Y P O Berenson-Allen Center for Noninvasive Brain Stimulation - PowerPoint PPT Presentation

Y P O Berenson-Allen Center for Noninvasive Brain Stimulation Department of Neurology C Beth Israel Deaconess Medical Center Harvard Medical School T O N Determining motor threshold O D Franziska Plessow, Ph.D. E S A E Intensive Course in Transcranial Magnetic Stimulation, L 10/23/2018 P

Y P O Questions this session will answer C T 1. What is motor threshold (MT)? O 2. Why do we determine MT? N 3. What types of MT can be determined? 4. What are the available methods to determine MT? O 5. What are the key steps for determining resting MT with D electromyography (EMG)? E S A E L � Hands-on practice P Determining motor threshold 2

Y P O What is motor threshold (MT)? C T � The minimum intensity (% of maximum machine output) to O elicit a motor response in at least 50% of all attempts N � Reflects excitability (reactivity) of the motor cortex: - Voltage-dependent ion channel function O - Inter- and intra-individual variance D � Physical parameters: - Device (stimulator and coil) E - Pulse waveform/shape/direction S - Activity of brain/muscle A - Method of determination (visual inspection vs. EMG) E L P Determining motor threshold 3

Y P O Why do we determine MT? C T � Easy to observe O � Objective measure of relative cortical excitability N � A way of calibrating TMS intensity to inter- and intraindividual physiologic variability in experimental O designs and therapeutic applications D � Consistent with safety limits (Rossini et al., 2009) E S A E L P Determining motor threshold 4

Y P O What types of MT can be determined? C T > Resting motor threshold (RMT) Active motor threshold (AMT) O N O D E S A E L P Determining motor threshold 5

Y P O What are the available methods to determine MT? C T Electromyography (EMG) Visual inspection O N O D E S + A E L P Determining motor threshold 6

Y P O RMT with EMG C T � Rossini-Rothwell method: O Minimum single-pulse stimulator output intensity to elicit motor-evoked potentials (MEPs) ≥ 50 μ V peak-to-peak amplitude in ≥ 50% of n N consecutive trials (typically n = 10) O D E μ V μ V S A E L s s P Determining motor threshold 7

Y P O What are the key steps for determining RMT with EMG? C T 1. Safety first O 2. Choosing an output target N 3. Locating the motor “hot spot” (adjusting location) 4. Finding the MT (adjusting intensity) O D E S A E L P Determining motor threshold 8

Y P O Safety first C T � Screen for contraindications and side effects O � Earplugs must be worn by participant/patient and operator N O D E S A E L P Determining motor threshold 9

Y P O Choosing an output target C T O N O D E S A E L P Determining motor threshold 10

Y P O Choosing an output target C T O N O D E S A E L P Determining motor threshold 11

Y P O Attaching EMG electrodes C Identify T O N O Clean D E S A Attach E L P Determining motor threshold 12

Y P O Locating the motor “hot spot” C T ≈ 5 cm lateral from the vertex O N O D E S A E L P (Jaspers, 1958) Determining motor threshold 13

Y P O Locating the motor “hot spot” C T ≈ 5 cm lateral from the vertex O N O D Preaurical point E S A E L P (Jaspers, 1958) Determining motor threshold 14

Y P O Locating the motor “hot spot” C T O N 5 cm O D Nasion E 5 cm B D S Left Right A C A ear ear E L P Inion Determining motor threshold 15

Y P O Locating the motor “hot spot” C T 1. Set intensity to 30% and deliver 3 pulses (6-10 s apart) O 2. Go up in steps of 5-10% until MEP is observed N 3. Deliver several pulses to ensure a consistent response (MEP) is evident (suprathreshold) O 4. Test four points around the location of the MEP D - 1 cm north, east, south, and west E - Deliver 3 pulses at each location S 5. Repeat Step 4 until the individual’s “hot spot” is identified A 6. The location that elicits the largest peak-to-peak MEP E amplitude is the motor “hot spot” L P Determining motor threshold 16

Y P O Locating the motor “hot spot” C T � Keep in mind: O - The hotspot is not at the interior curve of the TMS coil - The distance between center and the interior curve of a figure-of- N eight coil varies across vendors/coil types O D E S A E L P Determining motor threshold 17

Y P O Finding the MT C T 1. Record 10 MEPs O 2. Progressively lower intensity (1-2%) until <5/10 show an N MEP of ≥ 50 μ V 3. Always test one intensity lower O 4. The lowest intensity that elicits MEPs in ≥ 5/10 pulses D is your MT E S A E L P Determining motor threshold 18

Y P O Finding the MT C T � Alternatives under time constraints: O - ≥ 3/6 - Adaptive MT determination/Parameter estimation by sequential N testing (PEST) with the TMS Motor Threshold Assessment Tool O (clinicalresearcher.org) � Trouble shooting: D - No MEP detected (relaxation, AMT, silence period) E - MEP latencies >150 instead of 20-30 ms S - Expectation A E L P Determining motor threshold 19