Our protocols will facilitate the wider use of threshold tracking TMS techniques and enable direct comparisons with conventional amplitude measurements. These protocols have been designed to control three types of magnetic stimulator, and to allow recording, by a single operator, of the common single-and paired-pulse TMS protocols. These single-and paired-pulse TMS protocols are fast and easy to learn.
They allow high-quality recordings and analysis in the clinical setting. The advantage of the protocols described here that they are automated, both for recordings and analysis compared with the existing methods. Begin by assessing the subject's medical history and inquiring whether the subject has epilepsy, a pacemaker, or any kind of metallic implant in the body.
Explain to the subject the details about the application of magnetic stimulation to the scalp, such as, the stimulation will be heard as a click sound with a simultaneous muscle twitch. Each examination takes approximately 10 minutes. As some stimuli may feel slightly unpleasant, you can signal to turn off the stimulation at any time.
After describing the specifics of the procedure, invite the subject to give written consent, then ask the subject to wear a swimming cap. When the subject is ready, clean the hand of the subject contralateral to the hemisphere to be studied, then place the active recording electrode over the first dorsal intraosseous, or FDI, muscle, and the reference electrode on the second metacarpal-phalangeal joint of the subject. Place a ground electrode on the dorsum of the hand, and then connect the recording and ground electrodes to the amplifier.
Ask the subject to be relaxed and remain alert during the examination. Turn on the transcranial magnetic stimulation, or TMS, device, and use the protocol to start the semi-automated software for TMS recordings. From the menu, select the gain and gating options, and click O.K.to continue.
Then, from the main options, select the protocol CSP. For posterior/anterior current induction, place the figure-of-eight coil on the subject's head at approximately four centimeters left in the binauricular line from the vertex, and the handle pointing 45 degrees to the parasagittal plane. When done, click on the Insert key to manually increase the stimulus intensity until a motor-evoked potential, or MEP, is obtained.
Then, keep moving the coil slightly while monitoring MEPs on the screen and muscle twitches in FDI to find the hotspot for magnetic stimulation. Once the hotspot is located, draw the outline of the coil on the swimming cap to enable constant coil positioning, then click O.K.and initiate the recordings for the automated stimulation protocol. The recording continues automatically, starting with the determination of the resting motor threshold, or RMT, at 200 microvolts.
Select whether to measure the silent periods with or without pause. Instruct the subject to maintain comfortable activation of the FDI, then click O.K.to measure the silent periods. The three groups of 10 up and down cycles of stimuli are given automatically to measure the silent periods.
After the last stimulus, tell the subject to relax, and click on O.K.to return to the main menu. From the main options, select the protocol SICI then expand the tab SICI ISI options and choose the planned ISIs to be studied. If the default numbers of stimuli are not used, select the desired number from the tab No.of stimuli per ISI, then opt for the A-SICI from the menu to continue recording.
After determination of the RMT 200 and RMT 1000, A-SICI recording starts automatically and continues for approximately 10 minutes. Test stimulus is fixed at RMT 1000, and conditioning stimuli at 70%of RMT 200. Test-alone stimuli are given after each three-paired stimuli.
Each paired stimulus is delivered 10 times, making a total of 120 stimuli. When the protocol is complete, observe the screen to automatically return to the main menu before selecting T-SICIp. The recording continues automatically, starting with the determination of the RMT at 200 microvolts and then SICI recording for approximately 10 minutes.
RMT 200 is tracked constantly by decreasing stimulus by 1%maximal stimulator output if the response is more than 250 microvolts, and increasing it by 1%if the response is less than 160 microvolts. The test-alone stimuli alternate with paired stimuli, and the paired stimuli are delivered with pseudo-randomized ISIs, as explained before. After the screen returns automatically to the main menu, hit the Finish tab to stop the recording.
Finish the test by clicking on the Close file and save data button. To perform the TMS analysis offline, start the analyzing software program and select the recording to be analyzed by clicking O.K.From the TMS menu, select the Create TMS MEM File option, and save the pop-upped MEM file by clicking O.K.Then click on Plot TMS MEM/MEF options from the TMS menu to compare the individual subject's recording with a group of healthy controls. Click on the first option on the MEM file name menu, then click on the MEM file with which the comparison will be made from the list of MEM files.
Superimpose the MEM and MEF files using different options of 90%confidence intervals, standard deviations, or standard errors. For the A-LICI protocol, conditioning plus test stimulus were delivered at intervals of 50 milliseconds, and the corresponding MEP was monitored. In the T-LICI protocol, pulses were delivered from 50 to 300 milliseconds, and the thresholds for RMT 200 were tracked.
The SICF protocol was performed similarly, with the shorter interstimulus intervals. SAI protocols involved recording the effects of nerve stimulation on the MEP excited around 20 milliseconds later. It is crucial to locate an optimal hotspot for eliciting MEPs, and then maintain the coil in the same position throughout the whole recording.
The automated nature of the protocols described here allows the recordings to be performed by a single operator, so that the operator can fully concentrate on keeping the coil in a stable position. This software also allows selection of different interstimulus intervals, different numbers of stimuli for each interval, and different levels of conditioning stimulus. An important new feature is a gating function, which automatically removes traces when the subject is not relaxed.
