The overall goal of this methodology is to create a cost-effective approach of integrating studies of brain stimulation and human movement. This method can answer key questions in the neuromotor control field such as how neuro output from the motor cortex can be modulated during ongoing movement. The main advantage of this technique is that the delivery of brain stimulation is computer automated and is determined by the specific parameter of interest to the researcher, such as the joint angle or magnitude of muscle activity.
Demonstrating this procedure will be Aaron Bailey, a graduate student from my lab. See the manuscript accompanying this video for hardware and software setup instructions for this experimental protocol. The diagram seen here gives an overview of hardware configuration.
Begin by screening the participant for TMS safety and obtaining written and informed consent for the experiment. Then record the total body mass of the participant using a scale. Also use measuring tape to determine the length of the participant's hand, forearm, and upper arm, as these segments can later be used for kinematic and kinetic analysis.
Next, prepare the skin over the muscles of interest using a light abrasive gel. Then wipe the area clean with alcohol. Use an impedance meter to ensure that the skin electrode impedance is below 10 kiloohm to enhance EMG signal aquisition.
Now place two electrodes over the bellies of the muscles in a bipolar montage. For this experiment, place electrodes over the biceps brachii, triceps brachii, pectoralis major, posterior deltoid, and brachioradialis. Finally, using the NC cables, connect the outputs from the EMG amplifier to the analogue channels zero, one, three, four, and five on the AD box.
Locate the vertex using the International 10-20 Electroencephalography Electrode Placement System. Calibrate the TMS coil to the participant using neuronavigation software. Locating the motor hot spot for each muscle of interest is the most critical part of the experiment.
Incorrectly locating the motor hot spot or incorrectly orienting the coil can have effects on the data that is acquired. Next, to locate the motor hot spot, start by placing the coil on the contralateral hemisphere of the arm or hand being studied and five centimeters lateral to the vertex. The coil should be flat on the participant's head and oriented such that it is 45 degrees in relation to the sagittal plane.
Then begin with about 30%of the maximum stimulator output and deliver TMS pulses with an interstimulus interval of six seconds or greater as described in the suite-based data acquisition software. Move the TMS coil around to slightly different locations on the scalp while also slightly change the orientation until a motor-evoked potential is observed in the muscle of interest. Now determine the resting motor threshold by starting at the intensity that produces the most reliable response at about one millivolts.
Deliver single pulses and record the motor-evoked potential peek-to-peek amplitude online. Begin the experiment by first running the visual stimulus delivery software program. Then run the script file for the experimental trials within the suite-based data acquisition software, as described in the manuscript accompanying this protocol.
Input the desired information in the configuration dialogue box as seen on screen here. These values will configure the timing and other settings for the experimental trials. For example, the stimulus sets and the randomization value controls the number of times the trial type is performed in a block.
Motion-capture sensors are adhered to the patient. After this step, the software will run on its own with minimal user input. Ensure the participant understands all task instructions and then begin the experiment.
A trial begins when the participant places the cursor in the home position target. Then a new visual target position will appear. Next, an auditory go que is delivered via a digital-to-analogue output on the data acquisition box and the participant should move the cursor to the new target.
They should keep the cursor on this target position for one second and then return it to the home position to await the next trial. The analogue signal from the EMG will trigger the TMS pulse, which should be configured to occur 100 milliseconds following the auditory go que. Observe the participant and ensure that the cursor is placed in the home position and on the targets during the trials.
The experiment, as seen here, has 21 conditions consisting of seven target conditions with three different time points at which a TMS pulse is triggered. The approximate total duration of the experiment is three to four hours. In a single trial, the schematic on the left shows the starting position at the beginning of the trial, while the schematic on the right shows the end position during the trial.
Here we see the peek-to-peek amplitude of the MEP obtained from each muscle from the single TMS pulse during the EMG onset of this trial. The graphs seen here display the angular displacement of the shoulder and elbow joint, while these graphs show the angular velocity at the same joints. Here we see the kinetics at the shoulder and elbow joints, with the blue, green, and red lines each representing the net muscle and bone-on-bone contact moment respectively.
This figure shows example motor-evoked potentials recorded from the biceps brachii and pectoralis major, while reaching to a target that requires both these muscles to be active. Also shown are motor-evoked potentials recorded from triceps brachii and posterior deltoid, while reaching to a target that requires these muscles to be active. Once mastered, this technique can be performed in two to three hours if done properly.
While attempting this procedure, it is important to determine which analogue signal, such as EMG activity or joint angle will be used to trigger the TMS pulse. This information will be determined by the context of the experiment. Following this procedure, other methods like EEG can be performed to answer additional questions such as whether changes in brain oscillations are modulated in parallel with changes in corticospinal output.
