Transcranial Magnetic Stimulation From Wikipedia, the free encyclopedia.
rTMS In a Rodent.
_is_a_technique_for_noninvasive_stimulation_of_the_adult_brain.jpg){kind=spacer}
Background
The principle of inductive brain stimulation with eddy currents has been noted since the 20th century. The first successful TMS study was performed in 1985 by Anthony Barker and his colleagues in Sheffield, England. Its earliest application demonstrated conduction of nerve impulses from the motor cortex to the spinal cord, stimulating muscle contractions. The use of magnets rather than a direct electric current to the brain reduced the discomfort of the procedure and research and allowed mapping of the cerebral cortex and its connections.Effects on the Brain
The exact details of how TMS functions are still being explored. The effects of TMS can be divided into two types depending on the mode of stimulation:- Single or paired pulse TMS causes neurons in the neocortex under the site of stimulation to depolarize and discharge an action potential. If used in the primary motor cortex, it produces muscle activity referred to as a motor evoked potential (MEP) which can be recorded on electromyography. If used on the occipital cortex, 'phosphenes' (flashes of light) might be perceived by the subject. In most other areas of the cortex, the participant does not consciously experience any effect, but his or her behaviour may be slightly altered (e.g. slower reaction time on a cognitive task), or changes in brain activity may be detected using sensing equipment.
- Repetitive TMS produces longer-lasting effects which persist past the initial period of stimulation. rTMS can increase or decrease the excitability of the corticospinal tract depending on the intensity of stimulation, coil orientation and frequency. The mechanism of these effects is not clear although it is widely believed to reflect changes in synaptic efficacy akin to long-term potentiation (LTP) and long-term depression (LTD).
Risks
Although TMS is often regarded as safe, the greatest acute risk of TMS is the rare occurrence of induced seizures and syncope. More than 16 cases of TMS-related seizure have been reported in the literature, with at least seven reported before the publication of safety guidelines in 1998, and more than nine reported afterwards. The seizures have been associated with single-pulse and rTMS. Reports have stated that in at least some cases, predisposing factors (medication, brain lesions or genetic susceptibility) may have contributed to the seizure. A review of nine seizures associated with rTMS that had been reported after 1998 stated that four seizures were within the safety parameters, four were outside of those parameters, and one had occurred in a healthy volunteer with no predisposing factors. A 2009 international consensus statement on TMS that contained this review concluded that based on the number of studies, subjects and patients involved with TMS research, the risk of seizure with rTMS is considered very low.Besides seizures, other risks include fainting, minor pains such as headache or local discomfort, minor cognitive changes and psychiatric symptoms (particularly a low risk of mania in depressed patients). Though other side effects are thought to be possibly associated with TMS (alterations to the endocrine system, altered neurotransmitter and immune system activity) they are considered investigational and lacking substantive proof.
Other adverse effects of TMS are:
- Discomfort or pain from the stimulation of the scalp and associated nerves and muscles on the overlying skin; this is more common with rTMS than single pulse TMS,
- Rapid deformation of the TMS coil produces a loud clicking sound which increases with the stimulator intensity that can affect hearing with sufficient exposure, particularly relevant for rTMS (hearing protection may be used to prevent this),
- rTMS in the presence of incompatible EEG electrodes can result in electrode heating and, in severe cases, skin burns. Non-metallic electrodes are used if concurrent EEG data is required.
Clinical Uses
The uses of TMS and rTMS can be divided into diagnostic and therapeutic uses.Diagnostic Use
TMS can be used clinically to measure activity and function of specific brain circuits in humans. The most robust and widely-accepted use is in measuring the connection between the primary motor cortex and a muscle to evaluate damage from stroke, multiple sclerosis, amyotrophic lateral sclerosis, movement disorders, motor neuron disease and injuries and other disorders affecting the facial and other cranial nerves and the spinal cord. TMS has been suggested as a means of assessing short-interval intracortical inhibition (SICI) which measures the internal pathways of the motor cortex but this use has not yet been validated.Therapeutic Use
A TMS Therapy Device
Studies of the use of TMS and rTMS to treat many neurological and psychiatric conditions have generally shown only modest effects with little confirmation of results. However, publications reporting the results of reviews and statistical meta-analyses of earlier investigations have stated that rTMS appeared to be effective in the treatment of certain types of major depression under certain specific conditions. rTMS devices are marketed for the treatment of such disorders in Canada, Australia, New Zealand, the European Union, Israel and the United States.
A meta-analysis of 34 studies comparing rTMS to sham treatment for the acute treatment of depression showed an effect size of 0.55 (p<.001). This is comparable to commonly reported effect sizes of pharmacotherapeutic strategies for treatment of depression in the range of 0.17-0.46. However, that same meta-analysis found that rTMS was significantly worse than electroconvulsive therapy (ECT) (effect size = -0.47), although side effects were significantly better with rTMS. An analysis of one of the studies included in the meta-analysis showed that one extra remission from depression occurs for every 3 patients given electroconvulsive therapy rather than rTMS (number needed to treat 2.36). There is evidence that rTMS can temporarily reduce chronic pain and change pain-related brain and nerve activity, and TMS has been used to predict the success of surgically implanted electrical brain stimulation for the treatment of pain.
Other areas of research include the rehabilitation of aphasia and motor disability after stroke, tinnitus, Parkinson's disease, tic disorders and the negative symptoms of schizophrenia. TMS has failed to show effectiveness for the treatment of brain death, coma, and other persistent vegetative states.
It is difficult to establish a convincing form of "sham" TMS to test for placebo effects during controlled trials in conscious individuals, due to the neck pain, headache and twitching in the scalp or upper face associated with the intervention. "Sham" TMS manipulations can affect cerebral glucose metabolism and MEPs, which may confound results. This problem is exacerbated when using subjective measures of improvement. Placebo responses in trials of rTMS in major depression are negatively associated with refractoriness to treatment, vary among studies and can influence results. Depending on the research question asked and the experimental design, matching the discomfort of rTMS to distinguish true effects from placebo can be an important and challenging issue.
One multicenter trial of rTMS in depression used an active "sham" placebo treatment that appeared to mimic the sound and scalp stimulation associated with active TMS treatment. The investigators reported that the patients and clinical raters were unable to guess the treatment better than chance, suggesting that the sham placebo adequately blinded these people to treatment. The investigators concluded: "Although the treatment effect was statistically significant on a clinically meaningful variable (remission), the overall number of remitters and responders was less than one would like with a treatment that requires daily intervention for 3 weeks or more, even with a benign adverse effect profile". However, a review of the trial's report has questioned the adequacy of the placebo, noting that treaters were able to guess whether patients were receiving treatment with active or sham TMS, better than chance. In this regard, the trial's report stated that the confidence ratings for the treaters' guesses were low.
Technical Information
TMS - Butterfly Coils
TMS uses electromagnetic induction to generate an electric current across the scalp and skull without physical contact. A plastic-enclosed coil of wire is held next to the skull and when activated, produces a magnetic field oriented orthogonally to the plane of the coil. The magnetic field passes unimpeded through the skin and skull, inducing an oppositely directed current in the brain that activates nearby nerve cells in much the same way as currents applied directly to the cortical surface.[43] The path of this current is difficult to model because the brain is irregularly shaped and electricity and magnetism are not conducted uniformly throughout its tissues. The magnetic field is about the same strength as an MRI, and the pulse generally reaches no more than 5 centimeters into the brain.
Coil Types
The design of transcranial magnetic stimulation coils used in either treatment or diagnostic/experimental studies may differ in a variety of ways. These differences should be considered in the interpretation of any study result, and the type of coil used should be specified in the study methods for any published reports. The most important considerations include:- the type of material used to construct the core of the coil
- the geometry of the coil configuration
- the biophysical characteristics of the pulse produced by the coil.
With regard to coil composition, the core material may be either a magnetically inert substrate (i.e., the so-called ‘air-core’ coil design), or possess a solid, ferromagnetically active material (i.e., the so-called ‘solid-core’ design). Solid core coil design result in a more efficient transfer of electrical energy into a magnetic field, with a substantially reduced amount of energy dissipated as heat, and so can be operated under more aggressive duty cycles often mandated in therapeutic protocols, without treatment interruption due to heat accumulation, or the use of an accessory method of cooling the coil during operation. Varying the geometric shape of the coil itself may also result in variations in the focality, shape, and depth of cortical penetration of the magnetic field. Differences in the coil substance as well as the electronic operation of the power supply to the coil may also result in variations in the biophysical characteristics of the resulting magnetic pulse (e.g., width or duration of the magnetic field pulse). All of these features should be considered when comparing results obtained from different studies, with respect to both safety and efficacy.
A number of different types of coils exist, each of which produce different magnetic field patterns. Some examples:
- round coil: the original type of TMS coil
- figure-eight coil (i.e. butterfly coil): results in a more focal pattern of activation
- double-cone coil: conforms to shape of head, useful for deeper stimulation
- four-leaf coil: for focal stimulation of peripheral nerves
See the full article
Transcranial Magnetic Stimulation From Wikipedia, the free encyclopedia.
Bang-Speech Arrest
Uploaded on Feb 6, 2010Liz Bonin goes to University College London to meet Dr. Joseph Devlin and conduct an experiment using transcranial magnetic stimulation (TMS) to illustrate the importance of Broca's area in controlling speech.
Standard YouTube License @ neuroboffin
Berkeley Studies Brain Stimulation to Help With Stroke Therapy
Uploaded on Nov 19, 2010Through a technique called Transcranial Magnetic Stimulation (TMS), University of California neuroscientist, Flavio Oliveira is researching how decisions are made by studying which hand a person chooses for an action. Oliveira's findings are helping scientists better understand how the brain works which could one day lead to better treatments for stroke patients.
Standard YouTube License @ SmartPlanetCBS's channel
Why Stutterers Don't Stutter when They Sing?
Uploaded on May 24, 2008Why stutterers don't stutter when they sing? This surprising experiment of stuttering triggered by transcranial magnetic stimulation (TMS) answers this question.
Standard YouTube License @ IBF
rTMS for Stroke
Published on Aug 15, 2012Standard YouTube License @ drashoksinghal100's channel
Magnetic Therapy Helps Stroke Patients Regain Speech
Uploaded on Nov 25, 2011Scientists at the University of Queensland in Australia, have demonstrated that magnetic stimulation of the brain can help stroke patients regain their speech. The therapy is called Transcranial Magnetic Stimulation (TMS) and its impact on stroke survivors has been dramatic.
Standard YouTube License @ Latest news
Helping Kids Recover from Paediatric Strokes
Uploaded on Sep 14, 2010Using Transcranial Magnetic Stimulation (TMS), a brain mapping technique that's been around for 25 years, Dr. Adam Kirton of the University of Calgary's Faculty of Medicine is taking an old technology in a new direction to treat children who've suffered a stroke at or near birth. His research is being conducted at the Alberta Children's Hospital's Paediatric TMS laboratory, the only one of it's kind in Canada.
Read the full story in our magazine: http://medicine.ucalgary.ca/magazine/.
Standard YouTube License @ UCalgaryMedicine's channel
TED x Adelaide - Michelle McDonnell - Transcranial Magnetic Stimulation
Uploaded on Nov 21, 2011Can magnets be used to treat epilepsy?
For over 25 years, magnets have been used to stimulate the brain to investigate how nerve cells are connected in the brain. In many instances people with diseases affecting the brain such as stroke, epilepsy, dystonia and depression have been studied, to work out which pathways are affected. Michelle McDonnell explored how we might treat these conditions using transcranial magnetic stimulation (TMS) and if TMS treatments really work.
Standard YouTube License @ TEDxTalks
How Does TMS Therapy Work?
Uploaded on Apr 12, 2011A brief, animated video which explains the basic mechanism of action of Transcranial Magnetic Stimulation (TMS) Therapy when used in the treatment of depression. Copyright 2011 The TMS Center of New England. Permission must be granted to reproduce this video.
Standard YouTube License @ TMSNewEngland
Illustrating Cortical Localisation of Function Using TMS
Uploaded on Oct 23, 2009Michael Mosley participates in some experiments showing how magnetic brain stimulation can be used to selectively affect motor control of his right hand.
Standard YouTube License @ neuroboffin
Christmas Lectures 2011: TMS Verbal and Motor
Published on Jan 3, 2013Professor Vincent Walsh of University College London demonstates the lost of verbal and motor control through using a TMS (Transcranial magnetic stimulation). The TMS induces weak electric currents to the brain.
Standard YouTube License @ The Ri Channel
Neural Navigator Demonstration
Uploaded on Jun 12, 2011Demonstration of neuronavigation with the NeNa software (TM), and transcranial magnetic stimulation (TMS) of the motor cortex.
Details: before this demonstration, this volunteer was first scanned with fMRI while moving his right thumb, and an anatomical scan was acquired. This data was loaded into the navigation software. On the screen you see his skin, brain surface (blue) as derived from the anatomical scan, and fMRI BOLD activation (red) during thumb movements. The thumb activation was targeted. For more information on this system see http://www.neuralnavigator.com.
Standard YouTube License @ tgutteling
