Search

Your search keyword '"Rawji, Vishal"' showing total 32 results
Start Over Author "Rawji, Vishal"
32 results on '"Rawji, Vishal"'

1. Impulsivity in Parkinson's disease and Tourette syndrome, and human motor decision making

Author

Rawji, Vishal

Subjects
612.8
Abstract

Motor response inhibition pertains to the ability to inhibit motor actions. It is hypothesised that a breakdown in motor response inhibition might underlie impulsivity in Parkinson's disease and tics in Tourette syndrome. This thesis outlines how motor response inhibition is modulated in these clinical disorders by first characterising them in healthy subjects. We use TMS to show that one set of inputs to the motor cortex are inhibited during motor preparation whilst the other inputs reflect uncertainty about potential stopping. In the next chapter, we challenged an assumption that movement preparation during proactive inhibition always preceded movement execution and found that movement preparation and execution are two independent processes. With this in mind, we investigated features of motor response inhibition and movement preparation and execution in patients with Tourette syndrome, finding that these were remarkably similar to healthy controls, suggesting that volitional features of movement and inhibition are normal in Tourette syndrome. However, we did find a specific impairment of automatic inhibition in Tourette syndrome, which correlated with motor tic severity. As dopamine agonists are implicated as triggers for impulsivity in Parkinson's disease, we first investigated the influence of ropinirole on motor response inhibition in healthy control subjects, finding that motor response inhibition was globally impaired. This was accompanied by analyses suggesting that ropinirole impaired the ability to adjust the decision threshold when stopping might be required. However, investigation of motor inhibition in Parkinson's disease patients on dopamine agonists showed unremarkable effects compared to patients without dopamine agonist use. Our data provide a novel insight into the basic mechanisms of voluntary movement and propose a new theory for tic generation in Tourette syndrome.

Published
2019

8. Comparison between conventional electrodes and ultrasound monitoring to measure TMS evoked muscle contraction

Author

Kaczmarczyk, Isabella, Rawji, Vishal, Rothwell, John C., Hodson-Tole, Emma, and Sharma, Nikhil

Subjects
medicine.diagnostic_test, business.industry, medicine.medical_treatment, Ultrasound, Stimulation, Electromyography, Biceps, Peripheral, Transcranial magnetic stimulation, medicine.anatomical_structure, Tongue, medicine, medicine.symptom, business, Muscle contraction, Biomedical engineering
Abstract

BackgroundTranscranial Magnetic stimulation (TMS) is a non-invasive cortical stimulation method that has been widely employed to explore cortical physiology in health and a range of diseases. At the core of many TMS protocols is the measurement of evoked muscle contractions using surface electromyography (sEMG). While sEMG is appropriate for many superficial muscles such as abductor pollicis brevis (ABP) and first dorsal interosseous (FDI), there are situations where the study of less accessible muscles may be of interest. Peripheral ultrasound is a non-invasive method that could provide a solution. We explore the relationship between TMS evoked sMEP and TMS evoked muscle contractions measured with muscle ultrasound. We hypothesise that in a healthy population, we expect a positive correlation between EMG and ultrasound measures.MethodsIn 10 participants we performed a standard TMS recruitment curve and simultaneously measured MEP and peripheral muscle ultrasound (pUS). We targeted the following muscles: biceps (BI), first dorsal interosseous (FDI), tibialis anterior (TA) and the tongue (TO).ResultsWe report a very close relationship between the MEP and pUS contraction. Resting motor threshold (RMT) measurements and recruitment curves are consistent in sEMG and pUS. A key aspect of this work is the ability to examine clinically relevant muscles that are difficult to probe using surface EMG electrodes, such as the tongue.ConclusionWe find that TMS muscle contractions can be measured with muscle ultrasound in superficial and deep muscles, enable additional, previously hard to study muscles, to be investigated. This could be valuable for allowing TMS to be used to explore a new range of muscles in disorders such as ALS. In muscles less accessible by sEMG, such as the tongue, it may be possible to use pUS as an alternative output. This may be useful in conditions such as ALS and stroke that can differentially affect the tongue.

Published
2020
Full Text
View/download PDF

20. Modulation of iTBS after-effects via concurrent directional TDCS: A proof of principle study

Author

Tremblay, Sara, Hannah, Ricci, Rawji, Vishal, and Rothwell, John C.

Subjects
Adult, Male, M1, primary motor cortex, TDCS, transcranial direct current stimulation, Primary motor cortex, PA, posterior-anterior, Motor Cortex, Evoked Potentials, Motor, Proof of Concept Study, Article, lcsh:RC321-571, MEP, motor evoked potential, AP, anterior-posterior, Humans, iTBS, intermittent theta burst stimulation, Female, Transcranial direct current stimulation, Theta Rhythm, Intermittent theta burst stimulation, lcsh:Neurosciences. Biological psychiatry. Neuropsychiatry, Transcranial magnetic stimulation
Abstract

Background Polarising currents can modulate membrane potentials in animals, affecting the after-effect of theta burst stimulation (TBS) on synaptic strength. Objective We examined whether a similar phenomenon could also be observed in human motor cortex (M1) using transcranial direct current stimulation (TDCS) during monophasic intermittent TBS (iTBS). Methods TDCS was applied during posterior-anterior iTBS using three different conditions: posterior-anterior TDCS (anode 3.5 cm posterior to M1, cathode 3.5 cm anterior to M1), anterior-posterior TDCS (cathode 3.5 cm posterior to M1, anode 3.5 cm anterior to M1), and sham TDCS. Results When the direction of TDCS (posterior-anterior) matched the direction of the electrical field induced by iTBS, we found a 19% non-significant increase in excitability changes in comparison with iTBS combined with sham TDCS. When the TDCS was reversed (anterior-posterior), the excitatory effect of iTBS was abolished. Conclusion Our findings suggest that excitatory after-effects of iTBS can be modulated by directionally-specific TDCS., Highlights • M1 excitability can be modulated by concurrent TDCS and iTBS. • Posterior-anterior TDCS during iTBS induces a qualitative increase in M1 iTBS after-effects. • Anterior-posterior TDCS during iTBS abolishes the after-effects of iTBS over M1.

Published
2017

31. To MB/PhD or not to MB/PhD.

Author

Wan, Jonathan C. M., Teo, Ada E. D., Mcmurran, Christopher E., and Rawji, Vishal

Subjects
MEDICAL students, TRAINING of medical students, DOCTOR of philosophy degree, ANIMAL models in research, NEUROSCIENCES
Abstract

The article offers information on the MB/PhD programmes for medical students of Great Britain, which offer combined clinical and scientific training that last for 9 years. Topics discussed include research of students on research neurosciences and cardiovascular medicines and mentions work on genomic data sets and animal models.

Published
2018
Full Text
View/download PDF

32. Ropinirole, a dopamine agonist with high D 3 affinity, reduces proactive inhibition: A double-blind, placebo-controlled study in healthy adults.

Author

Rawji V, Rocchi L, Foltynie T, Rothwell JC, and Jahanshahi M

Subjects
Administration, Oral, Adult, Dopamine Agonists metabolism, Double-Blind Method, Female, Humans, Indoles metabolism, Male, Reaction Time physiology, Receptors, Dopamine D3 metabolism, Young Adult, Dopamine Agonists administration & dosage, Indoles administration & dosage, Inhibition, Psychological, Reaction Time drug effects, Receptors, Dopamine D3 agonists
Abstract

Response inhibition describes the cognitive processes mediating the suppression of unwanted actions. A network involving the basal ganglia mediates two forms of response inhibition: reactive and proactive inhibition. Reactive inhibition serves to abruptly stop motor activity, whereas proactive inhibition is goal-orientated and results in slowing of motor activity in anticipation of stopping. Due to its impairment in several psychiatric disorders, the neurochemistry of response inhibition has become of recent interest. Dopamine has been posed as a candidate mediator of response inhibition due to its role in functioning of the basal ganglia and the observation that patients with Parkinson's disease on dopamine agonists develop impulse control disorders. Although the effects of dopamine on reactive inhibition have been studied, substantial literature on the role of dopamine on proactive inhibition is lacking. To fill this gap, we devised a double-blind, placebo-controlled study of 1 mg ropinirole (a dopamine agonist) on response inhibition in healthy volunteers. We found that whilst reactive inhibition was unchanged, proactive inhibition was impaired when participants were on ropinirole relative to when on placebo. To investigate how ropinirole mediated this effect on proactive inhibition, we used hierarchical drift-diffusion modelling. We found that ropinirole impaired the ability to raise the decision threshold when proactive inhibition was called upon. Our results provide novel evidence that an acute dose of ropinirole selectively reduces proactive inhibition in healthy participants. These results may help explain how ropinirole induces impulse control disorders in susceptible patients with Parkinson's disease., (Copyright © 2020 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Published
2020
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results