سید کاظم ملکوتی دانشکده علوم رفتاری INTRODUCTION TO TDCS. Dr. SK Malakouti

Transcription

1 INTRODUCTION TO TDCS Dr. SK Malakouti

2 Transcranial Direct Current Stimulation A form of neuro-stimulation Constant low current delivered to the regions of interest via small electrodes Originally developed for the patients of brain injury Later demonstrated cognitive benefits in healthy adults Language and mathematical abilities Attention span Problem solving Memory

3 Modern era Brief rise of interest until 1960s DJ Albert Stimulation could affect brain function via changing the cortical excitability Positive and negative stimulations have different effects on cortical excitability

4 Eventual rise of interest, since introduction of modern techniques of brain stimulation and neuroimaging, such as rtms and fmri.

5 INSTRUMENT

6 Mechanism tdcs works by sending constant direct current via electrodes to specific areas of brain. Placement of electrodes induces intracranial current in desired regions. Therapeutic purposes Cognitive improvement and peak performance Researches on brain functioning

7 Material TDCS device 9V Battery (2x) Two rubber head bands Two conductive rubber electrodes Two sponge electrodes Cables NaCl solution Measurement Tape

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9 Parts Two electrodes An anodal (+) A cathodal (-) Different size: A smaller electrode => More focused stimulation A greater electrode => Ensures including the correct target Usual size : 70 x 50 mm Battery powered current generator Current from positive electrode to negative one

10 تغییری که Tdcs در قطبیت غشا سلولی ایجاد می کند تابعی است از چگالی جریان چگالی خود تابعی است از اندازه الکترود و شدت جریان هر چه چگالی جریان بیشتر باشد تایر tdcs قوی تر خواهد بود چگالی جریان در حدوده Ma/cm تا 0.08 ma/cm2 میباشد

11 After the stimulation, current flow should be ramped off as well. Note on High-Definition tdcs (HD-tDCS): electrodes smaller than approximately 2 cm 2 It is not recommended to apply tdcs using 1-2 ma of sponge electrodes 14,15.

12 Types of Stimulation Different types of stimulation Anodal + Increases the excitability Equal to high frequency stimulation in rtms Cathodal - Decreases the excitability Equal to low frequency stimulation in rtms Sham Brief current to induce sensation Then discontinue the current For research purposes and comparison

13 Types of electrode placement Unilateral stimulation Extracephalic reference electrodes Shoulder, Arm and Tibia Intracephalic reference electrodes Supraorbital Bilateral stimulation Left and Right

14 Mechanism of effect Lasting effect Related to length and strength of stimulation Positive stimulation Depolarization of resting membrane potential Negative stimulation Hyperpolarization of resting membrane potential Decreased neural excitability due to inhibition of spontaneous cell firing. Effects on neuroplasticity Alteration of synaptic transmission ability through modification of intracellular Ca and camp

15 neurotransmittters Dopaminergic GABA Glutamatergic ACH 5HT Increase Motor Evoke Potential, MEP Increase intercellular Ca++

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18 Environmental Conditions Ingress of Water Flammability Mode of Operation Dimensions Weight Cleaning Disposal Controls Dose Range Maximum Voltage Maximum Current Current Ramp Up Current Ramp Down Battery Transport and store 50 F to 131 F (10 C to 55 C). Operate 41 F to 104 F (5 C to 40 C). Humidity less than 90%. Atmospheric pressure from sea level to 9,842 feet (3,000m). Not protected against ingress of water. Do not use around flammable gases, liquids or materials. Continuous. 6.1 x 3.5 x 1.9 (15.5 x 8.9 x 4.8cm).4 lbs. (.18kg) Clean the case and lead clip wires as needed with an alcohol moistened cloth. Do not immerse in fluids. Dispose of according to local, state and federal regulations. Remove battery before disposal. Two (dose and current). 0 to 80 ma-min. 80V DC 4.0 ma Automatic (0 to 4.0 ma). Built-in option for manual override. Automatic at end of treatment; paused or turned off by depressing knob. Built-in option for manual override. Use only 9V DC Alkaline. Ensure battery door is in place before starting treatment. Remove battery from unit when not in use.

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20 The area of stimulation will be found through the measurement of the scalp. Usually the convention of the EEG 10/20 system is used 7. To locate the primary motor cortex, or M1, use 20% of the auricular measurement and use this measurement from Cz through auricular line This spot should correspond to C3/C4 EEG location. This method of localization is enough given the locality of traditional large electrodes tdcs. To locate the dorsolateral prefrontal cortex (DLPFC) 9,10 : One practical method is to measure five centimetres forward from the M1 location or to use the 10/20 EEG system. This should correspond to the F3 or F4 EEG location, as seen here (Figure 5).

21 The "10" and "20" refer to the fact that the actual distances between adjacent electrodes are either 10% or 20% of the total front back or right left distance of the skull. Figure 5: DLPFC Position. DLPFC= dorsolateral prefrontal cortex. Cortical areas marked according to the 10/20 system.

22 Change in cortical excitability due to current polarity and tdcs montage MEP amplitudes after stimulation are given in percent of MEP without stimulation. the motor cortex (M1) - contralateral supra-orbital (Fp2) montage setting leads to a significant increase of MEP size after anodal and a decrease of MEP amplitude after cathodal stimulation.

23 کوچک بودن آند و بزرگتر بودن کاتد میتواند چگالی بهتری را در درمان ایجاد کند حداقل چگالی 17 میکروآمپر بر مترمربع است برخی به 20 تا 25 میکروآمپر را الزم دانسته اند در بیمار افسرده: قرار دادن آند در F3 با 1 میلی آمپر با الکترود 35 سانتیمر مربع میتواند 28 میکروآمپر در متر مربع ایجاد کند که موثر است

24 If the overall resistance is abnormally high, this may indicate improper electrode set-up. If your device measure resistance - this would be recommended the indication field should display appropriate electrode contact. Ideally, one should aim to have the impedance under 5k Ohms. Some devices indicate the voltage across the path rather than resistance - in this case resistance can be calculated simply using ohms law (Resistance = Indicate Voltage / Current applied). Many devices continue to provide an indication of resistance during the course of stimulation, which provides a useful way to detect a potentially hazardous situation (such as a drying electrode).

25 The effects of one session of tdcs can last for several minutes, and its effects depend on polarity of stimulation, cathodal stimulation induces a decrease in cortical excitability, anodal stimulation induces an increase in cortical excitability

26 "Anode" always indicated the relative positive terminal where positive current flows intro the body "Cathode" indicates the relative negative terminal where the positive current then exits the body.

27 Inspect the skin for any pre-exiting irritation, cuts, or lesions To increase conductance, move hair away from the site of stimulation and clean the surface of the skin For subjects with thick hair, use of conductive gel may be necessary. If using re-usable electrodes, inspect the rubber insets and sponges for wear.

28 one of the elastic or rubber head straps around the head circumference. The elastic head strap should be placed under the inion as to avoid movement during stimulation. The elastic straps should be made of non-conducting material (or they will function as electrodes) and non-absorbent material (to avoid the straps absorbing fluid from the sponges). Each side of the sponges should be soaked with saline solution. For a 35 cm 2 sponge, approximately 6 ml of solution per side may suffice (total of 12 ml per sponge). Be careful not to over soak the sponge (not excessively wet- there should be no water leaking; but also not dry as to have a good electrode contact). Avoid fluid leaking across the subject. You can use a syringe to add more solution if needed.

29 There is evidence that electrolyte solutions with lower NaCl concentrations(15 mm) are perceived as more comfortable during tdcs than those solutions with higher NaCl concentrations (220 mm) 11,12. Since the ionic strength of deionised water is much less than that of all NaCl solutions, there is a significantly larger voltage required to carry current across the electrode and through the skin compared to NaCl solutions. Thus, it is recommended the use of solutions with moderate NaCl concentration, in the range 15 mm to 140 mm, as tdcs at these concentrations is more likely to be perceived as comfortable, requires moderately lower voltage while still allowing good conduction of current. 11 The use of gels (adapted from applications such as EEG) has also been considered a main limitation is the increased hassle of set-up clean-up following stimulation, without proven benefit regarding outcome when using perforated sponge electrodes.

30 Insert the connector cord pin securely into the opening of the receptacle on the conductive rubber inset. Slide the conductive rubber inset into the sponge. The insulated portion of cable will protrude from the sponge-pocket opening. Ensure the entire conductive rubber inset is covered by the sponge and that there is no part of the connector cord pin is visible. Place one sponge electrode below the elastic head strap. Ensure that excessive fluid is not ejected from the sponge unto the scalp during this process as this will spread current flow across the scalp and deplete the sponge of fluid. Connect the second elastic head strap to the first elastic head strap according to the electrode montage you want to use (Table 2). Other elastic head straps can be used.

31 Side effects slight itching sensation, peripheral nerve firing. dizziness or vertigo brief retinal phosphenes with electrodes near the eyes. These effects can be largely avoided by ramping the current up and down at the beginning and end of treatment.

32 After the procedure recommended to use a questionnaire of adverse effects. article of Brunoni et al. (2011) There is evidence that sham stimulation causes a comparable amount of itching and tingling sensations as active stimulation.

33 Safety Widely regarded as a safe method Too many studies have been held on safety and limitations Currently maximum accepted dose for human is 2 ma 20 minutes of duration is considered ideal No study is available on the long-term safety of repeated session of stimulation

34 Side effects There are minor side-effects of stimulation Nausea Electrodes above the mastoid Headache Dizziness Itching and skin irritation Electrode preparation with saline Skin preparation with conductive creams Gradual increase of current Phosphenes at the beginning of the stimulation Electrodes near the eyes seizure

35 Critical Steps: frequent headache, chronic skin disorder, or adverse reactions to a previous tdcs treatment. If he or she has any metal in the head or had a serious brain injury, the anatomical changes may modify current flow 23,24. History of seizure, pregnancy and history of a stroke are usually not strict contraindications - and indeed, might be inclusion criteria in some clinical trials.

36 Suitable situations for patients Knowing the procedure Acceptance Without any anxiety or fear Knowing the side effects Attending all sessions

37 Clinical purposes Clinical trials have shown promising results about the beneficial effects of tdcs on: Parkinson s disease Tinnitus Depression Fibromyalgia OCD Schizophrenia Migraine Craving Post stroke motor rehabilitation Post stroke speech dysarthria

38 PROTOCOLS

39 Anode Electrode Positioning Cathode Electrode Positioning Observations Caveats Primary Motor cortex (M1) Supra-Orbital This is the most used montage. It has been proven that the cortical excitability can be changed up to 40% 6 (Figure 6). Anodal stimulation results in neuronal depolarisation and increasing neuronal excitability while cathodal stimulation has opposite results 6. Only one motor cortex is stimulated might be a problem for bilateral pain syndromes. Also the confounding effect of the supraorbital electrode needs to be considered. Primary Motor cortex (M1) Primary Motor cortex - Interesting approach when there is a bihemispheric imbalance between motor cortices (such as in stroke) - Can be used with two anodal stimulation electrodes (see sixth row), where cathodal electrode is placed in the supraorbital area for instance. Electrodes might be too close to each otherissue of shunting. A decrease of the area of the electrodes will increase the degree of shunting along the skin 19 Therefore shunting might be related not only to electrode positioning but also to electrode size. The relative resistance of the tissues is dependent upon the electrode position and size- the overall resistance on which the current flows is dependent upon the electrode properties 19. Dorsolateral Prefrontal Cortex (DLPFC) Supra-Orbital Most used for DLPFC stimulation positive results for treatment of depression 20 and also chronic pain 3. Only unilateral DLPFC stimulation situation is possible with this montage. Dorsolateral Prefrontal Cortex - Interesting approach when there is a bi-hemispheric Dorsolateral imbalance. Prefrontal Cortex - Can be used for a two anodal stimulation situation (see sixth row), where cathodal electrode is placed in the Electrodes might be too close to each otherissue of shunting 19. (Please see second row, fourth column).

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41 MDD and F3/right shoulder

42 Addiction and F3/right shoulder

43 Cognitive improvement

44 Cognitive improvement

45 Examples of protocol parameters