ORCID Profile
0000-0002-5201-3044
Current Organisation
University of Oxford
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Publisher: Wiley
Date: 1992
Abstract: Five patients who presented with stimulus-induced jerking as part of an apparent myoclonic or pathological startle syndrome are reported. Neurophysiological observations in these patients suggested the jerks were voluntary in origin. These included (a) variable latencies to the onset of stimulus induced jerks, (b) latencies were greater than that seen in reflex myoclonus of cortical or brainstem origin, and were (c) longer than the fastest voluntary reaction times of normal subjects, (d) variable patterns of muscle recruitment within each jerk and, (e) significant habituation with repeated stimulation. It is argued that these features are consistent with a voluntary origin for the jerks and enable them to be distinguished from the stereotyped electrophysiological characteristics of myoclonus of cortical and brainstem origin. Electrophysiological recordings may help identify patients with this form of psychogenic movement disorder.
Publisher: Elsevier BV
Date: 2017
Publisher: Cold Spring Harbor Laboratory
Date: 03-10-2018
DOI: 10.1101/433334
Abstract: Both phase- litude coupling (PAC) and beta-bursts in the subthalamic nucleus have been significantly linked to symptom severity in Parkinson’s disease (PD) in humans and emerged independently as competing biomarkers for closed-loop deep brain stimulation (DBS). However, the underlying nature of subthalamic PAC is poorly understood and its relationship with transient beta burst-events has not been investigated. To address this, we studied macro- and micro electrode recordings of local field potentials (LFPs) and single unit activity from 15 hemispheres in 10 PD patients undergoing DBS surgery. PAC between beta phase and high frequency oscillation (HFO) litude was compared to single unit firing rates, spike triggered averages, power spectral densities and phase-spike locking, and was studied in periods of beta-bursting. We found a significant synchronisation of spiking to HFOs and correlation of mean firing rates with HFO- litude when the latter was coupled to beta phase (i.e. in the presence of PAC). In the presence of PAC, single unit power spectra displayed peaks in the beta and HFO frequency range and the HFO frequency was correlated with that in the LFP. Finally, PAC significantly increased with beta burst-duration. Our findings offer new insight in the pathology of Parkinson’s disease by providing evidence that subthalamic PAC reflects the locking of spiking activity to network beta oscillations and that this coupling progressively increases with beta-burst duration. These findings suggest that beta-bursts capture periods of increased subthalamic input/output synchronisation in the beta frequency range and have important implications for therapeutic closed-loop DBS. Identifying biomarkers for closed-loop deep brain stimulation (DBS) has become an increasingly important issue in Parkinson’s Disease (PD) research. Two such biomarkers, phase– litude coupling (PAC) and beta-bursts, recorded from the implanted electrodes in subthalamic nucleus in PD patients, correlate with motor impairment. However, the physiological basis of PAC, and it relationship to beta bursts, is unclear. We provide multiple lines of evidence that PAC in the human STN reflects the locking of spiking activity to network beta oscillations and that this coupling progressively increases with the duration of beta-bursts. This suggests that beta-bursts capture increased subthalamic input/output synchronisation and provides new insights in PD pathology with direct implications for closed-loop DBS therapy strategies.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 04-2004
DOI: 10.1161/01.STR.0000122622.73916.D2
Abstract: Background and Purpose— Magnetic resonance imaging (MRI) methods such as diffusion- (DWI) and perfusion-weighted (PWI) imaging have been widely studied as surrogate markers to monitor stroke evolution and predict clinical outcome. The utility of quantitative electroencephalography (qEEG) as such a marker in acute stroke has not been intensively studied. The aim of the present study was to correlate ischemic cortical stroke patients’ clinical outcomes with acute qEEG, DWI, and PWI data. Materials and Methods— DWI and PWI data were acquired from 11 patients within 7 and 16 hours after onset of symptoms. Sixty-four channel EEG data were obtained within 2 hours after the initial MRI scan and 1 hour before the second MRI scan. The acute delta change index (aDCI), a measure of the rate of change of average scalp delta power, was compared with the National Institutes of Health Stroke Scale scores (NIHSSS) at 30 days, as were MRI lesion volumes. Results— The aDCI was significantly correlated with the 30-day NIHSSS, as was the initial mean transit time (MTT) abnormality volume (ρ=0.80, P .01 and ρ=0.79, P .01, respectively). Modest correlations were obtained between the 15-hour DWI lesion volume and both the aDCI and 30-day NIHSSS (ρ=0.62, P .05 and ρ=0.73, P .05, respectively). Conclusions— In this small s le the significant correlation between 30-day NIHSSS and acute qEEG data (aDCI) was equivalent to that between the former and MTT abnormality volume. Both were greater than the modest correlation between acute DWI lesion volume and 30-day NIHSSS. These preliminary results indicate that acute qEEG data might be used to monitor and predict stroke evolution.
Publisher: Elsevier BV
Date: 05-2007
DOI: 10.1016/J.EXPNEUROL.2007.01.027
Abstract: Excessive synchronization of neuronal activity at around 20 Hz is a common finding in the basal ganglia of patients with untreated Parkinson's disease (PD). Correlative evidence suggests, but does not prove, that this spontaneous activity may contribute to slowness of movement in this condition. Here we investigate whether externally imposed synchronization through direct stimulation of the region of the subthalamic nucleus at 20 Hz can slow motor performance in a simple unimanual tapping task and whether this effect is frequency selective. Tapping rates were recorded on 42 sides in 22 patients with PD after overnight withdrawal of medication. Tapping was performed without stimulation and during bilateral stimulation at 20 Hz, 50 Hz and 130 Hz. We found that tapping rates were slowed by 8.2+/-3.2% (p=0.014) during 20-Hz stimulation in subjects with relatively preserved baseline function in the task. This effect was frequency selective. The current data provide proof of the principle that excessive beta synchrony within the basal ganglia-cortical loop may contribute to the slowing of movements in Parkinson's disease.
Publisher: Springer Science and Business Media LLC
Date: 16-03-2002
DOI: 10.1007/S00221-002-1113-X
Abstract: There is increasing evidence that the primary motor cortex is involved in the generation of electromyographic (EMG) oscillations at frequencies in the range of 15-30 Hz that are observed during performance of a precision grip task. Since the level of the corticomuscular coherence varies according to the nature of the object that is gripped, it seemed possible that somatosensory inputs from the hand might affect this coherence. The aim of this study was to investigate whether interrupting cutaneous inputs from the digits would affect the coherence between hand muscles during precision grip of a compliant object. Subjects performed a precision grip hold-r -hold task before, during and after digital nerve anaesthesia of the index finger and thumb. There were marked deficits in the performance of the task, particularly during the initial formation of the grip and first hold period. Local digital nerve anaesthesia reduced but did not abolish 14-31 Hz coherence between EMG activity recorded from different hand and forearm muscles. Coherence was measured during the second hold phase of the task. Digital nerve anaesthesia did not affect the predominant frequencies in the EMG power spectra compiled from the same phase of the task. We conclude that during a precision grip task, cutaneous input enhances oscillatory synchrony between pairs of hand muscles.
Publisher: Oxford University Press (OUP)
Date: 06-03-2012
DOI: 10.1093/BRAIN/AWS039
Publisher: Elsevier BV
Date: 03-2006
DOI: 10.1016/J.EXPNEUROL.2005.11.019
Abstract: Deep brain stimulation (DBS) of the subthalamic nucleus (STN) can be a highly effective treatment for Parkinson's disease (PD). However, therapeutic efficacy is limited by difficulties in consistently and correctly targeting this nucleus. Increasing evidence suggests that there is abnormal synchronization of beta frequency band activity (approximately 20 Hz) in the STN of PD patients, as reflected in the oscillatory nature of the local field potential (LFP). We hypothesized that an increase in the power of the LFP beta activity may provide intra-operative confirmation of STN targeting in patients undergoing STN implantation for the treatment of advanced PD. Accordingly, we recorded LFPs from the four contacts of DBS electrodes as the latter were advanced in 2 mm steps from a point 4-6 mm above the intended surgical target point in the STN, to a point 4 mm below this. Contacts were configured to give three bipolar recordings of LFPs. These were analyzed on 16 sides in 9 patients. The power in the 13-35 Hz band recorded at the lowest contact pair underwent a steep but focal increase during electrode descent. The depth of the peak beta activity showed excellent agreement with the level of the intra-operative clinical stun effect (k coefficient = 0.792). The depth of peak beta activity also showed 100% specificity and 100% sensitivity for placement within STN in comparison to pre- and Post-operative stereotactic MRI. Functional physiological localization of STN by the on-line spectral analysis of LFPs is quick to perform and may provide information directly relevant to the position of the electrode contact actually used for DBS.
Publisher: Elsevier BV
Date: 11-2006
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 12-09-2005
DOI: 10.1212/01.WNL.0000174438.78399.BC
Abstract: To elucidate the involvement of the human subthalamic nucleus (STN) region in the processing or transmission of emotional information. Local field potentials (LFPs) were recorded from this region in 10 patients with Parkinson disease (PD) undergoing bilateral implantation of the STN for high-frequency stimulation. LFP recordings were made while patients viewed pleasant and unpleasant emotionally arousing and neutral pictures. A significant decrease (event-related desynchronization [ERD]) in the local alpha power (8 to 12 Hz) was found for all stimulus categories starting at about 0.5 seconds after stimulus presentation. However, 1 to 2 seconds poststimulus, the ERD was larger in trials of pleasant (mean ERD: 21.6 +/- 2.8% p < 0.009) and unpleasant (mean ERD: 15.0 +/- 4.2% p = 0.018) stimuli compared with neutral stimuli (mean ERD: 4.4 +/- 4.2%). The delayed modulation of alpha activity recorded from the area of the subthalamic nucleus in PD may reflect the processing or transmission of information related to emotional stimuli. "Limbic" activation in the region of the subthalamic nucleus may explain why high-frequency stimulation of the subthalamic nucleus alters affect in some patients with PD.
Publisher: Elsevier BV
Date: 05-2008
Publisher: Oxford University Press (OUP)
Date: 17-03-2005
DOI: 10.1093/BRAIN/AWH480
Abstract: The role of changes in inter-regional cortical synchronization in the pathophysiology of Parkinson's disease and the mechanism of action of dopaminergic therapy and high frequency subthalamic nucleus (STN) stimulation is unclear. We hypothesized that synchronization between distributed cortical areas would correlate with parkinsonism and that changes in synchronization with treatment would correlate with improvements in parkinsonism. To this end, we recorded scalp EEG in parkinsonian patients off treatment (16 patients, 31 sides) and then separately during high frequency stimulation (HFS) of the STN (16 patients, 31 sides) and following drug treatment (12 patients, 24 sides). All recordings were made at rest to avoid the confounding effects of differences in task performance. The motor Unified Parkinson's Disease Rating Scale (UPDRS) score was determined in each state. We found that EEG-EEG coherence over approximately 10-35 Hz correlated with the severity of parkinsonism, and reductions in cortical coupling over this frequency range with both l-dopa and STN stimulation correlated with clinical improvement. These results suggest that both dopaminergic therapy and STN stimulation may support the restoration of normal cortico-cortical interactions in the frequency domain. This mechanistic similarity may underscore the strong clinical correlation between the therapeutic effects of these treatment modalities.
Publisher: Wiley
Date: 10-2008
Publisher: Elsevier BV
Date: 04-2016
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Peter Brown.