Étude des effets des antipsychotiques et schizotypie sur la N400 en fonction des potentiels d'événements liés et catégorisation sémantique

The overall goal of this procedure is to illustrate the steps of proper data acquisition using event related potential recording. This is accomplished by first placing an electrode cap on the participant. The second step is to insert electro gel into the electrodes of the cap using a syringe.

Next, a needle is used to scratch the surface of the scalp to gain good impedance as observed using data acquisition software such as neuro scan. The final step is to record the EEG waves. Ultimately, the raw data is processed to obtain event related potentials, which can be analyzed for characteristic waveforms such as the N one, the N 400, and the P 600.

The main advantage of this technique over existing methods like FMRI is its excellent temporal resolution, which allows researchers to follow the rapid temporal modulations of neuroactivity elicited by sensory, cognitive, and motor processes down to the millisecond. The visual demonstration of this method is critical because the technical steps are difficult to master. Due to the numerous details involved that when carried out incorrectly can jeopardize the interpretation of the findings.

Ola, a graduate student of my lab, will be demonstrating the procedure and Catherine, my research assistant, will be acting as a participant Upon participant arrival. Discuss the experiment and ask the participant to review and sign the consent form. Suggest using the bathroom and to spit out any gum being chewed.

Then sit the participant at the computer screen and have them untie hair and remove their earrings. Check that they are not wearing contact lenses as these cause too much blinking and will interfere with good data collection. Next, check the participant’s visual acuity by having them read small letters from a distance and by testing their color vision.

Also, set the room temperature so it is comfortable. The participant should not sweat or shiver during the experiment. Then proceeding with the experiment.

Mark the participant with red pencil at the bridge of the nose at the nasn measure from the and the in Indian, the bump above the neck at the lower base of the skull. Then from the nasn, go one 10th of the distance along this line and place a mark. Next, wrap the four color ribbon around the head from the mark to determine the color coded cap size needed from the mark at the level of the inion, obtain the cap of the corresponding size and ensure that the cap and its electrodes are clean and dry.

Now, place the ear electrodes onto the ear lobes. They serve as reference electrodes. Rub the ear lobes with alcohol, and then coat them with prepping gel Using a cotton applicator, then use an alcohol pad to wipe away the prepping gel.

It is crucial to have a good impedance on the reference electrodes because poor impedance on the reference electrodes would prevent good impedance on all other electrodes. This is because we’re recording the difference of potential between the reference electrodes and the other active electrodes. Next, apply electrolytic gel from a syringe onto the ear electrodes.

Then attach the gel filled electrodes to the ears. Now do the same preparation to the forehead as done to the ears. Then add disposable sponge discs to the cap on the prefrontal electrodes FP one and FP two.

The adhesive side must face the scalp. Line these electrodes up with the eyes and push them against the mark made near the hairline. Ask the participant to hold these electrodes in place and pull the cap firmly over his or her head.

Make sure the cap is a good fit. The sagittal subset of electrodes should be aligned along the middle of the head. The electrode leads can now be attached to an EEG amplifier.

Check that the parameters of the amplifier are set accordingly. Secure the cap by attaching a harness. Make sure there isn’t so much tension from the straps that they could change the caps position and affect data acquisition.

The ground electrode is very important because it serves to remove static electricity and other problematic activity for all of the other electrodes. Now, apply electrolytic gel from a blunted syringe into the ground electrode. Using two fingers, press on the ground electrode at the most anterior and central position on the cap.

This prevents electrolytic gel from spreading when it is applied. Before injecting it, rock the syringe back and forth to move aside any hair or dead skin that may interfere with proper connectivity. Then create a vertical column of gel by slowly pulling the syringe upwards.

Next, demonstrate to the participant how a sharp sterile needle will gently scratch the scalp under the ground electrode to remove dead skin. Then do this to the participant. This step will further improve electrical connectivity.

Continue by filling all the other electrodes with gel using the same steps. Now take a look at the display of the electrode schema on the computer monitor and abra the skin under the ear electrode using the needle. When the impedance drops below five kilo ohm indicated by a change in color from pink to black, do the same to the other ear electrode When the impedance will not drop, use a shortcut.

Put gel on the tip of a shortcut and insert it into the problematic electrode. Then connect the other end of the shortcut to the amplifier. Use tape to hold the shortcut in place.

Check the electrode schema on the computer monitor and ensure that the impedances have dropped After attaching the shortcut in place. Begin by reading the instructions for the experiment to the participant. If the participant asks questions, do not introduce any new words into the explanation.

Rather, repeat the instruction slowly. Now, open the software for EEG data acquisition and check for normal resting states on each electrode, any excessively active or inactive signals. Merit further refinement of the electrodes connectivity.

Before proceeding on the second computer setup, start the practice session in the EEG acquisition software. Check for myos and eye movements. The participant must be relaxed and refrain from excessive blinking or tensing of their jaw or forehead.

Once at rest beta or a rhythms may be detected during the practice trial. Check for excessive blinking occurring during stimulus. Presentation and design are important to adhere to.

Monitor the experiment software as it sends markers to indicate the onset of stimuli to the EEG acquisition software. These act as crucial reference points in the standard experimental paradigm. After the experiment, make sure the data has been saved.

Then remove the cap and help the participant get cleaned up. Lastly, detach the electrodes from the amplifier. Remove the disposable sponges and clean all the electrodes with shampoo and water.

Use a wooden stick to remove gel from the electrodes. Rinse it all thoroughly and let it air dry. To obtain ERP component data from the EEG readings, first determine which epoch will be studied to compute the N 400 amplitude.

Use the mean voltages in the 300 to 500 millisecond time window with the EEG epoch selected. Screen them for excessive eye movements. These trials may be rejected from the study based on the experimental parameters.

Then filter and average the ERPs, which can then be plotted if desired. Download and review the supplemental file containing further instructions on data processing with EEG lab and matlab. Successful completion of the protocol results in a data set of ERP waveforms that are recorded accurately.

However, if the experiment was not executed properly, recognizable ERP components will not be found. Common problems like eye movements, amplifier, saturation, and myos, all impede data collection and must be dealt with. These traces were all removed from analysis.

In the conducted experiment, this grand average of ERPs shows the placebo condition of an investigation into the effects of antipsychotics and schizo. Type on the N 400, which used a semantic categorization paradigm, red and black lines correspond to participants with high and low scores respectively. On the schizotypal personality questionnaire, the effects of medication were then tested with participants that had high schizotypal scores.

A red line depicts the participants that received medication and the black line indicates when placebos were given. Once mastered, this technique can be completed in less than 20 minutes if it’s performed properly. After watching this video, you should be able to understand how to obtain accurate ERPs through the proper placing of the cap and the gel.