Posts Tagged mechanism

[WEB SITE] Transcranial Direct Current Stimulation – Video

People have investigated brain stimulation since very early times, in ancient Rome torpedo fish were applied to the heads of some patients to relieve headaches, for instance, by their electrical currents. In 1802, Aldini of Italy applied electrical current to the exposed cortex of the human brain and attempted also to treat melancholia with a voltaic pile.

Human brain connected to cables and computer chips. Image Credit: Mopic / Shutterstock

Human brain connected to cables and computer chips. Image Credit: Mopic / ShutterstockEnter a caption

The voltaic pile led to accelerated interest in electrical brain stimulation to treat various disorders, including mental illness. The results were not always encouraging, of course, and it wasn’t until much later, in the middle of the 20th century, that direct current stimulation was used to alter the excitable patterns of the brain. This led to increased interest in using direct current to treat mania or depression. There was a brief upsurge in the use of electroconvulsive therapy to treat schizophrenia and other mental illnesses, but it came to an end in the last decade of the 20th century. Electrical stimulation of the brain became stigmatized and drug therapy took center stage as far as psychiatric treatment was concerned.

Recently, interest has arisen in electrical stimulation of the brain because of the finding that weak transcranial direct current stimulation (tDCS) of the brain produced changes in polarization and excitable thresholds of the neurons, which lasted long beyond the period of stimulation. This has led many to investigate the nature of the changes and the potential applications of this technique to major depressive disorder, schizophrenia, obsessive-compulsive disorder and other disorders of the mind with a basis in brain functioning.

Transcranial Direct Current Stimulation Method

The technique of tDCS depends upon non-invasive stimulation of the brain through the skull, by a small constant current applied through scalp electrodes to the head. This leads to currents flowing through the superficial cortex. The strength of the current is so low that it does not directly cause an action potential in the brain neurons, and so instead regulates the excitability of the brain by making them more or less refractory to other endogenous stimulation according to the polarity of the electrodes. Anodal current is generally stimulatory by inducing increased excitability, but cathodal current reduces it. The effect of a single stimulus lasts for 30-120 minutes.

The way in which the current acts depends upon the polarity and the orientation of the cells. Anodal tDCS produces an inflow of current directed inwardly, which hyperpolarizes the apical dendrites of neurons in the pyramidal cortex, but depolarizes those of the somatic areas. Cathodal tDCS on the other hand leads to the reverse effect. The third factor determining the effect of the current is its dose. The strength of the electrical stimulation may lie between 0.5 and 2 mA, its duration is between 5-40 minutes, and the electrode size ranges from 3-100 cm. By altering these variables, it is possible to regulate the current density and total charge, but it may still be difficult to exactly quantify the total current delivered to the brain because of other factors outside the experimental field, such as scalp and cranial impedance.

The electrodes are placed in accordance with the international Electroencephalogram

System, so that one is on the scalp (the active electrode) and the other on the scalp (bipolar or bicephalic placement) or another part of the body, most commonly the upper arm or the shoulder (termed unipolar or monocephalic placement). The current traces a path from the anode, scalp, cranium, cortex, subcortical region, and cathode, stimulating not only the cortex but deeper structures, both in the deep brain and in the midbrain and spinal cord if unipolar placement is adopted. Secondly, the area stimulated is not confined to that near the electrodes because the current flows into adjoining regions in between and around the electrodes.

Mechanism of tDCS

Electrical stimulation with tDCS seems to produce a two-way modification of post-synaptic neuronal connections which results in the same effects as long-term potentiation or long-term depression of cortical excitability does. This is mediated through NMDA receptors. Glutamate antagonists prevent these long-term effects, while NMDAR agonists increase theiramplitude. Work is still going on as to whether repetitive tDCS could cause a more prolonged alteration of behavior. The stimulation has been found to change motor and emotional functioning, as well as sensory, attention-related, and cognitive responses. It is therefore likely to be useful in several psychiatric disorders. It has been found that glutamate antagonists abolish tDCS after-effects, while NMDA-agonists enhance them.

The Advantages and Disadvantages of tDCS

The technique of tDCS is easy to use, in fact, capable of application at home. It is noninvasive and inexpensive. No serious adverse effects have been noted so far. On the other hand, this very ease of use lends itself to a high potential for misuse, such as recreational use, unsupervised medical use, and unethical use as, for instance, to improve one’s attention span while studying. Its long-term effects are also not well established. Thus while the potential has long been recognized, the implementation of this technique is still not widespread pending proper regulation of its use worldwide.

Further Reading

via Transcranial Direct Current Stimulation

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[ARTICLE] Post-stroke Spasticity: A Review of Epidemiology, Pathophysiology, and Treatments – Full Text

Summary

Spasticity is a common condition in stroke survivors, and may be associated with pain and joint contracture, leading to poor quality of life and increased caregiver burden. Although the underlying mechanisms are not well-understood, it may be due to disruption of the balance of supra-spinal inhibitory and excitatory sensory inputs directed to the spinal cord, leading to a state of disinhibition of the stretch reflex. The treatment options include physical therapy, modality and pharmacological treatments, neurolysis with phenol and botulinum toxin, and surgical treatment. A successful treatment of spasticity depends on a clear comprehension of the underlying pathophysiology, natural history, and impact on patient’s performances. This review focuses on the epidemiology, presumed mechanism, clinical manifestation, and recent evidences of management.

Keywords

  • stroke,
  • muscle spasticity,
  • mechanism,
  • symptom management

1. Introduction

Stroke is one of the leading causes of mortality and morbidity in adults in most countries.12 ;  3 Spasticity is a common, but not an inevitable condition, in patients with stroke. Spasticity following stroke is often associated with pain, soft tissue stiffness, and joint contracture, and may lead to abnormal limb posture, decreased quality of life, increased treatment cost, and increased caregiver burden.4 Early detection and management of post-stroke spasticity may not only reduce these complications, but may also improve function and increase independency in patients with spasticity.

Spasticity was first described by Lance5 in 1980 as a motor disorder characterized by a velocity-dependent increase in tonic stretch reflexes (muscle tone), with exaggerated tendon jerks, resulting from hyper-excitability of the neurons involved in stretch reflex, as a component of the upper motor neuron syndrome. This definition is useful in clinical practice, because the guideline “velocity-dependent increase in tonic stretch reflexes,” can distinguish spasticity from other similar movement disorders such as hypertonia, rigidity, and hyperreflexia. However, this definition ignores the important aspect of sensory input in the experience of spasticity. Some studies have found that abnormal processing of sensory inputs from muscle spindles leads to excessive reflex activation of alpha-motoneurons, and increases spasticity. The new definition from the Support Program for Assembly of a Database for Spasticity Measurement (SPASM) project defines spasticity as “disordered sensory-motor control, resulting from an upper motor neuron lesion, presenting as intermittent or sustained involuntary activation of muscles”.6This definition takes into account the contribution of viscoelastic properties of soft tissue to joint stiffness, and the roles of proprioceptive and cutaneous sensory pathways.[…]

Continue —>  Post-stroke Spasticity: A Review of Epidemiology, Pathophysiology, and Treatments

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[Abstract + References] A New Approach to Design Glove-Like Wearable Hand Exoskeletons for Rehabilitation – Conference paper

Abstract

The synthesis of hand exoskeletons for rehabilitation is a challenging theoretical and technical task. A huge number of solutions have been proposed in the literature. Most of them are based on the concept to consider the phalanges of the finger as fixed to some links of the exoskeleton mechanism. This approach makes the exoskeleton synthesis a difficult problem that compels the designer to devise approximate technical solutions which, frequently, reduce the efficiency of the rehabilitation system and are rather bulky.

This paper proposes a different approach. Namely, the phalanges are not fixed to some links of the exoskeleton, but they can have a relative motion, with one or two degrees of freedom when planar systems are considered. An example is presented to show the potentiality of this approach, which makes it possible: (i) to design glove-like exoskeletons that only approximate the human finger motion; (ii) to leave the fingers have their natural motion; (iii) to adapt a wider range of patient hand sizes to a given hand exoskeleton.

References

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    Agarwal, P., Hechanova, A., Deshpande, A.D.: Kinematics and Dynamics of a biologically inspired index finger exoskeleton. In: Proceedings of the ASME 2013 Dynamic Systems and Control Conference DSCC 2013, Palo Alto, CA, USA, pp. 1–10 (2013)Google Scholar
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    Heo, P., Min, GuG, Lee, S.J., Rhee, K., Kim, J.: Current hand exoskeleton technologies for rehabilitation and assistive engineering. Int. J. Precis. Eng. Manuf. 3(5), 807–824 (2012)CrossRefGoogle Scholar
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    Balasubramanian, S., Klein, J., Burdet, E.: Robot-assisted rehabilitation and hand function. Curr. Opin. Neurol. 23, 661–670 (2010)CrossRefGoogle Scholar
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    Troncossi, M., Mozaffari-Foumashi, M., Parenti-Castelli, V.: An original classification of rehabilitation hand exoskeletons. J. Robot. Mech. Eng. Res. 1(4), 17–29 (2016)CrossRefGoogle Scholar
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    Abdallah, I.B., Bouteraa, Y., Rekik, C.: Design and development of 3D printed myoelectric robotic exoskeleton for hand rehabilitation. Int. J. Smart Sens. Intell. Syst. 10(2), 341–366 (2017)Google Scholar
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    Foumashi, M., Troncossi, M., Parenti-Castelli, V.: Design of a new hand exo-skeleton for rehabilitation of post-stroke patients. In: Romansy 19-Robot Design, Dynamics and Control, pp. 159–169 (2013)CrossRefGoogle Scholar
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    Yap, H.K., Hoon, J., Nashrallah, F., Goh, J.C.H., Yeow, R.C.H.: A soft exoskeleton for hand assistive and rehabilitation application using pneumatic actuators with variable stiffness. In: 2015 IEEE International Conference on Robotics and Automation, ICRA, Seattle, Washington, USA, pp. 4967–4972 (2015)Google Scholar
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    Arata, J., Ohmoto, K., Gassert, R., Lambercy, O., Fujimoto, H., Wada, I.: A new hand exoskeleton device for rehabilitation using a three-layered sliding spring mechanism. In: 2013 IEEE International Conference on Robotics and Automation, ICRA, Karlsruhe, Germany, pp. 3902–3907 (2013)Google Scholar
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    Leonardis, D., Barsotti, M., Loconsole, C., Solazzi, M., Troncossi, M., Mazzotti, M., Parenti, C.V., Procopio, C., Lamola, G., Chisari, C., Bergamasco, M., Frisoli, A.: An EMG-controlled robotic hand exoskeleton for bilateral rehabilitation. J. Haptics 8(2), 140–151 (2015)CrossRefGoogle Scholar
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    Gulke, J., Watcher, N.J., Geyer, T., Scholl, H., Apic, G., Mentzler, M., et al.: Motion coordination pattern during cylinder grip analyzed with a sensor glove. J. Hand Surg. 35(5), 797 (2010)CrossRefGoogle Scholar
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    Li, J., Wang, S., Zheng, R., Zhang, Y., Chen, Z.: Development of a hand exoskeleton system for index finger rehabilitation. Chin. J. Mech. Eng. 25(2), 223–233 (2012)CrossRefGoogle Scholar

via A New Approach to Design Glove-Like Wearable Hand Exoskeletons for Rehabilitation | SpringerLink

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[ARTICLE] Virtual reality training improves balance function

Virtual reality is a new technology that simulates a three-dimensional virtual world on a computer and enables the generation of visual, audio, and haptic feedback for the full immersion of users. Users can interact with and observe objects in three-dimensional visual space without limitation. At present, virtual reality training has been widely used in rehabilitation therapy for balance dysfunction. This paper summarizes related articles and other articles suggesting that virtual reality training can improve balance dysfunction in patients after neurological diseases. When patients perform virtual reality training, the prefrontal, parietal cortical areas and other motor cortical networks are activated. These activations may be involved in the reconstruction of neurons in the cerebral cortex. Growing evidence from clinical studies reveals that virtual reality training improves the neurological function of patients with spinal cord injury, cerebral palsy and other neurological impairments. These findings suggest that virtual reality training can activate the cerebral cortex and improve the spatial orientation capacity of patients, thus facilitating the cortex to control balance and increase motion function.

via Virtual reality training improves balance function Mao Y, Chen P, Li L, Huang D – Neural Regen Res.

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