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

Y P Berenson-Allen Center for Noninvasive Brain Stimulation O Department of Neurology Beth Israel Deaconess Medical Center C Harvard Medical School T O N Determining motor threshold O D Franziska Plessow, Ph.D. E S A E L Intensive Course in Transcranial Magnetic Stimulation, P 02/28/2017

Y P What are the learning objectives of this session? O C 1. What is motor threshold (MT)? T 2. Why do we determine MT? O 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? E S A E L P à Hands-on practice Determining motor threshold 2

Y P What is motor threshold (MT)? O C § The minimum amount of machine output necessary to T elicit a motor response in a participant or patient in at least O 50% of all attempts N § Represents membrane-related excitability of cortical axons O § Depends on: D - Inter- and intraindividual variance E - Device (stimulator and coil) S - Type of MT A - Method of determination E - Hemisphere stimulated L P Determining motor threshold 3

Y P Why do we determine MT? O C § Easy to observe T § Objective (see phosphene threshold) O N § Indicator of relative cortical excitability § A way of calibrating and normalizing TMS coil output O energy for inter- and intraindividual physiologic variability D in experimental designs and therapeutic applications E § Determines dosage and safety limits S A E L P Determining motor threshold 4

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

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

Y P RMT with EMG O C § The minimum amount of machine output necessary to T elicit a motor response in a participant or patient in at least O 50% of all attempts N à Minimum single-pulse stimulator output intensity O resulting in motor-evoked potentials (MEPs) of at least D 50 µV peak-to-peak amplitude in ≥ 50% of n consecutive trials ( ≥ 5/10; Rossini-Rothwell method) E S µV µV A E L P s s Determining motor threshold 7

Y P What are the key steps for determining RMT with EMG? O C 1. Choosing an output target T 2. Setting up and ensuring safety O N 3. Locating the motor hotspot (adjusting location) 4. Assessing the MT (adjusting intensity) O D E S A E L P Determining motor threshold 8

Y P Choosing an output target O C T O N O D E S A E L P Determining motor threshold 9

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

Y P Setting up and ensuring safety O C T O N O D E S A E L P Determining motor threshold 11

Y P Locating the motor hotspot O C ≈ 5 cm lateral from the vertex T O N O D E S A E L P (Jaspers, 1958) Determining motor threshold 12

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

Y P Locating the motor hotspot O C T O N O D Nasion E B D S A Left Right C A ear ear E L P Inion Determining motor threshold 14

Y P Locating the motor hotspot O C 1. Set intensity to 30% maximum stimulator output (MOS) T and deliver 3 pulses (6-10 s apart) O 2. Go up in steps of 10% until you observe a muscle twitch N 3. Deliver several pulses to ensure a consistent response O (MEP) is evident (suprathreshold) D 4. Test points 1 cm anterior, medial, posterior, and lateral E - Move clockwise, starting with anterior spot S - Deliver 3 pulses at each location A E L P Determining motor threshold 15

Y P Locating the motor hotspot O C 1. Set intensity to 30% maximum stimulator output (MOS) T and deliver 3 pulses (6-10 s apart) O 2. Go up in steps of 10% until you observe a muscle twitch N 3. Deliver several pulses to ensure a consistent response O (MEP) is evident (suprathreshold) D 4. Test points 1 cm anterior, medial, posterior, and lateral E - Move clockwise, starting with anterior spot S - Deliver 3 pulses at each location A 5. Repeat Step 4 until the individual’s hotspot is identified E ✓ L P Determining motor threshold 16

Y P Locating the motor hotspot O C 1. Set intensity to 30% maximum stimulator output (MOS) T and deliver 3 pulses (6-10 s apart) O 2. Go up in steps of 10% until you observe a muscle twitch N 3. Deliver several pulses to ensure a consistent response O (MEP) is evident (suprathreshold) D 4. Test points 1 cm anterior, medial, posterior, and lateral E - Move clockwise, starting with anterior spot S - Deliver 3 pulses at each location A 5. Repeat Step 4 until the individual’s hotspot is identified E 6. The location that elicits the largest peak-to-peak MEP L amplitude is the motor hotspot P Determining motor threshold 17

Y P Locating the motor hotspot O C § Keep in mind: T - The hotspot is not at the interior curve of the TMS coil O - 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 18

Y P Assessing the MT O C 1. Set intensity to 30% MOS and deliver 3 pulses (6-10 s T apart) O 2. Go up in steps of 10% until you observe an MEP N 3. Deliver several pulses to ensure a consistent response O (MEP) is evident (suprathreshold) D 4. Record 10 MEPs E 5. Progressively lower intensity (1- 2 %) until <5/10 show an S MEP of ≥ 50 µV A 6. The lowest intensity that elicits MEPs in ≥ 5/10 pulses E is your MT L P Determining motor threshold 19

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