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Syam Krishnan

Bio: Syam Krishnan is an academic researcher from Sree Chitra Thirunal Institute for Medical Sciences and Technology. The author has contributed to research in topics: Parkinson's disease & Deep brain stimulation. The author has an hindex of 11, co-authored 35 publications receiving 481 citations.

Papers
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Journal ArticleDOI
TL;DR: Deep Brain Stimulation is currently the standard of care for patients with Parkinson's disease experiencing motor complications and alternatives to the traditional stereotactic frame based techniques of lead implantation are emerging, and these, along with the other recent technological advances, are likely to extend the availability of this therapy to an increasing number of patients in the future.
Abstract: Deep Brain Stimulation (DBS) was introduced into clinical practice nearly four decades ago and is currently the standard of care for patients with Parkinson's disease experiencing motor complications. Apart from this, it has several other established and emerging applications in movement disorders. The exact mechanisms by which DBS provides relief in movement disorders are still unclear; disruption of pathological neuronal synchrony and abnormal information flow through the neuronal circuits involved, are the most likely underlying mechanisms. DBS has been established to be a relatively safe procedure if patients are carefully selected and followed up by experienced multidisciplinary teams. Alternatives to the traditional stereotactic frame based techniques of lead implantation are emerging, and these, along with the other recent technological advances, are likely to extend the availability of this therapy to an increasing number of patients in the future.

101 citations

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TL;DR: The severity and domains of nonmotor symptoms involved in Parkinson's disease and normal aging have not been compared before and they affect health‐related quality of life of patients.
Abstract: Background: Nonmotor symptoms in Parkinson's disease are frequent and affect health-related quality of life of patients. The severity and domains of nonmotor symptoms involved in Parkinson's disease and normal aging have not been compared before. Methods: We performed a prospective case–control study to assess the frequency and severity of nonmotor symptoms in patients with Parkinson's disease (n = 174) and age-matched normal controls (n = 128) using the Non-Motor Symptoms Scale. Results: Nonmotor symptoms in Parkinson's disease were ubiquitous, more frequent, and more severe than in normal aging, particularly in women. Cardiovascular, mood/cognition, and perceptual problems/hallucinations domains were rarely involved in age-matched controls. Age had no effect and sex some influence on nonmotor symptoms in Parkinson's disease. In contrast, in controls, nonmotor symptoms increased with age, and sex had no effect. Conclusions: Nonmotor symptoms in Parkinson's disease differ from those in aging in frequency, severity, sex predilection, and domain involvement. © 2011 Movement Disorder Society

84 citations

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TL;DR: In this article, a single session of real inhibitory cerebellar stimulation but not sham stimulation was shown to restore the sensorimotor plasticity of primary motor cortex (M1) in patients with Parkinson's disease and levodopa-induced dyskinesias.
Abstract: The plasticity of primary motor cortex (M1) in patients with Parkinson's disease (PD) and levodopa-induced dyskinesias (LIDs) is severely impaired. We recently reported in young healthy subjects that inhibitory cerebellar stimulation enhanced the sensorimotor plasticity of M1 that was induced by paired associative stimulation (PAS). This study demonstrates that the deficient sensorimotor M1 plasticity in 16 patients with LIDs could be reinstated by a single session of real inhibitory cerebellar stimulation but not sham stimulation. This was evident only when a sensory component was involved in the induction of plasticity, indicating that cerebellar sensory processing function is involved in the resurgence of M1 plasticity. The benefit of inhibitory cerebellar stimulation on LIDs is known. To explore whether this benefit is linked to the restoration of sensorimotor plasticity of M1, we conducted an additional study looking at changes in LIDs and PAS-induced plasticity after 10 sessions of either bilateral, real inhibitory cerebellar stimulation or sham stimulation. Only real and not sham stimulation had an antidyskinetic effect and it was paralleled by a resurgence in the sensorimotor plasticity of M1. These results suggest that alterations in cerebellar sensory processing function, occurring secondary to abnormal basal ganglia signals reaching it, may be an important element contributing to the maladaptive sensorimotor plasticity of M1 and the emergence of abnormal involuntary movements.

72 citations

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TL;DR: Enhanced D3 receptor affinity due to gain-of-function conferred by the glycine residues could impair reward-risk assessment in the mesolimbic system and contribute to development of impulsive behaviour, in carriers of this genotype.

43 citations

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TL;DR: Benefits of STN stimulation on the cardinal signs, motor complications, and QOL of advanced PD were substantial and sustained till 5 years and the initial benefits in axial motor signs and emotional and psychological aspects of QOL did not show similar stability.
Abstract: Reports of long-term effects of subthalamic (STN) stimulation for Parkinson's disease (PD) are few, mostly open-label evaluations and from Western centers. We used single-blind and open-label motor, cognitive and quality of life (QOL) evaluations to study the effects of bilateral STN stimulation in 45 patients over 5 years. Our patients showed a stable and substantial reduction in the cardinal signs of PD, motor fluctuations, and dyskinesias but less so for axial signs. The reduction in medications and the intensity of electrical stimulation needed also remained stable during follow up. Although the total QOL and its parkinsonism and social components showed sustained benefits till 5 years, the gains in emotional and systemic subsets were short lasting. Global scores for mood and cognition did not show significant worsening. Benefits of STN stimulation on the cardinal signs, motor complications, and QOL of advanced PD were substantial and sustained till 5 years. The initial benefits in axial motor signs and emotional and psychological aspects of QOL did not show similar stability. In general, the procedure had insignificant impact on cognition and mood. This is the first report of STN stimulation in Asian patients with PD.

39 citations


Cited by
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TL;DR: There is a sufficient body of evidence to accept with level A (definite efficacy) the analgesic effect of high-frequency rTMS of the primary motor cortex (M1) contralateral to the pain and the antidepressant effect of HF-rT MS of the left dorsolateral prefrontal cortex (DLPFC).

1,554 citations

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TL;DR: These updated recommendations take into account all rTMS publications, including data prior to 2014, as well as currently reviewed literature until the end of 2018, and are based on the differences reached in therapeutic efficacy of real vs. sham rT MS protocols.

822 citations

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TL;DR: A systematic review and meta‐analysis of the literature was conducted to determine the diagnostic accuracy of the MoCA for differentiating healthy cognitive aging from possible MCI.
Abstract: Objective The Montreal Cognitive Assessment (MoCA; Nasreddine et al., 2005) is a cognitive screening tool that aims to differentiate healthy cognitive aging from Mild Cognitive Impairment (MCI). Several validation studies have been conducted on the MoCA, in a variety of clinical populations. Some studies have indicated that the originally suggested cutoff score of 26/30 leads to an inflated rate of false positives, particularly for those of older age and/or lower education. We conducted a systematic review and meta-analysis of the literature to determine the diagnostic accuracy of the MoCA for differentiating healthy cognitive aging from possible MCI. Methods Of the 304 studies identified, nine met inclusion criteria for the meta-analysis. These studies were assessed across a range of cutoff scores to determine the respective sensitivities, specificities, positive and negative predictive accuracies, likelihood ratios for positive and negative results, classification accuracies, and Youden indices. Results Meta-analysis revealed a cutoff score of 23/30 yielded the best diagnostic accuracy across a range of parameters. Conclusions A MoCA cutoff score of 23, rather than the initially recommended score of 26, lowers the false positive rate and shows overall better diagnostic accuracy. We recommend the use of this cutoff score going forward. Copyright © 2017 John Wiley & Sons, Ltd.

457 citations

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TL;DR: An overview of the impact non-motor symptoms have on persons with PD is provided, along with a brief description of some of the more common non-Motor features of PD.

314 citations

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TL;DR: There is unanimous consensus between the authors that future experimental and computational work is needed to understand the function of cerebellar-basal ganglia circuitry in both motor and non-motor functions.
Abstract: Despite increasing evidence suggesting the cerebellum works in concert with the cortex and basal ganglia, the nature of the reciprocal interactions between these three brain regions remains unclear. This consensus paper gathers diverse recent views on a variety of important roles played by the cerebellum within the cerebello-basal ganglia-thalamo-cortical system across a range of motor and cognitive functions. The paper includes theoretical and empirical contributions, which cover the following topics: recent evidence supporting the dynamical interplay between cerebellum, basal ganglia, and cortical areas in humans and other animals; theoretical neuroscience perspectives and empirical evidence on the reciprocal influences between cerebellum, basal ganglia, and cortex in learning and control processes; and data suggesting possible roles of the cerebellum in basal ganglia movement disorders. Although starting from different backgrounds and dealing with different topics, all the contributors agree that viewing the cerebellum, basal ganglia, and cortex as an integrated system enables us to understand the function of these areas in radically different ways. In addition, there is unanimous consensus between the authors that future experimental and computational work is needed to understand the function of cerebellar-basal ganglia circuitry in both motor and non-motor functions. The paper reports the most advanced perspectives on the role of the cerebellum within the cerebello-basal ganglia-thalamo-cortical system and illustrates other elements of consensus as well as disagreements and open questions in the field.

302 citations