The overall goal of the following experiment is to explore corticospinal. Excitability changes induced by action observation in interactive context to identify when the automatic tendency to emulate someone else's action becomes the preparation for a non-identical response. This is achieved by using single pulse transcranial magnetic stimulation over the primary motor cortex to assess corticospinal excitability with a relatively high temporal resolution as a second step.
Neuronavigation is used to maintain constant TMS coil positioning throughout the entire experiment. Next electromyographic activity is recorded from hand muscles in order to track excitability changes induced by action. Observation results are obtained that show an early switch from an emulative to a context related response in corticospinal activity based on a differential activation of the stimulated hand muscles.
This method can help answer key questions pertaining to the social neuroscience field and specifically action observation. Many questions remain unanswered with regard to how observed actions once mapped onto our motor system can be reconciled with the indication to prepare. A non-identical response are in fact, mechanisms underlying action observation susceptible to request in that did in social context.
The implications of this technique may extend toward future applications in clinical settings, since it has the ability to provide a direct assessment of motor cortical plasticity effects in individual affected by social disorders Prior to the experiment. Prepare videos of a model performing action sequences that involve manipulating objects on a table. These videos should include both non-social and social conditions.
The research subject will observe these body movements during the TMS experiment. Begin experimental procedure by preparing five centered monopolar silver, silver chloride electrodes with a nine millimeter sensor area to an isolated portable EXG input box. Link to the main EMG amplifier.
Provide an overview of the study to the participant and obtain written informed consent. Ask them to remove all metal objects and objects sensitive to magnetic fields as the rapid rate of change of current in the coil is capable of inducing a changing magnetic field. Then have the participant sit in a comfortable armchair and position the right arm on a full arm support.
Also, fix the head on a headrest. Instruct the participant to watch the visual stimuli carefully and to remain attentive. Also explain that they will be questioned later about the contents of the videos.
Begin by determining electrode position for the first dorsal interosseous and the abductor digit minimi muscles by palpation. During maximum voluntary muscle activation, clean the skin for all electrode locations. Then lightly apply an abrasive skin prepping gel to the entire site using a gauze pad.
Remove any excess with a clean pad. Then place two surface electrodes each containing a small amount of water soluble EEG conductive. Paste over each muscle and attach them to the skin using self adhering pads.
Next, perform a belly tendon montage by placing the active electrodes over the muscle bellies of the right FDI and A DM and the reference electrodes over the ipsilateral metacarpophalangeal joint. Also, attach a single ground electrode containing conductive paste on the participant's left wrist. Connect the electrodes to the common input of the EXG input box and check impedance values in the event they are above the threshold of five ohm re the skin.
Next place a 70 millimeter figure of eight coil connected to a Mag Stim 200 stimulator at a 45 degree angle with respect to the interhemispheric fissure and position it perpendicularly with respect to the central sulcus. Assure that the handle is placed so that it is pointing laterally and coddly to induce a posterior anterior brain current through the precentral gyrus. Then deliver a single pulse TMS to the scalp overlying the left primary motor cortex corresponding to the hand region.
Use a 10 20 international system with the stimulated site corresponding to the C3 location to establish the optimal scalp position for eliciting motor evoked potentials in the hand muscles. Move the intersection of the in approximately 0.5 centimeter steps around the target area and deliver TMS pulses at a constant intensity. After the target area has been correctly identified, stabilize the coil using a mechanical support to maintain the position.
Then use a neuro navigation system to maintain constant coil positioning throughout the entire experiment and prevent any bias due to small movements of the participant's head during data collection. Also apply passive spherical markers both on the coil and on the participant's head. Record the marker positions using an optical digitizer in order to reproduce them on the neuronavigation display.
Detect any difference in spatial coil location and orientation, and adopt a tolerance of two to three millimeters for each of the Cartesian coordinates. Also, utilize the three dimensional online information regarding initial and actual coil placements to allow for exact repositioning of the TMS coil during the experimental session. Next, to determine the individual resting motor threshold or RMT, detect the minimum stimulation intensity necessary to produce reliable meps in a relaxed muscle in five out of 10 consecutive trials.
Keep the stimulation intensity at a fixed value such as 110%of the RMT during the entire recording session, and use a band pass filter of 20 hertz to one kilohertz to record the raw myo graphic signals. Begin the experimental session by first recording 10 motor evoked potentials while the participant passively watches a white colored fixation cross on a black background on the computer screen. Then have the subject view the video while EMG data is recorded from the right a DM and FDI muscles and A TMS pulse is delivered at one of five possible time points on the video.
The first three time points are when the model's hand first makes contact with the thermos, when the model finishes pouring coffee into the third cup, and when the model begins to pull her hand away from the third cup, then stimulate at non-social and social conditions respectively being when the model's arm begins to return to the starting position or starts moving towards the fourth cup. And when the model's arm returns to the starting point or when it reaches the fourth cup, insert a ten second rest interval between the videos and have a message appear during the first five seconds reminding the participant to keep their hands resting quietly and fully relaxed. When the message disappears, have a fixation cross appear for the remaining five seconds.
Finally, record 10 more meps at the end of the experimental session. After amplification, digitize the myo signals and store them in the computer for offline analysis. Calculate the average peak tope MEP amplitude separately for the A DM and FDI muscles for each condition, exclude responses deviating more than two standard deviations from the mean next, check for corticospinal excitability variations related to TMS in each participant.
To do this, compare the two series of MEP amplitudes recorded from each muscle during the fixation baseline trials at the beginning and end of the experiment. The average amplitude of the two series can be used to set the individual baseline value for data normalization procedures in each muscle separately. Finally, compute ratio values using the participant's individual baseline value, observing a two-step action sequence implicitly containing a request for a complimentary movement caused a switch from emulation to responsiveness in the onlooker's corticospinal activity in the trials carried out.
This indicates exactly when the changeover took place. Inversely a variation heralding and emulative action takes place in the observer's meps. The moment the model's wrist started to return to its original position being the non-social condition, FDI as expected was actively involved in all observed movements and simulated actions.
After watching this video, you should have a good understanding of how to assess the specificity of cortico spinal facilitation during action observation by using single pulse transcranial magnetic stimulation over the primary motor cortex, neuro navigation, and registration of El electromyographic activity of end muscles. Once developed, This technique paved the way for researchers to explore model facilitation effect during action observation. In humans, this protocol permits us to study how and when matching mechanisms are transformed into complementary ones.
When a request for a non-IT action becomes evident.
