Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Transcranial Magnetic Stimulation (TMS) & clinical applications in neuropsychiatry Heider SH. Qassam MSC. PH. & TH. Electricity ,Magnetism and Biologic Effects • Electromagnetism was first discovered by Michael Faraday, who determined that a magnetic field could be generated by running an electric current through a wire coil. Conversely, a changing magnetic field can generate an electric voltage; the magnetic field must change to have any electrical effect. The biological effects of pulsating electromagnetic fields are due to electrical rather than magnetic forces. Magnetism generates a voltage in tissue according to the equation: V = n x a x dB/dt V = Voltage n = number of turns in the electromagnetic coil a = area of the loop dB/dt = The rate of change of magnetic field with time. What is TMS? • Relatively new technique that induces current in the brain by using a magnetic field outside the skull Can induce muscle twitch or phosphenes, or disrupt activity. • Not an imaging technique, but allows inferences about necessity of activity for a given task • An experimental treatment for some psychiatric/psychological and neurological disorders. Basic mechanics • Magnetic field used to transport electrical signal through the skull (high resistance, no impedance) • Short pulse of current in electromagnet creates large magnetic flux, and in turn induces current. http://www.thecamreport.com/?cat=99 Basic mechanics http://www.mcaturk.com/, reproduced from Magstim Company Bryan Christie, http://www.spectrum.ieee.org/print/3050 • Coils are generally figure-8 shaped to increase spatial resolution • Completely noninvasive, used in human & animal subjects • Possible to give single pulses (repetitive TMS or rTMS) up to 60 Hz and 10 s long. Mechanism of action in the brain • TMS causes synchronous activity of some subpopulation of neurons, sensitive to the orientation of the coils. • A 50-250 ms silencing effect follows due to sustained GABAergic effect Very similar to the start of an epileptic seizure. • Two important effects: direct activation of motor/visual areas; disruption of ongoing activity. TMS as a therapeutic technique UT Southwestern Medical Center, Reprod. www.sciencedaily.com • Single TMS over motor cortex can produce simple movements. • Interference with information processing and behavior is especially likely when TMS pulses are delivered rapidly and repetitively. Repeated rhythmic TMS is called repetitive TMS (rTMS). If the stimulation occurs faster than once per second (1 Hz) it is referred to as fast rTMS. • Most research on TMS has used magnetic field intensities near the motor threshold and, therefore, sufficient to cause neuronal depolarization. •Potential clinical applications Mood Disorders • The area of greatest public attention has been the use of TMS as an antidepressant. Several studies suggested that lowfrequency TMS over the vertex might have antidepressant effects. Based on findings of abnormal prefrontal function in depression and the evidence that modulation of prefrontal function is linked to the efficacy of ECT. Mood Disorders • prefrontal TMS can exert short-term antidepressant or antimanic effects. At the clinical level, TMS may ultimately offer an alternative to ECT for severe or treatmentresistant depression, particularly since the adverse effect profile of TMS is relatively benign. Repetitive TMS does not involve anesthesia administration or seizure induction and has no obvious cognitive sequelae . Another potential use of TMS may be as an augmentation agent to hasten clinical response in pharmacologically treated patients Anxiety Disorders • In a randomized trial of left and right prefrontal stimulation in patients with obsessive-compulsive disorder found that a single session of right prefrontal rTMS decreased compulsive urges for 8 hours. Mood was also transiently improved, but there was no effect on anxiety or obsessions. Using TMS probes, the same group reported decreased intracortical inhibition in patients with obsessive-compulsive disorder, reported that the condition with posttraumatic stress disorder improved during open treatment with 1-Hz rTMS over the right frontal cortex. similarly stimulated patients with posttraumatic stress disorder over motor cortex and found decreased anxiety. Schizophrenia • TMS has been rarely used to study schizophrenia, with 1 report of an open clinical series of slow rTMS resulting in reduced anxiety .In patients with prominent negative symptoms, found that session of fast rTMS to the left DLPFC was associated with slightly improved negative symptoms. Movement Disorders • Therapeutic applications of TMS in movement disorders are preliminary. Fast rTMS of the motor cortex has been reported to improve performance on several motor measures in Parkinson • Disease. Slow rTMS has been reported to improve dystonia. Epilepsy • The TMS motor threshold is reduced in patients with untreated epilepsy.Therapeutically, there is 1 report of potential beneficial effects of slow rTMS in action myoclonus. Emotion • There is evidence that rTMS can modulate mood systems in normal volunteers. Three studies found that rTMS over the left DLPFC transiently induced a mild increase in sadness,whereas right DLPFC rTMS produced a mild increase in happiness. SAFETY • Transcranial magnetic stimulation is not pleasant, and stimulation at higher intensities and frequencies is more painful. The pain experienced during rTMS is related to the repetitive stimulation of peripheral facial and scalp muscles, resulting in muscle tension headaches .These headaches respond to treatment with acetaminophen or aspirin. Magnetic stimulation also produces a highfrequency noise artifact that can cause short-term changes in hearing threshold. • This is avoided when subjects and investigators wear earplugs. • The most critical immediate safety concern is that rTMS has resulted in seizures.The TMS-induced seizures were self-limiting, and did not seem to have permanent sequelae. To avoid seizures the magnetic intensity delivered with rTMS is adusted for each individual relative to their motor threshold. CONCLUSIONS • During the next several years, it will become clearer whether rTMS has a role in the treatment of psychiatric disorders.trials in depression have focused on demonstrating antidepressant properties and have not demonstrated clinical utility. We need to know a good deal more about the patients who benefit from rTMS, the optimal form of treatment delivery, the magnitude and persistence of therapeutic effects, and the risks of treatment.. Regardless of its potential therapeutic role, the capacity of rTMS to alter functional brain activity should lead to important advances in our understanding of brain-behavior relationshipsand the pathophysiology of neuropsychiatric disorders. References 1. 2. 3. Jahanshahi M and Rothwell J. (2000). Trancranial magnetic stimulation studies of cognition: an emerging field. Exp Brain Res 131:1-9. Pascual-Leone A, Walsh V, and Rothwell J. (2000). Transcranial magnetic stimulation in cognitive neuroscience – virtual lesion, chronometry, and functional connectivity. Current Opinion in Neurobiology 10:232-237. Wu DA. (2005). How perception adheres color to objects and surfaces: studies using visual illusions and transcranial magnetic stimulation. Ph D thesis. Available at: http://resolver.caltech.edu/CaltechETD: etd-09282005-121349. THANK YOU