Tipu Aziz

Publications (43)209.47 Total impact

• Article: Pallidal Somatotopy Suggested by Deep Brain Stimulation in a Patient with Dystonia.

  Carole Joint, Wesley Thevathasan, Alex L Green, Tipu Aziz
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  ABSTRACT: The response of dystonia to deep brain stimulation (DBS) is variable among patients, and an important factor in determining outcome is the precise location of stimulation.(1) For globus pallidus interna (GPi) stimulation, the posteroventrolateral subregion is considered the optimal "target within a target" for dystonia.(1).
  Neurology 01/2013; · 8.31 Impact Factor
• Article: Frequency specific activity in subthalamic nucleus correlates with hand bradykinesia in Parkinson's Disease.

  Huiling Tan, Alek Pogosyan, Anam Anzak, Thomas Foltynie, Patricia Limousin, Ludvic Zrinzo, Keyoumars Ashkan, Marko Bogdanovic, Alexander L Green, Tipu Aziz, Peter Brown
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  ABSTRACT: Local field potential recordings made from the basal ganglia of patients undergoing deep brain stimulation have suggested frequency specific activity is involved in determining the rate of force development and the peak force at the outset of a movement. However, the extent to which the basal ganglia might be involved in motor performance later on in a sustained contraction is less clear. We therefore recorded from the subthalamic nucleus region (STNr) in patients with Parkinson's disease (PD) as they made maximal voluntary grips. Relative to age-matched controls they had more rapid force decrement when contraction was meant to be sustained and prolonged release reaction time and slower rate of force offset when they were supposed to release the grip. These impairments were independent from medication status. Increased STNr power over 5-12Hz (in the theta/alpha band) independently predicted better performance - reduced force decrement, shortened release reaction time and faster rate of force offset. In contrast, lower mean levels and progressive reduction of STNr power over 55-375Hz (high gamma/high frequency) over the period when contraction was meant to be sustained were both strongly associated with greater force decrement over time. Higher power over 13-23Hz (low beta) was associated with more rapid force decrement during the period when grip should have been sustained, and with a paradoxical shortening of the release reaction time. These observations suggest that STNr activities at 5-12Hz and 55-375Hz are necessary for optimal grip performance and that deficiencies of such activities lead to motor impairments. In contrast, increased levels of 13-25Hz activity both promote force decrement and shorten the release reaction time, consistent with a role in antagonizing (and terminating) voluntary movement. Frequency specific oscillatory activities in the STNr impact on motor performance from the beginning to the end of a voluntary grip.
  Experimental Neurology 11/2012; · 4.70 Impact Factor
• Article: The pathophysiology of brain swelling associated with subdural hemorrhage: the role of the trigeminovascular system.

  Waney Squier, Julie Mack, Alex Green, Tipu Aziz
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  ABSTRACT: INTRODUCTION: This paper reviews the evidence in support of the hypothesis that the trigeminal system mediates brain swelling associated with subdural bleeding. The trigeminovascular system has been extensively studied in migraine; it may play an important but under-recognized role in the response to head trauma. Nerve fibers originating in trigeminal ganglion cells are the primary sensors of head trauma and, through their collateral innervation of the intracranial and dural blood vessels, are capable of inciting a cascade of vascular responses and brain swelling. The extensive trigeminal representation in the brainstem initiates and augments autonomic responses. Blood and tissue injury in the dura incite neurogenic inflammatory responses capable of sensitizing dural nerves and potentiating the response to trauma. DISCUSSION: The trigeminal system may provide the anatomo-physiological link between small-volume, thin subdural bleeds and swelling of the underlying brain. This physiology may help to explain the poorly understood phenomena of "second-impact syndrome," the infant response to subdural bleeding (the "big black brain"), as well as post-traumatic subdural effusions. Considerable age-specific differences in the density of dural innervation exist; age-specific responses of this innervation may explain differences in the brain's response to trauma in the young. An understanding of this pathophysiology is crucial to the development of intervention and treatment of these conditions. Antagonists to specific neuropeptides of the trigeminal system modify brain swelling after trauma and should be further explored as potential therapy in brain trauma and subdural bleeding.
  Child s Nervous System 08/2012; · 1.54 Impact Factor
• Article: Subthalamic nucleus activity optimizes maximal effort motor responses in Parkinson's disease.

  Anam Anzak, Huiling Tan, Alek Pogosyan, Thomas Foltynie, Patricia Limousin, Ludvic Zrinzo, Marwan Hariz, Keyoumars Ashkan, Marko Bogdanovic, Alexander L Green, Tipu Aziz, Peter Brown
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  ABSTRACT: The neural substrates that enable individuals to achieve their fastest and strongest motor responses have long been enigmatic. Importantly, characterization of such activities may inform novel therapeutic strategies for patients with hypokinetic disorders, such as Parkinson's disease. Here, we ask whether the basal ganglia may play an important role, not only in the attainment of maximal motor responses under standard conditions but also in the setting of the performance enhancements known to be engendered by delivery of intense stimuli. To this end, we recorded local field potentials from deep brain stimulation electrodes implanted bilaterally in the subthalamic nuclei of 10 patients with Parkinson's disease, as they executed their fastest and strongest handgrips in response to a visual cue, which was accompanied by a brief 96-dB auditory tone on random trials. We identified a striking correlation between both theta/alpha (5-12 Hz) and high-gamma/high-frequency (55-375 Hz) subthalamic nucleus activity and force measures, which explained close to 70% of interindividual variance in maximal motor responses to the visual cue alone, when patients were ON their usual dopaminergic medication. Loud auditory stimuli were found to enhance reaction time and peak rate of development of force still further, independent of whether patients were ON or OFF l-DOPA, and were associated with increases in subthalamic nucleus power over a broad gamma range. However, the contribution of this broad gamma activity to the performance enhancements observed was only modest (≤13%). The results implicate frequency-specific subthalamic nucleus activities as substantial factors in optimizing an individual's peak motor responses at maximal effort of will, but much less so in the performance increments engendered by intense auditory stimuli.
  Brain 08/2012; 135(Pt 9):2766-78. · 9.46 Impact Factor
• Article: Possible seizure suppression via deep brain stimulation of the thalamic ventralis oralis posterior nucleus.

  Benjamin Wakerley, Patrick Schweder, Alex Green, Tipu Aziz
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  ABSTRACT: Surgical treatment of intractable epilepsy with deep brain stimulation (DBS) has been shown to be of therapeutic benefit in some patients and with the recent publication of a randomised control study its use is likely to increase in the future. We describe a patient who developed a focal epileptic seizure within a few seconds of momentarily turning off the DBS stimulator in the nucleus ventralis oralis posterior, with which she was successfully treated for tremor. The seizure was the result of a newly diagnosed primary brain tumor. We suggest that the nucleus ventralis oralis posterior may be another thalamic target of DBS in epilepsy.
  Journal of Clinical Neuroscience 07/2011; 18(7):972-3. · 1.25 Impact Factor
• Source

  Available from: Michele Tagliati

  Article: Early postoperative management of DBS in dystonia: programming, response to stimulation, adverse events, medication changes, evaluations, and troubleshooting.

  Andreas Kupsch, Michele Tagliati, Marie Vidailhet, Tipu Aziz, Paul Krack, Elena Moro, Joachim K Krauss
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  ABSTRACT: Early postoperative management in deep brain stimulation-treated patients with dystonia differs from that of patients with essential tremor and Parkinson's disease, mainly due to the usually delayed effects of deep brain stimulation and the heterogenous clinical manifestation and etiologies of dystonia. The present chapter summarizes the available data about and concentrates on practical clinical aspects of early postoperative management in deep brain stimulation-treated patients with dystonia.
  Movement Disorders 06/2011; 26 Suppl 1:S37-53. · 4.51 Impact Factor
• Source

  Available from: Michele Tagliati

  Article: Long-Term management of DBS in dystonia: response to stimulation, adverse events, battery changes, and special considerations.

  Michele Tagliati, Paul Krack, Jens Volkmann, Tipu Aziz, Joachim K Krauss, Andreas Kupsch, And Marie Vidailhet
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  ABSTRACT: Multiple independent case series have documented sustained benefit of bilateral pallidal deep brain stimulation (DBS) up to 3 years in patients with primary dystonia. Growing evidence exists for positive outcomes extending up to 10 years. The beneficial effects from DBS are usually reported to be stable, thus requiring little long-term modifications of the parameters of stimulation. Speech and swallowing abnormalities are less responsive than other dystonic symptoms. Symptom exacerbation after initial benefit has been reported in a few cases. It is not known whether this is related to potential tolerance or habituation to stimulation or to progression of the underlying disease. Failures of pallidal DBS, at least in primary dystonia patients, should not be accepted without further re-evaluation of each individual case, including possible revisions of the electrode location. Both hardware- and stimulation-related adverse effects, including insufficient relief of speech function, have been reported in the long-term. Despite early reports suggesting that hardware problems might be more frequent in dystonia, more recent studies did not confirm these observations. In patients with severe segmental (e.g., axial) or generalized dystonia, sudden cessation of stimulation may become a medical emergency and should be anticipated changing the neurostimulator before its natural end of life.
  Movement Disorders 06/2011; 26 Suppl 1:S54-62. · 4.51 Impact Factor
• Article: The incidence of deep brain stimulator hardware infection: the effect of change in antibiotic prophylaxis regimen and review of the literature.

  Robin Bhatia, Arthur Dalton, Mike Richards, Chris Hopkins, Tipu Aziz, Dipankar Nandi
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  ABSTRACT: The complication of hardware infection related to deep brain stimulator implantation (or revision) varies between 0 and 15.2% in the literature. However, no national guidelines exist at present to define an average or acceptable rate of infection associated with, nor the preferred antibiotic prophylaxis required for, this procedure. The aim of this study was to examine the effect of changing the antibiotic prophylaxis regimen used in a single neurosurgical centre on the incidence and outcome of hardware infection. A prospective cohort of 38 patients undergoing deep brain stimulation (DBS) implantation or internal pulse generator (IPG) replacement and receiving perioperative vancomycin (including intravenous gentamicin on induction) and pouch-installed gentamicin, was compared to a historical cohort of 35 patients receiving perioperative cefuroxime in the same unit. The infection rate over 2 years in the prospective group for DBS surgery was 0 compared to 1 (5.6%) in the historical cohort (p = 0.11, χ(2)); the infection rate for IPG replacements was 1(3.6%) in the prospective cohort, versus 3 (17.6%) in the historical (p = 0.44, χ(2)). In this article, we have also systematically reviewed the literature to date and derived an average infection rate of 4.7% (PI 0.9-22%, Random Effects Meta-analysis, Stata) for 35 studies comprising 3550 patients. There is no significant difference in infection rates between DBS procedures that are primarily internalised (n = 9) compared to those in which there is a period of electrode externalisation (n = 23) (p = 0.9, Meta-regression analysis, Stata).
  British Journal of Neurosurgery 04/2011; 25(5):625-31. · 0.88 Impact Factor
• Article: Animal testing: TV or not TV?

  Tipu Aziz, John Stein, Ranga Yogeshwar
  Nature 02/2011; 470(7335):457-9. · 36.28 Impact Factor
• Article: Rapid tremor frequency assessment with the iPhone accelerometer.

  Raed A Joundi, John-Stuart Brittain, Ned Jenkinson, Alexander L Green, Tipu Aziz
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  ABSTRACT: The physician is often seeking more efficient ways of performing patient assessments. Currently, measuring tremor frequency requires expensive and bulky equipment. We propose the use of the in-built accelerometer of the iPhone via the iSeismo application for rapid measurement of tremor frequency. We use this device in a series of 7 different tremor cases, and show that the frequency measurements on the iSeismo graph closely match the more sophisticated EMG analysis during tremor. This is a preliminary confirmation of the usefulness of this device in the clinical setting for quick assessment of the dominant frequency component in a variety of tremors.
  Parkinsonism & Related Disorders 02/2011; 17(4):288-90. · 3.80 Impact Factor
• Source

  Available from: Carole Joint

  Article: Permanent tremor reduction during thalamic stimulation in multiple sclerosis.

  Wesley Thevathasan, Patrick Schweder, Carole Joint, Nicola Ray, Pieter Pretorius, Ralph Gregory, Tipu Aziz
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  ABSTRACT: Unlike thalamic lesioning, thalamic stimulation is considered a reversible treatment for tremor. However, tremor in multiple sclerosis (MS) can sometimes permanently improve during thalamic stimulation. Such 'permanent tremor reduction' (PTR) has been attributed to limb weakness preventing tremor expression. In this study, 11 consecutive patients with MS tremor treated with thalamic stimulation were assessed for PTR. Eighteen upper limbs had tremor, of which 16 received contralateral stimulation. Tremor severity and limb strength were assessed preoperatively, early postoperatively (within 1 year) and late postoperatively (after 3 years). Tremor severity was rated using validated clinical scales both on and off stimulation. Following explantation, the parenchyma surrounding three electrode tracts was examined with MRI. At final review (mean 5.2 years) PTR was evident in 11 of the 18 upper limbs with tremor. PTR often rendered stimulation redundant. PTR could occur when limb strength was conserved and could arise remotely from the initial surgery. PTR was significant (and universal) in limbs that received long-term (>2 years) effective (tremor suppressing) stimulation. PTR was not a significant finding in limbs that had not received long-term, effective stimulation. Contralateral to a limb with PTR, MRI revealed a thalamic lesion adjacent to the electrode tract. Thalamic lesions were not identified contralateral to two limbs without PTR. MS tremor often permanently improves during thalamic stimulation, even when limb strength is conserved. PTR may simply reflect natural history. Alternatively, these findings appear consistent with the recent proposal that thalamic stimulation in MS might promote local 'demyelinative lesioning.'
  Journal of neurology, neurosurgery, and psychiatry 09/2010; 82(4):419-22. · 4.87 Impact Factor
• Article: Predicting falls in Parkinson disease: a step in the right direction.

  Wesley Thevathasan, Tipu Aziz
  Neurology 07/2010; 75(2):107-8. · 8.31 Impact Factor
• Article: The saccade-related local field potentials of the superior colliculus: a functional marker for localizing the periventricular and periaqueductal gray.

  Xuguang Liu, Parashkev Nachev, Shouyan Wang, Alexander Green, Christopher Kennard, Tipu Aziz
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  ABSTRACT: This study was intended to investigate the neural signals related to oculomotor and visual activity during horizontal saccades in humans and to explore the potential of using such signals as a functional marker for localizing the periventricular and periaqueductal gray. We recorded the local field potentials (LFPs) via implanted electrodes in the rostrolateral part of the periventricular and periaqueductal gray in four patients (six electrodes) who underwent deep brain stimulation for treatment of neuropathic pain. The functional composition of the saccade-related LFPs under different visual conditions was characterized using time-frequency analysis, and it was correlated with the anatomic placement of the electrodes on the postoperative magnetic resonance images. The magnitude of oculomotor signals varied predictably with the proximity of the recording electrode to the superior colliculus; the oculomotor activity was represented specifically in the alpha (8-13 Hz) and theta (4-8 Hz) bands for saccades and in the alpha band for fixation, whereas the visual activity was represented in the delta band (1-3 Hz) of the LFPs. The compound LFP signals of the superior colliculus embrace the synchronized population activity of multimodalities, which can be differentiated in the frequency domain. This is the first time LFP signals of the human superior colliculus have been characterized. Such signals may be used as a functional marker for electrode placement in the periventricular and periaqueductal gray for modulation of pain.
  Journal of clinical neurophysiology: official publication of the American Electroencephalographic Society 09/2009; 26(4):280-7. · 1.47 Impact Factor
• Source

  Available from: Ludvic Zrinzo

  Article: Involvement of the subthalamic nucleus in engagement with behaviourally relevant stimuli.

  Paul Sauleau, Alexandre Eusebio, Wesley Thevathasan, Kielan Yarrow, Alek Pogosyan, Ludvic Zrinzo, Keyoumars Ashkan, Tipu Aziz, Wim Vandenberghe, Bart Nuttin, Peter Brown
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  ABSTRACT: In this study we investigate how the basal ganglia (BG) may process the behavioural relevance of environmental cues by recording local field potentials (LFPs) in the subthalamic nucleus of patients with Parkinson's disease who had undergone implantation of electrodes for deep brain stimulation. Fourteen patients were recorded as they performed a paradigm dissociating warning cue presentation from programming related to execution of specific tasks. Target and non-target warning cues of differing behavioural relevance were contrasted, and we evaluated if warning cue-evoked activities varied according to whether the eventual task to be performed was motor or cognitive and whether patients were receiving or withdrawn from dopaminergic therapy. Warning cues evoked a complex temporal sequence of activities with three epochs over the 760 ms following the onset of the warning cue. In contrast to the initial evoked LFP, evoked activities over two later periods were significantly influenced by behavioural relevance and by treatment state. The early activity was likely related to the initial orientating of attention induced by a novel target, while the delayed responses in our paradigm may reflect processing related to the non-motor resource implications of cues. The results suggest that the BG are intimately involved in the evaluation of changes in the environment and of their behavioural significance. The latter process is partly modulated by dopamine. Weakness in this function might contribute to the behavioural impairment that can follow BG lesions and surgery.
  European Journal of Neuroscience 03/2009; 29(5):931-42. · 3.63 Impact Factor
• Source

  Available from: biomedcentral.com

  Article: The effect of the ventricular system on the electric current in deep brain stimulation

  Nada Yousif, Dipankar Nandi, Alexander Green, Tipu Aziz, Xuguang Liu
  BMC Neuroscience. 01/2009;
• Article: Pathological synchronisation in the subthalamic nucleus of patients with Parkinson's disease relates to both bradykinesia and rigidity.

  Andrea A Kühn, Alexander Tsui, Tipu Aziz, Nicola Ray, Christof Brücke, Andreas Kupsch, Gerd-Helge Schneider, Peter Brown
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  ABSTRACT: Parkinson's disease (PD) is associated with exaggerated oscillatory synchrony in the basal ganglia at frequencies over 8-35 Hz. Studies have demonstrated a suppression of local field potential (LFP) activity in the subthalamic nucleus (STN) upon treatment with the dopamine prodrug, levodopa, with the degree of suppression of power in the 8-35 Hz band correlating with the improvement in combined measures of bradykinesia and rigidity. However, these studies do not explicitly address the question of what is more important in predicting clinical change - synchronisation of neuronal activity or the specific frequency within the 8-35 Hz band over which the latter occurs. In addition, they have not demonstrated a relationship between treatment-induced changes in synchronisation and changes in bradykinesia or rigidity on their own. To this end, we collected and analysed LFP and clinical data in 30 patients with PD. We found significant correlations between levodopa-induced power suppression and rigidity and bradykinesia, when these clinical features were considered separately, but only when power suppression profiles were re-aligned to the frequency of peak synchronisation. Under these circumstances correlations with rigidity persisted despite partialising out the effect of bradykinesia and vice versa. These data suggest that levodopa-induced improvements in both rigidity and bradykinesia scale with the degree of suppression of oscillatory power in the STN LFP, and that this is true irrespective of the frequency at which synchronisation occurs across a broad band from 8-35 Hz.
  Experimental Neurology 12/2008; 215(2):380-7. · 4.70 Impact Factor
• Conference Proceeding: Identifying rhythms of subthalamic neural oscillations in time-frequency domain

  Shouyan Wang, Alex Green, John Stein, Tipu Aziz, Xuguang Liu
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  ABSTRACT: We aimed to identify neural oscillations in the time-frequency representation of local field potentials recorded from the subthalamic nucleus. The time-frequency representation was normalised over the global mean and standard deviation global normalisation, or against the baseline period at each frequency, local normalisation. The cross-correlation between beta and gamma oscillations was enhanced by global normalisation. Furthermore, voluntary movement related amplitude changes in the gamma band and frequency modulation in the beta band were revealed by local normalisation. Thus global or local normalisation of time-frequency representation provides a reliable and effective way to identify oscillatory rhythms in subthalamic neural activity by reducing noise and increasing frequency discrimination. It can be used to enhance the detection of obscure or hidden neural oscillations and improve the sensitivity of post-hoc analysis.
  Engineering in Medicine and Biology Society, 2008. EMBS 2008. 30th Annual International Conference of the IEEE; 09/2008
• Article: Motivation modulates motor-related feedback activity in the human basal ganglia.

  Andrea A Kühn, Christof Brücke, Julius Hübl, Gerd-Helge Schneider, Andreas Kupsch, Alexandre Eusebio, Keyoumars Ashkan, Peter Holland, Tipu Aziz, Wim Vandenberghe, Bart Nuttin, Peter Brown
  Current Biology 09/2008; 18(15):R648-R650. · 9.65 Impact Factor
• Article: Movement-related synchronization of gamma activity is lateralized in patients with dystonia.

  Christof Brücke, Florian Kempf, A Kupsch, Gerd-Helge Schneider, Joachim K Krauss, Tipu Aziz, Kielan Yarrow, Alek Pogosyan, Peter Brown, Andrea A Kühn
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  ABSTRACT: There is evidence for synchronization at frequencies both under 30 Hz and over 60-80 Hz in the so-called gamma frequency band in patients with Parkinson's disease (PD). Gamma activity increases after dopaminergic therapy and during voluntary movement, suggesting that it might be physiological and relate to motor processing in the basal ganglia (BG). We recorded local field potential (LFP) activity during a choice reaction time task in 11 patients with dystonia undergoing implantation of the internal globus pallidus for therapeutic stimulation. The spectral content of the LFP was averaged with respect to movement onset over 6-11 Hz, 18-25 Hz and 60-80 Hz, separately for responses ipsilateral and contralateral to movement. There was a perimovement increase in 60-80 Hz activity in the LFP, but only contralateral to movement. In contrast, low-frequency LFP activity decreased symmetrically during movement. This occurred earlier in the 18-25 Hz band than in the 6-11 Hz band, and was followed by a postmovement increase in oscillatory activity in the 18-25 Hz band that was contralateral to movement. The presence of a lateralized movement-related increase in gamma activity in the BG of patients with dystonia, similar to that recorded in patients with treated PD, suggests that this may be a residual feature of normal BG function. Moreover, the results provide further support for functional distinctions between BG oscillatory activities of different frequency.
  European Journal of Neuroscience 06/2008; 27(9):2322-9. · 3.63 Impact Factor
• Article: Amplitude modulation of oscillatory activity in the subthalamic nucleus during movement.

  Alexandros G Androulidakis, Christof Brücke, Florian Kempf, Andreas Kupsch, Tipu Aziz, Keyoumars Ashkan, Andrea A Kühn, Peter Brown
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  ABSTRACT: Depth recordings in patients with Parkinson's disease (PD) have demonstrated exaggerated local field potential (LFP) activity at frequencies between 10 and 30 Hz in the subthalamic nucleus (STN). This activity is modulated prior to single phasic movements, possibly as part of the feedforward organization of incipient voluntary movement, and after single phasic movements, as a consequence of afferent feedback processes. Here we test the hypothesis that this activity is also modulated during repetitive movements, reflecting a role in ongoing performance. Accordingly, we recorded LFP activity from the contralateral STN of seven patients with PD withdrawn from anti-parkinsonian medication while they performed repetitive index finger to thumb taps. Cross-correlograms of LFP activity at different frequencies in the 10-30 Hz band with finger position showed that LFP activity was modulated in amplitude by finger tapping. The modulation was higher at the beginning of each recording when tapping performance was better, and diminished as tapping became more bradykinetic over time. The best modulations were seen over those frequencies that were maximal in the power spectrum of the corresponding LFP, and for a given side were most marked at the contact pair that exhibited the highest power at these frequencies. In conclusion, subthalamic activity in the 10-30-Hz band is amplitude modulated during movement. This process fails as bradykinesia increases.
  European Journal of Neuroscience 04/2008; 27(5):1277-84. · 3.63 Impact Factor