparing these results). Our experience also suggests that there is still a role for DBS in the control of central pain. Here we present a series of eight consecutive cases of intractable chronic pain of central origin treated with PVG DBS with an average follow-up of 9 months. In each case, two electrodes were implanted in the PVG and the ventroposterolateral thalamic nucleus, respectively, under guidance of corneal topography/magnetic resonance imaging image fusion. The PVG was stimulated in the frequency range of 2-100 Hz in alert patients while pain was assessed using the McGill-Melzack visual analogue scale. In addition, local field potentials (FPs) were recorded from the sensory thalamus during PVG stimulation. Maximum pain relief was obtained with 5-35 Hz stimulation while 50-100 Hz made the pain worse. This suggests that pain suppression was frequency dependent. Interestingly, we detected low frequency thalamic FPs at 0.2-0.4 Hz closely associated with the pain. During 5-35 Hz PVG stimulation the amplitude of this potential was significantly reduced and this was associated with marked pain relief. At the higher frequencies (50-100 Hz), however, there was no reduction in the FPs and no pain suppression. We have found an interesting and consistent correlation between thalamic electrical activity and chronic pain. This low frequency potential may provide an objective index for quantifying chronic pain, and may hold further clues to the mechanism of action of PVG stimulation. It may be possible to use the presence of these slow FPs and the effect of trial PVG DBS on both the clinical status and the FPs to predict the probable success of future pain control in individual patients.

Adult↗
PubMed2002

Pallidal activity recorded in patients with implanted electrodes predictively correlates with eventual performance in a timing task.

Here we seek to establish whether there are activities in the human pallidum that may predict a specific aspect of performance, timing. When recording from two patients with Parkinson's disease and primary generalised dystonia following functional neurosurgery we found that the amplitude of oscillatory pallidal activity occurring prior to the completion of a bimanual timing task was strongly correlated with eventual task duration. The frequency of this oscillatory activity was around 25 Hz. We conclude that the human pallidum may be involved in the prediction of movement timings and that such internal estimates may be reflected in amplitude modulation of oscillatory activity around 25 Hz.

Beta Rhythm↗
PubMed2002

Electrical stimulation of the midbrain increases heart rate and arterial blood pressure in awake humans.

Electrical stimulation of the hypothalamus, basal ganglia or pedunculopontine nucleus in decorticate animals results in locomotion and a cardiorespiratory response resembling that seen during exercise. This has led to the hypothesis that parallel activation of cardiorespiratory and locomotor systems from the midbrain could form part of the 'central command' mechanism of exercise. However, the degree to which subcortical structures play a role in cardiovascular activation in awake humans has not been established. We studied the effects on heart rate (HR) and mean arterial blood pressure (MAP) of electrically stimulating the thalamus and basal ganglia in awake humans undergoing neurosurgery for movement disorders (n = 13 Parkinson's disease, n = 1 myoclonic dystonia, n = 1 spasmodic torticollis). HR and MAP increased during high frequency (> 90 Hz) electrical stimulation of the thalamus (HR 5 +/- 3 beats min(-1), P = 0.002, MAP 4 +/- 3 mmHg, P = 0.05, n = 9), subthalamic nucleus (HR 5 +/- 3 beats min(-1), P = 0.002, MAP 5 +/- 3 mmHg, P = 0.006, n = 8) or substantia nigra (HR 6 +/- 3 beats min(-1), P = 0.001, MAP 5 +/- 2 mmHg, P = 0.005, n = 8). This was accompanied by the facilitation of movement, but without the movement itself. Stimulation of the internal globus pallidus did not increase cardiovascular variables but did facilitate movement. Low frequency (< 20 Hz) stimulation of any site did not affect cardiovascular variables or movement. Electrical stimulation of the midbrain in awake humans can cause a modest increase in cardiovascular variables that is not dependent on movement feedback from exercising muscles. The relationship between this type of response and that occurring during actual exercise is unclear, but it indicates that subcortical command could be involved in 'parallel activation' of the locomotor and cardiovascular systems and thus contribute to the neurocircuitry of 'central command'.

Adult↗
PubMed2002

Hardware-related problems of deep brain stimulation.

Deep brain stimulation for the alleviation of movement disorders and pain is now an established therapy. However, very little has been published on the topic of hardware failure in the treatment of such conditions irrespective of clinical outcome. Such device-related problems lead to significant patient morbidity and increased cost of therapy in the form of prolonged antibiotics, in-patient hospitalization, repeat surgery, and device replacement. We report a prospective review of our experience at the Radcliffe Infirmary Oxford from the period of April 1998 to March 2001. Overall there is a 20% rate of hardware-related problems in this series, which falls between the 7% and 65% rates reported by other groups. The majority of these failures occurred early on in the series, and numbers declined with experience. Some of the problems may be idiosyncratic to the methodology of individual groups.

Adolescent↗
PubMed2002

Quality of life outcomes following surgical treatment of Parkinson's disease.

We assessed the impact of surgical treatment of Parkinson's disease on quality of life using generic quality of life instruments and utility scores. The Medical Outcomes Study short form health survey SF-36 and Parkinson's Disease Questionnaire PDQ-39 were used before and 3-6 months after surgery to assess quality of life, and the results were converted into utility valuations. Ninety-seven patients were studied; 33 underwent unilateral thalamotomy, 33 unilateral pallidotomy, 20 bilateral pallidotomy, six subthalamic nucleus (STN) lesions, four mixed lesions, and in one case bilateral STN stimulation. All dimensions of the SF-36 except role mental and mental health showed statistically significant improvement following surgery. The PDQ-39 recorded significant improvements in the mobility, stigma, and bodily discomfort dimensions. The rating scale and time trade-off scales showed statistically significant gains in utility of 8% and 3%, respectively. Gains were particularly marked in the bilateral pallidotomy group. Differences in patient characteristics and selection made direct comparisons between procedures unreliable. Quality of life in patients with advanced Parkinson's disease is amenable to measurement; such measurement provides tentative evidence of significant gains in quality of life following some neurosurgical procedures.

Adult↗
PubMed2002

Thalamic field potentials during deep brain stimulation of periventricular gray in chronic pain.

Stimulation of the central gray matter areas has been used for the treatment of chronic pain for decades. To better understand the mechanism of action of such treatment we studied the effects of stimulation of the periventricular gray (PVG) on the sensory thalamus in two patients with chronic central pain. In each case, two electrodes were implanted in the PVG (Medtronic 3389) and the ventroposterolateral thalamic nucleus (Medtronic 3387), respectively, under guidance of CT/MRI image fusion. The PVG was stimulated in the frequency range of 2-100 Hz in alert patients while pain was assessed using the McGill-Melzack visual analogue scale. In addition, local field potentials (FPs) were recorded from the sensory thalamus during PVG stimulation. Maximum pain relief was obtained with 5-25 Hz stimulation while 50-100 Hz made the pain worse. This suggests that pain suppression was frequency dependent. Interestingly, we detected low frequency FPs at 0.2-0.4 Hz closely associated with the pain. During 5-25 Hz PVG stimulation the amplitude of this potential was significantly reduced and this was associated with marked pain relief. At the higher frequencies (50-100 Hz) however, there was no reduction in the FPs and no pain suppression. We have found an interesting correlation between thalamic activity and chronic pain. This curious low frequency potential may provide an objective index for quantifying chronic pain, and may hold further clues to the mechanism of action of PVG stimulation.

Chronic Disease↗
PubMed2002

Peri-ventricular grey stimulation versus motor cortex stimulation for post stroke neuropathic pain.

Central post stroke pain is often difficult to manage satisfactorily with conventional treatment modalities for pain. In the last decade functional neurosurgery has offered hope with motor cortex stimulation achieving significant alleviation of pain in some patients. Unfortunately this has led to the neglect of chronic stimulation of deep grey matter as another modality of treating this condition. In this article we present our experience with motor cortex stimulation and that with deep grey matter stimulation in patients with post stroke pain. We argue that both modalities have a significant role and that what is required are better methods of identifying particular patients who are more likely to respond to one or the other.

Aged↗
PubMedDate not supplied

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Animal Experimentation↗